class programme type approval - dnv...class programme — dnvgl-cp-0185. edition march 2016 page 5...

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DNV GL AS

CLASS PROGRAMME

Type approval

DNVGL-CP-0185 Edition March 2016

Mechanical joints

FOREWORD

DNV GL class programmes contain procedural and technical requirements including acceptancecriteria for obtaining and retaining certificates for objects and organisations related toclassification.

© DNV GL AS March 2016

Any comments may be sent by e-mail to [email protected]

This service document has been prepared based on available knowledge, technology and/or information at the time of issuance of thisdocument. The use of this document by others than DNV GL is at the user's sole risk. DNV GL does not accept any liability or responsibilityfor loss or damages resulting from any use of this document.

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Class programme — DNVGL-CP-0185. Edition March 2016 Mechanical joints

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CONTENTS

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Section 1 General....................................................................................................51 Introduction.........................................................................................52 Documentation.....................................................................................5

Section 2 Material requirements............................................................................. 71 Introduction.........................................................................................72 Elevated temperature.......................................................................... 7

Section 3 Strength evaluation.................................................................................91 General................................................................................................ 92 Alternative burst strength evaluation..................................................9

Section 4 Test procedure and requirements......................................................... 101 General.............................................................................................. 102 Scope of prototype tests................................................................... 103 Test report.........................................................................................114 Selection of test specimen.................................................................115 Production testing............................................................................. 12

Section 5 Prototype testing...................................................................................131 Tightness test.................................................................................... 132 Repeated assembly test.....................................................................133 Burst pressure test............................................................................134 Pull-out test.......................................................................................165 Vibration (fatigue strength) test....................................................... 166 Pressure impulse test (pipe unions, compression couplings).............187 Fire resistance tests.......................................................................... 198 Oxygen shock test............................................................................. 209 Vacuum test.......................................................................................20

Section 6 Certification renewal............................................................................. 211 General.............................................................................................. 21

Changes – historic................................................................................................22

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SECTION 1 GENERAL

1 Introduction

1.1 ObjectiveThe objective of this class programme (CP) is to describe the type approval (TA) scheme for mechanicaljoints.For a description of the Society's type approval scheme in general and further information on generalconditions and procedures for obtaining the Society's TA certificate, see the Society's document DNVGL CP0338 Type approval scheme.The procedures and requirements described in this CP are applicable for obtaining the Society's TA certificatebased on requirements in:

— DNV GL rules for classification of ships RU SHIP Pt.4 Ch.6— DNV GL offshore standard DNVGL OS D201 as governed by applicable rules for offshore units.

1.2 ScopeThis CP gives a description of the procedures and requirements related to documentation, design and typetesting applicable for TA of mechanical joints.This CP does not set the design requirements for these components. TA is based on compliance with designrequirements given in the rules and/or other regulations and standards. The CP describes the applicabledesign requirements and how to document compliance with the requirements in order to obtain a TAcertificate for the equipment. This includes, where relevant, technical requirements for how the type testsshall be performed.

1.3 ApplicationThe DNV GL rules for classification of ships RU SHIP Pt.4 Ch.6 require that mechanical joints shall be typeapproved by the Society, and TA in accordance with this CP is thus mandatory for equipment to be installedon vessels classed with the Society.A TA certificate in accordance with this CP will confirm compliance with the requirements in RU SHIP Pt.4Ch.6. The TA certificate will not confirm compliance with requirements in other parts of the rules. In caseadditional requirements in other parts of the rules shall be covered by the TA certificate, this shall bespecified in the application for TA and will be stated in the TA certificate.The requirements in this document are applicable for following types of mechanical joints:

— compression couplings— pipe unions— slip on joints.

2 DocumentationFor TA of mechanical joints the following documentation shall be submitted:

— type approval application form— manufacturers catalogue, brochure or product specification.— if relevant typical sectional drawing(s) with all dimensions necessary for strength calculations and

reference to recognized standards, if applicable.— complete specification of material used in the different parts of the mechanical joint with reference to

recognized national/international material standard.

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— range of application— test reports (or/and test plan)— assembly, operating and installation instructions— manufacturing locations— description of quality assurance system or copy of ISO 9001 certificate including copy of last audit report.

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SECTION 2 MATERIAL REQUIREMENTS

1 IntroductionThe materials used in the mechanical joint parts shall comply with the requirements in this type approvalprogram and/or to the Society's rules for classification of ships. Used material for the pressurized parts shallbe delivered with material certificate according to RU SHIP Pt.4 Ch.6 Sec.1 [3.2] and RU SHIP Pt.4 Ch.6Sec.9 [5.2].Material may also comply with recognized national/international material standards such as ASTM, BS, DIN,EN, ISO etc. taking into account possible limitations or additional requirements given in the rules.

2 Elevated temperatureThe maximum pressure for which the mechanical joints will be type approved is defined as maximumallowable pressure for continuous service at +20°C. For elevated temperatures the maximum allowablepressure may have to be reduced dependent on the material quality. When no documentation of themechanical properties at elevated temperatures is available, the pressure will be reduced according to Table1 or according to manufacturer specification approved by the Society.

Table 1 Pressure reduction factors at elevated temperatures

Temperature Carbon steels, unalloyed Low alloyed steels Stainless steels

20ºC 1.00 1.00 1.00

50ºC 1.00 1.00 0.95

100ºC 1.00 1.00 0.85

150ºC 0.89 0.93 0.77

200ºC 0.81 0.87 0.71

250ºC 0.72 0.81 0.67

300ºC 0.65 0.75 0.63

350ºC 0.59 0.69 0.60

400ºC 0.54 0.63 0.58

450ºC 0.50 0.57 0.57

500ºC N/A 0.52 0.56

550ºC N/A N/A 0.55

600ºC N/A N/A 0.50

The maximum service temperature for mechanical joint accepted will be determined according to recognisedmaterial standard applicable.As guidance the following temperatures applies:

— carbon steels, unalloyed: +450°C— low alloyed Mo-steels: +500°C— low alloyed CrMo-steels: +550°C— stainless steels 304L and 316L: +400°C— stainless steels 304, 316 and 321: +550°C.

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If higher utilisation of the material is wanted, the mechanical properties of the material at elevatedtemperatures shall be documented.

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SECTION 3 STRENGTH EVALUATION

1 GeneralThe strength of the mechanical joints will be evaluated according to the requirements in this type approvalprogram.The type approval will mainly be based on results from prototype tests performed on test specimens takenfrom stock or production.

2 Alternative burst strength evaluationIn reasonable cases finite element analysis or experimental stress analysis may replace the burst pressuretesting.

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SECTION 4 TEST PROCEDURE AND REQUIREMENTS

1 GeneralWhere not specified, the length of pipes connected by the mechanical joint subject to test shall be at leastfive times the pipe nominal diameter. However, in reasonable cases pipe length can be reduced.Before assembling the joint, conformity of components to the design requirements, shall be verified. In allcases the assembly of the joint shall be carried out as for normal working conditions.No adjustment operations on the joint assembly, other than that specified by the manufacturer, are permittedduring the prototype testing.

Guidance note:The test specimen may be grouped for more than one test on the same test specimen.Example:

— Group I Tightness test, repeat assembly test, vacuum test, pull out test, burst test

— Group II Tightness test, vibration and impulse test

— Group III Tightness test, fire resistance test

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If a test specimen does not pass a prototype test, then the test which has not been passed shall be repeatedwith two additional specimens of the same size and type. If one of these test specimens fails the repeatedtest, the type and size of the mechanical joint will not be approved.

2 Scope of prototype testsTable 1 Overview of prototype tests

Types of mechanical joint

Slip-on joints

Test designationCompression

couplingsand pipeunions

Grip type, machinegrooved types and

other axial restrainingmechanical joints

Slip type

Notes

Tightness test X X X

Repeated assembly test X X - Compression couplings of swagetype and press type excluded

Burst pressure test X X X The burst test shall be witnessedby surveyor

Pull-out test X X -

Vibration (endurance) test X X -

Pressure impulse test X X -For application in piping systemssubject to impulse loading, e.g.hydraulic systems

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Types of mechanical joint

Slip-on joints

Test designationCompression

couplingsand pipeunions

Grip type, machinegrooved types and

other axial restrainingmechanical joints

Slip type

Notes

Fire resistance test X X X

Excluded joints with metallicsealing with melting point>925°CFor applications listed in RU SHIPPt.4 Ch.6 Sec.2[1.1.2], RU SHIPPt.4 Ch.6 Sec.8 [2.2.1] and RUSHIP Pt.4 Ch.6 Sec.8 [3.2.1]

Oxygen shock test X X X For oxygen application only

Vacuum test X X X Joints not vacuum tested arelimited to pressure application

X test required– no test required

3 Test reportThe test report shall at least contain the following information:

— name of the testing laboratory, and testing date— test equipment and calibration status— type designation and reference to drawings, product specification of the product(s) tested— a short description of the testing procedure— test results and possible test events— maximum design pressure— test temperature— temperature range (maximum and minimum temperature)— reference to design rules, codes, standards, or other regulations— field of applications and possible limitations— welding procedure specifications with qualification test if the couplings are welded— brazing/swaging specifications if the couplings are brazed or swaged— marking of product.

4 Selection of test specimen— the test specimens shall be selected at random from the production line or from stock. For burst test, it

shall be done in the presence of the surveyor— the test specimens shall be marked for traceability to the final test report— before assembling the components of the test specimens they shall be checked for compliance with the

design drawings, catalogue respectively— the assembly of the connection shall conform exactly to the instructions of the manufacturer— no adjustment operations on the test specimen, other than specified by the manufacturer, are permitted

during the prototype testing

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— in case of different sizes and materials shall be type approved, at least three sizes for each type ofmaterial, which are representative for the series, shall undergo prototype testing. The smallest, middleand biggest size of the diameter range of mechanical joint shall in all cases be tested

— in case of compression couplings and pipe unions the biggest size of each pressure range shall be tested— in some cases where the size range is very extensive, or the design of the couplings varies within the

range, the Society may extend the number and sizes of test pieces— in case of mechanical joint type series includes different configurations such as straight, elbows, crosses,

tees etc. the proto type test program shall also include burst tests and vibration and impulse test onelbow and tee test specimen

— this will in general qualify all other configurations with the same bores and pressure ratings.

5 Production testingFor hose assemblies and compensators to be delivered on vessels classed with the Society a production testaccording to RU SHIP Pt.4 Ch.6 Sec.9 is applicable.

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SECTION 5 PROTOTYPE TESTING

1 Tightness testIn order to ensure correct assembly and tightness of the couplings, all selected test specimens shall besubjected to a tightness test as follows.The coupling assembly shall be filled with test fluid and purged for air. The assembly shall then bepressurised to 1.5 times the design pressure. This test pressure shall be attained within a period of not lessthan 15 seconds and not more than 60 seconds. The pressure is then to be retained for a minimum period of5 minutes.For compression couplings a static gas pressure test shall be carried out to demonstrate the integrity ofthe coupling assembly for tightness under the influence of gaseous media. The pressure shall be raised tothe design pressure of the coupling or 70 bar, whichever is less. This test pressure shall be retained for aminimum of 5 minutes.

2 Repeated assembly testThe couplings shall be assembled and disassembled 10 times according to manufacturer's instructions. Thecouplings shall be tightness tested.

3 Burst pressure testThe test assembly consists of two pieces of tubing connected with the mechanical joint. The tubing shallbe strong enough to resist the specified burst pressure without failure. One end shall be unsupported andblinded; the other end shall be connected to a pressure source having sufficient pressure range for this test.The test rig shall be equipped with calibrated pressure/time recording instruments with sufficient range ofrecording.The burst tests shall be performed in the presence of a surveyor.The test assembly shall be filled with water or other suitable test medium, and care shall be taken that all airis purged before the assembly is pressurized. The pressure shall be raised slowly in steps up to the calculatedminimum burst pressure, giving enough time to check for leakage, and the pressure shall be held at thecalculated burst pressure for at least 5 minutes. At manufacturer's option, the test pressure may then beraised further till burst occurs.Burst pressure shall be 4 times the maximum allowable working pressure. For working pressure above 200bar the safety factor can be reduced according to Table 1 and Figure 1.The mechanical joint may have small visible deformations when under calculated burst pressure, but noleakage or visible cracks are permitted.

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Figure 1 Reduced values of safety factors f for nominal pressures above 200 bar

Table 1 Reduced values of safety factors f for nominal pressures above 200 bar

Nominalpressure

[bar]Safety factor, f

Nominalpressure


207 4.0 670 2.97

210 3.99 680 2.95

220 3.97 690 2.92

230 3.95 700 2.90

240 3.93 710 2.88

250 3.90 720 2.86

260 3.88 730 2.83

270 3.86 740 2.81

280 3.84 750 2.79

290 3.81 760 2.77

300 3.79 770 2.74

310 3.77 780 2.72

320 3.75 790 2.70

330 3.73 800 2.68

340 3.70 810 2.66

350 3.68 820 2.63

360 3.66 830 2.61

370 3.64 840 2.59

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Nominalpressure


Nominalpressure


380 3.61 850 2.57

390 3.59 860 2.54

400 3.57 870 2.52

410 3.55 880 2.50

420 3.53 890 2.48

430 3.50 900 2.45

440 3.48 910 2.43

450 3.46 920 2.41

460 3.44 930 2.39

470 3.41 940 2.37

480 3.39 950 2.34

490 3.37 960 2.32

500 3.35 970 2.30

510 3.32 980 2.28

520 3.30 990 2.25

530 3.28 1000 2.23

540 3.26 1010 2.21

550 3.24 1020 2.19

560 3.21 1030 2.16

570 3.19 1040 2.14

580 3.17 1050 2.12

590 3.15 1060 2.10

600 3.12 1070 2.08

610 3.10 1080 2.05

620 3.08 1090 2.03

630 3.06 1100 2.01

640 3.03 1104 2.00

650 3.01

660 2.99

Intermediate values may be interpolated linearly.

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4 Pull-out testIn order to determine the ability of a mechanical joint assembly to withstand axial load likely to beencountered in service without the connecting pipe from becoming detached, following pull-out test shall becarried out:

Pipe length of suitable size shall be fitted to each end of the mechanical joint assembly test specimen.The test specimen shall be pressurized to design pressure, imposing an axial load on the specimen. Whenthe pressure is attained, an additional axial load shall be applied with a value calculated by the followingequation:

where:

D = tube outside diameter, in mmP = maximum allowable working pressure, in N/mm2

L = applied axial load, in N.

The pressure and axial load shall be maintained for a period of 5 minutes. During the test, pressure shall bemonitored and relative movement between the joint assembly and the pipe measured.

The mechanical joint assembly shall be visually examined for drop in pressure and signs of leakage ordamage. There shall be no movement between mechanical joint assembly and the connecting pipe, and nosigns of leakage or damage.

5 Vibration (fatigue strength) testIn order to establish the capability of the mechanical joint assembly to withstand fatigue mechanical jointsassemblies to be subject to the following vibration test.

5.1 Compression couplings and pipe unionsCompression couplings, pipe unions and similar mechanical joints for the application in rigid connections ofpipe shall be tested according to the test procedures described below.

Rigid connections are joints, connecting pipe length without free angular or axial movement.

The vibration test and the pressure pulsation test shall be carried out simultaneously for this type mechanicaljoint.

Two lengths of pipe shall be connected by means of the joint to be tested. One end of the pipe shall be rigidlyfixed while the other end shall be fitted to the vibration rig. The test rig and the joint assembly specimenbeing tested shall be arranged as shown in Figure 2. The test specimen assembly shall be filled with testfluid, carefully de-aerated and pressurised to the design pressure of the joint. The test pressure as defined inFigure 4 shall be documented during the complete test duration.

The free end of one pipe is now loaded by vibrations with amplitude to be computed as follows:

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A = single amplitude, in mmL = length of pipe from pipe connection to vibration device, in mmS = bending stress, in N/mm2 (25% of yield strength of pipe material)E = module of elasticity of the pipe material, in N/mm2

D = outside diameter of pipe, in mm.

During the test the amplitude shall be kept with an accuracy of 5%.

After installation of the test specimen the actual bending stress shall be checked via strain gauges or thebending forces.

The test specimen shall withstand at least 107 vibration cycles with a frequency of 20 – 30 Hz withoutdamage or leakage. An adjustment of the arrangement of the test specimen is only allowed during the first1000 cycles.

No pressure drop or leakage is permitted.

Figure 2 Test arrangement for compression couplings and pipe unions

5.2 Slip on joints (grip type and machined grooved type)Grip type joints, machined grooved type joints and other similar joints containing elastic elements shall betested in accordance with the following method. A test rig of cantilever type used for testing fatigue strengthof components may be used. The test specimen being tested shall be arranged in the test rig as shown inFigure 3. Two lengths of pipes shall be connected by means of joint assembly specimen to be tested. Oneend of the pipe shall be rigidly fixed while the other end shall be fitted to the vibrating element on the rig.The length of pipe connected to the fixed end shall be kept as short as possible and in no case exceed 200mm. Mechanical joint assemblies shall not be longitudinally restrained. It will be permitted to re-tighten thecoupling once during the first 1000 cycles of the vibration testing due to possible bedding-in of the couplings.The assembly shall be filled with test fluid, de-aerated and pressurized to the design pressure of the joint.For the application of joints with impulse load the loading shall be done with pressure impulses according toFigure 4.Preliminary angle of deflection of pipe axis shall be equal to the maximum angle of deflection, recommendedby the manufacturer. The amplitude shall be measured at 1m distance from the center line of the jointassembly at free pipe end connected to the rotating element of the rig. Parameters of testing shall be asindicated in Table 2 and to be carried out on the same assembly.

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Pressure during the test shall be monitored. In the event of a drop in the pressure and visual signs of leakagethe test shall be repeated as described in [1]. Visual examination of the joint assembly shall be carried outfor signs of damage which may eventually cause leakage.No pressure drop or leakage is permitted.

Table 2 Parameters for tests with tension-proof pipe joints with cutting ring and grooved pipeends

Number of load cycles Amplitude, A [mm] Frequency [Hertz]

3 · 106 ± 0.06 100

3 · 106 ± 0.5 45

3 · 106 ± 1.5 10

Figure 3 Test arrangement for tension-proof pipe connections with cutting ring and grooved pipeends

6 Pressure impulse test (pipe unions, compression couplings)In order to determine capability of mechanical joint assembly to withstand pressure pulsation likely to occurduring working conditions, joint assemblies intended for use in rigid connections of pipe lengths, shall betested in accordance with the following method.The vibration test in [5.2] and the pressure pulsation test shall be carried out simultaneously for compressioncouplings and pipe unions.The mechanical joint test specimen shall be connected to a pressure source capable of generating pressurepulses of magnitude as shown in Figure 4.It will be permitted to re-tighten the coupling once during the first 1000 cycles of the vibration testing due topossible bedding-in of the couplings.In case of mechanical joint type series includes different configurations such as straight, elbows, crosses,tees etc. the test specimen for impulse test program shall also include elbow and tee joints fitted at the freeend of the test specimen.The pressure impulse shall be increased from 0 to 1.5 times of the design pressure pc with a frequency of 30– 100 cycles per minute. The total number of cycles shall not be lower than 5 · 105.

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No sign of leakage or damage is permitted.Guidance note:To finalize vibration and impulse test at the same time, the frequency of the vibration test shall be 20 times the frequency of pressureimpulse test.

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Figure 4 Pressure impulse diagram

7 Fire resistance testsThe fire resistance test for mechanical joints such as slip-on joints, pipe unions and other pipe connectingelements which include sealing elements with a melting point < 925 °C shall be tested according to ISO19921 Test method and ISO 19922 Test bench.Clarifications to the standard requirements:

1) If the fire test is conducted with circulating water at a pressure different from the design pressure of thejoint (however of at least 5 bar) the subsequent pressure test shall be carried out to twice the designpressure.

2) A selection of representative nominal bores may be tested in order to evaluate the fire resistance of aseries or range of mechanical joints of the same design. When a mechanical joint of a given nominalbore (DN) is so tested then other mechanical joints falling in the range DN to 2 · DN (both inclusive) areconsidered accepted. For nominal diameter less or equal to 150, the biggest size shall be tested.

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8 Oxygen shock testCouplings shall be oxygen shock tested when they shall be type approved for systems having oxygencontent by volume of more than 25%. A minimum of 3 couplings shall be tested. In case the couplings aremanufactured in a big range of sizes, where all the sizes are of same basic design, one small, one mediumand one of the bigger sizes shall be selected. The test shall be performed by quick opening of a ball valveproducing a shock wave that moves through a copper tube into the test specimen. The test medium shall beoxygen of normal industrial grade pre-heated to +60°C. The line shall be flushed with oxygen before the testcommences in order to remove as much air as possible. The pre-heater shall be switched on for sufficienttime ahead in order to ensure that all the oxygen has reached the required temperature before the testingstarts. The test samples shall be subjected to 20 shocks of pressure increase from atmospheric pressure tomaximum design pressure.

Figure 5 Pressure test curve for oxygen shock test

The full oxygen pressure, with refill if necessary, shall act on the test samples for 10 seconds, and the timebetween each shock shall be 30 seconds. See Figure 5.NOTE! This test is considered to be dangerous to personnel, as explosive fire may occur in the system. Strictsafety precautions shall therefore be taken, and it is recommended that the test is performed in a specialcontainer without any personnel inside the container during the testing.A test procedure as described in EN ISO 2503 or equivalent will be accepted.

9 Vacuum testIn order to establish capability of mechanical joint assembly to withstand internal pressures belowatmosphere, similar to the conditions likely to be encountered under service conditions, following vacuumtest shall be carried out.Mechanical joint assembly shall be connected to a vacuum pump and subjected to a pressure 170 mbarabsolute. Once this pressure is stabilized the mechanical joint assembly test specimen under test shall beisolated from the vacuum pump and this pressure shall be retained for a period of 5 minutes.Pressure shall be monitored during the test. No pressure increase is permitted.

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SECTION 6 CERTIFICATION RENEWAL

1 GeneralFor general terms refer to the Society's document DNVGL CP 0338 Type approval scheme. In addition asurveyor shall witness burst tests on selection of sizes.

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CHANGES – HISTORICThere are currently no historical changes for this document.

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