In a hydrotest loop there are pipes running with two materials of construction. Therefore when I calculate the Hydrotest pressure, I get two values obviously. How do I thereafter choose the hydrotest pressure of the loop? Kindly explain the basis of such selection.

I didnot find any relevant clause which helps to decide it in B31.3, say for example.

See para 345.4.2 Test Pressure

1.As you might have noted, B 31.3 stipulates the minimum test pressure requirement as a function of design pressure. It also states that the test pressure shall be such as not to produce stress in the piping exceeding material yield strength (the minimum of the yield strengths of the two materials in question, in your case) at test temperature etc……This directs you to the maximum test pressure that you can use. But additionally you need to take care of the following.
2.For the system test of a completed piping system, the test pressure shall not exceed the maximum allowable test pressure of any of the components, like flanges and valves and any other specialty items that are included in the test circuit.
3.As an example, refer to para 2.5 of B 16.5 and para 2.5.3 of B 16.34.
4.In case of B16.5 flanges, you should consider the pr./temp. rating chart and find out the rated pr. At 100 deg.F , multiply it by 1.5 and round it up to next higher 25 psi to get the max. allowable test pressure. This proves to be the limiting factor in many cases.

It is a good idea to make a search for the topics discussed in this forum and you may find that some questions were already previously answered.

Regards,

Why in hydrostatic test pressure expression in ASME B 31.1 the expression of ST/S - ratio of stress value at test temp & design temp (max value 6.5) in B 31.3 clause 345.4.2 is absent ?

Is in B 31.1 fluid leakage is tolerable, unlike B 31.3 ?

regards,

sam

From the forum members, my query is:

Why in ASME B 31.1 no temperature correction is there unlike ASME B 31.3 ?

In Indian IBR-350 pipe thickness calculation,no expression of corrosion/erosion allowance, but a fixed C=0.75mm is available. Is this the mandatory corrosion/erosion allowance or one has to consider corrosion/erosion allowance in addition to C=0.75 mm ?

regards,
sam

fair question, not sure why.. but this points out the fallacy of saying one code is more conservative than another... the codes cover so much ground that people that say one code is more conservative than another are in my opinion ignorant of the facts.

I suspect because the chemical industry has some more lethal fluids than in power plants that thus the emphasis on the higher test pressures for hot systems.

Luf-Sir,

Thank you for the reply. It is true that hydrotest at resonably high pressure as in ASME B 31.3 has turned out to be a good procedure to make leaktight piping. But, taking the cue from ASME B 31.1, for Catagory- D fluid of B 31.3 we may ignore temperature correction without much loss of safety, where the law does not forcefully impose ASME B 31.3 codal compliance on us. What do our forum members think about it ?

regards,
sam