Question about differential pressure on subsea pipelines.

  • Thread starter zeromodz
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Hi, I'm an engineer working on a subsea pipeline project. Right now Im working on a spreadsheet to calculate the differential net pressure on a sub sea pipeline. I am using API RP 1111 for offshore pipeline design. My question is the following.

For any pipeline with a nonzero wall thickness, the inner area will be less than the outer area. Consequently, there will be a larger force distribution on the outer wall than the inner wall. Pressure is not a vector, therefore area must be considered when finding the net effective pressure on the pipe wall. I am only concerned with pipe burst in this scenario.

After doing some searching, I found this equation to compensate for the area difference.

Peff = Po - Pi*(1-2t/d)

Where
t = wall thickness
d = outisde diameter
Po = external pressure (hydrostatic)
Pi = internal pressure (Shut in tubing pressure)

However, the context I found this equation is for collapse instead of burst. My question then becomes is it suitable to treat this equation for a burst?

It seems to just be just a summation equation so it could work both ways. The problem is I don't see anything mentioning this in the recommended practice I'm reading. It does say "For purposes of design, pressure shall be interpreted as the difference between internal pressure and external pressure acting on the pipeline." I'm not trying to argue with API, but it makes sense to compensate for the smaller area.
 
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Answers and Replies

  • #2
Nidum
Science Advisor
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If pipe wall is thin compared to mean diameter and resulting stresses come out well below yield then simple formulas are ok

If pipe is thick walled compared to mean diameter or if stresses come out any where near yield when estimated by simple formulas then the full analysis is nescessary .

Formulas in Roark and detailed analysis in Timoshenko .

Easy enough though to do the full analysis from first principles . I always like to work from first principles where possible .
 

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