API RP 14E Offshore Piping System Overpressured

[msharptx]

This is a continutation of the previous 'Hydrotest Pressure Exceeded' discussion:

Quick Summary: The hydrotest pressure (6,500#) was exceeded for a '6 in Pipe (.562” WT) and ANSI 900 RTJ Flange' Piping System (2220# MAWP) for 15 minutes, where gaskets began to leak and the hydrotest was stopped. The previous discussion dealt with the piping only, and the problem was solved.

I am currently reviewing the flanges to see if they need to be replaced. I am currently looking at ASME Section VIII, Division 2 and trying to calculate the longitudinal, hub, and radial stresses.


Question 1: Am I going in the right direction?

Question 2: Once I get the stresses, what do I compare them against?

Please help.

Thanks,

msharptx

 

[unclesyd]

It your previous post you stated that you were going to change out the gaskets, does this mean that you can physically access the flange to do some measurements?

Hopefully the flanges only defromed elastically and are OK.

 

[msharptx]

unclesyd,

This is all being done by an offshore crew. I was informed that they replaced the gaskets and fasteners. They reviewed the flanges and pipe, and there was no deformation, but I need to provide 'calculated proof' that nothing happened.

Is it true that when the MAWP in a pressure vessel is exceeded, the only prognosis under code is to check for deformations...if none, you're okay. Since flange stresses are governed by the pressure vessel code, i would think follow the same logic.

I'm in the dark on this one.

Marcus

 

[unclesyd]

In an over pressure excursion unless something has permanent deformation everthing is considered to OK. The only thing you will be able to calculate is the bolt stress and possible cupping of the flange.

You can calculate max stress based on the particular code that covers the pipeline or the code that the flanges were fabricated under. I should have added elastic deformation of the fasteners in my previous post.

One approach that we have used on several occasions where there was an excessive over pressure was to ask the manufacturer of the flanges for an opinion. Though our problem was with large SS flanges the manufacturer came through.

 

[msharptx]

How would you calculate flange cupping? I have all the flange parameters.

Thanks.

 

[unclesyd]

My flange program just flags calculations if the flange is overloaded. I don't know what the value is for the flag. Using a Class 900 flange I would have to say that rotation probably isn't the problem. Again in my program, the max bolt stress allowed is 65000 for B-7 bolting. It just want let me overload a flange.

ASME Section VIII addresses this but I'm not sure about small integral flanges. Someone needs to jump in and help.


Here is one approach to checking flange rotation, EN 1591-1. You might want to get a copy.

The article by Yann Guierout.

http://www.sealeng.com/ase/documents/EN1591_Basis/index_f.html

http://www.sealeng.com/ase/index.html