re-spg 31.29.00.00-005 rev0 rotor balancing

1 Introduction 1.1 SCOPE

This Rotating Equipment - Standard Practice and Guideline (RE-SPG) specifies requirements and gives recommendations to properly execute balancing on rotors or rotating elements. This procedure is designed to layout the requirements for Rigid and flexible rotors and Low and High speed balancing. As a minimum, all API General and Special Purpose rotors (un-spared, critical applications, rigid and flexible rotors) shall be balanced by using this RE-SPG in conjunction with API 687. These specifications are intended to meet the minimum requirements for balancing of rotors. Should further assistance be required in determining the requirements, contact the site Rotating Equipment Engineering Representative. This specification does not cover the setting of the impellers at overspeed. If the machine is sent off-site for repair, the Manufacturer, OEM or Repair shop may submit changes or exceptions to this RE-SPG for review and approval by the Technical Authority. Exceptions to this standard may be justified provided that substantiation data or engineering calculations can be produced to confirm the changes being proposed and that they are reviewed and approved by the Technical Authority before proceeding with the work.

1.2 DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS

Unless otherwise authorised by Shell GS, the distribution of this RE-SPG is confined to Shell companies and, where necessary, to (Integrated Service) Contractors and Manufacturers/Suppliers nominated by them. Any authorised access to RE-SPGs does not for that reason constitute an authorization to any documents, data or information to which the RE-SPG may refer. This RE-SPG is intended for use in facilities related to oil and gas production, gas handling, oil refining, chemical processing, gasification, distribution and supply/marketing. Application in other facilities may also apply. This RE-SPG describes a recommended practice that is intended to meet a desired performance or integrity standard. There may be alternative approaches to achieve the same result that are acceptable within the governance of the business entity. As such, this RE-SPG is not mandatory unless the business entity with ownership of the asset has declared it as mandatory. This document may not include regulatory requirements imposed by national and local jurisdictional authorities. Specific requirements of local laws and regulations should be included in a specific site procedure or practice. All jurisdictional requirements that are more stringent than those outlined in this document shall take precedence. Local requirements and preferences not covered in this document should be covered in a site procedure or practice. Such issues may include national, state and/or local jurisdictional requirements, optional choices contained in this document, site specific roles and responsibilities, and site specific record keeping requirements.

RE-IRSP XX-XX-XX-00X rev0 Page 2/31

1.3 DEFINITIONS The word shall indicates a requirement. The word should indicates a recommendation. The Vendor, Contractor, OEM or Repair Facility is the party that carries out all or part of the design, engineering, inspection, procurement, repair, maintenance, shop testing, or management of a inspection & repair project. The Manufacturer/Supplier is the party that performs the inspection or repair services or supplies equipment and services to perform the duties specified in this document. The Principal is the party that initiates the project and ultimately pays for it. The Principal will generally specify the technical requirements. The Principal may also include an agent or consultant authorised to act for, and on behalf of, the Principal. The Technician (Machinist, millwright, Instrument Technician, etc) is referred to as the person performing the work in the field or actual work on the equipment in the shop. The Rotating Equipment Representative is defined as the Rotating Equipment Engineering Representative, Rotating Equipment Inspector, Maintenance Engineer or other reporting to the Site Rotating Equipment Department who is responsible for performing technical evaluations on site machinery made during inspections and repairs.

1.4 SUMMARY OF MAIN CHANGES This IRSP document is a revision of the IRSP document of the same number dated mm yyyy. The following are the main, non-editorial changes.

Old section

New section

Change

1.5 COMMENTS ON THIS RE-SPG

Comments on this RE-SPG may be sent to the Principle Technical Expert (PTE) in Repair Technology SME (Subject Matter Expert) group. The PTE listing can be found on the Shell XREQ Homepage (http://sww.shell.com/pt/business_units/project_engineering_services/disciplines/discipline_rotating_equipment.html ).

1.6 DEVIATION CONTROL Deviations from these practices and guidelines may require review and approval of a Company technical authority via formal communication by email and to be documented in the final documentation package of an inspection and Repair project for future traceability. New inspection, repair or maintenance technology or design changes may necessitate periodic review of this inspection and repair practice to modify the specifications listed.


2 Low Speed Balancing 2.1 General Requirements

2.1.1 The pre-balancing part of the procedure is for preparing the parts to be balanced. Using the actual shaft when balancing is recommended, when not available, the use of a mandrel is acceptable. API 687 specifies only 2 methods of balancing: component balancing or assembly balancing:

2.1.2 Component balancing is performed by first balancing the shaft and all impellers separately, then assembling rotor and checking the balance of the total assembly. Balancing correction to the assembled rotor is not permitted. If out of tolerance, the rotor is disassembled and procedure is repeated. (Note: This procedure is typically used for diffuser type pumps or API Pump Multi-Stage Impeller applications.)

2.1.3 Assembly balancing, sometimes referred to as progressive or stack balancing, is performed by balancing the shaft first, then installing and making corrections to no more than two impellers at a time. All balance corrections shall be applied to the last elements added to the shaft during the stacking process. Minor correction of the other components may be required during the final trim balancing of the completely assembled rotor.

2.1.4 Any corrective work required to the impeller bore, diameters or machining of wear rings MUST be completed before the balancing commences.


2.2 General Rules and Guidelines 2.2.1 Verify the shaft or mandrel OD that rides on balance stand anti-friction support rollers is NOT

the same OD as the balance stand anti-friction support rollers. Experience has shown this to cause erroneous readings. The general rule is that the balance machine antifriction support rollers, which are within (+/-) 5% of the same nominal diameter as the shaft journal diameter(s), shall not be used due to possible roller noise masking the balance readings.

2.2.2 Avoid running the balance stand rollers on chromed or coated surfaces. Heavy rotors and over-hung rotors can exert very high local surface stresses on coated areas that cause the coating to crack (figure 2.1 for example of microcracks after PT). If there is no other option but to roll on a coated area use the widest rollers possible and NDT inspect before and after for cracks.

Figure 2.1: Microcracks on chromed surface

2.2.3 If the Rotor has been coated, corrections made on the rotor will be restricted to the furthest diameter between impeller vanes (scalloped configuration) on the Outer most diameter of the impeller. At NO time will any grind occur on the face of the impeller cover or hub after the coating is applied, without written approval of a Shell Rotating Equipment Engineering Representative. This will prevent any breakdown of the coating or coated surfaces that physically touch the compressor gas path. In addition, touch up coatings applied are strictly cosmetic and typically breakdown because of the in ability to sinter or cure the coated surfaces.

2.2.4 When using a mandrel to balance individual parts (i.e. impellers, coupling hubs, etc.), verify that the mandrel is balanced. Mandrels should be made from mild steel and should not have more than 0.0001 (0.00254mm) TIR (Total Indicator Runout). Ideally a ground finish to size mandrel is preferred, but is not required. The mandrel and impeller assembly shall be mounted onto the balance machine such that the impeller is located at the midspan between the balance machine rollers (not overhung).

2.2.5 When using the actual operating shaft to balance the mandral or impeller, verify that the shaft runout does not exceed 0.0002 (0.00508mm) TIR. If the shaft is used as the mandrel, the shaft must be component balanced to the 4W/N balancing specification before any component can be installed on it.


2.2.6 Verify that all interchangeable rotating parts (impellers, thrust disks, coupling halves, etc) are individually component balanced prior to being assembled on the shaft. Balance corrections on interchangeable components can be balanced using the shaft as a mandrel, provided the corrections are only made to the component being installed.

NOTE: The final trim balance planes used for correction shall always be limited to the outer most wheels of the rotating assembly. It is unacceptable to make final corrections on any component that can be removed or replaced in the Field. This requirement is necessary because experience has shown that large corrections have been made on the interchangeable components to achieve rotor balance in the past. When the component is changed or replaced in the field, the rotor then experiences a large unbalance vibration problem which may lead to significant equipment damage. Pump impeller wear rings shall also be installed on the impeller before balancing.

2.2.6.1 Examples of interchangeable rotating components are shaft sleeves, collars, nuts, over-speed trip mechanisms, non-integral thrust collars with or without key, and shaft deflectors.

NOTE: Coupling hubs should not be balanced with the rotor. Coupling hubs should be balanced as a separate unit to permit changing of hubs in the field without changing rotors.

2.2.7 Before component balancing, verify all components are tight on the shaft or mandrel. The fit requirement is for component balancing only, but needs to be verified for each individual component has an interference fit based on its design. The interference fit for component balancing on mandrels should be 0.0001 to 0.0002 (0.00254 to 0.00508mm) tight, as a minimum, per inch of shaft diameter. The fit for non-API equipment (ANSI, AGMA, etc) is specified on the respective Maintenance Repair Cards.

2.2.8 ANSI Style pumps. ANSI style pumps are typically designed with a loose fit on the impellers. This loose fit creates a certain amount of eccentricity. The eccentricity will affect the balance as described below:

2.2.8.1 How Eccentricity Effects Balance. Eccentricity effects balance by displacing the centre of gravity of the component. The amount of unbalance created by a known displacement can be determined as follows:

Unbalance x Radius (ounce-inches) = E (thousandth of an inch) x Wt (lbs) x 16

Unbalance = Total Unbalance (Ounces)

Radius = Radius of Unbalance Location (inches)

E = Displacement of Rotor (inches)

Wt. = Rotor Weight (lbs)

SI units: Unbalance x Radius (g.mm) = Wt (g) x E (mm)


2.2.8.2 If the amount of unbalance created by the eccentricity is greater than the 4W/N (in US Customary) balancing specification, then the rotor eccentricity must be corrected. Typically, this means that the loose fit is too great and a repair must be made.

2.2.9 When balancing always insert a fully crowned half key or an equivalent compensating moment

(weight) in all empty single key locations along shaft OD or in ID of impellers and couplings mounted on the mandrel or shaft. (NOTE: Rotors having 2 keyways which are 180 degrees apart in the same plane do not need to be filled.)

2.2.9.1 The purpose of the half-key is to replace the weight that is missing by not having the full

key installed during balancing. Note: The proper way to use full-keys is to fill the entire key slot in the shaft and the hub, with any excess material protruding from the hub would be milled away or removed. This would apply to either side of the coupling hub. See figure 2.2 below for an example drawing.

Figure 2.2: Properly designed full key used in the field.

HALF KEY WEIGHT ESTIMATES: There is a general rule of thumb for estimating half key weights. The rule is known as the 51% - 49% Rule. For simplicity purposes, the balancing technician can use a 51% factor of the total key weight as the half key weight for the shaft key and 49% of the total key weight for the hub key with acceptable accuracy. The half key weight can be calculated as follows:


Key Total_weight Key Height Key Width Key Length Key_material( ):=Key Total_weight = Key Total Weight (lbs)

Key Height = Key Height (inches)

Key Width = Key Width (inches)

Key Length = Key Length (inches)

Key_material = Density of the Steel (lbs/in^3)


Note: The density of steel varies based on the alloying constituents but usually ranges between 7,750 and 8,050 kg/m3 (0.280 and 291 lb/cubic inch).

2.2.9.2 An equivalent compensating moment (key weight) is acceptable and is more economical than machining half keys to size with a fully crowned shape. A suitable compensating moment (weight) can be made from either lead or steel. However, more accurate keys are required on high speed applications. Key weights for high speed applications can be more accurately calculated by the Area RE Engineer or the Site Vibration Specialist.

2.2.9.3 During Final assembly the key material shall be fabricated of the same material and quality

of the shafts.

2.2.9.4 All keys shall have all corners chamfered equal to the adjacent keyway radii, Chamfers shall be ground or cut at an angle 45 degrees with a tolerance equal to (+0.002 / - 0.000) of the respective keyway radii. (see figure 2.3)

Figure 2.3: Keyway chamfer

2.2.9.5 Keyway Clearances: Process to measure the Clearance 2.2.9.6 Step 1. With keys installed in shaft keyways, measure from the top of key to the opposite

side of the shaft. (Record reading). 2.2.9.7 Step 2. Measure across the bore of the component part to be installed to the bottom of the

keyway. (Record readings) NOTE: Item 2 (above) plus the total component interference fit minus Item 1. (above) equals the key clearance. Set the maximum (not to exceed) Key Clearance of 0.010 (0.254 mm) for top clearances and reference the ANSI B17.1-1967 Standard (or Equivalent) for compliance with all Class I Fits (side Tolerances).


2.2.10 Before balancing you must have weighed the assembled rotor. This step is required for all balancing tasks so that the correct balancing tolerance can be determined. (Warning: Do not exceed the load (weight) rating of the balancing machine. Both upper and lower limits are specified in the respective balancing machine manual.)

2.2.10.1 The Lower Limit. The lower limit on most balancing machines is 5 lbs (2.27Kg), but

should be confirmed by data found the manual of the balancing machine. This lower limit will require a more sensitive probe (as a rule of thumb consult with area inspector / engineer on rotors weighing less than 5 lbs (2.27Kg)).

2.2.10.2 The Upper Limit. If the specified upper limit is exceeded, the rollers and structural

supports on the balancing machine may be damaged. If weight is approaching the upper limit and the rotor is grossly out of balance, an overload condition can exist. If the rotor unbalance is extremely high on soft bearing balancing machines, the trunions will begin to hit the stops. If this occurs, consult Mechanical Equipment Department for assistance.

2.2.11 Some Coupling Manufacturers use vertical balancing machines to accomplish 2 plane

balancing, in which these machines are very sensitive to component weights. Care must be taken to confirm all weights when using these type of balancing machines

2.3 Balancing Machine Calibration Requirements 2.3.1 Each balance machine shall be calibrated on a yearly basis as a minimum. This calibration

shall include a certificate to document the calibration of the machine.

2.3.1.1 A calibration sticker shall be installed on the balancing machine as a notification to all users that the machine is ready for use. If the sticker is not present, then the balancing machine should not be used until it has been calibrated.

2.3.1.2 The calibration sticker shall contain as a minimum the date at which the calibration was

performed and a calibration renewal date.

2.3.2 Residual unbalance checks shall be performed on each balancing machine when the following balance requirements exist:

2.3.2.1 The rotor being balanced operates at a speed of greater than 3600 rpm.


2.3.2.2 If the balancing readings dont make sense or do not repeat during the final balance check, then a residual unbalance check must be performed on the balancing machine. Refer to Appendix 2 for Residual Unbalance Check Requirements.

Figure 2.4: Typical low speed balancing machine (courtesy: Schenck-Rotec) 2.4 Troubleshooting Guidelines to Use during Shop Balancing

2.4.1 Windage Effects: Windage effects have been known to affect the balance on both large and small impeller designs (i.e. closed face designed fan impellers and high speed light rotors found in integral gear compressors). The windage effects are typically determined by inconsistent or non-repeatable amplitude and phase readings on the balancing machines. Using duct tape to close off the inlet and discharge flow passages can eliminate this effect. The amount of duct tape used will not affect the final balance provided it uniformly distributed during installation. Spinning the rotor counter to the normal rotational direction can also help minimize the pumping effect the impellers produce. If a windage problem is identified, consult the Mechanical Equipment Department for assistance.

2.4.2 Multi-stage Impeller Pumps. This type of pump design is typically in boiler feed water

service. Various balancing methods can be used to obtain a truly balanced rotor. Concerns always exist because of the potential of galling a shaft during the assembly and disassembly process. The problem exists because of the stacking process of the inter-stage diffusers or stage pieces. Therefore, the method used should consider the potential consequences. A method used in the past consists of combining the component and assembly balancing procedures, typically used on critical services where a soft start up is required. This procedure is as follows:

2.4.2.1 Component balance each impeller.

2.4.2.2 Assembly balance the rotor using a progressive stacking procedure.


2.4.2.3 Record all face and diametrical runouts.

2.4.2.4 Match mark all components.

2.4.2.5 Disassemble rotor.

2.4.2.6 Stack rotor with all stationary components installed using the disassembly match marks established.

2.4.2.7 Place the rotor in the pump case and record the face and diametrical runouts on the impellers.

2.4.2.8 Correct the runout readings to repeat what was established in Paragraph 2.4.2.3, above.

2.4.2.9 This method will help ensure that the final rotor balance obtained without the stationary inter-stage diffusers (pieces) will meet the 4W/N specification.

2.4.3 Internal Cracks in Materials. Cracks can cause havoc during the balancing of a rotating assembly. When an internal crack exists, the typical response on a balance machine is that the impeller or shaft exhibits inconsistent or non-repeatable amplitude and phase readings. Unfortunately, this cannot be determined visually and an NDT Method (i.e. Dye Penetrant, Wet Magnetic Particle or Ultrasonic Inspection Method) would have to be deployed to identify the defect. If a crack is suspected as the culprit for not being able to obtain a proper balance, consult the Mechanical Equipment Department for assistance.

2.4.4 Liquid Under Sleeves or Impeller. During the cleaning or decontamination process on a

stacked rotor, liquid has been trapped under these components. The trapped liquid will cause an inconsistent or non-repeatable amplitude and phase reading on the balance machines. Unfortunately, this cannot be drained without complete disassembly of the rotating assembly. Consideration has been given to both applying heat to evaporate the trapped liquid and drilling holes in the component to drain the liquid. However, neither method has resulted in 100% removal of the trapped liquid.

2.4.5 Induced Heat Caused by the Removal of Material During Grinding. The grinding process

used to correct the amount of unbalance in the rotor can also cause an inconsistent or non-repeatable amplitude and phase reading on the balance machines. It has been indicated time and time again that the grinding process creates enough heat to thermally distort the material, which generates non-repeatable balancing data. The recommended practice is to grind the rotor to remove weight and then allow the rotor to return to ambient temperatures before the next balancing run is accomplished.

2.4.6 Induced Heat Caused By Drive Belt Friction. Repeated run-ups and run-downs on heavy

rotors using a drive belt as the means to rotate the rotor can induce heat from friction into the rotor. This can cause the rotor to thermal bow and make balancing impossible. Check between runs for rotor heating and slowly ramp up the speed for balance runs and slowly slow down to stop. Using a driveshaft to drive heavy rotors on the balance stand is a better option. Be sure to rotate the drive shaft 180 degrees after the first run to test for unbalance induced by the driveshaft. Any unbalance introduced by the drive shaft should be subtracted electronically by the balance machine software or the drive shaft should be balanced to remove the unbalance.


2.5 Balance Tolerance calculations 2.5.1 Single or two plane balancing API 610 11th Edition (6.9.4.2) states that a two-plane balance for components is required when the ratio of D/b is less than 6. Other than this, single plane balance is acceptable. Where: D = Component Diameter

b = Component Width.

Figure 2.5: Single plane balancing determination (API 61011th 6.9.4.2)

On some components (especially Single Stage Pump impellers) a 2 plane balance cannot be achieved because there is not enough physical separation between the identified balance planes. In this case a single plane balance is acceptable to perform and the coupled effects have proven not to be detrimental to the pump operation.

2.5.2 Acceptable Unbalance tolerance

It is the intention that all balancing be done on the rotor to the lowest possible unbalance tolerance to guarantee the lowest unbalance forces while the rotor is in operation. Therefore all rotors and components shall be balanced to 4W/N according API 687. The cost to achieve this unbalance limit is insignificant when the rotor is already in the balancing stand. Clarification: Clause 2.8.4.1 in the Balance section of API 610 8th Edition states: Impellers, balancing drums, and similar major rotating components shall be dynamically balanced to grade G 1.0 of ISO 1940 (4W/N) or 7 g-mm (0.01 oz-in.), whichever is greater. This implies that G 1.0 and (4W/N) are the same, but this is incorrect. The U.S. unit limits given in API 610 corresponds to approximately to the midpoint of the ISO range. In other words, the residual unbalance (4W/N) actually equates to G 0.665, not G 1.0!


Use the worksheet in Appendix 2 to calculate the acceptable unbalance tolerance. For all machines the total allowable unbalance tolerance is based on APIs balance tolerance which is four times the total rotor weight in pounds divided by the maximum continuous operating speed in revolutions per minute. This is then multiplied by 28.35 to convert ounce-inches to gram-inches. (NOTE: If using a 2 plane balancing technique, the total allowable unbalance tolerance should be divided by 2 or ratio if the balance plane is not in the centre.)

U = 4 x W x (28.35)

N U = Maximum Allowable Unbalance (gram-inches) W = Is the component mass (for components), expressed in pounds; or the load per balancing machine journal (for rotors), expressed in pounds N = Maximum Continuous Rotor Speed (rpm)

SI units: per plane U = 6350 x W / N gmm U = Maximum residual unbalance, gmm (gram millimeter) W = Weight of Impeller, kg N = Site running speed, rpm

EXAMPLE 1: A 500# rotor from a 3600 rpm single stage turbine is to be balanced. What is the total allowable residual unbalance?

U= 4 x 500 x 28.35 3600

U= 15.75 gram-inches

2.5.3 The allowable unbalance per plane (in a 2 plane Balancing Set-up) would be: U per plane = 4 x W x 28.35 or ; 2 x Wx 28.35 N x 2 (planes) N EXAMPLE 2: What is the allowable residual unbalance per plane from the above example?

Unbalance per plane = 15.75 2

Unbalance per plane = 7.88 gram-inches


where

2.5.3.1 This means that at each bearing location the allowable unbalance is 7.88 gram-inch. This prevents having the total allowable unbalance of 15.75 (gram - inch), unevenly split. Thus, having 10 gram-inch on one bearing and 5.75 gram-inch on the other is not acceptable if the component is in the middle of the shaft / mandrel. In case of asymmetrical position of the unbalance the allowable unbalance at each location should be calculated by means of the LA/L and LB/L.

Note: For more complex multi-stage rotors the Area RE Engineering staff may need to be consulted to determine the exact Resultant bearing loads to apply in the formulas above.

L = distance between supports LA = Distance from support A to unbalance LB = Distance from support B to unbalance

2.5.4 When to Consider Dynamic or Couple Unbalance versus Static Unbalance (General Note: For simplicity, the couple rule is used interchangeably within this document as well as within the industry to address both dynamic and couple effects. True definitions of each condition are given below for user reference.)

2.5.4.1 Static Unbalance. Static unbalance is that condition of unbalance where the central principle axis is displaced only parallel to the shaft axis (Center of Gravity). The unbalance shown in Figure 3 on the following page displaces the principle axis off the rotating centerline. The central principle axis is the axis about which the mass of the rotor (and its moments) is equally distributed. This displacement creates the unbalance (figure 2.6).

Figure 2.6: Static unbalance interpretation.

2.5.4.2 Static unbalance can be resolved with one correction placed at the center of gravity of the rotor.

2.5.4.3 Coupled Unbalance. Coupled unbalance is that balance condition for which the central

principle axis intersects the shaft axis at the center of gravity. Since the unbalance weights at each end of the rotor are equal but diametrically opposite, the rotor center of gravity has not been displaced from the shaft axis. Under these conditions, when rotating, the weights generate equal but opposite moments which cause the principle axis to tilt as shown in Figure 2.7.

2.5.4.4 Couple unbalance can be resolved by making two corrections, one placed in each of the

balance planes. However, it is often better to check the static component of unbalance first. Very often the static component represents the majority of unbalance present. Unnecessary grinding can be avoided by removing the static unbalance first, then checking the couple unbalance.


Figure 2.7: Coupled unbalance interpretation.

2.5.4.5 Dynamic Unbalance. Dynamic unbalance is the unbalance condition for which the principle axis is not parallel to and does not intersect with the shaft axis center of gravity

2.5.4.6 Dynamic unbalance can be resolved by making two corrections, one placed in each of the

balance planes. However, it is often better to check the static component of unbalance first. Very often the static component represents the majority of unbalance present. Unnecessary grinding can be avoided by removing the static unbalance first, then checking the dynamic unbalance. See Figure 2.8 for the physical rotor representation.

2.5.4.7 Dynamic and couple balance is easily obtained when the balancing planes are widely

separated. But for those cases where the planes are close together, achieving the allowable balance tolerance is difficult. However, the dynamic or couple unbalance need not be completely removed if the disc is narrow as compared to the distance between bearings. To determine the dynamic / couple tolerance divide the distance between rotor bearings by twice the separation of planes of the single disc and multiply the allowable residual unbalance tolerance calculated from the above equation by this value. This will be referred to as the couple rule. This is per ISO 1940-1973(E), Section 3.2, unbalance effects. Reference the correction method described Figure 6, Typical Rotor Set-up Sketches.

Figure 2.8: Dynamic unbalance interpretation.

2.5.4.8 General Couple Rule (Reference Figure 2.8): If (A) divided by (2 x B) is equal to or less

than one, then the allowable couple tolerance is the same as the allowable unbalance (dynamic) calculated in the 4W/N calculation above. If the value is greater than 1, then the unbalance tolerance can be corrected using the equation below. This will allow a greater balancing tolerance for final balance corrections. (NOTE: This general rule applies to both mandrels and shaft mounts in which the dimension A does not exceed the actual bearing span on the piece of equipment.)

Ucoupled = A x T 2B

Uc = Allowable couple unbalance (gr-in) A = Distance between rotor bearings (not the balancing machine bearings) in inches. B = Distance between balancing planes (width of disc) in inches. T = Maximum unbalance tolerance (4W/N calculation)


Figure 2.9: Typical rotor setup sketch.

EXAMPLE 3: A single stage turbine rotor weighing 300 lbs. with a maximum continuous speed of 3800 rpms is to be balanced. The distance between bearings is 24 inches and the distance between balance planes is 1 inch. What is the allowable static unbalance (total) and what is the allowable couple unbalance per plane? (Reference the worksheet in Appendix 2 for a step by step procedure and quick tool. Static unbalance (total unbalance)

U total = (4) x W x 28.35 N

U total = 4 x 300 x 28.35 3800 U total = 8.94 gram -inches Next, determine the ratio (A / 2xB); Static balance ratio = A 2B

Static balance ratio = 24 = 12 2 x (1)


Therefore; Ucorrected per plane = (A/2B) x (U total) 2 Ucorrected per plane = 24 x (8.94 / 2) gram - inches (2 x 1) Ucorrected per plane = 53.6 gram -inches.

Example 3 Conclusion: This unbalance correction is necessary due to the small moment generated between the potential balancing planes. If a correction was attempted to achieve the 4W/N balancing criteria, then a violation of the minimum wall thickness is expected (reference Section 3 below for general grinding rules). Therefore, the total (static) unbalance tolerance would be 8.94 gram -inches and the dynamic (coupled) unbalance tolerance would be 53.6 gram inches / plane. This will prevent having to add or remove weights (unnecessarily) to achieve an acceptable dynamic balance on the rotor.

2.5.5 When impellers are replaced or a weld repair was performed, the replacement impeller shall

require an overspeed spin test to the design limit specified by the OEM (per the DEP and API requirements), before it is component balanced and installed on the rotor.


3 High Speed Balancing

3.1 General Requirements 3.1.1 High speed balancing (HSB) may only be required on flexible rotors (running above first

critical speeds) and not on rigid rotors. All rigid rotors shall be only balanced by low speed balancing as covered by section 2.

3.1.2 In addition, all Dimensional inspections per the appropriate Inspection and repair documents shall be complete and within tolerances (axial and radial Runouts, diameters, etc).

3.1.3 Prior to High Speed balancing the components and rotor assembly shall be low speed balanced as per section 2 of this RE-SPG.

3.1.4 The latest edition of API 687 shall be adhered to. 3.1.5 High speed balancing shall be done in a vacuum bunker where it is safe to run the rotor and

limit the amount of windage which will be created. There is considerable risk with running a rotor up to higher speeds. A few of the Potential risk are:

3.1.5.1 Components/assemblies may break loose

3.1.5.2 Rotor destruction

3.1.6 Balancing shall be performed by qualified personnel at balancing facility suitable for high speed balancing, properly equipped with all applicable accessories.

The rotor shall be mounted on bearing pedestals of a balancing pit in pit bearings. The rotor shall be driven by a flexible drive shaft that will not affect the quality of balancing. The vibration measurement shall be done by velocity probes mounted on bearing housings. Parameters and number of the vibration probes shall correspond to the balancing pit instruction manual. Stiffness of the bearing pedestals shall be adjusted to rotor mass and rotating speed based on balancing facility experience.

3.1.7 Prior to balancing the calibration of the balancing machine shall be verified.


3.2 Evaluation if HSB is required 3.2.1 High Speed Balancing (extract API 687 sect 10.6, with minor modifications)

Generally, compressor and turbine rotors do not require high-speed (or at speed) balancing. There are, however, conditions where high-speed balancing should be considered which may include, but not be limited to the following:

3.2.1.1 Rotors which have exhibited high vibration as they pass through their critical speeds (identified by R&D, testing or historical field experience)

3.2.1.2 Rotors which accelerate slowly through their critical speeds (as part of an operational requirement).

3.2.1.3 Rotors which are running on or near a critical speed (1st or 2nd radial/axial modes). 3.2.1.4 Rotors which are sensitive to unbalance. 3.2.1.5 Rotors for equipment in extremely critical services. 3.2.1.6 Rotors going to inaccessible locations, such as offshore. 3.2.1.7 Very long, flexible rotors. 3.2.1.8 Places where a critical rotor cannot be run in its intended casing prior to installation.

NOTE: All OEMs are specifying HSB now for almost all repairs for NO reason. We have approached various OEMs and asked if the rotors required this from an engineering and design standpoint and both when questioned the recommendation was deleted. It is a cash cow for the OEMs that have a HSB machine (high margins are made and some rotors really don't require the HSB at all).

3.2.2 In general HSB would only be required just after the first assembly of the rotor in its life or

after significant modifications / repairs were done on the rotor which could change the unbalance of the rotor beyond the first critical speeds. Such modifications / repairs could be:

a. Depending on rotor design (Rotor-Dynamics model) b. Installing of new (design) impellers and shaft sleeves c. Welding of the rotor including Post Weld Heat Treatment (PWHT), disk welds, major shaft

restoration (should be assessed at each change even with shaft end restoration HSB may not be required)

d. Rotors having done a dynamic evaluation to reduce the Amplification Factor e. Rotors that have a history of high vibrations at start-up and/or shut-down. f. In case of disk or blade replacement an integrity check may be required and a HSB may be

performed.

3.2.3 A decision tree can be found in Appendix 1 to help determine if HSB is required.

Figure 3.1: Typical high speed balancing system (courtesy: Schenck-Rotec)


3.3 High Speed Balancing test procedure 3.3.1 Before starting, ensure the rotor has been low speed balanced to the correct tolerance (see

section 2 above).

3.3.2 Prior to placing the Rotor in the HSB Bunker the following shall be reviewed and approved: 3.3.2.1 OEM HSB Procedure 3.3.2.2 Balancing Speeds (MCOS, OST, etc) or any other speed that is required to confirm

balancing criteria. 3.3.2.3 Procedure for Influence Corrections to achieve the desired balance results at higher speed

where the rotor may be approaching the 2nd critical speed. 3.3.2.4 Sizing and selection review of the Bearings used in the HSB pedestals (Load rating, oil

flow requirements, cooling requirements, etc) 3.3.2.5 Calibration records of the HSB facility and scales used in the HSB process. 3.3.2.6 Agreement on Data collection (transient data, BODE Plots, Orbits waveform data, etc)

that will be used in the final report. All plots and data shall be transferred electronically for future reference. An agreement should be made that the ADRE data may be requested if issues are observed during the HSB process (This is sometimes hard to get after the balancing process begins).

3.3.2.7 Review of correction methods proposed and proper procedure to lock in any weights that are added to insure they don't become loose in operation.

3.3.3 Install the rotor into bearing pedestals and check bearing clearances with the standard facility

bearings. Tilt-pad bearings shall have babitted end seals to prevent oil starvation due to operating in a vacuum bunker. Rotor shall be fully assembled excluding interchangeable or loose parts (coupling hub, shaft end nuts, parts of shaft end seals and others if any). Half key shall be installed at the free shaft end if one key shaft end is applied.

3.3.4 All coating shall be applied before the LSB step. All balancing correction made on the rotor after the coating process has been completed will be restricted to the furthest diameter between impeller vanes (scalloped configuration) on the Outer most diameter of the impeller. At NO time will any grind occur on the face of the impeller cover or hub after the coating is applied, without written approval of a Shell Rotating Equipment Engineering Representative. This will prevent any breakdown of the coating or coated surfaces that physically touch the compressor gas path. In addition, touch up coatings applied are strictly cosmetic and typically breakdown because of the in ability to sinter or cure the coated surfaces.

3.3.5 Verify visually the rotor serial number to ensure your rotor is on the balancing machine. 3.3.6 When High Speed balancing, the speed shall not exceed Maximum Continuous Operating

Speed (MCOS). (Note: Some Manufacturers will request that a higher speed be used to settle the components (e.g. impellers, turbine blades, etc) since these are interference fits. If this request is made the speed used shall not exceed the OST (over-speed trip) speed and shall not run longer than 5 minutes.)

3.3.7 Verify again with the balancing machine operator that the correct MCOS will be used for the rotor in the balancing machine.

Note: It has happened before several times that there was some confusion on which rotor was being balanced and the rotors were accidentally swapped. This resulted in the rotor running higher than overspeed, resulting in detailed investigations into the rotor condition. Therefore it is important to ensure you have the latest machine data sheet and the correct rotor is on the balancing machine.


3.3.8 Accelerate the rotor to between 300 and 500rpm and measure the slow roll run-out. This is to verify the mechanical and electrical runout does not exceed the allowable levels and a proper

reading will be obtained from the measurement. Also it is important to understand for slow roll (vector) configuration for slow roll compensation, if it is required.

3.3.9 Accelerate the rotor to about 850rpm and measure the unbalance. In case the unbalance does not exceed five (5) times the calculated low speed balance tolerance (i.e. five times the 4W/N) accelerate the rotor to MCOS (per the directions below).

3.3.9.1 The speed of the rotor shall be increased by increments of 10% of the maximum continuous speed from zero up to the MCOS. Critical speeds, residual unbalances and vibration levels of the rotor shall be monitored and recorded. After recording the parameters at the maximum continuous speed the rotor speed shall be decelerated to 0 rpm.

3.3.9.2 Corrections to reduce the unbalance shall be made by the engineer in accordance with the

guidelines in chapter 4 and mutually agreed upon HSB procedure.

3.3.10 The rotor HSB acceptance criteria are defined in chapter 3. 3.3.11 Corrections for the tooling and the balancing machine support stiffness shall be done by the

engineer, based on his experience. If the rotor is starting to approach the 2nd critical speed the rotor shall be corrected to obtain both acceptable tolerance at Overspeed and MCOS. Sometimes an increase in amplification factor is required to achieve the acceptance criteria.

3.3.12 After the high speed balancing is completed, a low speed balance check should be done to record the profile of at low speeds, including all set-up information. This check can only be compared in the future if done on the same balancing machine and facility bearings.

Note: When the rotor has been in storage for long times, a low speed balance check can be performed. No re-balancing should be done without careful consideration. The rotor may have a temporary rotor bow due to long term storage or a temporary bow due to small temperature differences between the top and bottom of the rotor. This is why vertical storage is preferred. It can be attempted to remove the temporary bow in the rotor by slowly (as low as 10 rpm) rotating the rotor for 24 hours in a lathe.

3.4 High Speed Balance tolerance

The High speed balance quality at maximum continuous speed shall follow the below criteria, i.e. bearing pedestal vibrations and peak-peak amplitude of unfiltered vibrations in any plan. These vibrations are set with maximum pedestal stiffness.

3.4.1 Bearing pedestal vibrations (API 687 10.6.2)

The maximum allowable bearing pedestal vibrations shall be the following values (with maximum pedestal stiffness applied ):

N > 3000 rpm, max velocity =

, mm/s RMS or max 1 mm/s RMS (whichever is smallest)

N < 3000rpm, max 2.5mm/s. Where N equals the MCOS


3.4.2 Peak-Peak unfiltered vibrations (API 617 2.6.8.8) During the shop test of the machine, assembled with the balanced rotor, operating at its maximum continuous speed or at any other speed within the specified operating speed range, the peak-to-peak amplitude of unfiltered vibration in any plane, measured on the shaft adjacent and relative to each radial bearing, shall not exceed the following value or 25 microns (1 mil), whichever is less: SI units

25.412000

Or in US Customary Units

12000

A = Amplitude of unfiltered vibrations peak-peak (m) N = Maximum Continuous Operating Speed (MCOS)

3.4.3 Pedestal stiffness has a major influence in the response of the rotor on the balancing machine.

3.4.4 At any speed greater than the maximum continuous speed, up to and including the trip speed of

the driver, the vibration level shall not increase more than 12.7 m (0.5 mil) above the maximum value recorded at the maximum continuous speed. Install the rotor into bearing pedestals and check bearing clearances with the standard facility bearings. Tilt-pad bearings shall have babitted end seals to prevent oil starvation due to the rotor being operated in a vacuum bunker. Rotor shall be fully assembled excluding interchangeable or loose parts (coupling hub, shaft end nuts, parts of shaft end seals and others if any). Half key shall be installed at the free shaft end if one key shaft end is applied.

3.4.5 Caution: Subtraction of the Slow Roll Vector. Typically running a rotor below 500 rpm (at fixed speed note the slower the better) there is not enough energy or influence from centrifugal forces, wind loads or steam to effect the slow roll vector and the data is typically very reliable to record or capture the affects of the combined mechanical and electrical runout. Therefore, at the slow roll speed, the 1x amplitude and phase should be recorded. It should be noted; that the Slow Roll Vector subtraction can be misleading, whereas the vector applied may yield additive effects versus reduce the overall vibration depending on the phase angle. In most cases, in a controlled environment (under vacuum in an at speed balancing bunker) the readings are very stable. Although, when on a test stand during a Mechanical run test, there have been cases when a centrifugal forces, wind, or steam can cause the amplitude and phase to fluctuate. The shifting is typically due to external forces on the rotor that cannot be controlled during the FAT mechanical run testing and can sometimes be eliminated by slowing down the rotor speed or holding a tighter rpm tolerance on speed control. This fluctuation in phase and amplitude (from real time data) can be confusing to interpret if experienced. Before selecting a Slow Roll vector, it is advised to discuss with the other Senior Rotating Equipment Engineers or Vibration Specialist to insure that the fluctuation are not a design, manufacturing or assembly issue before the final vector is selected.


4 Basic Rules for adding and removing weights

4.1 Basic rules apply for adding and removing weight. These rules take into account the structural and mechanical integrity of the component being balanced.

Each rule is specific to a certain type of machine, but can be applied to other types provided an engineering evaluation is performed. The rules are as follows:

4.1.1 Turbine Disk. The most effective diameter to grind on a turbine wheel is the largest radius on

the disc (as measured from shaft centreline) located below the buckets. However, this is typically the most critical, or highest stressed, area on the wheel. The balancing rule for turbine discs is created by a no balance zone (illustrated in Figure 7). This no balance zone circumferential width around the turbine disc OD, bound by the OD of the wheel and a position located 1 below the internal blade root. A reduction of wall thickness in this area will increase the turbine disc stresses and reduce the life of the wheel. Grinding in the no balance zone must be avoided.

Figure 4.1: Turbine disc no balance zone.

4.1.2 Gears. The most effective way to balance a gear is by drilling a hole to remove weight, drilling

and tapping a hole to install a threaded plug to add weight or grinding for minor adjustments. There is a correct way to drill the balance holes and a incorrect way (Reference Figure 8, below). Typically, common sense says to drill the hole directly under the meat of the gear tooth. This is incorrect. Holes should never be drilled in this area because when a gear tooth fails, the crack propagates at a 45 degree angle from the radius at the bottom of the gear tooth. The hole acts as a stress riser within the typical crack propagation path. Therefore, the best place to drill a hole to correct for unbalance in the gear is directly between the gear teeth. The weight removed can be calculated by determining the area of the hole based on its diameter then multiplying it by the hole depth and the density of steel (0.294 lbs / cubic inch), as shown in the equation below. In addition, a no balance zone will be established in an area just below the gear tooth radii for a distance of at least 1 tooth height.


Weight Removal 3.14Diameterhole( )2

4 Hole Depth( ) Density steel

== SStteeeell WWeeiigghhtt RReemmoovveedd ((llbbss)) WeightRemoval == HHoollee DDiiaammeetteerr ttoo bbee DDrriilllleedd ((iinn)) Diameterhole

== HHoollee DDeepptthh ((iinn)) HoleDepth

== SStteeeell DDeennssiittyy -- llbbss.. //

Figure 4.2: Gear balancing technique using drilled holes.

4.1.3 Pump and Compressor Impellers. The most effective way to balance an impeller on either a

compressor or pump is by grinding. The grinding depth shall be limited to the following criteria:

4.1.3.1 Tip thickness. A thickness dimension shall be determined on the outside diameter of the impeller hub and cover (if applicable). A 15% reduction in thickness shall be considered acceptable during any grinding application (See Figure 4.3 & Example 4, below). This acceptance criteria is applicable provided the ground area is feathered smooth to remove any abrupt changes in wall thickness that can generate a stress riser. Any deviations from these acceptance criteria shall require an evaluation to determine fitness for service by the Rotating Equipment Area Representative.


Densitysteel in3

Figure 4.3: Pump or compressor impeller thickness limitation.

4.1.3.2 Riveted Impellers. Extreme caution shall be applied when making a balancing correction

on a riveted impeller. The rivets are designed to hold the cover, hub and blades together. The balancing correction made on the impeller shall avoid any contact with the heads of the rivet. Grinding on the heads of the rivets can weaken their mechanical fastening ability. Therefore, all grind corrections shall be made between the impellers. In addition, an NDT inspection shall be performed to identify cracked rivet heads and loose rivets before any balance correction is performed. (Reference Figure 4.4)

Figure 4.4: Riveted impeller grinding restrictions.


Example 4: A jet pump impeller has an OD of 24 inches. The tip thickness on the impeller cover is 0.256 and the pump impeller hub has a tip thickness of 0.388. What is the minimum wall thickness to which the impeller can be ground during the balancing procedure?

Calculate the cover minimum thickness as follows:

Cover Thickness 0.85 Cover Tip_thickness:= Cover Thickness 0.218in= Calculate the hub minimum thickness as follows: Hub Thickness 0.85 Hub Tip_thickness( ):= Hub Thickness 0.33in=

4.1.3.3 Fans. The most effective way to balance a fan rotor is by adding weight. Weights are typically added to fans and attached via welding. A plate is designed and sized to provide the proper weight at a known distance from the shaft centerline. This plate is typically designed with steel plate or a material compatible with the material of construction of the impeller. The corners on the plate are designed with a generous radii ( radius, minimum). These plates are then fillet welded on the fan impeller. (Note: Prior to welding on any fan assembly, machine, rotor or component, an approved weld procedure specification (WPS) and procedure qualification record (PQR) shall be obtained for review and approval). After welding, an NDT Dye Penetrant or Magnetic Particle Inspection shall be performed on the welded area by a Certified Level II inspector qualified in the inspection field being utilized. Contact a Rotating Equipment Representative for assistance in sizing a balancing plate.

4.1.3.4 Screw Compressor Rotors. The most effective way to balance a screw compressor rotor

is that method used in balancing a gear. Due to the asymmetric design of the screw compressor rotor, weight can either be removed or added to the rotor. To remove weights during balancing, grinding or drilling of holes is acceptable. To add weights during balancing, drilling and tapping a hole to install a threaded plug of (higher density) material other than steel is acceptable, provided the material selected is compatible with the process fluid and the plugs are staked in place to prevent them from backing out in operation. (Note: Welding of weights is typically not acceptable due to the small internal clearances of the screw compressor.)


5 References API 617, 2002 Axial and Centrifugal compressors and Expander-compressors for Petroleum, Chemical and Gas Industry Services. API 684 2nd edition, 2005 Rotor Dynamic tutorial: Lateral critical speeds, unbalance response, stability, train torsionals, and rotor balancing API 687 1st edition, 2009 Rotor Repair ISO 1940-1, 2003 Mechanical Vibration balance quality requirements for rotors in constant (rigid) state. Part 1: Specification and verification of balance tolerances ISO 11342, 2000 Mechanical vibration methods and criteria for the mechanical balancing of flexible rotors


APPENDIX 1 High-Speed Balancing decision tree


Is Hi-Speed Balancing required?

Is it a Gas Turbine Rotor

No Hi-Speed balancing requiredYES

Is it a new rotor or has it been

repaired

Separation Margin lower than 2.6.2.10

(API617-2002)

NEW

Has the rotor been disassembled, de-stacked or parts

removed

REPAIRMajor components

removed; impellers, discs,

YES

Only minor repairs; cleaning, minor blending

NO

No Hi-Speed balancing requiredYES

Has the rotor been severely grinded, welded or metal sprayed? PWHT

applied

NO

Yes Hi-Speed balancing required

NO

Does the machine exibit high

vibrations during operation (incl

transients) High amplification factor

AF

YES

Level II final log decrement results

APPENDIX 2 Residual Unbalance Procedure & Tool

Residual Unbalance Procedure.pdf

Calculation tool for determining the Allowable residual Unbalance

Residual Work Sheets 8pt.xls



APPENDIX 3 Training This section is designed to set the training requirements for everyone associated with balancing machinery in the mechanical discipline. The purpose of this section is to define guidelines regarding both initial training and refresher training associated with operating balancing machines at the Shell Norco Facility. The training will be designed with both classroom and performance or hands on applications. It will be offered to the following groups: Machinery Engineers. The Machinery Engineers are required to go through this training so that they understand the fundamentals of balancing. This will give them an understanding of how rotors are balanced and introduce them to the physical complications that a machinist may encounter during a rotor balance. Machinery Inspectors. The Machinery Inspectors will be required to go through this training to gain knowledge of how to apply the fundamentals of rotor balance. This will help them troubleshoot issues that one encounters during routine balancing activities. Machinist. The machinist will be required to go through this training both to understand the fundamentals of rotor balancing and to get some hands on training on various balancing machines on site. This training shall provide the basic knowledge regarding the dos and donts of balancing to preserve and protect the mechanical integrity of the rotating assembly. Initial training shall be provided to the groups listed above. Refresher training shall be offered per the following: If the machinist has successfully or actively balanced a rotor within a period of 1 rolling year, then refresher course is not necessary. The only exception to this rule would be if the need were identified as a request from the immediate supervisor. If the machinist has gone for longer than a 1 year period without balancing a rotor, then a refresher course is recommended. The refresher course would include the physical review of the Balancing procedure and review or the PowerPoint presentation located on the machinery web page. A refresher course may be required every 3 years, but is under the discretion of the immediate shop supervisor.

1 Introduction 1.1 SCOPE1.2 DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS1.3 DEFINITIONS1.4 SUMMARY OF MAIN CHANGES 1.5 COMMENTS ON THIS RE-SPG1.6 DEVIATION CONTROL

2 Low Speed Balancing2.1 General Requirements2.1.1 The pre-balancing part of the procedure is for preparing the parts to be balanced. Using the actual shaft when balancing is recommended, when not available, the use of a mandrel is acceptable. API 687 specifies only 2 methods of balancing: component balancing or assembly balancing: 2.1.2 Component balancing is performed by first balancing the shaft and all impellers separately, then assembling rotor and checking the balance of the total assembly. Balancing correction to the assembled rotor is not permitted. If out of tolerance, the rotor is disassembled and procedure is repeated. (Note: This procedure is typically used for diffuser type pumps or API Pump Multi-Stage Impeller applications.)2.1.3 Assembly balancing, sometimes referred to as progressive or stack balancing, is performed by balancing the shaft first, then installing and making corrections to no more than two impellers at a time. All balance corrections shall be applied to the last elements added to the shaft during the stacking process. Minor correction of the other components may be required during the final trim balancing of the completely assembled rotor.2.1.4 Any corrective work required to the impeller bore, diameters or machining of wear rings MUST be completed before the balancing commences.

2.2 General Rules and Guidelines2.2.1 Verify the shaft or mandrel OD that rides on balance stand anti-friction support rollers is NOT the same OD as the balance stand anti-friction support rollers. Experience has shown this to cause erroneous readings. The general rule is that the balance machine antifriction support rollers, which are within (+/-) 5% of the same nominal diameter as the shaft journal diameter(s), shall not be used due to possible roller noise masking the balance readings.2.2.2 Avoid running the balance stand rollers on chromed or coated surfaces. Heavy rotors and over-hung rotors can exert very high local surface stresses on coated areas that cause the coating to crack (figure 2.1 for example of microcracks after PT). If there is no other option but to roll on a coated area use the widest rollers possible and NDT inspect before and after for cracks./2.2.3 If the Rotor has been coated, corrections made on the rotor will be restricted to the furthest diameter between impeller vanes (scalloped configuration) on the Outer most diameter of the impeller. At NO time will any grind occur on the face of the impeller cover or hub after the coating is applied, without written approval of a Shell Rotating Equipment Engineering Representative. This will prevent any breakdown of the coating or coated surfaces that physically touch the compressor gas path. In addition, touch up coatings applied are strictly cosmetic and typically breakdown because of the in ability to sinter or cure the coated surfaces.2.2.4 When using a mandrel to balance individual parts (i.e. impellers, coupling hubs, etc.), verify that the mandrel is balanced. Mandrels should be made from mild steel and should not have more than 0.0001 (0.00254mm) TIR (Total Indicator Runout). Ideally a ground finish to size mandrel is preferred, but is not required. The mandrel and impeller assembly shall be mounted onto the balance machine such that the impeller is located at the midspan between the balance machine rollers (not overhung).2.2.5 When using the actual operating shaft to balance the mandral or impeller, verify that the shaft runout does not exceed 0.0002 (0.00508mm) TIR. If the shaft is used as the mandrel, the shaft must be component balanced to the 4W/N balancing specification before any component can be installed on it.2.2.6 Verify that all interchangeable rotating parts (impellers, thrust disks, coupling halves, etc) are individually component balanced prior to being assembled on the shaft. Balance corrections on interchangeable components can be balanced using the shaft as a mandrel, provided the corrections are only made to the component being installed. NOTE: The final trim balance planes used for correction shall always be limited to the outer most wheels of the rotating assembly. It is unacceptable to make final corrections on any component that can be removed or replaced in the Field. This requirement is necessary because experience has shown that large corrections have been made on the interchangeable components to achieve rotor balance in the past. When the component is changed or replaced in the field, the rotor then experiences a large unbalance vibration problem which may lead to significant equipment damage. Pump impeller wear rings shall also be installed on the impeller before balancing.2.2.6.1 Examples of interchangeable rotating components are shaft sleeves, collars, nuts, over-speed trip mechanisms, non-integral thrust collars with or without key, and shaft deflectors.

NOTE: Coupling hubs should not be balanced with the rotor. Coupling hubs should be balanced as a separate unit to permit changing of hubs in the field without changing rotors.2.2.7 Before component balancing, verify all components are tight on the shaft or mandrel. The fit requirement is for component balancing only, but needs to be verified for each individual component has an interference fit based on its design. The interference fit for component balancing on mandrels should be 0.0001 to 0.0002 (0.00254 to 0.00508mm) tight, as a minimum, per inch of shaft diameter. The fit for non-API equipment (ANSI, AGMA, etc) is specified on the respective Maintenance Repair Cards.2.2.8 ANSI Style pumps. ANSI style pumps are typically designed with a loose fit on the impellers. This loose fit creates a certain amount of eccentricity. The eccentricity will affect the balance as described below: 2.2.8.1 How Eccentricity Effects Balance. Eccentricity effects balance by displacing the centre of gravity of the component. The amount of unbalance created by a known displacement can be determined as follows:

Unbalance x Radius (ounce-inches) = E (thousandth of an inch) x Wt (lbs) x 16 Unbalance = Total Unbalance (Ounces) Radius = Radius of Unbalance Location (inches) E = Displacement of Rotor (inches) Wt. = Rotor Weight (lbs) SI units: Unbalance x Radius (g.mm) = Wt (g) x E (mm) 2.2.8.2 If the amount of unbalance created by the eccentricity is greater than the 4W/N (in US Customary) balancing specification, then the rotor eccentricity must be corrected. Typically, this means that the loose fit is too great and a repair must be made.

2.2.9 When balancing always insert a fully crowned half key or an equivalent compensating moment (weight) in all empty single key locations along shaft OD or in ID of impellers and couplings mounted on the mandrel or shaft. (NOTE: Rotors having 2 keyways which are 180 degrees apart in the same plane do not need to be filled.)2.2.9.1 The purpose of the half-key is to replace the weight that is missing by not having the full key installed during balancing. Note: The proper way to use full-keys is to fill the entire key slot in the shaft and the hub, with any excess material protruding from the hub would be milled away or removed. This would apply to either side of the coupling hub. See figure 2.2 below for an example drawing. 2.2.9.2 An equivalent compensating moment (key weight) is acceptable and is more economical than machining half keys to size with a fully crowned shape. A suitable compensating moment (weight) can be made from either lead or steel. However, more accurate keys are required on high speed applications. Key weights for high speed applications can be more accurately calculated by the Area RE Engineer or the Site Vibration Specialist.2.2.9.3 During Final assembly the key material shall be fabricated of the same material and quality of the shafts. 2.2.9.4 All keys shall have all corners chamfered equal to the adjacent keyway radii, Chamfers shall be ground or cut at an angle 45 degrees with a tolerance equal to (+0.002 / - 0.000) of the respective keyway radii. (see figure 2.3)2.2.9.5 Keyway Clearances: Process to measure the Clearance2.2.9.6 Step 1. With keys installed in shaft keyways, measure from the top of key to the opposite side of the shaft. (Record reading).2.2.9.7 Step 2. Measure across the bore of the component part to be installed to the bottom of the keyway. (Record readings)

2.2.10 Before balancing you must have weighed the assembled rotor. This step is required for all balancing tasks so that the correct balancing tolerance can be determined. (Warning: Do not exceed the load (weight) rating of the balancing machine. Both upper and lower limits are specified in the respective balancing machine manual.) 2.2.10.1 The Lower Limit. The lower limit on most balancing machines is 5 lbs (2.27Kg), but should be confirmed by data found the manual of the balancing machine. This lower limit will require a more sensitive probe (as a rule of thumb consult with area inspector / engineer on rotors weighing less than 5 lbs (2.27Kg)).2.2.10.2 The Upper Limit. If the specified upper limit is exceeded, the rollers and structural supports on the balancing machine may be damaged. If weight is approaching the upper limit and the rotor is grossly out of balance, an overload condition can exist. If the rotor unbalance is extremely high on soft bearing balancing machines, the trunions will begin to hit the stops. If this occurs, consult Mechanical Equipment Department for assistance.

2.2.11 Some Coupling Manufacturers use vertical balancing machines to accomplish 2 plane balancing, in which these machines are very sensitive to component weights. Care must be taken to confirm all weights when using these type of balancing machines

2.3 Balancing Machine Calibration Requirements2.3.1 Each balance machine shall be calibrated on a yearly basis as a minimum. This calibration shall include a certificate to document the calibration of the machine. 2.3.1.1 A calibration sticker shall be installed on the balancing machine as a notification to all users that the machine is ready for use. If the sticker is not present, then the balancing machine should not be used until it has been calibrated.2.3.1.2 The calibration sticker shall contain as a minimum the date at which the calibration was performed and a calibration renewal date.

2.3.2 Residual unbalance checks shall be performed on each balancing machine when the following balance requirements exist: 2.3.2.1 The rotor being balanced operates at a speed of greater than 3600 rpm. 2.3.2.2 If the balancing readings dont make sense or do not repeat during the final balance check, then a residual unbalance check must be performed on the balancing machine. Refer to Appendix 2 for Residual Unbalance Check Requirements.

2.4 Troubleshooting Guidelines to Use during Shop Balancing2.4.1 Windage Effects: Windage effects have been known to affect the balance on both large and small impeller designs (i.e. closed face designed fan impellers and high speed light rotors found in integral gear compressors). The windage effects are typically determined by inconsistent or non-repeatable amplitude and phase readings on the balancing machines. Using duct tape to close off the inlet and discharge flow passages can eliminate this effect. The amount of duct tape used will not affect the final balance provided it uniformly distributed during installation. Spinning the rotor counter to the normal rotational direction can also help minimize the pumping effect the impellers produce. If a windage problem is identified, consult the Mechanical Equipment Department for assistance.2.4.2 Multi-stage Impeller Pumps. This type of pump design is typically in boiler feed water service. Various balancing methods can be used to obtain a truly balanced rotor. Concerns always exist because of the potential of galling a shaft during the assembly and disassembly process. The problem exists because of the stacking process of the inter-stage diffusers or stage pieces. Therefore, the method used should consider the potential consequences. A method used in the past consists of combining the component and assembly balancing procedures, typically used on critical services where a soft start up is required. This procedure is as follows:2.4.2.1 Component balance each impeller.2.4.2.2 Assembly balance the rotor using a progressive stacking procedure.2.4.2.3 Record all face and diametrical runouts.2.4.2.4 Match mark all components.2.4.2.5 Disassemble rotor.2.4.2.6 Stack rotor with all stationary components installed using the disassembly match marks established.2.4.2.7 Place the rotor in the pump case and record the face and diametrical runouts on the impellers. 2.4.2.8 Correct the runout readings to repeat what was established in Paragraph 2.4.2.3, above.2.4.2.9 This method will help ensure that the final rotor balance obtained without the stationary inter-stage diffusers (pieces) will meet the 4W/N specification.

2.4.3 Internal Cracks in Materials. Cracks can cause havoc during the balancing of a rotating assembly. When an internal crack exists, the typical response on a balance machine is that the impeller or shaft exhibits inconsistent or non-repeatable amplitude and phase readings. Unfortunately, this cannot be determined visually and an NDT Method (i.e. Dye Penetrant, Wet Magnetic Particle or Ultrasonic Inspection Method) would have to be deployed to identify the defect. If a crack is suspected as the culprit for not being able to obtain a proper balance, consult the Mechanical Equipment Department for assistance. 2.4.4 Liquid Under Sleeves or Impeller. During the cleaning or decontamination process on a stacked rotor, liquid has been trapped under these components. The trapped liquid will cause an inconsistent or non-repeatable amplitude and phase reading on the balance machines. Unfortunately, this cannot be drained without complete disassembly of the rotating assembly. Consideration has been given to both applying heat to evaporate the trapped liquid and drilling holes in the component to drain the liquid. However, neither method has resulted in 100% removal of the trapped liquid.2.4.5 Induced Heat Caused by the Removal of Material During Grinding. The grinding process used to correct the amount of unbalance in the rotor can also cause an inconsistent or non-repeatable amplitude and phase reading on the balance machines. It has been indicated time and time again that the grinding process creates enough heat to thermally distort the material, which generates non-repeatable balancing data. The recommended practice is to grind the rotor to remove weight and then allow the rotor to return to ambient temperatures before the next balancing run is accomplished. 2.4.6 Induced Heat Caused By Drive Belt Friction. Repeated run-ups and run-downs on heavy rotors using a drive belt as the means to rotate the rotor can induce heat from friction into the rotor. This can cause the rotor to thermal bow and make balancing impossible. Check between runs for rotor heating and slowly ramp up the speed for balance runs and slowly slow down to stop. Using a driveshaft to drive heavy rotors on the balance stand is a better option. Be sure to rotate the drive shaft 180 degrees after the first run to test for unbalance induced by the driveshaft. Any unbalance introduced by the drive shaft should be subtracted electronically by the balance machine software or the drive shaft should be balanced to remove the unbalance.

2.5 Balance Tolerance calculations2.5.1 Single or two plane balancing

API 610 11th Edition (6.9.4.2) states that a two-plane balance for components is required when the ratio of D/b is less than 6. Other than this, single plane balance is acceptable.2.5.2 Acceptable Unbalance tolerance2.5.3 The allowable unbalance per plane (in a 2 plane Balancing Set-up) would be:2.5.3.1 This means that at each bearing location the allowable unbalance is 7.88 gram-inch. This prevents having the total allowable unbalance of 15.75 (gram - inch), unevenly split. Thus, having 10 gram-inch on one bearing and 5.75 gram-inch on the other is not acceptable if the component is in the middle of the shaft / mandrel. In case of asymmetrical position of the unbalance the allowable unbalance at each location should be calculated by means of the LA/L and LB/L.

2.5.4 When to Consider Dynamic or Couple Unbalance versus Static Unbalance2.5.4.1 Static Unbalance. Static unbalance is that condition of unbalance where the central principle axis is displaced only parallel to the shaft axis (Center of Gravity). The unbalance shown in Figure 3 on the following page displaces the principle axis off the rotating centerline. The central principle axis is the axis about which the mass of the rotor (and its moments) is equally distributed. This displacement creates the unbalance (figure 2.6).2.5.4.2 Static unbalance can be resolved with one correction placed at the center of gravity of the rotor.2.5.4.3 Coupled Unbalance. Coupled unbalance is that balance condition for which the central principle axis intersects the shaft axis at the center of gravity. Since the unbalance weights at each end of the rotor are equal but diametrically opposite, the rotor center of gravity has not been displaced from the shaft axis. Under these conditions, when rotating, the weights generate equal but opposite moments which cause the principle axis to tilt as shown in Figure 2.7. 2.5.4.4 Couple unbalance can be resolved by making two corrections, one placed in each of the balance planes. However, it is often better to check the static component of unbalance first. Very often the static component represents the majority of unbalance present. Unnecessary grinding can be avoided by removing the static unbalance first, then checking the couple unbalance.2.5.4.5 Dynamic Unbalance. Dynamic unbalance is the unbalance condition for which the principle axis is not parallel to and does not intersect with the shaft axis center of gravity2.5.4.6 Dynamic unbalance can be resolved by making two corrections, one placed in each of the balance planes. However, it is often better to check the static component of unbalance first. Very often the static component represents the majority of unbalance present. Unnecessary grinding can be avoided by removing the static unbalance first, then checking the dynamic unbalance. See Figure 2.8 for the physical rotor representation. 2.5.4.7 Dynamic and couple balance is easily obtained when the balancing planes are widely separated. But for those cases where the planes are close together, achieving the allowable balance tolerance is difficult. However, the dynamic or couple unbalance need not be completely removed if the disc is narrow as compared to the distance between bearings. To determine the dynamic / couple tolerance divide the distance between rotor bearings by twice the separation of planes of the single disc and multiply the allowable residual unbalance tolerance calculated from the above equation by this value. This will be referred to as the couple rule. This is per ISO 1940-1973(E), Section 3.2, unbalance effects. Reference the correction method described Figure 6, Typical Rotor Set-up Sketches.2.5.4.8 General Couple Rule (Reference Figure 2.8): If (A) divided by (2 x B) is equal to or less than one, then the allowable couple tolerance is the same as the allowable unbalance (dynamic) calculated in the 4W/N calculation above. If the value is greater than 1, then the unbalance tolerance can be corrected using the equation below. This will allow a greater balancing tolerance for final balance corrections. (NOTE: This general rule applies to both mandrels and shaft mounts in which the dimension A does not exceed the actual bearing span on the piece of equipment.)

2.5.5 When impellers are replaced or a weld repair was performed, the replacement impeller shall require an overspeed spin test to the design limit specified by the OEM (per the DEP and API requirements), before it is component balanced and installed on the rotor.

3 High Speed Balancing3.1 General Requirements3.1.1 High speed balancing (HSB) may only be required on flexible rotors (running above first critical speeds) and not on rigid rotors. All rigid rotors shall be only balanced by low speed balancing as covered by section 2.3.1.2 In addition, all Dimensional inspections per the appropriate Inspection and repair documents shall be complete and within tolerances (axial and radial Runouts, diameters, etc). 3.1.3 Prior to High Speed balancing the components and rotor assembly shall be low speed balanced as per section 2 of this RE-SPG.3.1.4 The latest edition of API 687 shall be adhered to.3.1.5 High speed balancing shall be done in a vacuum bunker where it is safe to run the rotor and limit the amount of windage which will be created. There is considerable risk with running a rotor up to higher speeds. A few of the Potential risk are:3.1.5.1 Components/assemblies may break loose3.1.5.2 Rotor destruction

3.1.6 Balancing shall be performed by qualified personnel at balancing facility suitable for high speed balancing, properly equipped with all applicable accessories.3.1.7 Prior to balancing the calibration of the balancing machine shall be verified.

3.2 Evaluation if HSB is required3.2.1 High Speed Balancing (extract API 687 sect 10.6, with minor modifications)3.2.1.1 Rotors which have exhibited high vibration as they pass through their critical speeds (identified by R&D, testing or historical field experience)3.2.1.2 Rotors which accelerate slowly through their critical speeds (as part of an operational requirement).3.2.1.3 Rotors which are running on or near a critical speed (1st or 2nd radial/axial modes).3.2.1.4 Rotors which are sensitive to unbalance.3.2.1.5 Rotors for equipment in extremely critical services.3.2.1.6 Rotors going to inaccessible locations, such as offshore.3.2.1.7 Very long, flexible rotors.3.2.1.8 Places where a critical rotor cannot be run in its intended casing prior to installation.

NOTE: All OEMs are specifying HSB now for almost all repairs for NO reason. We have approached various OEMs and asked if the rotors required this from an engineering and design standpoint and both when questioned the recommendation was deleted. It is a cash cow for the OEMs that have a HSB machine (high margins are made and some rotors really don't require the HSB at all). 3.2.2 In general HSB would only be required just after the first assembly of the rotor in its life or after significant modifications / repairs were done on the rotor which could change the unbalance of the rotor beyond the first critical speeds. Such modifications / repairs could be:3.2.3 A decision tree can be found in Appendix 1 to help determine if HSB is required.

3.3 High Speed Balancing test procedure3.3.1 Before starting, ensure the rotor has been low speed balanced to the correct tolerance (see section 2 above). 3.3.2 Prior to placing the Rotor in the HSB Bunker the following shall be reviewed and approved:3.3.2.1 OEM HSB Procedure3.3.2.2 Balancing Speeds (MCOS, OST, etc) or any other speed that is required to confirm balancing criteria.3.3.2.3 Procedure for Influence Corrections to achieve the desired balance results at higher speed where the rotor may be approaching the 2nd critical speed.3.3.2.4 Sizing and selection review of the Bearings used in the HSB pedestals (Load rating, oil flow requirements, cooling requirements, etc) 3.3.2.5 Calibration records of the HSB facility and scales used in the HSB process. 3.3.2.6 Agreement on Data collection (transient data, BODE Plots, Orbits waveform data, etc) that will be used in the final report. All plots and data shall be transferred electronically for future reference. An agreement should be made that the ADRE data may be requested if issues are observed during the HSB process (This is sometimes hard to get after the balancing process begins).3.3.2.7 Review of correction methods proposed and proper procedure to lock in any weights that are added to insure they don't become loose in operation.

3.3.3 Install the rotor into bearing pedestals and check bearing clearances with the standard facility bearings. Tilt-pad bearings shall have babitted end seals to prevent oil starvation due to operating in a vacuum bunker. Rotor shall be fully assembled excluding interchangeable or loose parts (coupling hub, shaft end nuts, parts of shaft end seals and others if any). Half key shall be installed at the free shaft end if one key shaft end is applied.3.3.4 All coating shall be applied before the LSB step. All balancing correction made on the rotor after the coating process has been completed will be restricted to the furthest diameter between impeller vanes (scalloped configuration) on the Outer most diameter of the impeller. At NO time will any grind occur on the face of the impeller cover or hub after the coating is applied, without written approval of a Shell Rotating Equipment Engineering Representative. This will prevent any breakdown of the coating or coated surfaces that physically touch the compressor gas path. In addition, touch up coatings applied are strictly cosmetic and typically breakdown because of the in ability to sinter or cure the coated surfaces. 3.3.5 Verify visually the rotor serial number to ensure your rotor is on the balancing machine.3.3.6 When High Speed balancing, the speed shall not exceed Maximum Continuous Operating Speed (MCOS). (Note: Some Manufacturers will request that a higher speed be used to settle the components (e.g. impellers, turbine blades, etc) since these are interference fits. If this request is made the speed used shall not exceed the OST (over-speed trip) speed and shall not run longer than 5 minutes.) 3.3.7 Verify again with the balancing machine operator that the correct MCOS will be used for the rotor in the balancing machine.

Note: It has happened before several times that there was some confusion on which rotor was being balanced and the rotors were accidentally swapped. This resulted in the rotor running higher than overspeed, resulting in detailed investigations into the rotor condition. Therefore it is important to ensure you have the latest machine data sheet and the correct rotor is on the balancing machine.3.3.8 Accelerate the rotor to between 300 and 500rpm and measure the slow roll run-out. This is to verify the mechanical and electrical runout does not exceed the allowable levels and a proper reading will be obtained from the measurement. Also it is important to understand for slow roll (vector) configuration for slow roll compensation, if it is required.3.3.9 Accelerate the rotor to about 850rpm and measure the unbalance. In case the unbalance does not exceed five (5) times the calculated low speed balance tolerance (i.e. five times the 4W/N) accelerate the rotor to MCOS (per the directions below). 3.3.9.1 The speed of the rotor shall be increased by increments of 10% of the maximum continuous speed from zero up to the MCOS. Critical speeds, residual unbalances and vibration levels of the rotor shall be monitored and recorded. After recording the parameters at the maximum continuous speed the rotor speed shall be decelerated to 0 rpm. 3.3.9.2 Corrections to reduce the unbalance shall be made by the engineer in accordance with the guidelines in chapter 4 and mutually agreed upon HSB procedure.

3.3.10 The rotor HSB acceptance criteria are defined in chapter 3.3.3.11 Corrections for the tooling and the balancing machine support stiffness shall be done by the engineer, based on his experience. If the rotor is starting to approach the 2nd critical speed the rotor shall be corrected to obtain both acceptable tolerance at Overspeed and MCOS. Sometimes an increase in amplification factor is required to achieve the acceptance criteria.3.3.12 After the high speed balancing is completed, a low speed balance check should be done to record the profile of at low speeds, including all set-up information. This check can only be compared in the future if done on the same balancing machine and facility bearings.

3.4 High Speed Balance tolerance3.4.1 Bearing pedestal vibrations (API 687 10.6.2)3.4.2 Peak-Peak unfiltered vibrations (API 617 2.6.8.8)3.4.3 Pedestal stiffness has a major influence in the response of the rotor on the balancing machine. 3.4.4 At any speed greater than the maximum continuous speed, up to and including the trip speed of the driver, the vibration level shall not increase more than 12.7 m (0.5 mil) above the maximum value recorded at the maximum continuous speed. Install the rotor into bearing pedestals and check bearing clearances with the standard facility bearings. Tilt-pad bearings shall have babitted end seals to prevent oil starvation due to the rotor being operated in a vacuum bunker. Rotor shall be fully assembled excluding interchangeable or loose parts (coupling hub, shaft end nuts, parts of shaft end seals and others if any). Half key shall be installed at the free shaft end if one key shaft end is applied.3.4.5 Caution: Subtraction of the Slow Roll Vector. Typically running a rotor below 500 rpm (at fixed speed note the slower the better) there is not enough energy or influence from centrifugal forces, wind loads or steam to e

re-spg 31.29.00.00-005 rev0 rotor balancing

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