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UCS66(b) Reduction For SA106 Gr. B

I have performed a calculation with Advanced Pressure Vessel software which says I can take the UCS66(b) reduction for a lower MDMT. Is this correct (assuming 3/8" Tn and E* of 85%)? There are no calculations printed in order to verify that they are correct. The link is to the calculation sheet 

hakkik (Mechanical) 
31 Mar 10 18:10 
Yes, UCS66(b) allows some reduction on MDMT. The rationale behind this is simple. MDMT rating assumes you are fully stressing(Table 1A allowable stress) the part, but in reality generally you are not. so your part is stronge (and thicker) than the required thickness. Read UCS66(b) carefully. You will find your answers :)
Sometimes using this reduction not allowed. Check eng specs also.


Hakkik, Thanks for responding. The thing that has me concerned is the fact that SA106 Gr. B is not listed in Fig. UCS66 under curves "B", "C", or "D". Therefore, you would have to use curve "A". Unless I am using Fig. UCS66.2 incorrectly, I'm coming up with a ratio of .9078. Using Fig. UCS66.1, that ratio is subsequently not giving me the reduction I need for curve "A". I need this vessel to be designed for an MDMT of 49 deg. F. If this material won't work, can anyone lead me in the direction I need to be in?
Thanks in advance!! 

sethevans,
Curve "B" applies to SA106B. I don't think you could rate SA106B to 49°F MDMT. Try SA3336. 

doct9960, I did the calculation by hand, and I'm still not getting by with it. UsingFig. UCS66.2, I'm coming up with the following:
tr E*/tn – c = (.2598)(.85)/(.312.125) = .22083/.187 = 1.18
If I'm calculating this ratio correctly, SA333 Gr.6 won't work either. Can someone confirm that my calculations aren't totally out of whack?
Thanks again! 

hakkik (Mechanical) 
1 Apr 10 11:33 
sethevans,
doct9960 is right, Curve B applies for pipes(Fig UCS66 Note(2)(c) ) So you have 20°F without impact testing and UCS66(b) reduction.
all values taken from your calc. rep. ratio = (0,2881x0.7)/(0.3750.125) = 0.80 with the ratio calculated above you can reduce MDMT without impact testing 20°F approx. so your MDMT=40°F
looks like you have no chance to rate your pipe(SA106B) 49°F without impact testing. again doct9960 is right :)
you have two options. 1) impact tested SA106B. (see UG84) 2) using SA333Gr6(same allowable stress value at375°F)
I would prefer the second option.


hakkik (Mechanical) 
1 Apr 10 12:10 
sorry i miscalculated calculated ratio above. i forgot about pipe undertolerance 12.5% and tr in corroded condition.
Correct one
ratio = ((0.28810.125)x0.7)/((0.375*0,875)0.125) = 0.562 so you get ~50°F reduction. you have no problem with SA106B.
again sorry for the mistake, 

eliebl (Mechanical) 
1 Apr 10 17:20 
I wouldn't try impact testing SA106 B. It's very unlikely that it would pass. SA333 gr6 is acceptable under UCS66(g).
EJL 

sethevans,
Keep in mind that the MDMT and MAWP are related to each other. As you decrease the MAWP, you decrease the coincident ratio, thus decreasing the MDMT.
Let's assume that the vessel MAWP is limited by the shell with the following conditions: design pressure = 200 psi design temp. = 375°F design MDMT = 49°F joint efficiency = 0.85 corrosion allowance = 0.125" shell material = SA106B (14" STD pipe) MAWP = S x E x t / (Ro  0.4t) = 17100 x 0.85 x 0.203 / (7  0.4 x 0.203) = 426.46 psi
Now let's calculate for the rated MDMT for three different cases of MAWP.
Case 1: MAWP = 426.46 psi tn = 0.375" x 0.875 = 0.328" Unadjusted MDMT = 20°F (Curve B) tr = MAWP x Ro / (S x E + 0.4 x MAWP) = 426.46 x 7 / (17100 x 0.85 + 0.4 x 426.46) = 0.203" Coincident ratio = tr x E* / (tn  c) = 0.203 x 0.85 / (0.328  0.125) = 0.85 From Fig. UCS66.1, temperature reduction = 15°F Adjusted MDMT = 20  15 = 35°F Since the adjusted MDMT of 35°F is warmer than the design MDMT of 49°F, you need to impact test or change material.
Case 2: MAWP = 350 psi tn = 0.375" x 0.875 = 0.328" Unadjusted MDMT = 20°F (Curve B) tr = MAWP x Ro / (S x E + 0.4 x MAWP) = 350 x 7 / (17100 x 0.85 + 0.4 x 350) = 0.167" Coincident ratio = tr x E* / (tn  c) = 0.167 x 0.85 / (0.328  0.125) = 0.699 From Fig. UCS66.1, temperature reduction = 30°F Adjusted MDMT = 20  30 = 50°F Rated MDMT = 50°F (no impact test required)
Case 3: MAWP = design pressure = 200 psi tn = 0.375" x 0.875 = 0.328" Unadjusted MDMT = 20°F (Curve B) tr = MAWP x Ro / (S x E + 0.4 x MAWP) = 200 x 7 / (17100 x 0.85 + 0.4 x 200) = 0.096" Coincident ratio = tr x E* / (tn  c) = 0.096 x 0.85 / (0.328  0.125) = 0.402 From Fig. UCS66.1, temperature reduction = 92°F Adjusted MDMT = 20  92 = 112°F Rated MDMT = 55°F (per UCS66(b)(2))(no impact test required)
As you can see, MDMT decreases as MAWP decreases. If you still want to use SA106B without impact test, you need to rate your vessel with an MAWP that will satisfy the design MDMT of 49°F. This is assuming that your vessel MAWP and MDMT is governed by the SA106B shell. 

rneill (Mechanical) 
2 Apr 10 10:57 
Given the relatively small cost difference between A106B and A3336, I wouldn't even bother with A106B below its normal Curve B temperature. I have had A106B material fail impact testing at temperatures well above 20F (for thick material) and for any use now below the normal regularly accepted MDMD on Curve B, I just default to A3336. myself, I don't bother with the stress ratio reduction.
Locally, A3336 is readily available and has a very small cost premium over A106B. 

doct9960, If I'm using the calculations with the new MAWP correctly, my adjusted MDMT would be as follows:
Case 4: MAWP = 395 psi tn = 0.375" x 0.875 = 0.328" Unadjusted MDMT = 20°F (Curve B) tr = MAWP x Ro / (S x E + 0.4 x MAWP) = 395 x 7 / (17100 x 0.85 + 0.4 x 395) = 0.188" Coincident ratio = tr x E* / (tn  c) = 0.188 x 0.85 / (0.328  0.125) = 0.787 From Fig. UCS66.1, temperature reduction = 22°F Adjusted MDMT = 20  22 = 42°F Since the adjusted MDMT of 42°F is warmer than the design MDMT of 49°F, I need to impact test or change material.
The other materials that are on this vessel are SA234 Gr. WPB and SA105, so the design is governed by SA106 Gr. B & SA234 Gr. WPB which are both 17,100 at this temperature.
Thanks for Everyone's help on this! 

rneill (Mechanical) 
2 Apr 10 14:43 
With the SA105 you might want to consider SA105N. there is quite a bit of data out there that SA105 in the as forged condition is not suitable for the MDMT's permitted by Code.
If it were me, I'd switch to SA3336 (pipe), SA350LF2Class 1 (flanges), and SA420WPL6 (fittings).
The cost of this would be less than conducting impact testing on alternative materials. 

To all, Would I be correct in assuming that by using SA333 Gr. 6 pipe, SA350 LF2 Class 1 flanges, and SA420 WPL6 fittings for the vessel, then postweld heat treating the vessel, per UCS68(c), I would get a 30 deg. F reduction which would put me @ 50 deg. F?
This seems like the easiest way to go if it is true.
Thanks in advance! 

SnTMan (Mechanical) 
9 Apr 10 11:09 
sethevans, you should be able to get 55F without the PWHT using the materials in your post, see UCS66(g). These materials are all tested at 50F.
Regards,
Mike 



