Asme/metric 1

[Giuss]

I have to make the calculation of a coke drum thikness at the conical section.
1.design Temp. 480 deg celsius
2.design pressure 6.158
3.halh apex angle 30 deg
4.diameter 9800mm.
now from asme II part D table 1-A the value of the maximum allowable stress is 14.22 ksi at the designed temperature converted in barg it gives 980barg the final thickness is 35.7mm.My result is 36 mm.

the manufacturer has calculated 34.9mm because it takes the maximum allowable stress from the ASME METRIC and it gives 1002barg.His result is 35mm.

he wants to stand on his calculation!

Who is Right?? and why??

tank you very much

 

[GregLamberson]

A couple of questions, did you both use the same joint effeciency? Any corrosion allowance differences?

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[Giuss]

scuse me..
same joint efficiency 1 internal diameter corroded 9806mm

 

[jte]

Giuss-

I'd go with the fabricator on this one since you are using conversions and the fabricator is using a consistent system of units. The fabricator has two things going for him:

from VIII Div 1 U-4:
Either U.S. Customary, SI, or any local customary units may be used to demonstrate compliance with all requirements of this edition, e.g., materials, design, fabrication, examination, inspection, testing, certification, and overpressure protection. In general, it is expected that a single system of units shall be used for all aspects of design except where unfeasible or impractical.

from II-D Appendix C-100:
It is the responsibility of the individual and organization performing the calculations to ensure that appropriate units are used. Either U.S. Customary or SI units may be used as a consistent set.

The engineer supplying the official Code calc's gets to choose which units to use. Where possible, the unit system should be kept consistent. So, since you are converting units for your calc's and the fabricator is staying consistent, the fabricator is following the Code guidance better than you are.

jt

 

[CodeRef]

In addition to jte's comments,

One should read all of Section II-D NMA Appendix C. As stated in C-200(b),

.....separate SI tables are provided if interpolation is expected......

It seems, as jte described, that you are not using the separate Table provided in metric units. Additionally, C-200 states the following

.........the precision of the conversion was determined by the Committee on a case-by-case basis. More significant digits were included in the SI equivalent if there was any question. The values of allowable stress in Section II, Part D generally include three significant figures.......


I agree with jte


There are three kinds of people in this world; those who can count and those who can't.

 

[Giuss]

1.SUPPOSE THAT NO METRIC TABLE IS AVAILABE !

I obtained the value of 14.22ksi making the interpolation between the values in Farenaith the vlue in Mpa is 980. the value given from the metric table is 1002 Mpa. the difference is about 2% in my opinion the difference is too big and the difference in thikness is bigger!!

 

[jte]

Giuss-

But a Metric table IS available. You simply do not appear to be using one. That does not make the fabricator's use of a Metric table incorrect.

Ask him to send you a copy of that particular page so you can confirm the interpolation. Besides the allowable stress value, is there any other discrepancy between the fabricator's and your calc's?

What is your role in this anyway? Are you working for an engineering and construction firm, the owner/user, insurance agency, jurisdiction, or something else?

jt

 

[Giuss]

I am a young mechanical eng. working for an e.p.c. company and I am making comments to the mechanical design of a very big licensor.

In my company nobody use metric table...
(is unbeliveable but it is)

the licensor sent me the calcuation note and the only difference is on the allowable stress 1002 Mpa (its)
980 mine

Tanks jte!