Selecting Correct Studs and Nuts 1

[jgibbs22]

Had a general question for the group regarding studs and nut selection based on flange selection. An issue I was having with 16.5 is it lists bolting specs based on strength or special alloys. Is thre a website out there or a reference where if you have the temperature range, pressure, and material type, and chosen flange, it will suggest the proper bolting and studs?

 

[gr2vessels]

I don't know of any particular standard to make comprehensive recomandations on bolting selection, I believe there is not such thing.
The bolting selection is a such wide issue, depending on many more conditions than you have listed, including gasket type, internal fluid, external environment, insulation, etc.
However, for specific applications, there is a variety of sources for info, starting with your friendly bolt supplier. I know it sounds disappointing, but if there was that list you want, you don't need engineers anymore, everything being listed.

 

[SnTMan]

jgibbs22, use B7, you'll be right 90% of the time

 

[Duwe6]

concur with SnTMan. For any carbon steel flanges, including 5-Chrome and 9-Cr, made under B16.5 the correct answer is "B7 studs and 2H nuts" They are even available with plating for severly corrosive conditions, like off-shore.

For s/s to s/s flanges use B8 - 304 s/s, or B8M - 316 studs & nuts. If the normal operating pressure in the line is approaching the pressure limit for that flange class, think about using strain-hardened [much stronger] Class "X" B8 or B8M studs.

 

[TechThreads]

This is a super common question... most fastener houses live in the grade 2/5/8 world and don't know the difference between ASME or ASTM and a flat washer!

Our website has a listing of some common specs for flanges & piping applications. This should help narrow down your choices and then you can check the exact data on each:

http://www.tech-threads.com/wp/?page_id=141

 

[gr2vessels]

Interesting reading from Tech-Threads. It is also highlighting the inconsistencies of ASME codes, conflicting each other more or less. The ASME piping systems don't mind of using ASTM denomination for the fasteners, but ASME VIII allows only the ASME SA equivalent. In piping system, the headed bolt per A 193 is common, but in ASME VIII the SA-193 refers to stud bolts with 2 nuts per ASME SA-194. The Stainless Steel 304, 316 turns into a long list of austenitic stainless Steel bolts per ASME SA-193. Who do you trust when joining the pipe flange to the vessel nozzle, use 304 stainless bolts or use SA-193 B8 bolts??
SnMan, you'll be wrong 100% of the time using B7 bolts on stainless steel piping system. B7's for 90% of applications is not an engineering advice. The OP asked for a comprehensive reference for selecting correctly the fastener material for a particular application and/or every imaginable application. Do you know such reference?
Cheers,
gr2vessels

 

[TechThreads]

ASTM is the more common nomenclature used to call out the spec for fasteners... and when you're talking "process" fasteners... i.e. B7, B8, B8M... they're typically dual-rated. The brokers that import the material (which are responsible for most of what is sold in the market) buy dual rated to both ASME and ASTM specs... i.e. nuts are A194/SA194. (Of course, it's always important to check this-- there are exceptions).

 

[SnTMan]

gr2vessels, did you miss the " " at the end of my post?

 

[MJCronin]

jgibbs22...

Does your question regarding flange fasteners pertain to piping systems or ASME pressure vessels ?

This is significant because if this is a piping system application, the piping line spec should define which fasteners are acceptable for the particular system.

If this is a pressure vessel application, either the original design drawing or the certified ASME U1 data form will define the fastener requirements.

Since most MBA plant owners discard all engineering documentation during thier annual ownership changeover, you might find some luck by contacting the original vessel fabricator or perhaps the National Board (You will, of course, need ASME/Board registration numbers)

If this is indeed a carbon steel vessel/piping system....I then agree with SNtMan.

My opinion only

 

[r6155]

Studs and nuts selection based on flange selection include: material, tension method, corrosion protection, stud long, etc., etc.
Careful analysis should be made.

regards

r6155

 

[rmw]

I will weigh in on this one since I have suffered sufficiently enough to be qualified to do so.

The answer is... "it depends."

It depends upon the standard to which you are designing. For example, if you are designing a PV to Section VIII, then go with what Section VIII dictates. If you are designing to piping codes, and I say codes, then go with what your particular code dictates.

I have noted in other threads that a Section VIII vessel with flanged construction can have A193 B7 studs holding it all together down to some really cold temperature, something like -55 (F I think - doesn't really matter too much down there) while the piping attached to that very same vessel if designed to ASME B31.1 has to switch to A320 L(several choices) at -20F.

So I ask, why if a A193 B7 stud is sufficient to hold a vessel together down to -55F, isn't that same stud sufficient to attach a pipe to that vessel to that temperature?

It has to do with the fact that the Code Committees that determine these things are independent and often IMO uncommunicative, so their standards aren't harmonized. One code committee memeber that lurks here once stated that it would be like "herding cats" to get them all on the same page. I understood the comment and offered no further resistance.

We the individual Engineers have to wade through the morass of the differing applicable codes and specify what the governing code dictates, often to the derision of our peers (yes, been there too) and expense of our companies.

rmw

 

[Duwe6]

To add a little; and the Engr has to determine if Code-minimum is adequate for a long, safe, uneventful operating life. The cold flanges rmw mentioned are one place a prudent Engr would probably switch from B-7's to L-rated studs on his vessel at the temperature that his piping Code [-20°F] required it. Code requirements are minimums, and when working at the outer limits of allowable temp's and pressures, you may want to do a little better than the minimum required.

 

[payaam2000]

Dear All

where can i find allowable shear stress for bolts?