Nozzle Reinforcement Calculations and 12.5% Undertolerance 4

[roca]

When preparing nozzle reinforcement calculations is it necessary to remove from the available nozzle pipe thickness the 12.5% mill undertolerance?
Eg there will then be less nozzle pipe material available for reinforcement.

I have always removed this tolerance in my calculations for a conservative design

 

[LSThill]

Hi roca (Mechanical)

ASME SECTION VIII - DIVISION 1, APPENDIX L-7 OPENNG AND REINFORCEMENT WELDING CONNECTIONS EXAMPLE.

L-7.2.3 Minimun Nozzle Wall Thicckness by UG-45

L-7.2.3.2 UG 45(a) required minimun nozzlw wall thickness to be not less than that computed for the applicable loading plus corrosion allowance. From L-7.2.2, trn = 0.89 in. This thickness is compared with the minimun thickness provided which for pipe material would include a 12.5% undertolerance. 0.875 x 0.500 = 0.438 in Since 0.438 in is larger than 0.089 in, the rule is met.

Please Read UG-45 a,b,c,d.

 

[TomBarsh]

When considering nozzle opening reinforcement (area replacement) per UG-37 it is not necessary to deduct the mill tolerance from the nozzle neck. The definition of "tn" given in UG-37 states "for pipe, use the nominal thickness".

However, you must deduct the mill tolerance from the thickness of the shell if made from pipe. Again, "t" as defined in UG-37: "for pipe it is the nominal thickness less manufacturing tolerance allowed in the pipe specification".

You must deduct the corrosion allowance from both "t" and "tn".

 

[xerex]

Per para. UG-37(a) the definition of "tn" states to use the nominal thickness.

L-7.2.5(d) confirms the use of the nominal thickness.

 

[JoeTank]

roca,
Although your approach is conservative, the 12.5% undertolerance does not have to be removed from the nozzle neck when doing ASME nozzle reinforcement calculations. Just for the record, the 12.5% tolerance is only nozzle necks that are made of piping. That would not be true for nozzle necks made of rolled plate.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[bvi]

Be careful and more specific when stating ASME requirements. For example, in ASME B31.3, it is required to remove the mill tolerance when doing nozzle reinforcement checks.

 

[DSB123]

bvi,
You are dead correct in that ASME B31.3 does require the removal of the mill tolerance.

roca,
You did not specify the actual Code which you are using and whether the mill tolerance should be considered or not is dependant upon which Code is to be implemented.

 

[roca]

Hi All
Thanks for the responses
Yes - I was asking about ASME VIII
In PD5500 the tolerance is removed. In Europe everywhere I worked would take off the 12.5% tolerance as a conservative design - no matter what the code.
Although these with the software available - Compress, PV Elite et al you just accept what the program does
Thanks again

 

[TomBarsh]

One should never "just accept" what a program does. In the end it is the designer, not the software vendor, who is responsible for all the calculations, including anything that the software may not be able to handle. You should have an understanding of how the software applies the Code requirements, as well as limitations of the software.

 

[LSThill]

I agree with TomBarsh (Structural) and Additional Recommendations to keep in mine:

o All users of manufacturer-verified computer software should perform several independent verification calculations when first utilizing new software to determine its accuracy. Independent calculations may be performed by hand or by utilizing other independent preverified (and checked) computer programs.

o All buyers of preverified computer software should purchase or otherwise obtain agreement from the manufacturer to receive Errata as it becomes available.

o If errors in software are found, all work performed with the software that could be affected must be thoroughly checked for error and the appropriate corrective action taken if error is found.

o Notify the software manufacturer of errors. Notify other software user groups within your department, any contractors you know who may use Computer Software and Office of Environmental Health and Safety, that the software results may be invalid.

o Maintain qualification records and Errata for software versions. Allow only properly trained personnel who are thoroughly familiar with software program limitations to use the software to perform critical work and keep these users updated on changes and errors in the software.

Leonard@thill.biz

http://www.thill.biz

 

[bmoorthy]

Are there any approval/rating system in existance for the softwares for CODE use (Say a group of pannelists review the soft ware and rate the same or vouch the product as compliant with all the requirement of code)

 

[roca]

Hi TomBarsh
Of course I don't "just accept" what the program does.
I was talking in general terms.
In my experience and I still see it now - especially since the PV design software has taken over - young engineers just punch numbers in and accept numbers out. Most have never done a hand calculation in their lives......aah the good old days...!!