Do we need washers for pressure vessel?

[PAN]

I used to find the washers at manhole of some columns (pressure vessel). Is this a requirement in any codes or engineering standards (ASME Sect. VIII or others)? Please comment.

 

[ElderX]

Are you referring to gaskets on the sealing surface or washers on the bolts?

 

[prex]

No washers required by any pressure vessel code that I know of.
I suppose this is because nut seating conditions (bolt hole diameter, flange stiffness, flange material) are otherwise specified by codes, so the bolt will always sit under predetermined conditions.
prex
motori@xcalcsREMOVE.com

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[amexhts]

While washers are usually not a Code issue, they can be part of the manufacurers requirements. Sometimes Belville style washers are used to keep gasket loaded after operation especially in cyclic duty. Some lock style washers are often a manufacturers requirement where vibration can loosen nuts and allow gaskets to leak.

 

[kstaylor]

Hardened flat washers are often used to provide a bearing surface that the nut can mate against to keep from galling the backside of the flange ring. This is especially done on large, high pressure, high temperature bolting applications.

 

[VDK44]

Yes I fully agree with kstaylor please.Designs with hardened flat washers under bolting, especially with Metallic and Metal Jacketed gaskets are very successful in Hydro test as well as in service on pressure vessels and Heat Exchangers.
V.Dwarakakrishna.

 

[tjrush2000]

I have a large custom designed replacement blind flange being put into service. It is mating with an existing flange with blind tapped holes. As a result the bolt holes will require oversizing to allow fittup with the existing flange. 1 1/8" studs in holes as large as 1.614".

Where in the ASME code or other relavent pressure vessel related standards is bolt hole size specified.

What are the relavent issues and standards to specify washers for this situation?

 

[lakeroadster]

There is a lot to consider here. If the fasteners will not be removed frequently and the through holes are not oversized, then washers are not required.

Another thing to keep in mind with hardened washers is corrosion. We have experienced high corrosion rates with the hardened washers. The corrosion can lead to relaxation of proper bolt torque and eventual bolt failure.