Material A 106 B MDMT -29¦C

[Degas]

Dear All

I just received a calculations with the results bellow and I dont know how to interpretate the results,my need is pipe to nozzel neck in A106 and MDMT -29ºC, the calculations is fine to this condition?

Minimum Design Metal Temperature (Noz. Neck to Flange Weld), UCS Curve: B
Nozzle, tg = 14.980 , tr = 3.397 , c = 3.0000 mm , E* = 1.00
Stress Ratio = tr * (E*) / (tg - c) = 0.284

Minimum Temp. w/o impact per UCS-66 -16 C
Minimum Temp. at required thickness -94 C
Minimum Temp. w/o impact per UG-20(f) -29 C

 

[metengr]

Degas:
No, this calculation does not appear to be correct. If you review ASME Section VIII, Div 1 UCS 66.2, the equation for determining the MDMT without impact testing is based on a similar equation except there is no t_g. The variable is t_n, which is nominal noncorroded thickness.

You need to review UCS-66.

 

[Degas]

Tks, meteng
But if I supose this calculations are correct and tn or tg is the sam figure, can I consider that A106 B is ok for MDMT -29ºC or not. How can I rad the figures above.

 

[SJones]

As part of your investigation why not establish the specific basis for setting an MDMT of -29 deg C in the first place? Then you will be in a position to confirm that UG-20 (f) may be applied correctly. It appears as if somebody is trying to go the hard way of allowing an MDMT reduction based on stress ratios.



Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[metengr]

Degas;
Let's start from the beginning. What is the thickness of the SA 106 Grade B pipe to nozzle neck flange butt weld?

If the flange is manufactured to ASME B16.5, you are ok to use at -29 deg C or higher temperature with no impact testing.

 

[Degas]

Metengr, tks
The pipe tick is 17,12 mm (xxs). How can I interpretate the value- Minimum Temp. w/o impact per UCS-66 -16ºC ?

 

[doct9960]

Degas,

If your vessel or portions of your vessel satisfies ALL the requirements of UG-20(f), MDMT is good to -29°C with no impact testing. If not exempted by the rules of UG-20(f), you are now bound by the rules of UCS-66.

For a 17.12 mm nominal thick pipe, the governing thickness would be 17.12 x 0.875 = 14.98 mm. Using Curve B at this thickness, you would get MDMT = -16.725°C from Fig. UCS-66M or Table UCS-66. -16.725°C is the "unadjusted" MDMT. You can further reduce this MDMT using the rules of UCS-66(b). Now assuming the tr and coincident ratio (stress ratio as you called it) in your original post are correct, go to Fig. UCS-66.1M and see what you end up with your coincident ratio. Since your coincident ratio (0.284) is less than 0.35, Figure UCS-66.1M tells you to see UCS-66(b)(3). Your pipe's MDMT is good for -155°C with no impact testing.

But that does not end there. Your nozzle is a welded assembly composed of more than 2 components (e.g. pipe to shell joint and repad, pipe to flange). You need to follow the rules of UCS-66(a) and determine the MDMT of each welded component. The warmest MDMT should be the MDMT of your nozzle assembly.

 

[doct9960]

Your pipe's MDMT is good for -155°C with no impact testing.

Correction...pipe MDMT should be -105°C not -155°C