Washers on flanged connections? 1

ASME B16.5 references B18.2.1 for bolts.

B16.8 includes lots of stuff including the Bearing Surface issues. Bearing surface shall be flat and washer faced. Diameter of washer face shall be equal to the maximum width across flats within a tolerance of minus 10%.

Also search the web for hydraulic tensioners.

Thanks Seagull. I saw the B18.2 reference, but that's just a general fastener reference (dimensions, tolerances, materials etc) and has nothing on connections.

I phoned ASME and they said B16.8 is obsolete. They're phoning me back to let me know why its obsolete and what superceded it.

Anyone else have some info that'll help?

Are washers are allowed between the nut and flange of a bolted, flanged connection?

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Yes, they are allowed, but it is up to the Owner if he requires or DO NOT require them.

I can't find anything in ASME B16.5 except one clause (6.6) that says the bolt bearing surfaces must be parallel within 1 deg. And I searched the forum without success.

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Check your piping code. If your piping code is ASME B31.3, paragraph 309 says "Bolting includes bolts, bolt studs, studs, cap screws, nuts, and washers."

Also, if washers are allowed, what materials would be allowed?

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What are you flange and nut materials? I normally see hardened steel washers specified on CS flanges with SA-194-2H nuts to reduce friction.

I don't often see washers used on flanges. Generally when I have seen washers, they are on flanged joints which have previously been identified as "bad actors," i.e. joints which have proven difficult for the plant staff to achieve a seal on. I think doct put it well in pointing out that the use of washers becomes mandatory when the owner/user puts it in their spec's or other document.

ASME PCC-1, Pressure Boundary Bolted Joint Assembly explicitly states that the use of washers is optional. Note that this standard is being revised, I'm not aware of the target publishing date.

jt

We often use washers when using carbon bolting on a stainless flange to reduce galling and improve torque.

I agree with jte...

Although there are exceptions, most of the flanged joints I have encountered in power plants and process plants do not use washers.

The carbon steel/stainless steel flange noted above is an exception.

-MJC

Washers are sometimes considered to be superfluous. However, if the fasteners are "torqued", washers can be very useful: Not only is "torquing" a fastener highly inaccurate, the process also chews-up spotfaces like there's no tomorrow. The use of washers, although not eliminating it, tends to reduce this effect.

When "bolt tensioners" are used, washers become redundant because the tensioner applies an axial rather than a torsional load onto a fastener. To retain the load prior to the hydraulic being released, the nut is simply turned down to the spotface "finger-tight" - preventing any potential galling.

This well-recognzed method of controlled bolting provides as elegant solution to some of the myriad problems associated with "torque"!

* One should be careful that if a flange that has been torque-tightened in the past but is now being converted to tension-tightened (simply by using longer studs), most manufacturer's standard bolt tensioners may be obstructed if the washers stay in place.

Ciao,

HevïGuy