Maximum allowable of stresses during pipeline installation 2

[KVdA]

Hi everybody. I have a question that's been bothering me for quit some time. An extra point of view on things would be appreciated. If a pipeline is installed in a trench it is going to be manipulated with cranes and the pipeline will be bent. The bending stress can be estimated but compared to what? Could the stress be categorized as a secundary bending stress? Most codes i have come across seem to limit the allowable to the 90% yield value... What would you chose to be the allowable when the design code is ASMEB31.3?

 

[KVdA]

BI, yes clear - thanks, now I understand the point TGS4 was trying to make. Very difficult discussion (for me that is) formulating real-life situations into words. The fact that I had different scenarios in my head also didn't help much.

 

[BigInch]

Great!

Richard Feynman's Problem Solving Algorithm
1. Write down the problem.
2. Think very hard.
3. Write down the answer.

 

[TGS4]

BI - excellent and clear explanation at 15 Jun 17 11:08. Apologies again for the earlier "sniping". I think that we've provided some worthwhile advice - and unfortunately there are no easy answers to this, if there were, we wouldn't need smart engineers...

 

[BigInch]

Thanks TGS! I do think we finally got on the right track. Communication is 50% of problem solving, of which the technical aspects is often the easier part. Plus the old 3X rule, "Tell them once, twice, three times."

It is also said that residual stesses left over from the pipe fabrication process itself can be lowered, neutralized, or at the least redistributed-neutralized during the yield-strain process, so the combined result of all residual stresses might be +/0/-.

It was for that reason the Flatlander policy of the largest gas transmission company, in terms of length of pipelines, whom I worked for a long time ago was to hydrotest all their new pipelines to 105% yield pressure. To their credit they did of course keep an eye peeled on the P-V curves when approaching yield. I started working for them after they opened an offshore office in Houston, where I convinced them that the risk-reward to repair costs of that test policy just wasn't as great as it might have been for grassland work. Actually I did't want to spend any more time than necessary on a construction barge making repairs for something what really wasn't broken. Least until they played around with it too much. Actually that policy wasn't really great for onshore city work either.

Richard Feynman's Problem Solving Algorithm
1. Write down the problem.
2. Think very hard.
3. Write down the answer.