The inspection of new pipeline projects reveals many issues that, if unresolved, could adversely affect the pipeline's long- and short-term integrity.
The pipeline industry has seen unparalleled growth as energy needs are being met and new sources of supply are being introduced. Inspections of new pipeline projects reveal several problems that could adversely affect the pipeline's long and short-term integrity. The Pipeline and Hazardous Materials Safety Administration (PHMSA) inspect pipeline construction to ensure compliance with these requirements. Inspectors check operator-prepared construction procedures to make sure they comply with regulatory requirements. Construction activities are then observed in the field to ensure they are conducted according to the procedures of inspectors.
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PHMSA inspectors bring pipeline constructors' attention to issues identified by the inspector. The concerns may be resolved through revisions to procedures, personnel training, changes to construction practices, physical pipeline repairs, pipeline coatings, or auxiliary pipeline features. Through pre-commissioning integrity hydrostatic pressure tests and inline inspection tool runs, PHMSA ensures the issues are corrected before the pipeline is buried and before the pipeline commissioning.
Hydrogen-assisted cracking:Hydrotests during pipeline construction have revealed through-wall weld cracks. The discovery of cracked welds during the nondestructive testing and repair phase of pipeline construction is extremely troubling since they are typically found, repaired, or removed. Metallurgical investigations concluded hydrogen assisted cracking (HAC) was the cause of the failures in high-strength pipes 20 inches or larger in diameter. A welded metal or heat-affected zone containing hydrogen may crack, a process known as hydrogen-induced cracking (HIC). Construction records associated with the leaks and additional investigations were reviewed. It turned out that most ultrasonic inspections and radiography were performed the same day as the welds; no Nondestructive Testing (NDT) reports indicated cracks - confirming Delayed HAC. NDT was completed in some cases the following day, but cracks were undetected. Mechanized projects used ultrasonic testing (UT), while manual welding projects used radiography.
Low strength in high-grade pipe: PMSA released Advisory Bulletin ADB-10-03 to warn owners and operators of recently constructed large-diameter natural gas pipelines and hazardous liquid pipeline systems that girth welds may fail of welding quality issues. A misalignment during welding large diameter pipes can lead to leaks and ruptures in service at pressures well below 72 percent of the specified minimum yield strength (SMYS). Many recent projects with a diameter of 20 inches or more, Grade X70 or higher line pipe, were reviewed by PMSA in 2008 and 2009. Tests of girth welds that failed in pipe wall thickness transitions have revealed misalignment of line pipe welds, improper bevels, improper wall thickness transitions, and other welding practices during construction were observed in pipe segments. As a result of support and backfill issues, several failures were found in line pipe segments with concentrated external loading. To ensure that girth weld failures do not occur due to misalignment and other issues, owners and operators of recently constructed large-diameter pipelines should review construction and operating records and conduct engineering reviews.
As part of quality assurance, qualified technicians take radiographs of the pipeline welds to ensure they meet federally prescribed quality standards. To achieve this, qualified technicians take radiographs of the pipe welds. If the technician detects any flaws, they repair or cut out the weld, and a new weld is made. NDT technicians use real-time radiographs or process film in a portable darkroom at the site. Ultrasonic testing (UT) is another way of weld quality inspection.
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