Pressure Containing and Non Pressure containing 1

[symphony123]

Can anyone define what is a pressure containing and what is a Non pressure containing part.
Per API 6A 3.1.72 Pressure containing part is a part whose failure to function as intended result in a release of retained fluid to the atmosphere. But does not mention anything about Non pressure containing. Please suggest.
Thanks,
VLE

 

[JLSeagull]

Search and find several threads. For a valve, the body, bonnet, packing follower and some types of trim are pressure containing components.

 

[gerhardl]

In addition to JLSeagulls correct an sensible answer: The answer should actually be obvious, any part that is directly exposed to pressure difference in/out or an integrated part part strengthening the exposed part is a pressure containing part. Left over is yokes, if not exposed to pressure, built on extras (not bypasses obviously!), depending on construction some inner parts etc.

Spindle or stems could be depending on valve construction in a yes/no area.

If you are in doubt if any special part for a certain construction is pressure containing or not, you shold be able to get opinions from this forum.

The question rises most often from the requirement of tests in bidding or offering forms specifications: pressure bearing parts to be of material such and such or pressure bearing parts tested with such and such test.

If this is the case, practice can vary a bit. The way out is obviously to ask the originator of the direct meaning for the given valvetype/pressure class and certification/requirement.

You can also go the other way round and state what you usually do and ask if this is satisfactorily, or if extra tests or other parts should be included.

 

[reverman]

what type of valve are you asking about? Also do you want the definition as it indicated in the ASME boiler code or some other standard?

for example the pressure containing parts per ASME SECTION III for a bolted bonnet wedge gate valve would be Body, bonnet, wedge, and body-bonnet bolting.

The API 6A definition you have above in my mind is too vague because you could make an argument for almost every part of the valve being pressure containing using that definition.

 

[bcd]

This is one of the typical chiken or egg circular discussion. You will get many different answers based on opinions. It is not specified in any codes or standards as there is too many variables.

I have heard the definition "If you can drill a hole through the part and get wet, then it is pressure retaining."

I have heard "if you remove the part and pressure is released, then it is pressure retaining."

The PED has a good definition in stating "if pressure is a significant design factor". In other words, if the stress on the part is not affected by pressure, then it is not to be documented like it is pressure retaining. For example, cover bolting, if tightened correctly, will not be subject to additional stress when the valve is pressurized. Same is true for the gland studs and compression plate.

Naturally others will argue that cover bolts, gland studs and compression plates are pressure retaining. If you use the rule "if you remove them, the valve will not hold pressure" then they are right.

In you the end, this is a commercial issue. For every part you declare is pressure retaining, there is a cost for test reports and other quality documentation. Each case will need to be agreed between the manufacturer and customer. In the meantime, pick the rule you want to use. But don't be surprised if someone using a different rule disagrees and argues their point. Who's right in the end. The person willing to pay for the certification is right.

 

[reverman]

bcd post is pretty much spot on however there is a standard that defines pressure containing parts. ASME Section III does define pressure retaining for valves as valve body, bonnet, disc, and any bolting joining pressure containing parts.

ASME Section III is for nuclear power plants so it may be not be applicable in most cases but this is the only spec I have seen that clearly defines what parts are to be considered pressure retaining.


As a side note some Nuclear power plants add the stem to the list however this is per plant specs not the ASME code.