High Temperature Flange Bolting

[cycguy]

On a ss304H Sect.8, Div.1 pressure vessel with a design temperature of 1380 F, and max. operating temperature of 1310 F there is a class 600 flange subjected to high external nozzle loads. Per my Compress program if the loads were imposed on the flange, the flange would need to be a class 1500 flange for sustained loads and class 2500 for occasional loads. However the client has accepted a ASME, Sect.3, NC3658 analysis showing a class 600# flange is suitable. The Compress program will only allow an SB-575 bolt which conforms to both the temperature limit, and high strength bolting for a class 600# flange. However the client would rather use A453 Gr.660 class C bolting because it has a 85 ksi yield strength, as opposed to the SB-575 bolt which has 35 ksi yield strength. The A453 Gr.660 bolts per Compress and ASME sect.2,Part D are limited to 1000 F. Applying the B31.3, 301.3.2 the oper temp can be reduced by 80% which gives 1048 F,which is still over the ASME limit. Any ideas for an appropriate bolt selection?

 

[tothepoint]

You also should factor in the assembly bolt load required to seat your gasket. In a class 600 flange you're probably using a FG or THM filled spiral wound gasket, and you may not have adequate compressive load available with a 35 ksi yield fastener.

 

[metengr]

I would not recommend using the Grade 660 (A 286) bolt material. The hardening treatment is 1325 deg F for this material. You don't want to be anywhere near this temperature in service.

Look at Refractaloy 26. It might be expensive, but it is used on high pressure steam turbine bolting at 1050 deg F.

 

[doct9960]

From Section 4.2.3 of MTI Publication No. 14 (Manual on Closure Bolting for the Chemical Process INdustries...
"Creep resistant, nickel-base superalloys can provide acceptable mechanical properties for use as fasteners up to 1600 [°]F (870 [°]C), dispersion strengthened nickel and cobalt-base alloys or refractory metals can be used. Care must be taken to protect materials from oxidation and scaling at these temperatures. Closure fasteners for this temperature range are seldeom required in the chemical process industry.(Most bolts of this type are used in jet engines and turbines.)"

I guess the Refractaloy 26 mentioned by metengr falls in this range.

Have a look at these websites. They discuss material issues on turbines in ultra supercritical steam.

http://www.ms.ornl.gov/researchgroups/corrosion/staff/pdf/IGW-0417.pdf

http://www.ornl.gov/sci/fossil/pdf/Proceedings19/PAPERS/Session II/maziasz.pdf

 

[metengr]

Forgot to mention, you can even look at Inconel 718, Inconel X-750,

 

[TomBarsh]

cycguy, A bit late to the game but... The method of ASME Sect III NC-3658 flange analysis for external loads is the same as that used by COMPRESS to "derate" standard B16.5 flanges for external loads. Something seems wrong when one analysis passes a class 600 flange but another analysis requires class 1500. It seems there must be a difference in some of the numerical values. It is understandable that "occasional loads" (higher value) will produce a higher derate from the flange MAWP than will "sustained loads" (lower value). But to get from class 1500 to class 600 using the same method of analysis there must be a difference in gasket dimension, loads, etc, or else an error (maybe in combining bending moments?).

COMPRESS uses the paragraph NC-3658 method when analyzing Section VIII Div 1 App 2 flanges. It can be seen that the formulas are identical to the method used to derate "standard" flanges (discussed at

http://www.codeware.com/support/faq/1051.html)

Tom Barsh
Codeware Technical Support