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Fact Sheet: Direct Assessment (DA) - Hazardous Liquid Pipelines

Quick Facts:

  • Direct Assessment of hazardous liquid (and carbon dioxide) pipelines involves data collection and analysis, indirect inspection, direct examination, and post-assessment evaluation. Operators use direct assessment not only to find existing corrosion defects but also to prevent future corrosion problems.
  • Direct Assessment for hazardous liquid pipelines is limited to evaluating the risk of external corrosion, which is a time-dependent threat to the integrity of a pipeline segment.
  • External Corrosion Direct Assessment (ECDA) is identified in the Hazardous Liquid Pipeline Integrity Management (IM) Rule (§195.452) as one of the three acceptable methods for evaluating the integrity of an onshore hazardous liquid or carbon dioxide pipeline segment.
  • ECDA may be used either as a primary or a supplementary method, implemented in conjunction with one of the other primary assessment methods, i.e. inline inspection ( ILI) or hydrostatic pressure testing.
  • The Hazardous Liquid IM rule contained in Subpart F of 49 CFR Part 195 provides for specific standards for applying ECDA that are identified in Subpart H, §195.588.
  • In general, the requirements of NACE Standard RP0502–2002, “Pipeline External Corrosion Direct Assessment Methodology,” which is incorporated into the rule by reference, must be followed in the application of ECDA.
  • The operator must develop and implement an ECDA plan that includes provisions for applying more restrictive criteria when conducting ECDA for the first time on a pipeline segment.

Why do pipeline operators use external corrosion direct assessment to evaluate the integrity of a pipeline?

ECDA is a valuable integrity assessment method that operators may select where other integrity assessment methods are not feasible or where ECDA may be more effective, as an alternative to ILI and hydrostatic pressure testing for evaluating a pipeline’s integrity.

How is ECDA carried out?

The hazardous liquid IM rule specifies a four-step approach for evaluating external corrosion threats using ECDA, as specified in §195.588.

Step One: Pre-assessment – In this step the operator gathers and integrates data to determine the feasibility of using ECDA for a segment, identifies ECDA regions, and determines which two indirect examination tools should be used on the ECDA region.

Step Two: Indirect Examination – In this step the operator evaluates the pipe segment using two complementary tools to identify indications of potential external corrosion, classifies the severity of those indications, and determines the urgency for their excavation and direct examination. The operator must have criteria for identifying and documenting those indications that must be considered for excavation and direct examination, for defining the urgency of excavation and examination of each indication and for scheduling the excavations.

Step Three: Direct Examination – In this step the operator must excavate the pipe and examine its condition and environment to determine actions to be taken should corrosion defects be found, and to identify and address root causes. The operator must have criteria for deciding what action should be taken if either: (A) corrosion defects are discovered that exceed allowable limits or (B) if root cause analysis reveals conditions for which ECDA is not suitable.

Step Four: Post Assessment – In this step the operator must determine the appropriate interval for performing reassessments and the effectiveness of using ECDA as an assessment method. The post assessment evaluation is one way in which the ECDA process undergoes continuous improvement.

Date of Revision: 12012011