Bolt for high temperature Process line 1

[ispengg]

Greetings,

I was reviewing a piping specification for high temperature austenitic stainless steel operating at 1200 deg F [635 deg C].But the operating pressure is low [1 kg/cm2]. The metallurgy for the bolt material specified is SB 408 UNS N08811. This bolt material is not listed in [Design stress values for bolting material] Table-A2 of ASME B31.3. But I found the stress values in Table A-1. But it cannot be used for bolting.

My understanding is, for bolting higher yield strength is required. The yield strength and creep strength of SB 408 UNSN08811 is not encouraging [atleast when compared to B8T,B8M or B8C].Even though the pressure is very low this may under go stress relaxation and loose the clamping force.

When I consider SA 453 GR 660B which is having higher yield strength & creep strength and matches the thermal co-efficient of expansion of Aus. Stainless steel. But the stress values are available only up to 1050 deg F [due to heat treatment it undergoes].

Any body using SB 408 UNSN08811 / SA 453 GR 660B for Temperature above 600degC? Please share your experience..

 

[metengr]

Please review ASME Section II, Part D, Table 3. There is a stress line for SB408 UNS N08810 to 1650 deg F. There are also other high temperature bolting materials with stress lines.

 

[ispengg]

Metengr,
Thank you. I want your opinion on the following

1.But there is a subtle difference in the Chemical compostion [Carbon, Aluminium + Tiatanium] of UNS N08810 (800H) & UNSN08811 (800HT) to enhance the creep strength. I could not find stress value in both ASME Section II part D, Table-3 and in ASME B 31.3 Table A-2 as well. So my query is wheteher this is accepeted as a bolting material as per ASME codes? Practically speaking we can use the stress values of UNSN08810 for design calculation. But in actual condition for leak free joint, wont it relax quickly because its yield strength and creep strength is low?

2. Is it acceptable to use SA 453 GR 660B for temperature of 1200 deg F? As per specification it is Solution treatment @ 1800 degF for 1 hr min and Hardening @ 1325 degF for 16hr followed by air cooling.

 

[XL83NL]

Ive used inconel 800H bolts for an application where the design conditions where 725 C and 55 bar(g). No problems so far. Check the bolt stress and torque using VIII-1 app 2 and PCC-1.

As metengr indicated there are other bolt materials available in table 3 as well, but most of them probably cost a fortune. 660B's arent cheap but may be the cheaper option compared to bolts with higher creep rupture stress values. You could even consider B8M Class 1's, but you have to do calculations on bolt stress and torque to verify that. Make sure you use bolts with the same (approximate) coefficient for thermal expansion.

Could you share more data on your application? The pressure i1 bar(g) (kg/cm2 is not a commonly used un it). What size are you on? Is it for a B16.5 flange? Is it thermally cycling? Is the temperature in oparting or for design? Etc.

 

[metengr]

Since this material is unlisted for use in ASME B31.3 you can reference 323.1.2 Unlisted Materials. You are permitted to use N08811 as bolting material provided the following are met;

(1) they conform to a published specification
covering chemistry, physical and mechanical properties,
method and process of manufacture, heat
treatment, and quality control, and otherwise meet the
requirements of this Code

and

(2) Allowable stresses shall be
determined in accordance with the applicable allowable
stress basis of this Code or a more conservative basis.

For your case, there are stress lines for annealed N08811 bar material in ASME Section II, Part D, Table 1B. If the stress line is as conservative as that for use in determining stress lines for bolting material, you can use the N08811. Otherwise, you will be forced to use N08810 stress lines.

The same would apply to the unlisted ASME SA 638 Grade 660 material.

 

[ispengg]

Thank you XL83NL,

The line operating pressure varies between is 15 to 50 Psi depending on the operating case and design pressure is 100 Psi. The operating temperature varies between 1175 deg F to 1200 deg F. The design temperature is 1250 deg F. The size of the flange is 42" and 50". So its not as per B16.5. Its not in thermal cycling.

Thank you Metengr,

The design factor for determination of allowable stress is different in Table 1B and 3B only for below creep range. i.e 1/4 of tensile and 2/3 of yield strength for bolt. But the criteria is same for creep range i.e. minimum of below
1.100% of the average stress for a creep rate of 0.01% per 1 000 h
2.67% of the average stress for rupture at the end of 100 000 h
3.80% of minimum stress for rupture at the end of 100 000 h

So i believe I can use the stress values of UNS N08811 in Table A-1 of B31.3 or Table 1B of Section II part D. So we can design the bolts for the flange.

When we tighten the bolt due to high stress being generated between the threads, it may settle i.e may creep or yield at high temperature so bolts are selected with high yield point. So these high nickel alloys with low yeld stress can withstand the clamping force was my doubt.

 

[AndrewFinAustralia]

I can't add anything to the above, but must ask:

Does it have to be a bolt?

We used to hot rivet the high service temperature components (eg: coke oven beams) - if this is acceptable, it widens your choice of available materials.

AF