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Pipeline Failure Analysis

                                          

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Failures of Pipelines

Gas and oil pipelines have established an impressive safety record over the years.  However, failures have occurred  for an assortment of reasons.  Some of the causes of failure are identified in this commentary.

Since the 1940s, all of the oil and gas transmission lines have been built by welding.  In general,  American Petroleum Institute (API) 5L specification steels are used in pipelines.  Pipeline wall thicknesses are established on the pressure in the line and on the allowable hoop stress levels for the material.  The allowable stress levels for gas pipelines vary based on the location of the pipeline and are regulated by the U.S. Department of Transportation (DOT).

Pipe line failure analysis pipe

Failure Analysis - stress corrosion cracking.jpg (5337 bytes)

Pipelines are pressure tested in addition to nondestructive testing prior to being put into service.  Normally, pipelines are  hydrostatically stressed to levels above their working pressure and near their specified minimum yield strength.  This pressure is held for several hours to ensure that the pipeline does not have defects that may cause failure in use.  This proof test of pipelines  provides an additional level of confidence that is not found in many other structures.

Pipeline Failure Analysis

Some of the causes of pipeline failures are listed below:

  •   Mechanical damage
  •   Fatigue cracks
  •   Material defects
  •   Weld cracks
  •   Incomplete fusion
  •   Improper repair welds
  •   Incomplete penetration
  •   External or internal corrosion
  •   Hydrogen blistering

Mechanical damage normally consists of gouges and dents.  They generally are created by excavation or handling equipment during construction.  

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Last modified: September 11, 2007