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Piping hydrotest pressure

Piping hydrotest pressure


In carrying out hydrotest of piping for an offshore platform we have carried out hydorotest at a pressure of
1.5 x Operating pressure based on our hydrotest procedure
developed for the project.
But the reference code requires the test pressure to be 1.5x maximum working pressure.

Is max working pressure equivalent to design pressure?
if so we have carried out hydrotest at a  pressure lower
than the code requirements??

Kindly clarify

Thanks in advance


RE: Piping hydrotest pressure

Design pressure is the maximum pressure you can find in your test system, it may involve pumps (pressure at closed valve, this is the maximum pressure the pump develops), safety systems, etc.

You have to take corrections for temperature also, the place where you should look at for more information is the ASME B31.3 code, chapter VI, Inspection, examination and testing(2004 ed.).

You have definitions (design pressure, test pressure, etc.), testing procedures, etc. Below you will find the definition the code gives for DESIGN PRESSURE:

(a) The design pressure of each component in a piping
system shall be not less than the pressure at the most
severe condition of coincident internal or external pressure and temperature (minimum or maximum) expected
during service, except as provided in para 302.2.4.
(b) The most severe condition is that which results
in the greatest required component thickness and the
highest component rating.

RE: Piping hydrotest pressure

Yes, your "design pressure" is your "MAWP" is "test pressure"/ 1.5


RE: Piping hydrotest pressure

Usually, design pressure = (max operating pressure as defined by the pertinent B31 code) + a margin of 25 psi or more, all properly taking into account the derating effect of temperature.  Then this design pressure is compared to the individual MAWPs of the components in the line, e.g., valve bodies.  This procedure is iterated until a defensible and reasonable number is arrived at.

Your hydrotest pressure is then 1.5 x this design pressure.  It is NOT 1.5 x the flange rating.  Unless your flange rating happens match your design pressure...

I hesitate to count the number of arguments and discussions I have had with clients and owners who do not understand the concept of design pressure, who have never heard of the code section cited above, who don't know what their own company's pipe specs/line class specs say, and who swear up and down that the design pressure is the same as the ANSI flange class.  Yikes... (rant mode off)


RE: Piping hydrotest pressure

If a client is using standard wall 8-inch pipe and ANSI 300 flanges, then at 100C the flanges do define the system MAWP, design, and test pressures.  

It so common in upstream Oil & Gas that the pipe we use is way over-capable and the flanges control that people stop checking the pipe and valve capacity.  I was designing a drip today (24-inch standard wall) and the MAWP of the pipe was 470 psig at 100C, the client fussed at me for specifying a test pressure of 705 psig in an ANSI 300 system.


RE: Piping hydrotest pressure

"If a client is using standard wall 8-inch pipe and ANSI 300 flanges, then at 100C the flanges do define the system MAWP, design, and test pressures."

Hi David.  Well put.  The project documentation would be written up to say just that - that the system design pressure is blah blah and is based on/limited by the MAWP for ANSI 300 at 100 C.

I recently had an owner get animated with me over the hydro pressure for a steam line that was going to run at 40 psig.  It is an ANSI 150 system.  He and his construction rep could not understand why his hydro pressure was not 1.5 x 285 psig.  For some reason he (and a lot of folks, at least in the oil patch) think that the 'design pressure' is equal to the flange rating, as I said earlier.  I had to bust out his own corporate spec book and show him in black and white how the cow ate the cabbage.  Crazy.  Guess that's why they pay us though huh...  It all pays the same!  smile  Thanks!  Pete

RE: Piping hydrotest pressure

Where I work....

For Refinery Projects our hydrotest pressures are normally defined by the pertinant B31 code (usually B31.3) based on the design conditions of the system.

On our Upstream Projects (topsides for offshore platforms) our clients generally what all systems hydrotested at 1.5 X the ambient temp. flange rating as a minimum regardless of the system design conditions or per the applicable code if the test pressure is greater. Those clients also want the piping specifications to be flange limited. The thinking is that this will give the platform operators the flexibilty to change the service on a piping system down the road without having to re-hydro the line as long as they remain in the pipe specification limits.

Houston, Texas

RE: Piping hydrotest pressure

a couple of other observations:

some pressure vessel codes have increased  the allowable stresses for components operating below the creep range ( < 800F), and those codes then require the hydrotest to be 1.33 times design pressure. If the piping system uses 1.5 times MAWP but the PV limits it to 1.33 MAWP, you either limit the hydro to 1.33 MAWP or buy a new PV following the PV failure.

the hydro test must be conducted at a fluid and metal temp hotter than the ASME minimum for the materials ( piping,welds, valves, castings, PV's)  in question, or else you risk a brittle farcture.

RE: Piping hydrotest pressure

"If a client is using standard wall 8-inch pipe and ANSI 300 flanges, then at 100C the flanges do define the system MAWP, design, and test pressures."

I will go with Pete on this one and say this is only true where the client wants the "give me all you can" solution.

But usually, also as Pete has said, you don't choose the materials and then go and decide what the design pressure is going to be. You pick the design pressure and then choose materials to meet that design pressure.

As an extreme example, I had client in the past that specified the same wall thickness pipe and flanges on low-pressure systems (like glycol heating) as they did on their high pressure natural gas systems. They certainly didn't hydrotest the glycol system at 1500 psi (although they could have). Why would you do that? So that when you get to the field and construction guys weld it all together, there is reduced risk of having a thin-wall pipe welded into a high-pressure gas application (pretty hard to check pipe wall thickness once everything is welded together). Overkill I think, but they wanted to be sure nothing went boom from a construction mistake.


RE: Piping hydrotest pressure

It works both ways. I would not let the flanges control design pressure if there was 1,500 miles of 42 x 0.750 wt pipeline to buy and only 202 flanges?  I would let the pipe wall set the design pressure, otherwise your pipe cost would simply be too expensive to ever consider building.

no matter what the design pressure was when it left engineering, at the end of the day it is superseded by MAOP = Test Pressure / Test Factor.

BigInchworm-born in the trenches.

RE: Piping hydrotest pressure

Dear all

Thanks for the valuable inputs


RE: Piping hydrotest pressure

Dear All:

I want to hydro a 2" drain line going to an open sump or drain funnel.  This 2" line is tie-in from a 16" line with a socket weld in one side of the 2"valve and screwed on the other end of the valve.  Should I hydrotest the line after the 2" valve with 1.5 x design pressure and after the 2" valve what should the hydro be?  should it be still 1.5 x D.P. or less than this?  This is all per ansi b31.3 process piping.


RE: Piping hydrotest pressure

I think the design press. is zero,
so you don,t have to test.


RE: Piping hydrotest pressure

If the pipe ends open (atmosferic pressure), you don't have to test it.

RE: Piping hydrotest pressure

I think that reference code must be ASME B31.4, para.437.4.1 Hydrostatic Testing of Internal Pressure Piping

RE: Piping hydrotest pressure

Reference code must be ASME B31.4, title A437 TESTING

RE: Piping hydrotest pressure

Please see the exclusions listed in 300.1.3 (a) of B31.3.

Note that the Owner is responsible for "establishing the requirements for design, construction, examination inspection and testing which will govern the entire fluid handling or process installation of which the piping is a part." ref. 300 (b) (1).

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