Ring type joint hardness vs flange hardness

[YuJie_PV]

hi all,
we have flanged joint with ring type joint. flange is 304, ring type joint 304 too. we mandate that the hardness of flange shall be larger than that of ring type joint by min.30HB.
now the materials are purchased already, and test result is beyond original expectation:
the hardness of ring type joint (304) is 147HB;
the hardness of flange material 304(raw material, not fabricated into finished product yet) is 158HB.
is there any method which may help achieve a wider hardness difference between ring type joint gasket and flange?
thanks in advance.

 

[EdStainless]

Not with the material that you have.

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P.E. Metallurgy, consulting work welcomed

 

[YuJie_PV]

THanks Edstainless.
and i still have some issues as below:
1. if we reject the material purchased, and ask vendor to repurchase to satisfy the hardness requirements of 30HB difference. is the requirement too demanding for such a material combination? i mean, both 304, hard to get hardness difference. i am not familiar with forging fabrication, just wonder if it is possible to accurately control the hardness of forgings fabricated by the means of, let's say, heat treatment. or something else.
2. is such a hardness difference of around 10HB between RTJ and flange acceptable for application, if i consider a compromise? have you ever experience similar application?

Thanks so much.

 

[GDHTX]

ASME B16.20, Table RJ-3.2-1 specifies a maximum hardness of 160 Brinell / 83 Rockwell "B" for Type 304 Ring Gaskets.
ASME SA182 does not specify a hardness requirement for F304 or F304L.
ASTM A182 does not specify a hardness requirement for F304 or F304L.

I personally think you'll have better luck if you specify a hardness requirements for the F304 flange.

 

[BJI]

If you really want less deformation of the flange groove, you could machine out and weld build-up / overly with a higher alloy around the groove, then finish machine the groove. Regardless, of the achieved hardness of the flange, it will likely make limited difference to the overall performance in this instance.

 

[Krausen]

So long as your RTJ gasket is ultimately softer than your RTJ flange, you should be okay. Having a wider range would be nice though. There is no way to heat treat austenitic stainless steel (e.g. 304SS) to change its material properties.

 

[r6155]

Design pressure is???

Regards

 

[YuJie_PV]

thanks, BJI. weld overlay is good idea.
@r6155, the design pressure is 14.5MPa.

 

[YuJie_PV]

@Krausen, thanks for your reply.
i still confused if the forging fabricator control the parameters of solution annealing, such as holding time at particular temperature, cooling rate/method, etc, isn't possible to accurately achieve some hardness number?
hope for some insight in this subject.
thanks in advance.

 

[r6155]

1) What spec did you get this 30 HB difference from?.
2) Try a new hardness test with another instrument.

Regards

 

[LittleInch]

This useful little guide from the Fluid Sealing Organisation

https://www.fluidsealing.com/

notes that whilst a difference in hardness is generally welcome (though doesn't specify how much) it also says

"It is recommended that the gaskets be softer than the flanges although this may not be possible with certain
alloys, i.e., stainless steel alloy flanges heat-treated for optimum corrosion resistance will have the same
range of hardness as the ring gasket of the same material annealed to minimum hardness. "

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[YuJie_PV]

@r6155, 30HB difference comes from the owner's spec, which, i believe, is based on the experience.

@LittleInch， it's so nice of you to share that handbook, it's very useful, thanks.

 

[DBreyer]

I have seen the 30 HB being specificed on a couple of units.
The reason is you want to avoid deformation of the RTJ groove in the flange, which could lead to problems with resealing after breaking the flange for maintenance.

So far we had no luck in reliably sourcing low hardness rings.

We careflully check flange seatings surfaces for deformations and cracks after breaking the flanges und look closely reagrding correct torque when bolting the flange.

 

[r6155]

@ DBreyer
Never use torque, use stud elongation.

Regards

 

[YuJie_PV]

thanks DBreyer,

i get a freakish idea, maybe surface hardening, like nitriding is an option to increase the surface hardness of flange. but i never see such application in flange. there must be some reason.
what do you think?

Thanks.

 

[DBreyer]

Jay_pv: Nitriding sounds certainly doable. But I would be worried about introducing new damage mechanisms when doing this. E.g. a decreased resistance to SCC.
It also depends on the amount of flanges you are worried about. Only some vessel flanges or all the piping flanges in a new unit?

What is sometimes done, but typically only for something like 2 1/4 Cr base metal heavy wall reactors is a weld overlay of the flange face. In newer units with alloy 625.
In one unit they used something like 410s as weld overlay. The flange was in operation for 60 years without issues.