PIPELINE CONSTRUCTION WELDING: ONE OF THE LEADING CAUSES OF PIPELINE FAILURE

Pipeline Construction Welding: one of the leading causes of pipeline failure

The applicable regulations addressing welding are in Subpart E of Part 192 for gas pipelines and Subpart D of Part 195 for hazardous liquid pipelines. Additional discussion on welding can be found at the Stakeholders Communications web site. Some specific concerns identified related to welding applications during construction are provided below:

• Improperly qualified procedures or the use of wrong procedures. All welding procedures must be qualified and welding must be controlled to strict specifications. As part of the quality-assurance process, each welder must pass qualification tests to work on a particular pipeline job, and each weld procedure must be approved for use on that job in accordance with welding standards.
• PHMSA inspection has found that some constructors do not have welding procedures on site or are not following procedures.
• Part of the welding process is pre-heating of the pipe joint prior to beginning welding. Welders have not always ensured that the pre-heating requirements, established and documented in qualified welding procedures, are maintained. Improper pre-heating can lead to weld cracking after the completion of successful nondestructive testing of the weld. Refer to Hydrogen Assisted Cracking (HAC) for additional discussion.

PHMSA issued advisory bulletin ADB-10-03 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 percent specified minimum yield strength (SMYS). PHMSA has found pipe segments with:

• Line pipe weld misalignment,
• Improper bevel and wall thickness transitions,
• Out of roundness due to cut induction bends, and
• Other improper welding practices.

PHMSA and independent experts' inspection has seen the following types of concerns when inspecting new pipeline construction:

 

Mechanized Welding Coating damage caused by welding band Incomplete weld procedure qualification Pre-heat crew not using Tempilstiks Pipe size - Hi-Lo alignment issues NDT falling behind main gang Lack of padding between pipe and skids Incorrect or inadequate placement of skid cribbing Lack of inspector oversight Not following procedures Incorrect pre-heat or interpass temp Improper use of Tempilstik - too near weld Amps and Volts measured at machine not weld (only long leads) Moving pipe during root bead welding Initial high defect rates Inadequate defect repair tracking Inadequate quality and documentation of MUT

Manual Welding Not following procedures Improper fitup (misalignment) Improper bevel and wall thickness transitions Improper fitup of cut induction bends (ovality and out-of-roundness) Lack of inspector oversight Early clamp release Arc burns due to poor welding practices Incorrect pre-heat or interpass temp Inadequate visual weld inspection Improper storage of low hydrogen rods Welding inspectors not in possession of welding procedures Use of 'hinging' technique to aid with pipe line-up Pipe size - Hi-Lo alignment issues Improper gas flow rate for gas shielded processes Inadequate defect repair tracking Incomplete qualification documents for welders Amps and Volts measured at machine not weld (for long leads) Inadequate defect removal on repair welds