Use the FRETT approach to prevent pipeline failures

Use two-part failure analyses to determine the cause of pipeline failures.

By Heinz P. Bloch P.E., Process Machinery Consulting

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In brief:

  • This article will convey the essence of two-part failure analyses that have been used for a number of decades with great success.
  • These four basic agents or component failure mode sets are always force, reactive environment, time, and temperature (FRETT).
  • The first of the two failure-analysis steps is called the “Seven Root Cause Category Examination.”

In 2006, Plant Services published my article on using the FRETT approach to make problem pumps a thing of the past. With questions over pipeline failures, it may be time to revisit the topic. This article will convey the essence of two-part failure analyses that have been used for a number of decades with great success. Originally devised for machinery, the two-part analyses apply equally to pipeline issues. This will be confirmed when the dust settles or, to be more exact, when the flow slows to a trickle.

Failure analysis step no. 1: The “Seven Root Cause Category” approach

The first of the two failure-analysis steps is called the “Seven Root Cause Category Examination.” It accepts the premise that all equipment or hardware failures fall into one or more of only seven possible cause categories.

  1. design errors
  2. material defects
  3. fabrication and processing errors
  4. assembly and installation deficiencies
  5. maintenance-related or procedural errors
  6. unintended operating conditions
  7. operator error.

Using logical thought processes, we might ask ourselves which of these seven cause categories are influenced by the pipeline operator and which ones are under the full jurisdiction of the pipe manufacturer or pipe installers. The answer determines the cause categories where failure analysis efforts should be concentrated.

Suppose there was a case of a failed pipeline. It had been properly leak-tested when it was first commissioned years ago. At that time, all welds had been examined and their integrity verified by suitable non-destructive means.

If that pipeline had been designed by responsible engineers and was in service for a number of decades, we could rule out (1) design error. Next, assume it had been ascertained that no operator error occurred. Accordingly, category (7) is now being ruled out. Assume further that failure occurred in a buried portion of pipe — a segment unaffected by (5) pipeline maintenance. It would be reasonable to say there is thus no logical causal event falling into either the assembly and installation or maintenance and procedural error categories. Categories (4) and (5) can now be ruled out. One might focus next on items (2) material defects and (3) fabrication and processing errors. So, we might investigate these two.

Figure 1. Suppose one found no metallurgical evidence of flaws in the base material selected by the pipe manufacturer and the pipe had burst near a straight length buried in the same type of soil as all the undamaged sections of buried pipe. Blaming the calamity on a very old unseen pre-existing metallurgical defect would be like attributing the death of a 90-year-old to mistakes made by nurses present at the man’s birth.
Figure 1. Suppose one found no metallurgical evidence of flaws in the base material selected by the pipe manufacturer and the pipe had burst near a straight length buried in the same type of soil as all the undamaged sections of buried pipe. Blaming the calamity on a very old unseen pre-existing metallurgical defect would be like attributing the death of a 90-year-old to mistakes made by nurses present at the man’s birth.

But suppose one found no metallurgical evidence of flaws in the base material selected by the pipe manufacturer and the pipe had burst near a straight length buried in the same type of soil as all the undamaged sections of buried pipe (Figure 1). Blaming the calamity on a very old unseen pre-existing metallurgical defect would be like attributing the death of a 90-year-old to mistakes made by nurses present at the man’s birth.

Anyway, the reviewer would now be left with the cause category (6), operation under conditions not envisioned in the design. However, the analysis is still incomplete at this point in time. It will have to shift to Step 2, often abbreviated as the FRETT phase of an investigation.

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