Failure Analysis

Establishing The Severity And Extent Of A Corrosion Problem After A Piping Failure

A piping failure can produce a substantial volume of damage in a relatively short period of time.  While most water leaks are relatively small and can be easily repaired, the most extensive pipe breaks can cause damages of $5 million or more.  The failure of a 4 in. pipe section operating at 200 PSI, a pressure common to most high rise office building properties, will release over 3,500 gallons of water per minute.

The response to a piping failure may be as small as a pipe clamp and the hope that it will not happen again, to a full blown investigation followed by pipe replacement, repairs, and / or corrective actions.  Five questions are tpyically raised in response to a pipe leak:

  1. What caused the failure?
  2. How extensive is the problem?
  3. What is the condition of the pipe?
  4. What is the remaining service life of the piping system?
  5. What actions should be taken?

Investigative Options

While all five questions are inter-related, answering them often requires different disciplines.  A pipe failure at a grooved clamped fitting, longitudinal or circumferential weld seam, fixture such as strainer or PRV, or other individual component suggests a localized failure best defined by submitting the failed item for metallurgical analysis.  Every failed piping component should be saved for inspection, although remarkably, the answer to many pipe failure problems are just thrown away.

A general rule of investigation is that where the failure can be isolated and the pipe section or component removed, submitting that example to a metallurgical laboratory for failure analysis is unquestionably the best first step.

Where no specific failure location has occurred, such as commonly where heavy rust deposits exist without a failure condition, then ultrasonic testing is often the best first step.  Ultrasonic testing allows the evaluation of a large number of piping locations from which the most appropriate examples of pipe can be identified for removal should further metallurgical testing be appropriate.  Rather than selecting a section of pipe at random for metallurgical testing and basing a decision upon results which may not be representative of the system or the problem, ultrasound allows a much larger sampling of test locations from which a more accurate piping assessment is possible.

Ultrasound provides a cost-effective method of establishing total pipe condition at approximately 1-2% of the cost to cut out pipe samples for metallurgical testing.  Ultrasonic testing followed by the metallurgical analysis of specific pipe samples, is the best procedure to follow in defining most corrosion problems; providing a baseline assessment of pipe condition followed by a visual confirmation to the ultrasonic results.  Property performed, the raw ultrasonic thickness data can be analyzed to provide an estimate of corrosion loss and subsequently an estimate to the remaining service life of the system.

Even where extensive service life may be indicated, most investigations will result in recommendations toward system improvement.  Where ultrasonic analysis shows severe pipe deterioration beyond repair, pipe replacement is often the only answer.  Generally, however, investigation is prompted by one or more physical failures or suspicion to a problem likely resulting in some corrective recommendations.

Other Interests

Far too often, mistaken or self- benefitting influences direct attention to corrective actions that may not be appropriate, or worse – will prevent the needed investigation into the source and extent of a problem.  To a high corrosion problem, filtration representatives will cite the need for filtration, chemical suppliers may suggest a modification in the chemical treatment program, mechanical contractors will recommend pipe replacement of the affected area or direct attention to a suspected cause – such as the need for dielectric fittings.  All such speculative corrective recommendations, without a solid understanding of current pipe condition, frequently waste valuable time and resources to actually correcting the problem at hand.