THE CONCEPT OF proof testing engineering structures has its origins in antiquity. The precommissioning hydrostatic test (also known as the pre-service pressure test) has been an important part of the process of commissioning a newly-constructed pipeline for over 50 years, since its beginnings in the 1950s in the USA. The purpose of the hydrotest is several-fold: to prove the leak tightness of the pipeline system at a pressure above the design pressure, as a strength (proof) test to identify (fail) defects and sub-standard pipe, and to prove a safety margin above the pipeline design pressure.
Historical data, from PARLOC (Pipeline and Riser Loss of Containment), the OPS (Office of Pipeline Safety) 30-day Incident Reports, and the published literature on the number and causes of precommissioning hydrotest failures has been reviewed. The historical data covers onshore gas transmission pipelines in the USA and the UK, and gas and liquid pipelines in the North Sea. The data covers the period from 1952 to 2005, although there are significant gaps in the data (for instance, the OPS data for the USA does not report test failures after 1984). In this paper, the historical data is summarized over this period, by year, in terms of the number of failures per km, and trends in the frequency and type of failures are identified.
Comparison of USA and UK experience, or onshore and offshore experience, is contentious because of the influence of different design codes, and local custom and practice. The USA and UK pipeline design code requirements for the hydrotest are summarized in the paper, and it is shown that some of the trends in the failure data may be explained by the differences between the codes.
Failures during the hydrotest are rare, but occasionally they do occur. The general consensus is that failures during the precommissioning hydrostatic test are now less common, and that failures due to defective linepipe (rather than due to leaking fittings) are rare. The historical data supports this consensus, but it also highlights that it is largely based on anecdotal evidence rather than data and analysis, because information on test failures is not now routinely gathered and published.
The results of the historical review demonstrate that understanding the causes and reasons for hydrotest failures is important for learning from past mistakes, and also for identifying those cases where it may be possible to dispense with a precommissioning hydrotest. Reliable historical data on hydrotest failures is necessary to quantify trends over time, and to understand the causes of failure. The pipeline industry as a whole is not coherently recording this data: it should be.
1. Anon., 1960. Oil & Gas Journal, 58, 17, April 25, p.105.
2. Anon., 2004. Code of Practice for Pipelines: Part 2: Subsea Pipelines, PD 8010-2, British Standards Institution, London.
3. Anon., 2001. Steel pipelines for high pressure gas transmission. IGE/TD/1 Edition 4, Recommendations on transmission and distribution practice. Institute of Gas Engineers, Communication 1670.
4. Anon., 2003. Gas transmission and distribution piping systems. ASME Code for pressure piping, B31, ASME B31.8 – 2003 Edition (Revision of ASME B31.8 – 1999), American Society of Mechanical Engineers, New York.
5. Anon., 2002. Pipeline transportation systems for liquid hydrocarbons and other liquids. ASME Code for pressure piping, B31, ASME B31.4 – 2002 Edition (Revision of ASME B31.4 – 1998), American Society of Mechanical Engineers, New York.
6. D.G.Jones, 1992. Notes on the philosophy and history of pressure testing. IMechE seminar on Developments in pressure vessel technology, London.
7. Anon., 1991. Pipeline and riser loss of containment study – 1990 (PARLOC 90), Prepared by Advanced Mechanics & Engineering Ltd for The Health and Safety Executive, OTH 91 337, HMSO, London.
8. Anon., 1993. PARLOC 92: The update of loss of containment data for offshore pipelines. Idem, OTH 93 424, HMSO, London.
9. Anon., 1996. PARLOC 94: The update of loss of containment data for offshore pipelines. Idem, OTH 95 468, HMSO, London.
10. Anon., 1998. PARLOC 96: The update of loss of containment data for offshore pipelines. Idem, OTH 551, HMSO, London.
11. Anon., 2003. PARLOC 2001: The update of loss of containment data for offshore pipelines. 5th Edition, Prepared by Mott MacDonald Ltd for The Health and Safety Executive, The UK Offshore Operators Association, The Institute of Petroleum, and the Energy Institute, London.
12. FOIA on-line library: Distribution and transmission accident and incident data. (http://ops.dot.gov/stats/IA98.htm)
13. A.R.Duffy, G.M.McClure, W.A.Maxey, and T.J.Atterbury, 1968. Study of the feasibility of basing natural gas pipeline operating pressure on hydrostatic test pressure. Final report to the American Gas Association, AGA Catalogue No. L30050, Battelle Memorial Institute.
14. M.G.Kirkwood and A.Cosham, 2000. Can the pre-service hydrotest be eliminated? Pipes and Pipelines International, pp 5-19.
15. J.L.M.Robertson, D.Smart, and T.Al-Hassan, 1996. Offshore North Sea pipeline and riser loss of containment study (PARLOC) – Applications and limitations in the assessment of operating risks. Journal of Offshore Mechanics and Arctic Engineering, 118, pp115-120.
16. Anon., 2004. Pipeline Safety Regulations, Code of Federal Regulations, Title 49 Transportation, Subtitle B Other Regulations Relating to Transportation (Continued), Chapter I Research and Special Programs Administration, Department of Transportation (Continued), Subchapter D Pipeline Safety, Parts 190 to 199, 49CFR190-199, October 1.
17. D.J.Jones and R.J.Eiber, 1988. An analysis of reportable incidents for natural gas transmission and gathering lines 1970 through 1986. Topical Report to Line Pipe Research Supervisory Committee of the Pipeline Research Committee of the American Gas Association, NG-18 Report No.174.
18. B.N.Leis, D.L.Rudland, and R.J.Eiber, 1997. Final report on evaluation of the benefits of hydrotesting gas-transmission pipelines. Prepared for the Offshore and Onshore Design Applications Supervisory Committee of the Pipelines Research Committee International (PRCI), Program PR-3-9523, American Gas Association (AGA).
19. Idem, 1997. Towards alternatives to hydrotesting to ensure safe serviceability of pipelines. Proc. EPRG/PRC 11th Biennial Joint Technical Meeting on Line Pipe Research, Washington, USA.
20. Anon., 1987. A statistical record of the gas industry: 1987 data. American Gas Association, Publication Catalogue No. F10186.
21. D.Kovacs, 1998. Ultrasound locates freak laminations. The Pipevine, A newsletter from Pipetronix on the Science of Pipeline Integrity, Spring 1998. (www.pipetronix.com/Pipevine/issue3/page2.html)
22. Private communication with DNV Pipeline Committee, December, 2001.
23. J.-J.Crolet and M.Sauvage, 1999. Reliability of ERW pipes: a case history. Materials Performance, 38, pp63-68.
24. Press Release, 23 November 2004: Commissioning of pipeline Zomergem-Zelzate postponed: Fluxys to replace all pipes not complying with its safety standards. (www.fluxys.net/index_corporate_press.htm)
25. B.N.Leis, 2004. Hydrostatic testing of transmission pipelines: when it is beneficial, and alternatives when it is not. Proc. Fourth Pipeline Technology Conference, Ostend, Belgium, 4, R.Denys, Ed., Scientific Surveys Ltd, pp1895-1919.