PRCI Report 204

L51682e

Battelle Memorial Institute

Need: Developments in steel processing and pipeline manufacture have given rise to steels that are very strong and flaw tolerant compared with earlier vintage pipe and so can sustain significant stable flaw growth prior to failure. The need for an engineering tool to assist in pipeline design and operation decisions that can account for this significant growth and the associated inelastic straining was recognized by the Pipeline Research Council International, Inc. They initiated a combined analytical and experimental program to develop a validated model that could be used to account for flaw growth during hydrostatic testing. This new analysis capability accounts for flaw growth during both the load and the hold portion of a hydrotest and so assist in the design of hydrotests for specific lines or the development of failure criteria for flaws found by in-line inspection.

Benefit: This report presents the results of Structural Integrity (SI) Task 1.11-1990, which was initiated to develop the properties for a steel that was typical of lower strength early vintage pipe and anothersteel that represents the more recent controlled-rolled high-strength and high-toughness pipe. Samples of X42 and X80 steels were chosen as the basis for study. The approach was to compare the properties for these steels with the behavior assumed in the analysis and embedded in the model formulation. If the behavior of the new materials is compatible with the current formulation then it can be concluded that the model can with minor changes and related validation be extended to a much broader scope of pipeline applications. This report presents the ductile-fracture and mechanical properties needed to implement the ductile-flaw-growth model and then comments on the modifications needed to adapt the model to this broader class of steels by comparison of the results presented with the formulation developed to address the steels in the earlier study.

Result:The properties included are the usual tensile properties as well as some mechanical and fracture properties that are unique to the analysis of stable ductile-flaw-growth using the ductile flaw growth model. The results indicate that the ductile flaw growth model could be extended to deal with steels like the X80 without much difficulty. However, the results for the X42 showed that its creep response was not similar to the X52 to X70 grades and its behavior was inconsistent with the present form of the model. Therefore, extension of the model to deal with steels similar to the behavior of would involve extensive rework of the model formulation and the computer algorithm.

Product Details

Published:

10/01/1992

Number of Pages:

56

File Size:

1 file , 770 KB