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Good usable information on pipe stress analysis is hard to come by these days. So, we requested a few field experts to write us articles on this subject. Please feel free to browse, share and print this information. The opinions expressed by the author are his own and do not necessarily reflect SST's opinions.

List of Articles

How Did the Tee Fail?

An ANSI B16.9 NPS 10 XXS Welding Tee in a piping system was designed and constructed in accordance with ASME B31.1, sized for an operating pressure of 3,500 psi, operating at ambient temperature, 21C (70F). The system contained water. Yet, this tee FAILED within 3 months of operation.
How did the TEE fail?

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Problem with piping "Liftoff"

Contemporary commercial piping analysis programs deal differently with the problem of apparent lift-off of an operating pipe at a rod hanger or a one-way vertical support, such as a pipe on a support rack. A few programs provide error messages; others show a vertical movement with a possible increase in sustained (weight) stress. A proper understanding of the standard piping design practice is the key to...

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Stress Intensification Factors

A B31 (B31.1, B31.3, B31.4, B31.5, B31.8, B31.9, B31.11) stress intensification factor (SIF) is an empirically derived parameter that allows the designer...

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Proposed changes to Allowables in ANSI B31.1 (Power Piping code) and ASME Section III

Recently the Boiler and Pressure Vessel Code (BPVC) has passed Code Cases to change the allowable stress bases for some of the "design by rule" codes (Section I and Section VIII, Division 1) from the lesser of 1/4 of the tensile strengths or 2/3 of the yield strengths at temperature to...

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"Dynamic Susceptibility" Method for Piping Vibration

When addressing vibration issues, the piping designer does not have the specific requirements, nor the analytical tools and technical references typically available for other plant equipment such as rotating machinery. Typically, piping vibration problems only become apparent at the time of commissioning and early operation, after a fatigue failure or degradation of pipe supports. Discovery of a problem is then followed by an ad hoc effort to assess, diagnose and correct as required. The "Dynamic Susceptibility" analysis, now included in CAEPIPE, provides a new analytical tool to assist the piping designer at any stage, from preliminary layout to resolution of field problems.

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Temperature Limitations in Piping Component Materials

ASME B31.3, Para. 323.2 Temperature Limitations describes low temperature requirements to assure adequate material toughness in piping components. In B31.3, if adequate toughness is assured, the basic design premise of "shakedown" or "self-springing is maintained and the allowable stresses or strains (see Note 2) are appropriate. The situation addressed by the B31.3 toughness requirements is if the piping system is cold enough and the stress high enough and the piping component material thick enough a failure, a brittle fracture, can occur. Two potential interrelated conditions can lead to that failure: ...

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Comments on Butt Welds

User Question: In reviewing the section on SIF's, I realize that in many cases there would be an SIF for a simple butt weld. This is because the mill tolerance for wall thickness alone could result in an internal ID misalignment that would result in a required SIF. Would the SIF for a butt weld be applied at a butt-welding fitting in addition to the SIF of the fitting itself?

The SIF for an as-welded butt weld is 1.0 because the SIFs are referenced against the as-welded butt-weld. The ...

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