ASME Sect VIII div I 1966 code

[Headsup]

Does anyone know if the Sect VIII div 1 1966 code required calculations for area reinforcement around manway openings? I am evaluating (using pre 99 stresses) several old tanks and they all fail area of reinforcement calculations on the manway openings.

If I need to rerate these tanks (260F to 290F) is it acceptable to evaluate the entire tank (except manway AOR) according to Sect VIII div I and then evaluate stresses around the manway using FEA to validate adequate reinforcement? I know the allowable stresses do not change that much with the small temp increase, but the manway failed ASME AOR at original temp.

Thanks

 

[JoeTank]

To the best of my knowledge the area replacement calcs are essentially unchanged compared to current rules. It is not entirely unheard of to find an old problem like this. You might want to look at your calcs again. Did you use E=1.0 in the shell Treqd calc? That is sometimes the problem when the openeing does not pass thru a Category A weld.

For new ASME vessels an FEA does not eliminate requirement to meet Code requirements. I'd follow same approach here if possible.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[JStephen]

First off, I'd suggest to go back and double check the calculations to make sure you're not missing anything. IE, calculated thickness vs. as-built, excess plate thickness area, neck area inside and outside, weld metal area, cut-out dimensions, reductions for external pressure, correct design pressure, etc.

I don't know, but would guess that the reinforcing requirements have been in there right from the beginning. It IS possible that they have been revised somewhat.

Were these tanks all built by the same company at the same time? If so, it's possible that someone just made design errors. But if it's different tanks built at different times by different people, it's more likely a problem in your present design methods.

 

[jte]

Headsup-

I checked the 1965 Section VIII (no Division - Div. 1 and Div. 2 were introduced in 1968) and the opening reinforcement requirements are nearly identical. Two differences: The F factor in the current UG-37 is not in the 1965 Code.

Second, and more likely to impact your situation is how the A2 calc is spelled out. I think the intent is the same, but the more I look at it, the more I'm thinking that there is a mistake in the formula provided in Fig. UG-37.1 for when the nozzle thickness governs the equation. In the 1965 ed. the equations are listed as A2=(tn-trn)5t or A2=(tn-trn)(5tn+2te); use the smaller value. In the current edition, the formula for the second version is changed to exclude the 2te term. Yet if you look at the sketch provided, the te terms (on both sides) are intended to be included...

Another issue you may have is that since you are dealing with a manway you may be unnecesserely including the 12.5% tolerance on piping thickness when you evaluate the available tn. This would not be necessary per UG-16(d).

jt

 

[jte]

Hmmm... if I were to actually *complete* reading the page and equaitons before jumping to conclusions... The formulas are the same if you look at the lower section with formulas for the case with a repad: The second formula is A2=2(tn-trn)(2.5tn+te) [assuming fr2=1].

jt