Though B31.3 may allow ASTM A325 bolts but it's up to the engineer/designer to match the components to the application.

While ASTM A325 bolts may be fine for some services covered by B31.3, a low pressure water line for example, why on earth wood you want to consider those bolts for Hydrocarbon Service?

What kind of gaskets are you using? A doubt an ASTM A325 bolt would seat a spiral wound gasket. What about flange moments due to bending?

Normally, the objective is to reduce or eliminate risks by providing a well designed safe system.

NozzleTwister
Houston, Texas

Aside from NozzleTwister's post and concerns there is another very big one and that is commingling of the fasteners.  
If you are talking Hex bolts of both materials they will get used in the wrong place.  Very few mechanics look at the markings on the bolt as all there after is a size that is just close.

I personally wouldn't have A325 bolts around or near any pipe flanges.

NozzleTwister/unclesyd - great feedback.  I appreciate you taking time to respond.   It looks like we are going to go with the A193 bolts.  This construction was going on back East...with a contractor that apparently was not too familiar with this type of construction - and we had a "hole" in our piping specs which was not clear on bolt material for bolts less than 1" in diameter (that hole is now closed!).  

In your case I would definately keep tight control of the fastening and even give a little demonstration of the proper tightening of pipe flanges.

I would require an MTR of fasteners used on the piping flanges.

If the installer isn't familiar with process pipe installation make sure whoever is representing you is aware of this fact.

UW1981,

An issue not addressed thus far in these postings is the "mixing and matching" problem of bolting materials at the jobsite.

Because A325 bolts & matching nuts are not acceptable for all kinds of service, saving a few bucks on cheaper bolts can cause a nightmare when materials are identified at the job site.

On many jobsites I have seen, only A193/A194 materials (stud bolts & full nuts) are permitted, with the full knowledge that they are probably "over specified" for some types of piping service.

They savings in headaches is worth more than the cost differential in materials...


My opinion only

-MJC

  

I work on bridges and we use ASTM A325 bolts for nearly all our work.  I would like to know what makes these bolts unsuitable for joining pipes.  Am I missing something?

Review ASME B16.34, Table 1 - Group 4 Bolting Materials Specification. Read all of the notes carefully.