Washers on manway flange 1

[jtseng123]

Dear all,
I have a vessel fabricator who supplys zinc galvalized washers for bolting on carbon steel manway flange. I have never seen using washers for manway in the past.

What is the con of using washer ?

 

[Compositepro]

Washers help prevent wear between the nuts and the manway flange from repeated tightening and loosening.

 

[TGS4]

Make sure your washers are through-hardened per ASME PCC-1. I'm not sure that galvanized is a good idea, though.

 

[jtseng123]

I guess I did not get my question straight. Sorry for that.

99.99 % of flange joints at sites, including manways, no washers were ever used. So what is the reason NOT using washers if washers proved to be a good idea ?

 

[Compositepro]

The more frequently the nut is removed, the greater the benefit of using washers.

 

[GenB]

The ASME Code does not prohibit washers. Since washers tend to loose up the joint and takes more time to assembly its not use on normal assembly. There is no need for washers on a flanged joint when the designer and assembler know what he or she is doing.lube yournuts as required and forget about washers.

 

[TGS4]

Actually, GenB, ASME PCC-1 recommends washers be used. They prevent galling between the nut and the flange face and add additional stretch length to the bolt. Provided that they are through-hardened, washers are all upside and no downside.

 

[Dean8573]

Washers in teheory are great but if the protective coating becomes damaged you expose the base material which will suffer corrsion, if corrsion occurs then the washer thins in size.When the washer thins the bolt pre-load reduces and therfor the torque decreases until a point when a pressure release occurs. i worked for Hydratight for a number of years in this field and we do not promote the use of washers on pressure joints.

 

[davefitz]

Washers can also be designed as "belleville washers" which can accomodae differential thermal expansion between the bolt and the flange face,which may be important on high temperature flanges where the bolt and flange material are not identical.

"Whom the gods would destroy, they first make mad "

 

[doct9960]

jtseng,

99.99 % of flange joints at sites, including manways, no washers were ever used. So what is the reason NOT using washers if washers proved to be a good idea ?

I believe the main reason is that the use of washers is OPTIONAL. If the Codes mandated the use of washers, 100% of flange joints at sites will have washers.

Dean8573 raises a good point regarding corrosion. A similar scenario will also occur for painted flanges, especially when there is excessive paint thickness under the washers. Over time, the paint will deteriorate.

 

[LittleInch]

Not using washers is ,IMHO, a good idea because the risk of using incorrect strength washers is too high compared to their limited advantages for most flange joints. Some companies also found that washers could be used to allow use of incorrect (smaller) sized stud bolts which obscured the gap between the hole and the bolt and essentially placed the washer as a component then under bending and shear stress. These failed on occasion leading to personnel injuries and damage.

The idea that the washer helps spread the load is fairly ludicrous when you look at the relative thickness of the washer compared to the nut for most pressure flanges. If used they need to be no larger than the outer diameter of the nut and made from hardened material.

Basically washers are something which can be abused with use of non hardened material very difficult to verify on site and the safest way to avoid this is simply to avoid using them in the first place.

If you search a bit more on this site you will find this debated many times before with some fairly different views...

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way