TMBV - is the cavity vent plug considered a pressure retaining part?

[mbelly84]

a customer is asking me to repeat the shell test on all my trunnion mounted ball valves, for the simple reason that during the seat test we are removing the cavity vent device and putting it back

now this is something new to me
API 6D asks for checking seat leakage through cavity drain or vent, but it does not ask to retest the shell afterwards

attached the cavity vent plug design
basically it consists of a needle valve, actuated by the plug rotation

in my opinion this is not to be considered a pressure retaining part, but a pressure controlling part, hence the simple operation of venting the body cavity does NOT invalidate the shell test previously done

also, this vent has been designed as per API 6A par 10.11 figure 19. API 6A states:
10.11.4 Testing
The equipment furnished under 10.11 is not regularly subjected to a hydrostatic test, but shall be rated for the
hydrostatic test described in 7.4.9.

my interpretation is: of course it has to withstand the shell test pressure, but it's not to be regularly tested (hence, operating it does not invalidate the shell test)

what do you guys think

 

[gerhardl]

Regarding the technical viewpoint, I personally agree with you.

On the juridical side, the question is if the test is clearly described in the written order and/or offer or order confirmation. If this is not the case, and if still wanted, it is an addition at added cost.

If this is (as it seems) a disagreement on of how to understand an agreed-upon standard test procedure text, you might check following:

1. If certified, your factory should have available an written internal procedure of how to do this test. Has your customer accepted this procedure, been informed that it exists, or is this incorporated in your order confirmation?

2. If still not solved, is the customer right in claiming this is a normal procedure (as you a trying to clarify)? First to be questioned is the issuer of the standard, then other suppliers.

3. Can the customer tell if similar valves with this extra test is supplied earlier, and if yes, how is this described by the reference order contract.

 

[SPDL310]

So you shell tested the valve with the vent plug installed, and then opened the valve to perform a seat test, which your customer now claims invalidated your original shell test? If that is the case I believe that your customer is incorrect.

You are incorrect as well in labeling this vent a pressure controlling part. If you look at the definition in section 3.1.81 of API 6A what you have is a pressure-boundary penetration. As far as 10.11.4 is concerned the items not regularly subjected to testing are gages and injection fittings with internal ball checks that could be damaged by the shell test. Those components are usually replaced by a blind plug much like the one you have illustrated for shell test purposes.