Being able to estimate the tensile strain capacity (TSC) of vintage girth welds is sometimes necessary in the integrity management of vintage pipelines.  For instance, assessing the girth weld integrity could be a top priority after a confirmed ground movement event.  Decisions may also be needed about the disposition of a girth weld when weld anomalies are found.  Typical fitness-for-service (FFS) procedures, such as API 1104 Annex A and API 579/ASME FFS-1, generally target materials under nominally elastic conditions and strain demands less than 0.2%.  These procedures can produce overall conservative results when the strain demand exceeds 0.2%.

This paper summarizes the development and validation of a TSC estimation tool for vintage girth welds.  The tool development process generally follows the Level 4a procedures of the PRCI-CRES tensile strain models.  Finite element analysis (FEA) was performed to develop a crack-driving force database with consideration of the salient features of vintage girth welds, such as larger weld caps and weld strength mismatch levels.  A TSC model was then derived from the crack-driving force database and representative apparent toughness of vintage girth welds based on an initiation-controlled limit state.  A graphical user interface (GUI) was developed to facilitate the application of the TSC model.  The tool produces TSC estimates based on given geometry and material characteristics of a girth weld, such as pipe strain hardening capacity, weld strength mismatch, heat-affected zone (HAZ) softening, girth weld high-low misalignment, girth weld flaw dimensions, and operating pressure.  For inputs that might not have readily available values, recommended values are provided.  The tool allows the evaluation of the impact of various input parameters on TSC.

The TSC tool is evaluated against eight purposely-designed curved-wide plate (CWP) tests.  Accompanying small-scale material characterization tests, including chemical composition, round bar tensile, microhardness, and Charpy impact tests, were performed to provide inputs for the evaluation of the tool.  The tool is shown to provide reasonably conservative estimates of TSC.  Gaps and future work to refine the assessment of vintage girth welds are highlighted at the end of the paper.


Estimation of Tensile Strain Capacity of Vintage Girth Welds

Division / Sponsors: 
Pipeline Systems Division

Paper Proceedings: https://asmedigitalcollection.asme.org/IPC/IPC2020/volume/84447

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