Hi,

The following has been bothering me for some time:

When hydro testing according to ASME B31.3, is it necessary to take all components into account when calculating the correction factor due to temperature? The test temperature of the system would then be the largest of the calculated hydro test pressures for each component.

E.g. Given a piping system that contains a 6” Sch 40 API 5L B pipe with one Sch 40 A181 Cl 60 with one CL150 A105 flange with one valve out of A216 WCC at a temperature of 260°C at 1000kPa:

API 5L B: All. Stress at 260°C: 18.9ksi
All. Stress at 25°C: 20ksi Resulting in Hydro test pressure of: 1587.3kPa
A181 Cl 60: All. Stress at 260°C: 16.2ksi
All. Stress at 25°C: 20ksi Resulting in Hydro test pressure of: 1851.9kPa
A105: All. Stress at 260°C: 19.4ksi
All. Stress at 25°C: 23.3ksi Resulting in Hydro test pressure of: 1801.5kPa
A216 WCC: All. Stress at 260°C: 21.6ksi
All. Stress at 25°C: 23.3ksi Resulting in Hydro test pressure of: 1618.1kPa

Thus the system should be hydro tested at 1851.9kPa provided that the stresses during hydro test do not exceed the yield strength of any component during hydro test. To date my company has only taken the pipe into account.

Any comments would be appreciated. Does your company calculate the hydrotest pressure in this way?

Paragraph 345.4.2(b) in B31.3 - 2008 has changed a little here.

It now reads -
"(b) when the design temperature is greater than the test temperature, the minimum test pressure, at the point under consideration, shall be calculated by eq. (24). When the piping system contains more than one material or more than one design temperature, eq. (24) shall be used for every combination, excluding pipe supporting elements and bolting, and the maximum calculated value of P-sub-T is the minimum test gage pressure.
P-sub-T = 1.5*P*R-sub-r (24)
where
P = internal design gage pressure
P-sub-T = minimum test gage pressure
R-sub-r = ratio of ST/S for pipe or components without established ratings, but shall not exceed 6.5
R-sub-r = ratio of the component pressure rating at the test temperature to the component pressure rating at the component design temperature for components with established ratings, but shall not exceed 6.5
S = allowable stress value at component design
temperature (see Table A-1)
S-sub-T = allowable stress value at test temperature"

Notice that line "at the point under consideration".

I think you should be able to make better sense out of the complete 2008 text.

Thanks Dave, B13.3-2008 has yet to filter down to the rank and file in my company. I'll be sure to give it a good look once I have it.