HYDROSTATIC TEST PRESSURE ISSUE (B16.5 vs B31.3) 1

[vargaslu]

We have a piping system designed under B31.3 (2", SCH 160, ASTM A106, Gr B, seamless, design pressure = 1370 psig, operating pressure = 1200 psig, hydrostatic test pressure 1.5 * design pressure = 2055 psig). The flanges selected for this system are 2" #600 ASTM A105, RF, SW, manufactured under code B16.5.

The QA-QC team say that the hydrostatic test pressure can not reach more than the value gives in ASME B16.5 - 2003, in this case 1480 psig. (table F2-1.1 working pressure for class 600 = 1480 psig @ 100°F)
But also, B16.5, para 2.6 System Hydrostatic testing says "Flanged joints and flanged fittings may be subjected to system hydrostatic tests at a pressure of 1.5 times the 38°C (100°F) rating rounded off to the next higher 1 bar (25 psi) increment. Testing at any higher pressure is the responsibility of the user, taking into account the requirements of the applicable code or regulation".

The questions are:
In your criteria, ¿which is the correct hydrostatic test pressure 2055 psig (according with B31.3), 1480 psig (working pressure for flages #600)?
¿Can we compare the value obtained from B16.5 para. 2.6 with the value from B31.3 to select the minor value of both?
I would appreciate your comments on this issue.
Regards
LV

 

[jte]

You need a new QA/QC team. Otherwise, all flanged piping would be limited by 2/3 of the flange rating, which is quite silly.

Test to the B31.3 pressure - after all, you are testing a B31.3 system and while some components are fabricated to another standard, you are not testing the system to the other standard. Besides, what part of B16.5 paragraph 2.6 is confusing?

jt

 

[vargaslu]

Is it valid to compare the value of test pressure obtained using B16.5 paragraph 2.6 with a test pressure obtained using B31.3, (in the same piping system)?

 

[hakkik]

Table F2 gives operating pressures not test pressures. B16.5, para 2.6 is about hydrotest as you mentioned. You can hydrotest a B16.5 CL600 flange up to 1480 x 1.5 = 2220psi @100F without any other calculaton, analysis etc.

So your weakest link is pipes thus system hydrotest pressure shoud be 2055psi

 

[SNORGY]

Most folks around here tend to set the design pressure at the hot flange rating and the test pressure at 1.5 times the cold flange rating. Flanges in the sizes of pipe we typically deal with are usually the "weak link". If a component exists that is "weaker" than the flange, it is usually judged to be a "wrong" component.

Gone are the days, I fear, when engineers actually understood the process and could arrive at design pressures and test pressures on the basis of calculations.

So, we see the occasional produced water tank farm with API-650 tanks; A-333-6 pipe and A-350-LF2 Class 1 flanges to deal with the B31.3 toughness / MDMT issues for -45 C; 1965 kPag design pressure and 2948 kPag to deal with the pressure design issues.

For piping connecting atmospheric storage tanks.

About 12 m high.

In water service.

Apparently operating at -45 C.

Perhaps with some increase in viscosity, or resistance to flow...

You get the idea.

Regards,

SNORGY.

 

[rneill]

I concur with Snorgy. To keep things simple we usually test to 1.5 times the cold working pressure rating of the flange unless the pipe is weaker than the flange and then it becomes limiting. There is no issue with hydrotesting a flange to 1.5 times its rated pressure.

 

[SNORGY]

rneill...

...concurs with me...but only to the point where things still make sense. In my subtly sarcastic message and hypothetical example, designing a water system between atmospheric storage tanks and an MDMT - for water - of -45 C probably doesn't make much sense, given the nature of water at -45 C and the difficulty one might experience in flowing it from tank to tank using only hydrostatic head as the driving force. In such instance, one might not need high design & test pressures and low temperature, impact-test qualified materials...but that's what one would arrive at if designing to full flange rating.

Regards,

SNORGY.

 

[rneill]

I kind of skipped over the subtly sarcastic part of the message and responded to the more general issue of testing to flange rating

 

[SNORGY]

Kinda what I figured.

The OP (vargaslu) put some rational thought into the question and the issue. I was a bit caught up in my frustration with seeing a lot of engineers who, too often, don't do that - not in these forums, but, if you will, "IRL".

Regards,

SNORGY.