Validation of Assessment Methods for Production Scale Girth Welding of High Strength Steel Pipelines with Multiple Pipe Sources

016436152012Issue: 1.0PDFTech ReportReport Number: 10361DTPH56-07-T-000006 WP #275DefectsEvaluation and assessmentFlaw detectionGas metal arc weldingHigh strength steelMechanical propertiesPipePipelinesValidationWeldsResearch HubUnited States;United KingdomGL Noble DentonSwankie, TroyGL Noble DentonUnited States. Dept. of Transportation. Pipeline and Hazardous Materials Safety AdministrationKieba, MaxPipeline and Hazardous Materials Safety AdministrationThere is an increasing need to deliver energy from sources in remote areas to demand centers. Forexample, in North America, the delivery of gas from Alaska to demand centers in the lower 48 states is ofmajor economic and strategic interest. This will require the design and construction of large diameter, longdistance pipelines through adverse environments. The economics of these pipelines are dependent on theuse of high strength steels to reduce the tonnage of steel required and on high productivity girth weldingprocesses to shorten the construction period.Robust inspection methods are required to reliably detect and size any defects which may occur duringwelding, and an equally robust method is required to assess the impact of those defects on the safeoperation of the pipeline.There are a number of methods that are commonly used for the assessment of a girth weld containing a\u2018fabrication\u2019 defect. These range from the more generic workmanship (or weld quality) defect acceptancelimits to the more complex pipeline specific engineering critical assessment (ECA) methodologies wheredefect limits are derived based on the pipe size, material properties and pipeline loading conditions.The ECA approach is widely used to derive girth weld defect acceptance limits that are specific to apipeline. They are based on either semi-analytical methods or on the results of large-scale tests on pipelinegirth welds. There is no one standardized method.The guidance produced by the European Pipeline Research Group (EPRG) is an example of an establishedmethodology based on the results of large-scale tests, while commonly used pipeline specific analyticalassessment methods include API 1104aand CSA Z662a. Other commonly used semi-analytical methods,which are more generic in application, include API 579-1/ASME FFS-1aand BS 7910a.The application of any of these methods has certain limitations. For example, there is no \u2018upper limit\u2019 to linepipe strength specified for use of the ECA methodology presented in API 1104, although there arelimitations to some of the equations used within the procedure which limit their range of applicability up tograde X80 line pipe. Similarly, the EPRG guidelines are limited to pipelines constructed from grade X70 linepipe; although much work has been undertaken to demonstrate the applicability of the guidelines topipelines constructed from grade X80 line pipe, an updated guidance document has yet to be published.The objective of this project was to investigate the applicability of these \u2018established\u2019 methods for defininggirth weld defect acceptance criteria for pipelines constructed from grade X100 line pipe.BP provided the project with ten girth welds following completion of their full-scale X100 operational trial atGL Noble Denton\u2019s Spadeadam test facility located in Cumbria, England. This BP project involved theconstruction of two sections of 48in diameter pipeline. The construction process replicated full-scalepractice, where the pipeline was welded above ground and then lowered into the ditch and backfilled. Thepipeline test sections were then pressure cycled at a frequency to simulate 40 years of operation over a twoyear period. The project team selected the most appropriate girth welds that they considered would enablethe effects of material variability between abutting pipes, different heats, and different pipe manufacturers tobe investigated.A materials test program was developed to fully characterize the performance of each girth weld. In total,217 tensile tests, 108 Charpy impact tests and 54 fracture mechanics tests were undertaken, in addition toweld macro sections and hardness surveys. The test program concluded with 30 curved wide plate (CWP) \u2018mid-scale\u2019 tests, of which 19 specimens contained machined surface breaking defects of specified depthand length dimensions. The remaining CWP specimens contained either natural welding defects (e.g., lackof penetration, lack of side wall fusion or porosity), deliberate defects that were introduced during welding,or combinations of natural and deliberate defects.Each CWP test was assessed using the procedures given in API 1104 (Option 2), EPRG, CSA Z662,BS 7910 and API 579-1/ASME FFS-1. The results of the small-scale test program for each weld were usedas input into each assessment. The results of the assessments were compared with the results from theCWP tests to assess the limitations of each assessment method.In general, each assessment method performed well, giving a conservative prediction of failure stress.However, the accuracy of the prediction was found to vary significantly