Frequently Asked Questions

Here you will find a listing of the most frequently asked questions (FAQs) concerning pipe susceptible to low yield strength.
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• browse the complete listing of FAQs below, or
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Yes. Operator may use three upstream and three downstream joints for comparison. PHMSA has found that internal diameter variation is unlikely to extend this far. Operator should review pipe diagrams of the expanded and comparison pipe joints. The diagrams should include “expansion markers or lines” showing the: pipe nominal internal diameter, API 5L pipe tolerance – nominal diameter plus 0.25-inches or 0.60% of nominal diameter for 42-inch pipe, 1.0% expansion line, and 1.5% expansion line. These expansion markers on the diagram will a good review of pipe expansion.

Section 2.b covers additional testing of expanded pipe when initial testing in 2.a does not meet requirements. Mixed results in 2.b for two pipe joints expanded beyond 1% require the fitness for service justification indicated in 2.b.ii or further material testing to establish statistical confidence. PHMSA observations indicate that mixed results for expanded pipe segment tests may reflect testing errors. (Mixed results with minor variances from requirements may indicate the border between pipe meeting requirements and pipe not meeting requirements.) PHMSA recognizes there may be minor differences in properties test results. Should there be properties test result variances (a few properties test results that are slightly below requirements) that do not meet API 5L or alternative MAOP Special Permit standards, these results would need to be handled in accordance with one of these methods: a) reviewed with PHMSA, b) Operator may elect to remediate these pipe joints by removal from the pipeline, or c) PHMSA would let Operator take one additional set of test samples in a similar area of the pipe joint and retest to verify pipe properties. A situation could occur where the Operator finds that the pipe properties test results meet standards, but there is wall thinning over the API 5L and 49 CFR Part 192 requirements due to lower original wall thickness and/or test pressures.

Follow 2.a for testing joints above 1.5% and 2.b if tests in 2.a do not meet requirements. If 2.b indicates low property issues, then Operator must address mitigative measures in a fitness for service plan as indicated in 2.b.ii. Operator must also excavate, inspect and remediate for wall thinning as referenced in 2.c of the “Interim Guidelines for Confirming Pipe Strength in Pipe Susceptible to Low Yield Strength” dated September 10, 2009.

The design and operation of the deformation tool (including the sensors) must assure that tool performance meets all specifications and achieves an accuracy of +/- 1% or less to identify expanded pipe and dents. PHMSA’s understanding of the usage of urethane cups between the sensors and pipe wall is that the accuracy of the tool may be compromised.

The design and operation of the deformation tool (including the sensors) must assure that tool performance meets all specifications and achieves an accuracy of +/- 1% or less to identify expanded pipe and dents. Excessive wear in the sensors could adversely affect tool performance to achieve the required accuracy and should be accounted for by the ILI vendor’s tool design and/or ILI procedures.

Internal coatings such as flow efficiency coatings should not be damaged by a deformation tool. Where internal coatings are present, deformation tools that will not damage the coating should be used by the operator.

The interim guidelines and advisory bulletin apply to any pipe susceptible to having an actual yield strength less than the specified minimum yield strength (SMYS) whether in natural gas pipelines under 49 CFR Part 192 or hazardous liquid pipelines under 49 CFR Part 195.