Intermediate/High Strength Low Temp Bolting Materials

[vehazle]

-SA-320, B8, Cl1 bolt material is classified as low strength in ASME B16.5.

-ASME B16.5 limits low strength bolting to 300# ratings or less.

-SA-320, B8, Cl2 bolting is classified as intermediate strength per ASME B16.5 and can be used in any flange rating (with qualifications on verifying the integrity).

The problem is that the allowable stress for Cl2 bolting above 1.25" diameter is the same as Cl1 bolting per II-D. I need stronger bolts for a 900# flange (1.375" diameter bolts) at a temperature of -270°F. Both SA-320 B8, Cl1 & Cl2 are OK at this temperature, but in the larger sizes the Cl2 offers no apparent benefit.

Is anyone familiar with another low temperature bolting material, acceptable by ASME VIII-1 that has higher strength than B8, Cl1?

Thanks in advance for the assistance.

 

[unclesyd]

Could you comeback with more information on you application.

Why are you using a Class 900 flange?
Is the -270°F temperature the operating temperature?

Cl 2 B8s' are hardened by cold work and cold is ineffective above 1.25 nominal size.

 

[vehazle]

The application is for non-corrosive service, hydrocarbons (mostly LNG), under high pressures. It is mainly piping, but also ASME VIII-1 vessels and pressure casings.

The operating temperature for LNG service is -270F but the non-pressurized/service temperature can sometimes go to about 150F.

I was aware the reasons for that the Cl2 has essentially the same allowables as Cl1 above 1.25", and that is the fundamental problem.

I'm sure there are other people that use ASME high pressure flanges/piping in cryogenic service that must have this same problem and I am looking for how they have met the requirements of B16.5 on bolt strength.

 

[metengr]

What size studs do you need for your application?

If you need greater than 1.25" diameter studs for your application, and you need higher strength than offered by ASTM A 320 Grade B8 Class 2, your other option would be a nickel-base stud material like ASTM B335 N10001 or even ASTM B574, N10276 (refer to Table A-2 in ASME B31.3 Process Piping Code, Appendix A).

 

[vehazle]

For the immediate problem I need 1.375", but we have ASME VIII-1 vessel applications that can go up to 2.25-2.5". Unfortunately I have not worked with B31.3 and the copy I have available is dated (1984) and does not have these materials in table A-2. Do you perchance know how VIII-1 looks upon materials/allowables from B31.3? I did look at the ASTM B335, and ASME II-D, which gives higher allowables for the N10001 material, but neither reference gives the minimum allowable temperature, nor reference cryo Charpy values. I assume that these materials are ok for the -270F temperature, but would like to cite a reference if possible.

The other option investigated is a Nitronic 60 material(UNS S21800) which I believe is listed under A-193 as B8S. It has higher strength that I am looking for but it is not listed in A-320. I am reasonably sure that this material is OK for the cryo temps since the Armco bulletin list decent cryo Charpy values and we use the material at these temperatures for a different application.

Can anyone give a rough idea on a cost delta between B8, N10001 and B8S (Nitronic 60/S21800) along with any comments on availability in sizes from 1.375-2.5" diameter?

I am also open to other suggestions from others that have attacked the same problem.

Thanks

PS: Don't try to use the term "cost delta" with anyone other than tech. types. I inadvertantly used it when discussing a purchase with a car salesman and just got a blank stare.

 

[metengr]

ASME B31.3 2004 edition lists that minimum temperature for these bolting materials as -320 deg F. For use of acceptable bolting materials and low temperature service refer to ASME Section VIII, Div 1 Part UNF Table 23.3.

 

[Elvie]

I recommend A453 Gr.660 bolts and nuts, Impact tested @-196°C which are now widely used for LT & Cryo applications.