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