Increasing Importance of Rapid Crack Propagation (RCP) for Gas Piping Applications - Industry Status

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1 Increasing Importance of Rapid Crack Propagation (RCP) for Gas Piping Applications - Industry Status Dr. Gene Palermo P Cubed Consulting Dr. Dane Chang The Dow Chemical Co.

2 Outline Background RCP Test Methods RCP Requirements in Industry Product Standards RCP Test Data Conclusions

3 Background RCP is a fast fracture 200 m/sec DuPont two RCP incidents in HDPE pipe 300 ft and 800 ft distance Only a few incidents is gas applications Typical features are a sinusoidal crack path and hackle marks indicating the direction of travel

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6 PE Pipe Dependant Variables Wall thickness (pipe size) Internal pressure Temperature Material properties/resistance to RCP Pipe processing

7 Outline Background RCP Test Methods RCP Requirements in Industry Product Standards RCP Test Data Conclusions

8 RCP Test Methods Full Scale (FS) Test ISO long pipe samples - very expensive Small Scale Steady State (S4) - ISO smaller pipe samples - test done in a laboratory - easier to get data and correlates to FS test

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10 Critical Pressure (P C ) Constant temperature 0 C Vary internal pressure Defined as the pressure above which the crack propagates and the pressure below which the crack arrests

11 Critical Pressure (P C )

12 FS/S4 Correlation Equation P C,FS = 3.6 P C,S bar (ISO 4437 Equation)

13 Patrick Levers Paper Although the configuration of an ISO Full Scale RCP test does not exactly simulate that of installed pipe, the method is justifiably regarded as the gold standard. The S4 test method aims to simulate the internal pressure and wall hoop stress distribution around an axially propagating crack tip in the FS test. However, because of the difference in specimen sizes, these distributions diverge further away, and as a result the critical pressure results are different.

14 FS S4 Differences The disparity originates mainly in the dynamics of the pressurizing fluid. In a full-scale configuration the contained nitrogen or air is relatively free to exhaust from an effectively infinite reservoir ahead of the crack tip to the flared-out fissure behind it. In the S4 test, this backflow is almost eliminated.

15 The ISO Correlation Equation The correlation factor was derived by assuming that the crack-arrest condition (i.e. the critical pressure) in each test corresponds to the same crack-tip pressure. A one-dimensional axial flow analysis for air or nitrogen then yields the equation enshrined in ISO 13477: Pc(FS) = 3.6 Pc(S4) bar. (Eq. 1)

16 Whence Commeth the Numbers This is based on the result that if a long pipe is guillotined at a fixed plane along its axis, only a constant fraction, 1/3.6, of the initial pressure remains at the outflow. Critical pressures pc in Eq (1) are gauge pressures: the 2.6 bar offset arises because 3.6 bar absolute pressure is needed to drive the gas out against a 1 bar atmospheric pressure.

17 FS S4 Correlation Equation It is understood that the correlation equation in ISO is very conservative If a manufacturer does the FS test, then that is the value that is used If a manufacturer only does S4 testing, then he uses the conservative ISO correlation equation We could determine 100 different correlation equations, one for each material, but the industry just uses the conservative ISO correlation equation

18 Critical Temperature (T C ) Constant pressure 5 bar (75 psig) Vary temperature Defined as the temperature above which the crack arrests and the temperature below which the crack propagates

19 Critical Temperature (T C )

20 Outline Background RCP Test Methods RCP Requirements in Industry Product Standards RCP Test Data Conclusions

21 ISO ISO has long recognized the importance of RCP, and has included an RCP requirement in its gas product standard for PE pipes ISO 4437 Also, European gas companies have been installing large diameter pipes operating at high pressures, both of which increase susceptibility to RCP

22 ISO 4437 Requirements P C,FS > 1.5 MOP* P C,FS = 3.6 P C,S bar PE pipe testing is only required when the wall thickness of the pipe is greater than the wall thickness of the pipe used in the RCP test to qualify the compound * MOP = Maximum operating pressure

23 ISO/TC 138/SC 4/RCP AHG

24 CSA Project to add requirement in CSA B137.4 (product standard) that RCP testing must be done has been completed Similar wording to ISO 4437 based on wall thickness Project to incorporate RCP required values in CSA Z662 Clause 12 (Code) is complete Similar critical pressure requirements as ISO 4437: -P C,FS > 1.5 X MOP -P C,FS = 3.6 P C,S bar

25 ASTM ASTM D 2513 had no RCP requirements Several years ago, AGA PMC requested that ASTM D 2513 be revised to include the ISO 4437 RCP requirements Balloting completed ASTM F17 agreed to include a requirement that RCP testing must be done, but no values are included in ASTM D 2513

26 AGA PMC PMC agreed with this approach PMC initiated a task group to develop a White Paper that would provide guidance on what the RCP test values should be Drafts of this White Paper have been, and are being, circulated

27 PMC White Paper P C,FS > leak test pressure (1.5 X MOP) P C,FS = 3.6 P C,S bar Insure the critical temperature, T C, is below the minimum anticipated service temperature, T S

28 Outline Background RCP Test Methods RCP Requirements in Industry Product Standards RCP Test Data Conclusions

29 Critical Pressure Values PE Material 12 SDR 11 Pipe S4 Critical Pressure at 32 F Unimodal MDPE Bimodal MDPE 1 bar (14.5 psig) 10 bar (145 psig) Unimodal HDPE Bimodal HDPE 2 bar ( 29 psig) 12 bar (180 psig)

30 Critical Pressure Values PE Material 12 SDR 11 Pipe Full Scale Critical Pressure Unimodal MDPE Bimodal MDPE 6.2 bar (90 psig) 35 bar (500 psig) Unimodal HDPE Bimodal HDPE 9.8 bar (140 psig) 46 bar (650 psig)

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33 Critical Temperature Values PE Material 12 SDR 11 Pipe Critical Temp. at 5 bar (75 psig) Unimodal MDPE Bimodal MDPE 15 C (60 F) -2 C (28 F) Unimodal HDPE Bimodal HDPE 9 C (48 F) -17 C (1 F)

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36 Outline Background RCP Test Methods RCP Requirements in Industry Product Standards RCP Test Data Conclusions

37 Conclusions RCP is more important for larger pipe sizes and higher pressures FS and S4 are the key test methods used RCP requirements to do testing and required values are in ISO 4437 RCP requirements are in CSA B137.4 and required values have been added to CSA Z662 Clause 12 RCP requirements have been added to ASTM D 2513, with suggested values in a proposed AGA White Paper

38 Conclusions In general HDPE has slightly better RCP resistance than MDPE Bimodal MDPE and bimodal HDPE have significantly better RCP resistance than unimodal PE about 10 times higher P C and significantly lower T C Based on superior RCP performance, increasing recognition of RCP in product standards, and increasing demand in the gas industry for RCP resistance, the trend will be to the higher performing bimodal PE materials for gas applications

39 THE END Prepared by Palermo Plastics Pipe (P 3 ) Consulting