ASME B16.34 NDE for special class valves

[anakbaru]

Hi all,

I have problem in reviewing QC document for Pressure reducing desuperheating valve (PRDS)

material: A216 WCC
rating : ASME 600#
Plug and seat ring material: 410 SS (ANSI 410)

my question: i asked for NDE liquid penetrant (PT) test for hard facing area for plug and seat ring material.

The contractor replied:
1. NDE (PT) test is not required since the material is 410 SS, if the material is 316 SS (A276-316) then it is required.

2. the contractor said according to the ASME 16.34 the valves required for NDE are only for special class valve, otherwise not required for standard class valve.

What i want to know:
1. is the contractor explanation acceptable, according to the ASME 16.34. But the our agreed inspection plan covers NDE (PT).
2. what are the special class valves?

thanks.

 

[rneill]

ASME B16.34 does not require as mandatory and NDE on cast valve bodies for standard class valves. Special class valves do require mandatory NDE as specified in Clause 8 of B16.34. Special class valves are valves that have been assigned a higher pressure temperature rating than would normally be permitted by the standard on the basis of this additional examination.

However, this does not mean that the end user cannot specify examination beyond the minimum requirements of ASME B16.34. In other words, the end user can specify additional NDE if they like. In my experience, it is not uncommon for end users to specify additional examination (MT, PT or RT) on cast valve bodies for use in steam service.

If the purchase contract specified NDE and it was agreed to in the inspection plan then you are within your rights to insist upon this.

Note: I don't fully understand the comments about NDE not required on 410 SS but is required on 316 SS. This is not addressed by B16.34 so I assume they are referring to requirements in the applicable ASTM standards ? Ask the contractor for additional details with regards to where they are finding these requirements specified ...

 

[anakbaru]

can you be specific, what is special class valves, can valves having 3500 class and above be considered as special class since they seve higher pressure & temperature.

 

[rneill]

anakbaru,

I recommend you get a copy of ASME B16.34 and review the information on special class. It is quite straight forward. For example, a Class 150 valve can be a Class 150 "Standard Class" or a Class 150 "Special Class". The special class is still called Class 150 but has a different rating. These ratings are tabulated in ASME B16.34.

I don't think this has any bearing on your situation since it does not sound like you asked for special class nor does it sound like they are providing special class.

 

[anakbaru]

thanks neill,
I will read the soft copy.