A325-N Grade Bolts with flat or spring washers?

[synthetic]

Dear All,

I have gone through the forum and found a few articles citing ASTM-A325 grade bolts, but I am here to find an answer which I couldn't find in previous topics.

I've got a drawing that is specifying A325-N type high strength bolts with spring washers for the stuctural bolting of an industrial building. It is ok. But our donut brain procurement people have been purchased flat washers and they have already been used for installation.

Now, what I want to know is which standard should I go through to find out if there may be any relief for us to use flat washers instead of spring washers. I'd appreciate your assistance.

Synthetic

 

[mog69]

I think the question is not so much the compatibility of the washer with that particular grade of Bolt, as the fitness for purpose of the alternative.
The spring washer would have been specified to ensure that the bolt didn't back off after being tightened to the recommended torque. It was obviously a concern for the designer that this could happen in service, maybe from thermal cycling or vibration effects. A flat washer won't do that. It has no locking properties. You don't say if the bolt is tightened into a tapped hole or a nut. If it's a nut and you have sufficient access and thread length, could you perhaps retrospectively tighten on an additional (half)nut to all the assembled joints to ensure they remain locked? You don't say how many fasteners are involved, but I guess it might be quite a number! If it's structural, it doesn't sound like doing nothing is an option.

 

[synthetic]

Dear Mog,

Thank you for your reply. You are absolutely right and each of eight building has more that 5 thousands of bolts and nuts in average.

At the moment, all the bolts have been fastened up to torque values. Our client is emphasizing that we will be relieved if we are able to prove that "spring washers may not be required when the bolts are tightened up to torque values". I don't know if I can find such a statement in any standard, but I know that we will be asked to replace all the structural bolting material.

Thank you very much,

SYnth.

 

[CoryPad]

Can you provide more information regarding the item you call a spring washer? Helical split washer, toothed, conical (Belleville), something else?

What torque (and especially preload) is required? What is the bolt size?

In general, washers are used to provide increased bearing area (lower surface pressure), not to maintain preload.

For structural bolting, you should read every word in these documents:

http://www.boltcouncil.org/download RCSC Specification.pdf

http://www.boltcouncil.org/2nd Edition Guide.pdf

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[mog69]

Hi Synth
Sounds like a deep hole your purchasing guys have dropped you in!
Any bolted joint by it's nature is required to stay tight, but the specification of the type of fasteners to be used for any given joint can be many and varied depending on factors such as safety criticality, environment, maintenance intervals, etc.
Spring washers would have given you some mechanical locking of the bolt / nut and therefore some element of "fit and forget" since it would have made the assembly less critical to tightening torque. Assuming the bolts and nuts were purchased to the correct spec so the joint is mechanically ok (size / strength grade / type of finish etc) can you trade off the substitution of flat washers against inspection records from assembly of the torque setting used, calibration certification for the torque wrenches, documented working procedures specifying the frequency of torque wrench re-checking during assembly, inspection intervals (sample inspection plan) of assembled joints to ensure tightness, etc, to build an assurance for yourselves and your Customer that the joints are maintained in a known state?

 

[oldrunner]

I think your purchasing department saved you. Per the specification for Structural Joints Using ASTM A325 or A490 Bolts, Section 2.5:

"Flat circular washers and square or rectangular washers shall meet the requirements of ASTM F436, except as provided in Table 6.1. The type and finish of such washers shall be given in Table 2.1."

Reviewing ASTM F326, Table 2, you will find only hardened circular, clipped circular and extra-thick washers. No spring washers.

On the other hand, if the original designer designed the A325 bolts to be installed with "Snug-Tighened Joints", then there might be an argument for using the spring washers. The engineer of record is required to identify the joint type in the contract documents.

I believe that if spring washers were to be allowed, that a specific ASTM specification would be indicated in the bolt ASTM specification.