How to calculte the maximum allowable non shock pressure

[Curious_92]

Dear All,

Right now i am assigned to a project which is out my area of expertise. I am asked to supervise the hydrotesting activity.

So we have to make the Flushing a Testing Header. The Materials for the same has already been procured.

I just need to check if the materials that has been procured is able to withstand the Pressure during Hydrotesting.

The Hydrotest Pressure Range is 3400- 5200 PSIG.

So i humbly request you to advise me on how to calculate/find out what is the maximum pressure these below mentioned materials can hold upto?

1. 6” x ½” Threadolet 9000#
2. ASTM A 105 RF WNRF Flange 6” 2500# SCH.XXS
3. ASME B16.5 6” 2500# Spiral Wound Gasket.
4. 6”x3” Eccentric Reducer SCH.XXS

Gentleman,

I request you to advise me that do i need to look upon any chart or table to find the maximum pressure these materials can withstand, or is there any formula for that.


Regards..!
Thank you

 

[XL83NL]

Whats your design code? Have you reviewed that in order to determine the MAWP?

 

[Curious_92]

Dear XL83NL

I am sorry that i missed those details.

The Code that has to be followed are ASME B31.4 & ASME B 31.8.

Regards.

 

[XL83NL]

Well, you start out with

Right now i am assigned to a project which is out my area of expertise.

That would be enough reason to leave this work to an expert. If you dont know the risks involved in hydrotesting, nor have experience in this field of work, leave it to someone who can do this.

Neverthless, review the applicable design code to determine the answer to your question. Even though it may not provide a direct formula which youre looking for, the answer will be in there.

 

[LittleInch]

"Right now i am assigned to a project which is out my area of expertise. I am asked to supervise the hydrotesting activity." That's never a good start.

Hydrotesting is potentially lethal. Placing someone in a supervisory capacity who does not have the expertise or experience is criminal, especially at the pressures you're talking about. I would make sure you have in writing something telling your superiors that you don't have the expertise or experience for this task and need some assistance. If anything goes wrong, they will vanish and leave you out to dry.

"The Hydrotest Pressure Range is 3400- 5200 PSIG." - Doesn't make sense. Hydrotest pressure is a set figure, not a range.

However I'm feeling generous.

1. 6” x ½” Threadolet 9000# - Can't remember what code this is but at cold working pressure this is good for 9000 psi
2. ASTM A 105 RF WNRF Flange 6” 2500# SCH.XXS ASME B 16.5 gives you the pressure ratings for different materials, temperatures and flange class. A class 2500 flange at cold working temperature is 6,170 psi
3. ASME B16.5 6” 2500# Spiral Wound Gasket. See above, but are you sure?? I can't recall seeing a spiral wound gasket at that pressure rating before. Normally RTJ, not RF flanges.
4. 6”x3” Eccentric Reducer SCH.XXS. You need to know the material to get SMYS and then do a reverse calculation according to the code for stress to find pressure. Thickness of a 6" XXS pipe is 21.95mm. Looks pretty thick to me, but crunch the numbers according to the design code.


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

 

[Curious_92]

Dear Little Inch & X83NL

Thanks for taking the time to respond.

Cheeers!

 

[GD2]

Curious_92,
I am assuming you are planning to fabricate and hydrotest a test header assembly in order to use it for testing ASME B31.4 and ASME B31.8 pipelines.
Unfortunately both codes doesn’t give the requirement for a test-head asslembly but here is what I draw from the Canadian CSA Z662 code:
1.Max Working Pressure (MWP) during pressure testing of the piping shall not
a) produce hoop stress in excess of 75% of SMYS of any piping or fitting in the test head assly
b) be higher than Max cold working pressure of any flange or valve in the test head assly.
c) ancillary piping(pressurizing line connected to the test head assly shall not be operated at pressure that would produce hoop stress in excess of 50% of SMYS of the ancillary pipe.

Usually, the flange rating limits the hydrotest pressure. Your numbers 3400-5200 psig are well below the hydrotest pressure of 9275 psig (1.5 * 6170 psig MAWP) for the 2500 class flange. To be due diligent, calculate the max hydrotest pressure limit for the test head pipe (I would assume you are using Astm A106 Gr. B) by the hoop stress equation, Test Pressure= 2St/D. I would take S value at 90% of SMYS to avoid any deformation. You will normally see the flange limiting the hydrotest pressure. Your fittings are correctly matched to the pipe so don’t bother checking for these.
You can find the value SMYS from many places. ASME sec II, ASME B31.4 or even in ASME B31.3 table A-1.
Hope it helps.

Ganga D. Deka, P. Eng
Canada

 

[LittleInch]

GD2 - I totally agree with your points 1 a) to c). I've always viewed the test pressure of the test header assembly as it's design or MAWP and hence it gets tested to a higher pressure than the test pressure of the pipeline.

I would though challenge your statements "Usually, the flange rating limits the hydrotest pressure". Given that the test pressure is lower than the MAWP of the flange ( 6170)Psi the limiting factor is the thickness and SMYS of the pipe, which for most pipelines> 12-16" is usually the case.




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

 

[GD2]

Hi LittleInch,
You are right, LittleInch. Not in all cases the Flange pressure is the limiting factor.
In this situation, by the spec. Of the fittings, I would assume they will be using a A106 XXX pipe for the test head with 2500 class flange. The max test pressure will be limited by the pipe (9275 psi for flange and 8231 psi for the pipe at 0.9SMYS, 9130 psi at SMYS).

Ganga D. Deka, P. Eng
Canada

 

[Curious_92]

Dear Little Inch & GD2

Thanks for taking the time to respond.

Cheeers!