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PETRONAS Management Training Sdn Bhd 2006.

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PART C : Inspection of UPV

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Philosophy of UPV inspection

The basic reasons for inspection are;

To determine the physical condition of the vessel

To determine the type, rate, and causes of deterioration

To determine if vessel can still perform its intendedfunction

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The BIG questions for you.

How do you inspect your vessels?

When do you inspect them?

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PETRONAS corporate policy statement on HSE

PETRONAS shall ensure that the facilities it designs,builds, and operates, the product it manufactures, andthe services it provides, are in accordance with

appropriate legal requirements, industry standards, andbest practices

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Local regulations vs. industry best practices

In one aspect, pressure vessels inspection is governedby local regulations

On the other hand, in order to be competitive, we needto follow the guidelines outlined by industry bestpractices otherwise, we would be left behind

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Local regulations with respect to pressure vessel inspection

Local authority Department of Occupational Safety & Health(DOSH)

DOSH outlined inspection requirements of pressure vessels &boilers

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Local regulations with respect to pressure vesselinspection

Generally, every vessel will undergo 5 types ofstatutory inspection;

1. Initial inspection

2. Regular inspection every 15 months

3. Supplementary inspection

4. Special inspection5. Further inspection

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Industry best practices

Reflects whats the best out there

American Petroleum Institute produced documentsrelating to vessel inspection, among them:

API 510 Maintenance, Inspection, Repair,Rerating, and Alteration of Pressure Vessels

API 572 Inspection of pressure vessels (Towers,Drums, Reactors, Heat Exchangers, Condensers)

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Industry best practices

API 510 Section 4: Risk Based Inspection

Contains provision that allows an operating plant toextend the inspection interval of its pressure vessel,provided it has performed risk based analyses

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Brief overview of pressure vessel design

ASME Boiler & Pressure Vessel Code Section VIII

Perhaps the most well known & widely used pressurevessel design code in the world today

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History

In early 1900, a number of factory explosions in USAhad killed many workers and civilians

In 1911, the American Society of Mechanical Engineersset up a committee to formulate standard rules for theconstruction of steam boilers and other pressurevessels, that will perform in a safe and reliable manner

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History..continued

The scope includes;

Made of nonferrous materials, cast iron, high alloyand carbon steel

Made by welding and forging

Applying a variety of construction methods and

details

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History..continued

The prime concern of ASME Code is to construct avessel that will operate safely

It is not concerned about non-safety issues e.g.whether the vessel should be painted or not

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Common materials of construction

Carbon steel is most common e.g. rolled plates SA 516Grade 70

For special purposes, alloys of chromium, molybdenum,nickel, vanadium, etc. are used

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Materials that will most economically resist the type ofcorrosion expected in service, are selected

Cladding plain carbon steel with stainless steel is aneconomical way of saving cost of alloy steel

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Metallic liners are installed using various methods weld overlay (small sections), rolled, or explosion

bonded

Nonmetallic liners are also used to resist erosion andcorrosion, or to insulate vessel shell e.g. rubber lining,refractory material

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However if the operating pressure and temperature aretoo high, solid alloy steels may be the only choice

Lists of ferrous and nonferrous materials allowed byASME are found in ASME Section II

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Loadings on vessels

Vessel materials usually degrade in two manners;

1. Corrosion2. Metallurgy

The Code only handles metallurgy failures:

Creep

Brittle fracture

Fatigue

Etc.

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Loadings on vessels

Loadings exert stresses on vessel components

Types of loadings include: Internal or external pressure

Weight of vessel and content

Static reactions from attachments piping, ladders,

supports, etc.

Wind pressure

Temperature gradients

Abnormal pressure during plant upset

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Loadings on vessels

Operating pressure due to normal processoperation

Design pressure used in design of vessel typically30 psi or 10% higher than operating pressure

Maximum allowable working pressure MAWP.The highest pressure allowed at the top of the vessel

Hydrostatic test pressure at least 1.3 times theMAWP

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Pressure & load retaining components

The common components of pressure vessels are:

Shell cylindrical, spherical, spheroidal, boxed Heads flat, hemispherical, ellipsoidal, conical,

toriconical, torispherical

Supports steel columns, cylindrical plate skirts,plate lugs

Nozzles

Jacketed vessel built with casing or outer shell

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Figure 2.1: Variousshapes of vessel heads



The common components of pressure vessels

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Figure 2.2: Variousvessel shapes



The common components of pressure vessels

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Lets do calculations..

P = 120 psi design pressure

S = 20,000 psi allowable stress value for SA 515Grade 70 @ 500oF

E = 1.00 joint efficiency

R = 60 inches radius

D = 120 inches diameter

= 30o one half of apex angle

L = 120 inches dish radius

t = required wall thickness, which we want to

calculate

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Formula

For cylindrical shell

For spherical shell or hemispherical head

For 2:1 ellipsoidal head

PSE

PRt

4.0

PSE

PRt

8.02

PSE

PDt

8.12

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Formula

For conical section

For torispherical head with small knuckle section

For flat head

)4.0(cos2 PSE

PDt

PSE

PLt

8.0

885.0

SE

Pdt

33.0

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Calculation results

Shape Thickness required (inch) Ratio

Hemispherical 1

Cylindrical

2:1 ellipsoidal

Conical

Torispherical

Flat

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Questions

What is the best shape to resist pressure?

What is the worst shape to resist pressure?

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Other learning points..

For vessel under static pressure, which welds aremost critical?

Figure welds on PV

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Other learning points..

For vessel under cyclic pressure, which welds aremost critical?

Figure welds on PV

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Internals

Figure 2.3:Examples of vesselinternals

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Essential fittings for pressure vessels

One or more pressure relieving device

A pressure gauge

The manufacturers nameplate

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