Should most bolting ( ie. blind flanges to weld neck flanges, for example) use washers or not?

I have seen pictures of pressure vessels and heat exchangers with and without washers.

What is your opinion on this matter?

Thanks in advance for any insight you can shed on this matter.

Jim

First, an eplanation what is a bolt and what is a screw.
You put a bolt into a hole and turn the nut with a wrench. The bolt has flat hexagon face in contact with the member being connected, so it gets blocked by means of friction, and all you have to do is to torque the nut. So the bolt doesn't need a washer, but it's good to have a washer under the nut to reduce friction.
A screw is something that you turn by its head, usually putting into a threaded hole, but not necessarilly- you can use screws in flanged connections with a nut. But in this case it takes two guys to tighten a flange: one with a wrench from the screw side and one from the nut side.

So in real life the main difference between screw and bolt is whether you put a washer under its head. Ie whether you want to act simultaneusly on the head and on the nut or it's just enough to act on the nut only. It depends on the torque you need to obtain and accuracy of the stress you need in the bolt. The designer decides.

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Konrad Anikiel