Does washer needed for flange connection? 4

[nickcaiyh]

Hello all,

would you please do me a favor to answer the question?

Dose washer needed for flange connection? In my experience, we never asked for washer in piping material specifications for chemical engineering. While I looked a PMS for FLNG, I found the washer required. I did not found any standard or practice required for washer even for the cryogenic service. (I assumed that the Belleville washers may help on bolt tension on cryogenic flange connection)

Does the washer required for offshore marine engineering?

Thanks a million in advance.

 

[XL83NL]

https://www.linkedin.com/groupItem?...oups_most_popular-0-b-ttl&goback=.gmp_4791646

https://www.linkedin.com/groups/Flange-washers-is-it-very-4439477.S.159970289

http://www.eng-tips.com/viewthread.cfm?qid=223700

http://www.eng-tips.com/viewthread.cfm?qid=301302

http://www.eng-tips.com/viewthread.cfm?qid=364145

http://www.eng-tips.com/viewthread.cfm?qid=134091

http://www.eng-tips.com/viewthread.cfm?qid=98238

http://www.eng-tips.com/viewthread.cfm?qid=165408

http://www.eng-tips.com/viewthread.cfm?qid=81706

http://www.eng-tips.com/viewthread.cfm?qid=314597

 

[nickcaiyh]

XL83NL, Thank you very much for you attached links, I have read the viewthreads, it seems that people prefered flange installation without washers, however, it still under discussion.

 

[TGS4]

ASME PCC-1 recommends the use of through-hardened washers. Their use increases the bolt stretch length. And prevents embedment of the nut on the flange surface. They do make the assembly more complicated.

 

[rconner]

Just a couple questions. In most common applications of most common e.g. steel or ductile iron flanged items, is there really practical harm if some slight "embedment of the nut on the flange surface" were to occur (or I guess vice-versa, if the flange were harder than the nut?) Also, if there were say vibration imparted to a piping system/ joint where there had been say some embedment e.g. near the corners of nuts into the flange surface, might that make the connection less likely to loosen?

 

[TGS4]

The disadvantage of embedment is that some (an unknown) amount of the bolt torque is lost to the embedment rather than going in to bolt stress. Therefore, you are much less likely to get the bolts stress that you expect for a given torque.

 

[rconner]

Thanks. I was aware of some past threads e.g. at

http://www.eng-tips.com/viewthread.cfm?qid=81706

that appeared to hash this issue out to some extent. I was/and am still somewhat unsure that just saying "washers" are required for a joint (when not calling out specifically the metallurgical conditions and dimensions etc. of all joining members, as well as service) would necessarily be of great benefit. While I understand there is perhaps a general perception of some that "washers" in and of themselves would be helpful or even necessary in some cases e.g. to spread loads, it seems like that conclusion is not necessarily what all practicioners, standards or even what the researchers in the more recent actual testing e.g. at

http://archetypejoint.com/?page_id=128

have concluded (I think now after about three and a half centuries of some piping applications!)
I also noticed that (while perhaps not directly related to piping joints) some detailed research half a century ago at

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CCMQFjAB&url=https://

http://www.ideals.illinois.edu/bits...k4GoDw&usg=AFQjCNH36068L4IQ1LBfuNgd08dg3mFmdQ

stated even hardened washers didn't appear to make much of a bolt tension difference when the "turn of the nut" method was used, whether or not even these washers were used, in those structural connections (see Figure 5 etc.) I saw however, that hardened washers would protect softer flange surface from "galling" in the substantial preload of harder/high strength bolt wrenching e.g. in that testing program, it this were objectionable in the application, and per their Figure 6 etc. while preload was achieved with or without washers at least hardened washers did indeed reduce some the torque required to get a proof tension load for at least some mild steel structural connections with this high strength (some harder) steel bolts/nuts.
With regard particularly to "hardened washers," it is however interesting as well that some manufacturers e.g. at

http://www.portlandbolt.com/products/washers/hardened_round_washer.html

now say with regard to these washers, "They are the recommended washer for any fastener other than a low carbon steel bolt." Also, I know the scope to ASTM F436 Standard Specification for Hardened Steel Washers per

http://www.astm.org/Standards/F436.htm

states, "These washers are suitable for use with fasteners covered in Specifications A325, A354, A449, and A490." (I see for whatever reason all of these spec numbers are for high strength, not even mentioning their application to quite common lower strength e.g. ASTM A307 Standard Specification for Carbon Steel Bolts, Studs, and Threaded Rod 60 000 PSI Tensile Strength that have been traditionally specified for a whole lot of low and mid-pressure joining of steel and ductile iron flanged plant etc. piping).
Finally, while I believe most joints are still "wrenched", there are of course now also other means to tension some critical joint bolting e.g. with variously designed "tensioners", as opposed to conventional wrenches.
In the end, this may well be one of those "it depends" type questions (with perhaps a lot of things to consider

 

[TGS4]

One of the important things about "hardened washers" is to ensure that they are "through-hardened" and not just surface hardened. The advantages of through-hardened washers disappear if they are not hardened through-thickness. Another advantage is that they increase the grip length, which makes the joint more flexible - which is desirable when there is a gasket in the joint. In fact, it's the gasket in the middle that makes piping bolted flamhe joints much more interesting (and difficult to assess) as compared to structural joints without gaskets. Well, that and the potential for changing (sometimes rapidly) temperatures inside the pipe.

That said, I usually only start recommending through-hardened washers on bad-actor flange joints as one of variety of improvement measures. I also highly recommend them on joints in cyclic service, especially if the cycles include thermal variation.

So, yes - it depends indeed.