The US Pipeline and Hazardous Materials Safety Administration issued an advisory bulletin Mar. 18, 2010, to notify owners and operators of recently constructed large-diameter natural gas pipeline and hazardous liquid pipeline systems of the potential for girth weld failures due to welding quality issues. Misalignment during welding of large-diameter line pipe may cause in-service leaks and ruptures at pressures well below 72% specified minimum yield strength.
PHMSA reviewed several recent projects constructed in 2008 and 2009 with 20-in. OD or greater, Grade X70 and higher line pipe. According to Oil & Gas Journal data published in its annual Worldwide Pipeline Construction report, a total of more than 8,600 miles of pipeline meeting this description was planned for construction in the US during 2008 and 2009 (OGJ, Feb. 18, 2008, p. 48, and Feb. 9, 2009, p. 55).
PHMSA found metallurgical testing results of failed girth welds in pipe wall thickness transitions in pipe segments with line pipe weld misalignment, improper bevel and wall thickness transitions, and other improper welding practices that occurred during construction. A number of the failures occurred in pipeline segments with concentrated external loading due to support and backfill issues.
PHMSA advised owners and operators of recently constructed large diameter pipelines to evaluate these lines for potential girth weld failures due to misalignment and other issues by reviewing construction and operating records and conducting engineering reviews as necessary.
Background
Federal pipeline safety regulations in 49 CFR Parts 192 and 195 require operators of natural gas transmission, distribution, and hazardous liquids pipeline systems to construct their pipelines using pipe, fittings, and bends manufactured in accordance with 49 CFR and incorporated standards and listed design specifications. This involves reviewing the manufacturing procedure specification details for weld end conditions for the line pipe, fitting, bend, or other appurtenances from the manufacturer to ensure weld-end conditions are acceptable for girth welding.
During the 2008 and 2009 pipeline construction periods, several newly constructed, 20-in. or greater OD, high strength (API 5L X70 and X80) natural gas (see photo) and hazardous liquid pipelines experienced field hydrostatic test failures, in-service leaks, or in-service failures of line pipe girth welds. Postincident metallurgical and mechanical tests and inspections of the line pipe, fittings, bends, and other appurtenances showed pipe with weld misalignment, improper bevels of transitions, improper back welds, and improper support of the pipe and appurtenances. In some cases, pipe end conditions did not meet the design and construction requirements of the applicable standards.
Postincident findings were that in some cases the pipe and induction bend girth weld bevels were not properly transitioned and aligned during welding. In some cases, the girth weld pipe ends did not meet API 5L pipe end diameter and diameter out-of-roundness specifications. Many of the problematic girth welds did not meet API 1104 misalignment and allowable high-low criteria, according to PHMSA.
Some girth welds that failed in-service had nondestructive testing quality control problems. NDT procedures, including radiographic film and radiation source selection, were not properly optimized for weld defect detection and repairs. This was particularly the case where there were large variations in WT at transitions. In some situations, NDT procedures were not completed in accordance with established API 1104 and operator procedures.
Many of the integrity issues with transition girth welds occurred on pipelines being constructed in hilly terrain and high stress concentration areas such as at crossings, streams, and sloping hillsides with unstable soils. These girth welds had high stress concentrations in the girth weld transitions due to the combination of large variations in WT and improper internal bevels with inadequate pipe support, poor backfill practices, and soil movement due to construction activities.
Advisory bulletin
PHMSA Advisory Bulletin ADB-10-03 called on owners and operators of recently constructed large-diameter pipelines to evaluate them for potential girth weld failures due to misalignment and other issues by reviewing construction and operating records and conducting engineering reviews as necessary.
Assessments should include material specifications, field construction procedures, caliper tool results, deformation tool results, welding procedures including back welding, NDT records, and any failures or leaks during hydrostatic testing or in-service operations to identify systemic problems with pipe girth weld geometry, out-of-roundness, diameter tolerance, and WT variations that may be defective, according to the advisory.
With respect to the construction process, ADB-10-03 advises pipe, fittings, factory bends, and induction bends must be made in accordance with the applicable standards to ensure weld-end dimension tolerances are met for pipe-end diameter and diameter out-of-roundness. API 1104 specifies girth weld misalignment and allowable high-low criteria.
Sec. 7.2, Alignment, specifies pipe ends of the same nominal thickness should not have an offset exceeding 0.125-in. (3 mm) and when there is greater misalignment, it shall be uniformly distributed around the circumference of the pipe, fitting, bend, and other appurtenance.
PHMSA's advisory bulletin cited numerous other standards in reference to the assessments, covering pipe manufacturing, construction processes, and NDT as well as construction mechanics.1
Regarding NDT, the bulletin said each material component of a pipeline such as line pipe, fittings, bends, and other appurtenances must be able to withstand operating pressures and other anticipated external loadings without impairment of its serviceability in accordance with 49 CFR 192.143 and 195.110. In order to ensure pipeline integrity, the operator must take all practicable steps to protect each transmission line from abnormal loads while backfilling and other work continues along the right-of-way and to minimize loads in accordance with 49 CFR.
PHMSA said operators should give special attention to girth welds with variations in WT occurring in pipeline segments where significant pipe support and backfill settlement issues after installation may be present, specifically in hilly terrain and high stress concentration locations such as at crossings, streams, and sloping hillsides with unstable soils.
Even if no girth weld concerns are identified by reviewing construction records, according to the advisory, if an operator has any knowledge, findings or operating history that leads it to believe that its newly constructed segments contain these types of girth weld transitions, the operator should conduct engineering reviews as described with those operating pipelines to ensure material, engineering design, and field construction procedures were in compliance with 49 CFR Parts 192 and 195, concluding that failure to conduct engineering reviews and remediate findings may compromise the safe operation of the pipeline.
Reference
1. US Department of Transportation, Pipeline and Hazardous Materials Safety Administration, "Pipeline Safety: Girth Weld Quality Issues Due to Improper Transitioning, Misalignment, and Welding Practices of Large Diameter Line Pipe," Docket No. PHMSA-2010-0078, Federal Register, Vol. 75, No. 56, Mar. 24, 2010.
More Oil & Gas Journal Current Issue Articles
More Oil & Gas Journal Archives Issue Articles
View Oil and Gas Articles on PennEnergy.com
