Abstract API/ISO TC67 SC5 Workgroup 2B is currently undertaking the modernisation of API Bulletin 5C3/ISO 10400 for casing and tubing performance property equations. This paper describes the test data and analysis methods being used to develop and evaluate proposed new collapse equations for quenched and tempered (Q&T) pipe. As the work is still at committee stage, presentation of detailed results must await a future publication; however, sufficient detail is given to allow a full understanding of the various analysis techniques, as wellas the final results when they appear. Introduction Limitations of Existing Approach. The technical basis of the current Bulletin 5C31 was prepared in the early 1960s. Various limitations have been identified since its first publication, as follows.The collapse test data2 upon which the equations are based is now rather old, and pipe production practices have improved considerably in the intervening period. It is therefore likely that the equations do not accurately represent the performance of modern tubulars.The majority of the collapse tests were for short specimens (L/Do = 2), which are now known to overestimate the collapse strength of real pipe 3–6.The collapse strength equations result in a widely varying margin between the ultimate and design collapse strengths over the Do/t range for well tubulars7, and thus also in predicted failure probability (Pf)8,9.The mean value equations are relatively poor predictors of ultimate collapse strength compared to modern formulations, which have been shown to be much more accurate10.The same equations were used for both Q&T and non- Q&T pipe. However, recent work11,12 has shown that the two classes have different collapse behaviour, and therefore need individual strength equations.The collapse test specimens were manufactured using a wide range of production methods (e.g., seamless and ERW, cold and hot rotary straightening), and no attempt was made to determine the various effects on collapse strength. Subsequent work12 has demonstrated that both straightening and heat treatment have a significant effect on collapse strength, and thus should be included explicitly in any modern treatment.The present formulation for plastic collapse strength is implicitly based on the assumption that collapse strength is proportional to the specified minimum, rather than the actual, yield stress. This is acceptable as long as the ratio of actual to specified minimum yield stress is constant for all grades. However, analysis of production quality data10 has shown that this ratio varies considerably by grade, and thus that the current treatment can and should be improved.Finally, the present approach cannot accommodate non- API grades, such as high-collapse (HC) pipe. Choice of Calibration Method. For the reasons above, it was decided to proceed with the modernisation of Bulletin 5C3, and the task was allotted to API/ISO SC5 workgroup 2b in mid-1998.
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