ASME B31.8 Hydrostatic Testing Interpretation

[Primeaux]

A847.4 Test Procedure
(c) [highlight #FCE94F]maintenance[/highlight] of the test and recording of results
on pipeline and assemblies for a minimum of eight continuous
hours at or above the specified pressure. All
variations in test pressure shall be accounted for. Test
duration of prefabricated piping may be 2 hr.

What is the intent of the word "Maintenance"? I am interpreting maintenance to be maintain the pressure at or above the minimum pressure.

ASME is very vague on hydro testing requirements.

My main question is can I increase pressure to keep my test above the minimum pressure, and my time doesn't start over if I pressure up?????

API has a clear direction as to how the test is performed. I am trying to find out if ASME follows this same guide lines.

API RP 1110

Pressure and temperature should be continuously monitored during the test, and all of the pressure and temperature
readings should be recorded. Deadweight tester comparisons with pressure recorder readings should be made at the
beginning of the test, periodically during the test, and at the end of the test. The results of the deadweight tester
checks and temperature readings should be recorded on the pressure and temperature logs for the predetermined
intervals during the pressure test. [highlight #8AE234]Typically, temperature and pressure data are recorded every 1/2 hour throughout
the duration of the test. Weather changes, such as the development of rain or clouds, that could affect the pressure
and temperature should be documented on the test log. The volume or pressure of any added or subtracted test
medium should be documented on the test log, as well as the temperature and pressure at that time and be
accounted for in the assessment of the results of the pressure test[/highlight]. It is mandatory that the volume of any test medium
added or removed be accounted for to determine if the pressure test has been completed without evidence of
leakage for any pressure test of piping that cannot be 100 % visually checked for leaks

 

[bimr]

Maintenance is poorly worded. In this case, it means to continue the test.

Use the procedures in the paper linked below:

http://www.wmhuittco.com/images/Leak_Testing.pdf

 

[BigInch]

I agree with your interpretation. Any water added to maintain test pressure should correspond to that volume which would be expected to be needed to compensate for temperature changes, specifically not being the result of any leak. Do not stop the test timing period, unless the pressure dropped below minimum. You could restart the timing period again where you left off once the minimum pressure was reached, but only if the pressure drop was not the result of leakage.

 

[LittleInch]

My main question is can I increase pressure to keep my test above the minimum pressure, and my time doesn't start over if I pressure up?

The only way to increase pressure is to add water. Yes you can, but you should already be identifying the reasons why, i.e. a drop in temperature of the water in the pipe. A steady temperature or rising temperature could show the reason is a leak.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Primeaux]

If I can determine that its not a leak and its the temperature that is fluctuating causing my pressure to go down or up than I should be able to increase my pressure (and not restart time) before it goes below my minimum test pressure. My interpretation on a hydro test is that you are testing the entire system to validate that it can with stand the required pressure for set time.

I haven't seen in any ASME code that states I can't pressure back up (but it also doesn't say I can). It does state that you can bleed off if pressure exceed the maximum test pressure. My problem is, I have TPI that bring past project requirements onto my project and argue that my interpretation is incorrect.

Scope of my project. 105' jumper, 7.750"OD x 1.875" WT with coating/insulation and buoyance modules.
Test requirements. Minimum Test Pressure 16,250 psi, Target Test Pressure 16,500 psi, Maximum test pressure 16,737.5 psi, for 8 hours

 

[LittleInch]

105 feet? This is surely piping? If it's not buried then just visually examine it for a shorter pressure test.

At that length it'll be really difficult to keep pressure in that sort of range.

Codes don't always say what you can and can't do, there are too many variables to be prescriptive so it's up to each system to work it out to Brett the basic principle.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[zdas04]

I've always found the code to have a lot of wiggle room for engineering judgement. When I write a hydrostatic test procedure under B31.8 I specify a test pressure and allow an hour to add or remove water to maintain the pressure. At the end of the hour the test starts and the operator is allowed to remove water, but not add any. If the final pressure is above MAWP (well below test pressure), I call it a good test. Never had an auditor or inspector take me to task over it. I've found that as long as you specify pass/fail criteria before the test starts, people are pretty willing to follow where led.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[LittleInch]

Zdas04 - Out of curiosity, why don't you add water?

B31.8 states that the strength test needs to maintain the minimum pressure as stated in table 841.3.2-1 - "the minimum pressure shall be obtained and held at the highest elevation" - my italics. That table states no maximum pressure other than air tests

Sorry to be picky but B 31.8 doesn't have MAWP, it has MAOP and MOP.

I do agree that what you need to do is write a specific test procedure and acceptance criteria and get it reviewed and approved / accepted by all parties before you start so you don't get this conversation going on after or during the test.

A lot of the time, so long as someone signs it and states the test is good and has passed, everyone just wants to move on and commission it / get paid....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[zdas04]

I don't add water because I can't control how much is added. Early on, my procedures allowed adding water from a measured container and noting how much was added, but I couldn't get agreement on what the volume meant.

There are a lot of words in B31.8 that require a lot of interpretation. Table 841.322f is quite illuminating. It talks about a minimum pressure in terms of maximum operating pressure and the maximum test pressure as a multiple of design pressure (which is defined as MAOP). So in a system with an MOP of 400 psig and a MAOP of 600 psig, a class 1 div 2 location would be an acceptable test with air at any pressure between 440 psig and infinity, but the table defines MAOP as test pressure/1.25. With those sorts of ranges I feel justified in accepting tests that finish above MAOP.

Just out of curiosity I did a search for "maximum allowable working pressure" and found a dozen occurrences before I stopped. as I said, the document requires some interpretation.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[Primeaux]

I have procedure written and signed by the client with step by step instructions that state we will pressure up to keep the test pressure above the minimum. My problem is we have TPI that come onsite and argue that we are not allowed to pressure up, but they can't tell me where it says I can't. So I wanted to see if anyone else had the same issue, and to make sure my interpretation was correct.

I have an email into ASME to get their intent of the word maintenance. Once I get something back I'll upload the to the post.

 

[LittleInch]

zdas04 - Which version of 31.8 are you using? I searched the 2014 version and found only 2 MAWP instances. Definitions section 805.2.1. only lists MAOP and MOP. MAOP is commonly DP, but doesn't have to be. MAOP is linked back from test pressure so if you didn't achieve the test pressure you aimed for - for whatever reason - the MAOP is back calculated. Therefore the aim should be to achieve, as the code says, a minimum test pressure of at least 1.25 what you want your MAOP to be.

Normally when you add pressure/water, you're using a PD pump of some sort. Volume you can measure by number of revolutions with a set volume per revolution. For short sections this might not work so well, but the pressure increase will be the same calculation as the pressure decrease due to bleeding water off.

How did you get 440 psig as an air pressure test in a class 1 div 2 location?

Primeaux - I had missed the first part about the test to A847.4 and shows how the offshore part of the code is rather different ot the main bit. You'll be waiting a long time for ASME to get back to you.

Your TPI is incorrect. Simply point him or her to A 847.4 and the requirement to issue a specified procedure. The remainder of the items a to d, are "as a minimum". You say you have that plus it is approved by the client. The TPI will not be able to argue this point especially as there is no such writing in B 31.8, either onshore or offshore sections.

Maintenance means maintain, i.e. keep in original condition.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BigInch]

If your project is in the USA do not follow ASME B31.8. Instead follow the requirements of CFR Title 49 Part 192, which are the specific legal requirements. Write to DOT PHMSA if you require design requirement and testing interpretations.