DESIGN/OPERATING TEMP FOR EXPANSION ANALYSIS 1

[judeotuks]

Hi

I am currently working on thermal expansion analysis based on Palmer and Ling theory
for a 75km offshore pipeline.

I want to know if its the DESIGN OR OPERATING TEMPERATURE PROFILE I should use for
my calculations, because my PROCESS team supplied me with just the operation temp profile (that they don't run for design case owing to the fact that its not a realistic scenario).

 

[BigInch]

Use the actual temperature profile. The design parameters may only indicate the highest temperatures and pressures that often are only seen at the inlet to the pipeline, if at all. You should also inquire into any possible variations of pressure and temperature due to various operating, such as minimum flow and maximum flows and to what the pressure profile might look like when the pipeline is shutdown.

Independent events are seldomly independent.

 

[RandomAxe]

Yeah I'd agree with BigInch, it would be overly conservative to use a constant temperature profile at the design temperature. Use the maximum temperature profile the pipe will see, and obviously the minimum possible ambient temperature during installation for initial conditions.

 

[judeotuks]

Oh yes I have gotten the pressure and temp profile (operating case) ...so I have gotten the temp decay from the inlet to outlet. so am okay using this information.

Also during the hydrotest, how do I get the temp profile because I wasn't given this data by my process team (using PIPEPHASE)? So was wondering how I can determine the temperature decay during hydrotest.

 

[LittleInch]

I agree with the above. The issue is making sure that you have the worst case operating case(s) for the entire life of the system. Also make sure they give you the coldest case (start-up) as well as this sometimes is worse that the hot case. For hydro test case you should allow sufficent time during the test, before applying the test pressure for the water to become the same as the ambient conditions so that the pressure test is not affected by the water cooling down and reducing in volume. Most times I have seen hydro done with ambient (seabed) temperature.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[BigInch]

Ambient temperature water will most likely be used for testing. I have never heard of testing an offshore pipeline with hot water. You are not testing an some kind of arctic sea pipeline I presume. The pipeline will normally reach a near uniform temperature of the surrounding water at the pipeline's depth in a very short time, so there should be little to no need to include temperature variations. Perhaps a slight difference for a short time between test water taken at the surface, but normally nothing to worry about there. I have never felt the need to consider unusual thermal conditions simultaneously with test pressures.

Independent events are seldomly independent.