Monday, September 21, 2015

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:


  1. Improperly qualified procedures or the use of wrong procedures. All welding procedures must be qualified and welding must be controlled to strict specifications. 
  2. 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.
  3. 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:


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

PHMSA 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