Determining hydrotest pressure using all system components 1

[Berndt]

I have encountered the following two trains of thought with regarding to the calculation of hydrotest pressures according to ASME B31.3:

1. Determine the hydrotest pressures for different pipe materials according to 345.4 and choose the greatest (given that yield is not exceeded for any pipe). Ensure that 1.5 times the 100 Deg F pressure rating is not exceeded for flanges in the system. No calculations are done with regards to fittings such as elbows & tees, as these are deemed to have been tested during manufacture.

2. Same as 1. apart from the fact that since the material of the elbows and tees are different with different allowables, the greatest calculated pressure of all components is chosen.

Which of these two approaches is commonly used and/or correct?

 

[gerhardl]

Question: Just pipes or pipes mounted with valves and instrumentation?

If mounted with other components than pure pipe components (elbows, T's etc) you have to take the limits for those into considerations.

 

[BigInch]

Wouldn't you want to use the lowest test pressure of any given component? Using the greatest might put some components at a test pressure over 1.5

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[Berndt]

gerhardl, valves could obviously also be taken into account if they were to form part of the system. My question is however focused on "pure pipe" components as you call them.

BigInch, B31.3 indicates that hydrotest should not be LESS than 1.5 times design pressure, thus some components could certainly be pressurized at more than 1.5 times the design pressure. Thus the highest minimum test pressure of the components occuring in the system is chosen and a back check is done so that no component is stressed above yield. Furthermore a check would also be done so that the 1.5 times 100 Deg F rating of the flange is not exceeded.

These questions are however a bit off topic as I want to know whether it is common practise to take the minimum test pressure of components such as elbows and tees into account when determining the system test pressure.

 

[BigInch]

thus some components could certainly be pressurized at more than 1.5 times the design pressure.

Yes but they don't have to be tested at greater than 1.5, thus your minimum pressure would be set to 1.5 x the minimal working pressure capacity component.

Look, what you're asking happens a lot in pipeline work and there is no reason the same method cannot be used in plant work.

In pipeline work pipe is tested to a minimum pressure = K x Design pressure. The nature of pipeline work, with often widely varying elevations, usually makes it necessary to test the line in segments where pressure can be held over the minimum test pressure, yet less than the maximum test pressure of the "thinest" component. The "differential test pressure", max test pressure - thinest component test pressure will define the allowable elevation differential you can have in any possible segment chosen for testing, thereby, in combination with elevations in the segment, setting the length of any particular test segment.

For plant work, typically elevation difference is not that great to worry about, but it is possible to have considerable elevation differences for pipework attached to columns, so I don't know why you would not adopt the same method for plants too.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[JLSeagull]

I don't deal much with B31.3. The piping tees should be OK but protect the instruments (my piece of the game). Key on the "design pressure" not the maximum pressure at 100 degrees for the ASME B16.5 piping class for table 2-1.2. The instrument piping connections and isolation valves should meet the design pressure. Many instruments such as pressure gauges won't. I saw a $100k analyzer that the piping test people blew up on an offshore platform. Not pretty.

Assure that all instruments are isolated by the piping block valve etc. Control valves may be rolled out and replaced with a spool - or the air supply connected in a manner that the valve is open. Even if rated for higher pressure we don't like to expose the instruments to that rusty hydrostatic stuff that some call water. Drain all that rusty hydrostatic fluid, clean etc. instead of letting it stand for the next year or so.

 

[BigInch]

Body testing a valve is OK, but testing against any closed valve isn't a good idea. All valves should be opened that can be opened and those things that shouldn't be tested sould be completely disconnected and blanked off.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[Berndt]

Ok, maybe my initial question was not clear enough so here goes:

Given a system that consists only of pipe, elbows and tees. Would you calculate the system hydrotest pressure considering only the pipe, assuming that the tees and the elbows were tested during manufacturing? OR Would you calculate the required hydrotest pressure for tees and elbows as well and choose an appropriate system hydrotest pressure?

 

[BigInch]

There is still at least some chance that any of either pipe, flange or fitting might have been speced wrong and installed in the line. It certainly wouldn't be the first time that that would have happened. IMO, its definitely better to check test pressures for all items in the material list. As all items should be in the material list database anyway, it should be a very easy job to do too. I doubt it will increase the CPU time very much either.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/