AS1210 Class 1 MDMT Nozzle derivation

[stehill777]

I have a pressure vessel design to AS1210 Class 1, wall thickness t2 of 25.4 with a set in nozzle of wall thickness t3 of 71.3, nozzle and shell material are A350 LF2 CL1 (impact tested 20J at -46C which equates to 27J at -41C).
AS4458 will allow me to do this as an AS-WELDED construction since the weld through-thickness is only 25.4mm.



How though do I ascertain the MDMT of the nozzle as the tR for Table 2.6.4 (iv) is 71.3mm but the chart only goes up to 40mm? Is it acceptable to take the value at the 40mm line since assessment beyond the 40mm is irrelevant? (I don't want to extrapolate out to 71mm as that would be too hot).

 

[Spoonful]

What is your required MDMT or TR?

I think the reason fig 2.6.2(A) stops at 40mm is normally over 32mm you would have done PWHT, hence to fig 2.2.2(B). For your case if you using fig 2.6.2(A) I would extrapolate the curve, as if think theoretically as material get thicker the severe the effect of low temperature brittleness. But I would guess since your nozzle is forged. Is there any heat treatment during or/and after the forging process, that may equivalent to a PWHT? then you may use fig 2.6.2(B)? see note for T PPWHT in section 2.6.3.2

My 2 cents

 

[stehill777]

Thanks Spoonful,
FYI the MDMT must be colder than the design temp which is -29oC.
Happily I now have clarification from a AS1210 Committee member that it is acceptable practice in this instance to use the value at the 40mm ordinate. This is good as it gives me a Tr of approx -29.5oC.
Curve used is -41oC as the impact spec for A350LF2CL1 is 20J @ -46oC and this equates to 27J @ -41oC

 

[Spoonful]

Hi Stehill777

Good to know.

If read the -40C curve, The reading I have is about -28C. and for -50C curve read at -37.5. Liner interpolation for -41C will get -28.95