Odd Bolting ASME Code Jurisdiction Question 2

[KiddT]

I'm looking at an elliptical manway application in a pressurized tank, which is IAW Section VIII, Div. 1, and as part of the assembly there are bolts that are used to tighten the manway cover to the ring and seat it on the gasket. My question is whether the bolts, which are outside of the manway, fall under the jurisdiction of the code and hence must be a code bolt material and have code allowable stresses. The bolts are used primarily to position the manway as well as acheive an initial gasket seating load until the internal pressure takes over and pushes the manway onto the ring enough to seat the gasket on its own. There is some negative pressure considerations for the case where the unit trips and the tanks drain into the condenser.

Its an odd sort of case because the pressure relieves the bolts rather than trying to pull on them further and at working pressure the pressure itself is responsible for maintaining the pressure boundary on the gasket not the bolts.

Any help would be greatly appreciated so I can sort out what the real allowable stress will be in those bolts. Thanks.

 

[CodeRef]

When I read your question, I remembered asking a similar question a few years back. This interpretation helped explain the steps needed to verify compliance.

Interpretation: VIII-1-95-66
Subject: Section VIII, Division 1 (1992 Edition, 1994 Addenda); Manway Assemblies
Date Issued: June 19, 1995
File: BC95-067
Question (1): A vessel is to be built and Code Symbol stamped for Internal Pressure and Full Vacuum. The Manufacturer intends to use an elliptical manway assembly consisting of an elliptical pressed steel cover, elliptical ring, bolting and clamping bars, all supplied as standard parts by another Manufacturer, under the provisions of UG-11. If the clamping bars and bolting are subjected to stress induced by the internal or external pressure, are they considered to be pressure parts?
Reply (1): Yes.
Question (2): If Reply (1) is yes, must the clamping bars and bolting be in conformance with UG-4?
Reply (2): Yes.
Question (3): May the vessel Manufacturer discard the clamping bars and bolting supplied by the manway Manufacturer and substitute other materials which conform to UG-4 for these parts if the vessel Manufacturer can show by calculations or proof test (UG-101) that the design configuration meets all Code requirements?
Reply (3): Yes.

Also read UG-46(j) which is considered by the manway Manufacturer.
UG-46(j) Manholes of the type in which the internal pressure
forces the cover plate against a flat gasket shall have a
minimum gasket bearing width of 11?16 in. (17 mm).

Thus, design stress of the bolting would be based on the vaccuum condition since the bolts are only holding the manway in place at other than a vacuum condition.

This should also be considered by the vessel designer if purchasing UG-11 (Manufacturer's Standard) parts for vacuum conditions.

 

[KiddT]

Ok that is definitely helpful for the vacuum part of the consideration because of the way the question is worded. But for bolts that only see stress due to gasket preload, do the requirements apply? I only ask because in the wording of this interpretation its asking about clamping bars and bolting subjected to stress as a result of pressure, where they wouldn't be without the vacuum condition if they were just to obtain the initial gasket preload. Thanks very much for the reference though.

 

[prex]

In my opinion your bolts aren't pressure containing parts and as such are outside of code scope.
Of course I'm not considering what you mention as negative pressure that requires consideration based on the value of negative pressure and on the function requested to the bolts during the event.

prex

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[jte]

Sounds to me like the bolts are Code components: The bolts apply some initial preload and the argument which is being made is that the internal pressure, which I presume is the steady state internal pressure, creates more force than the bolts. However, the vessel is operating as soon as you introduce the first fraction of pressure into it. It enters "normal" or "steady state" operations only after passing through some initial transients. Similar situations occur on shutdown, and perhaps during the run depending on your process. If you can tighten the bolts to seat the gasket, then remove them before placing the vessel into startup perhaps one could argue that they are not Code components. But if you need even some fraction of a psig before you could remove the bolts, then the bolts are necessary for operation and fall within the code.

 

[CodeRef]

Although I agree w/jte's position and consider the bolting as Code components, there are interpretations in Section IV and Section I that support prex's approach.

Additionally, I do not believe all UG-11 Manufacturers' identify the bolting by ASME Specification. From perusing the available literature of one specific manufacturer, the only items identified to be in accordance with ASME Code material specifications are the formed plates and rings(and of course welding to Section IX). Their design was by proof test also.
I am confident the proof test documentation would provide the bolt spec if an inquiry were to be made.