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Technical Discussions
Ramakrishnan Muruganantham
Ramakrishnan Muruganantham
09:02 Jun-16-2000
Radiography vs High Pressure Helium Leak Test

One Specification calls for the following testing for high pressure valves used on HYDROGEN service.

Specification:

“All class 900 or greater cast valve bodies and integral flanges in hydrogen services shall be examined in accordance with ASME Sec VIII Div 1 paragraphs 7.2 and 7.3 of Appendix 7 regardless of casting quality factor. Repairs and identification shall meet the requirements of paragraphs 7.4 and 7.5 of Appendix-7.

For sizes 2” (50 mm) or less where radiography is impractical, the following examination shall be performed.

1. 100% magnetic particle or liquid penetrate examination

2. A high pressure leak test of the valve body using helium at a minimum of 1.5 times design pressure/rated working pressure at 100 deg F (38 deg C) for a minimum of ten minutes. No leakage is permitted.”

Related Details:

1. This specification is applicable for valve made of cast material.
2. This rated working pressure and the required test pressure of different classes are given below.

Pressure Rating Working Pressure Test Pressure
psi (bar) psi (bar)
Class 900 2250 (155) 3375 (233)
Class 1500 3750 (259) 5625 (389)
Class 2500 6250 (431) 9375 (647)

Questions:

1. How does high pressure helium test help detect casting defects for small size valve?
2. Since helium test by evacuation method or with a pressure of 15 psi (1 bar) gives good results, Why such a high pressure test is required?



 
 Reply 
 
David Hermanutz
Consultant,
Hbndt.com, China, Joined Jul 2012, 85

David Hermanutz

Consultant,
Hbndt.com,
China,
Joined Jul 2012
85
02:53 Jun-16-2000
Re: Radiography vs High Pressure Helium Leak Test
w.

: Pressure Rating Working Pressure Test Pressure
: psi (bar) psi (bar)
: Class 900 2250 (155) 3375 (233)
: Class 1500 3750 (259) 5625 (389)
: Class 2500 6250 (431) 9375 (647)

: Questions:

: 1. How does high pressure helium test help detect casting defects for small size valve?
: 2. Since helium test by evacuation method or with a pressure of 15 psi (1 bar) gives good results, Why such a high pressure test is required?

Some basic answers:

1.0 Helium is a slightly larger gas molecule than Hydrogen which is known to travel in an intergranular mode through many cast materials. The helium test at 1.5 times operating pressure would allow the integrity of the valve to be tested similar to the expected in service conditions.

A 15 PSI test gives good results but when dealing with hydrogen perfect results are a must. I have seen the results of two failures due to hydrogen seepage through a valve body. One failure killed an operator as he tried to close a suspecting leaky valve (the ignition source was suspected to be the snipe he was using on the valve handle).

He died while trying to remove his plastic hard hat from his head...


 
 Reply 
 
Dent McIntyre
Consultant, NDE Manager NDELevel III/3
NDT Consultant, Canada, Joined Nov 1998, 252

Dent McIntyre

Consultant, NDE Manager NDELevel III/3
NDT Consultant,
Canada,
Joined Nov 1998
252
05:20 Jun-16-2000
Re: Radiography vs High Pressure Helium Leak Test
lated Details:

: : 1. This specification is applicable for valve made of cast material.
: : 2. This rated working pressure and the required test pressure of different classes are given below.

: : Pressure Rating Working Pressure Test Pressure
: : psi (bar) psi (bar)
: : Class 900 2250 (155) 3375 (233)
: : Class 1500 3750 (259) 5625 (389)
: : Class 2500 6250 (431) 9375 (647)

: : Questions:

: : 1. How does high pressure helium test help detect casting defects for small size valve?
: : 2. Since helium test by evacuation method or with a pressure of 15 psi (1 bar) gives good results, Why such a high pressure test is required?

: Some basic answers:

: 1.0 Helium is a slightly larger gas molecule than Hydrogen which is known to travel in an intergranular mode through many cast materials. The helium test at 1.5 times operating pressure would allow the integrity of the valve to be tested similar to the expected in service conditions.

: A 15 PSI test gives good results but when dealing with hydrogen perfect results are a must. I have seen the results of two failures due to hydrogen seepage through a valve body. One failure killed an operator as he tried to close a suspecting leaky valve (the ignition source was suspected to be the snipe he was using on the valve handle).

: He died while trying to remove his plastic hard hat from his head...




 
 Reply 
 

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