Relationship between hydrotest pressure and working pressur

Date 09-13-2016 00:41

While there are some general guidelines in various codes for this, many times you will actually find what you want in the Job Specifications. One job I was on back in the 80's we did the hydro to many times higher than design or working pressure after some bad sections of pipe were found from the supplier who was supposed to have completed testing before we ever received pipe on the job. Discovering several holes in the straight seam over about a 5' span that measured from 1/32" up to a high of 3/16" was a dead give away that something wasn't as it was supposed to be.

He Is In Control, Have a Great Day, Brent

By Metarinka (****)

Date 09-14-2016 19:47

From my engineering perspective design pressure is generally determined based on factors and assumptions on the life-time conditions. For example even most low pressure air systems are designed and specified at 150psi although the working pressure is <60 because there is the assumption that some guy at some point will hook it directly to shop air. Likewise I've seen many design pressures based off worst case assumptions for over pressure events.

I'm not familiar with the design portion of those structural codes. They provide some guidelines on the safety factors for design pressure but you still need to know all the engineering intent and assumptions on what is in the system.

By purode333 Date 09-13-2016 05:46

Code of construction is B31.3

By pipewelder_1999 (****)

Date 09-14-2016 13:27

That's the place to get an accurate answer. I am not sure but each piping category may have specific information that applies to that category. MAWP is referred to I am sure but without a code handy I cannot say.

By Joey

Date 09-20-2016 10:13

maximum allowable working pressure (MAWP)
The maximum internal pressure permitted in the piping system for continued operation at the most severe condition of
coincident internal or external pressure and temperature (minimum or maximum) expected during service. It is the
same as the design pressure, as defined in ASME B31.3 and other code sections, and is subject to the same rules
relating to allowances for variations of pressure or temperature or both.

By MBSims

Date 09-21-2016 21:23

The key words here are "...at the most severe condition of coincident internal or external pressure and temperature (minimum or maximum) expected during service...". These conditions must be determined by the piping designer and typically consider conditions that may result from abnormal or upset conditions, maximum pump dead head pressure, failure of a pressure regulator, or other possible events. The maximum design pressure may also include some additional margin above the operating pressure to allow for possible changes or uprates in operating pressure or equipment design. The piping designer has the responsibility to specify a design pressure that ensures safe operation.

By Joey

Date 09-22-2016 09:44

There is always an original design pressure, which is equivalent to MAWP. But generally the actual working pressure is normally set below the MAWP. Critical lines, or equipment like steam drum, air reciever are installed with safety relief valve to prevent over pressure. When the lines are found not be able to operate on required operating pressure, derating below the original design conditions to provide increase in corrosion allowance normally happens.