Tag Archive for: Stress Corrosion Cracking (SCC)

News & View, Volume 43 | In-Line Inspection An Improvement Over Pressure Testing for Pipeline Integrity Management

News & Views, Volume 43 | In-Line Inspection – An Improvement Over Pressure Testing for Pipeline Integrity Management

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By:  Scott Riccardella, Dilip Dedhia, and Peter Riccardella 

News & View, Volume 43 | In-Line Inspection An Improvement Over Pressure Testing for Pipeline Integrity ManagementStructural Integrity recently performed probabilistic fracture mechanics (PFM) analysis of a gas transmission pipeline for a major U.S. operator.  The analysis yielded interesting insights in several areas:

Pressure Testing versus In-Line Inspection
Pressure testing has long been considered the gold standard for assuring pipeline integrity.  By testing at a factor (e.g., 1.25x or 1.5x) above the Maximum Allowable Operating Pressure (MAOP), any size critical flaws in the line would fail at this pressure level and are thus removed prior to future service.  Subcritical flaws that remain after the test will be smaller than the critical flaw sizes during operation, and thus can be assumed to have some margin for growth before they become critical in service.  Flaw growth rates can be calculated based on operational and environmental factors to establish a reassessment interval for future testing or inspections.

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News & View, Volume 43 | A Strategic Approach for Completing Engineering Critical Assessments of Oil and Gas Transmission Pipelines

News & Views, Volume 43 | A Strategic Approach for Completing Engineering Critical Assessments of Oil and Gas Transmission Pipelines

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By:  Scott Riccardella and Steven Biles

Regulatory Overview
News & View, Volume 43 | A Strategic Approach for Completing Engineering Critical Assessments of Oil and Gas Transmission PipelinesIn January 2012, the Pipeline Safety, Regulatory Certainty, and Job Creation Act of 2011 was signed into law directing PHMSA to take steps to further assure the safety of pipeline infrastructure.  PHMSA issued the related Notice of Proposed Rulemaking (NPRM) for Safety of Gas Transmission and Gathering Pipelines on April 8, 2016.  Included in the NPRM were significant mandates regarding:

  • Verification of Pipeline Material (§192.607); and
  • Maximum Allowable Operating Pressure (MAOP) Verification or “Determination” (§192.624)

The NPRM proposes requirements for operators to verify the MAOP of a gas transmission pipeline when:

  1. The pipeline has experienced an in-service incident (as defined by §191.3) due to select causes1 in a High Consequence Area (HCA), “piggable” Moderate Consequence Area (MCA), or Class 3 or 4 location since its last successful pressure test
  2. The pipeline lacks Traceable, Verifiable, and Complete pressure test records for HCAs or Class 3 or 4 locations
  3. The pipeline MAOP was established by the grandfather clause (§192.619 (a)(3)) for HCAs, “piggable” MCAs, or Class 3 or 4 locations.

To verify the MAOP of a pipeline, the NPRM provides the following options:

  • Method 1: Pressure Test
  • Method 2: Pressure Reduction
  • Method 3: Engineering Critical Assessment (ECA)
  • Method 4: Pipe Replacement
  • Method 5: Pressure Reduction for segments with small potential impact radius (PIR) & diameter
  • Method 6: Use Alternative Technology

The ECA Approach
Per the NPRM, Method 3 (ECA) is defined as an analysis, based on fracture mechanics principles, material properties, operating history, operational environment, in-service degradation, possible failure mechanisms, initial and final defect sizes, and usage of future operating and maintenance procedures to determine maximum tolerable sizes for imperfections. 

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