Piping fatigue and corrosion

ASME B31.3 contains the footnote ‘Corrosion can sharply decrease cyclic life; therefore, corrosion resistant materials should be considered where a large number of major stress cycles is anticipated’. But what happens if carbon steel with high corrosion allowance has been selected and changes are out of the question? Or you may be assessing an existing … Read more

Calculating pressure containment of welding tees

photo of B16.9 tee

There are at least three recognised methods for assessment of branch intersections. These are most often applied to fabricated connections on pressure vessels and piping rather than welding tees. Welding tees to ASME B16.9 are normally qualified by vendor burst tests, but that doesn’t help if you need to assess a corroded or eroded fitting, … Read more

B31.3 branch stress own-goal

image of stress at reducing branch from CAESAR II

Quick summary This article may pique your curiosity if you’re interested in the finer details of pipe stress analysis, but if you’d rather just get the overall takeaway – Sustained bending stresses in ASME B31.3 2016 calculations are underpredicted at some branches As long as the stress analyst remembers to split the branch pipe model … Read more

Pipe Support Selection for Bare Pipe

There are many ways to go about supporting pipe, from putting it straight on steel to sophisticated sliding shoe designs. Too often, this aspect of piping design is not given enough thought, resulting in problems later on in the life of a facility. Early on in detail design, the responsible party should prepare a flow-chart … Read more

Salad Postprocessor for CAESAR II

Salad Postprocessor

The Salad Post-processor takes data exported from CAESAR II to do additional calculations and summaries. The software is now updated to version 1.40, and is available at no cost here. Lets go through some of the things you can do with this software . Make a summary of your stress model On one page you … Read more

Replacement of an existing piping system

Modified header layout

Background When process plants have been in service for a long time or approach their end of life the engineering challenges take a different form. It is more complex than laying out a new plant in a greenfield situation. This article discusses some important observations of a project the author had been closely associated with … Read more

Determining SIF of Non-Standard Fitting

Lateral tee with crotch plate

Background Some instances in piping stress engineering we come across fittings not defined in ASME B 31.3, due to their sheer size and/or the diameter to thickness (D/t) ratio. Without understanding the stress intensification factors (SIFs) of fittings, flexibility analysis becomes impossible. This discussion is about how a challenge for the determination of SIFs of … Read more

‘Quick and Dirty’ FFS of Fittings

Assessing fitness for service of pipe fittings is tricky. Whilst we’d encourage you to assess them carefully, what about when you just want to know if you should expend the effort to do more detailed analysis or FEA ? Here is a simple approach that can sometimes be employed when you need a first pass … Read more

‘Hot’ sustained stress – method comparison

compressor station piping

In the past few years there has been an increased focus on the so-called ‘hot sustained’ stress in piping system analyses. The ASME B31.3 2006 edition clarified that Sustained stress requirements must be met for all operating conditions of a piping system. There had always been practitioners whose view was that any stress due to change in temperature should … Read more

B31.3 Code Issue – Non-conservative Sustained Stress

I would like to highlight an issue in ASME B31.3 that’s been sitting there underneath most of our noses for several years. Depending on your interpretation of the Code (or that of your pipe stress software) this can result in significant under-prediction of sustained and occasional bending and torsional stresses at reducing intersections. [Edit March 2017: this … Read more