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B31.1 Piping Code - Hydro Test Required ?

B31.1 Piping Code - Hydro Test Required ?

B31.1 Piping Code - Hydro Test Required ?


The application I have is to replace a couple of drain lines and a blow down line that empty into an exhaust pit. In one case I have a drain line that services a steam system operating at 540psig.
This 540 drain line (happens to be 1-inch line) tees into a 4-inch blow down line which services a separate steam system that operates at 600psig. My job is to replace all the 4-inch line and the 1-inch lines from its open end at the exhaust pit back to the first upstream valve in each line.

I initially thought this would require no hydro test because B31.1(2012)paragraph 137.3.2 states,"Lines open to the atmosphere, such as vents or drains downstream of the last shutoff valve, need not be tested."

However, the 1-inch line includes a check valve whose purpose is to block any blow down from the 4-inch line from going back upstream of the 1-inch line (this large 4-inch line is called a bottom blow which means there will be large discharge of steam and water when the valve is opened). So how does this check valve enter into a decision to perform a hydro or not ? There are two situations that don't seem to be addressed by the Code:
1. if the check valves ever fails shut, then the 1-inch line can become a pressure line;
2. if the check operates properly and remains closed during blow down in the 4-inch line then there will be some build-up of back pressure that any joint down stream of the 1-inch check valve will see.

Any suggestions out there on my dilemma ? to hydro or not to hydro?

RE: B31.1 Piping Code - Hydro Test Required ?

The test pressure is governed by the design pressure. If your design pressure is the value that you say, then you must test.

RE: B31.1 Piping Code - Hydro Test Required ?

Thanks for that TSG4, I appreciate your reply but it doesn't help me resolve the question of whether or not the hydro is required at all.

Does the check valve in the drain line negate the hydro exemption stated in ASME B31.1 paragraph 137.3.2 ??

RE: B31.1 Piping Code - Hydro Test Required ?

What have you selected as the design pressure of these "drain" lines?

RE: B31.1 Piping Code - Hydro Test Required ?

The system was built in the 70's and no design data is available. Since these lines are open ended, except for the above described check valve, we are guessing the design pressure may have been zero. Is this a correct assumption (?) we have no idea. Is there an ASME B31.1 requirement to base the design of drain and blow down lines on the system pressure ??? Even if there was such a pressure requirement for drain lines, how do I reconcile the apparent hydro test exemptions of paragraph 137.3.2 ?

RE: B31.1 Piping Code - Hydro Test Required ?

If you're "replacing" lines, then you can choose the design pressure. Set it to zero and have no hydrotest to worry about.

What you're seeing is likely Code-speak for setting the design pressure to zero for that portion of the drain downstream of the last block valve.

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