ASME VIII D1 Beginner Question 1

[soletto]

Hallo guys,

im new to ASME and i have a question:

I need to calculate a normal pipe. But im not sure how to add the corrosion and mill tolerance to the equation correctly:

I have that 2 equations:


R .... inner radius (nominal)
Ra ... outer radius (nominal)
c1 corrosion
c2 mill tol.
t0 ... nominal thickness
t ... min required wall thickness

t= P*R/(S*E-0.6*P) if t0<(Ra-t0)/2 or p<0.385*S*E +c1 +c2

otherwise

t= R*e^[(P/(S*E))-1] +c1 +c2

-------------------------------------------

Or should i increase the inner Radius R to R` to the corroded inner radius and add c1 and c2 to that new equation

so that R`=R+c1+c2

and use this equation:

t= P*(R+c1+c2)/(S*E-0.6*P) +c1 +c2 if t0<(Ra-t0)/2 or p<0.385*S*E

otherwise

t= (R+c1+c2)*e^[(P/(S*E))-1] +c1 +c2

----------------------------------------------

For me equation system 2 is more logical because the inner radius is bigger because of corrosion and so that the pressurised area is bigger because of R+c1+c2

-------------------------------------

Thx,
best regards Stefan!

 

[XL83NL]

There's plenty of stuff regarding the (hard to understand/all over the place) question you ask. Do a search on this site and youll find it. First of, talking about pipe and mentioning those equations, you need ASME B31.3 and not ASME VIII Div 1. The latter is for vessels.

 

[DSB123]

soletto,
Please define what a "normal pipe" is since in my 45 in engineering I have never heard of a "normal pipe".

 

[soletto]

I have to calculate a pipe according ASME VIII Division 1 according to customer enquiry.

I only dont know how to take the corrosion into account.

According to ASME DIV 1 i dont know which dimension for R should i take when calculating pipe wallthickness.

this is the formula:

t= P*R/(S*E-0.6*P if t0<(Ra-t0)/2 or p<0.385*S*E

but what is the inner pipe Radius.

is it the nominal inner radius or is it the nominal inner radius + corrosion?

Because the Radius is getting bigger with lifetime because of corrosion. This leads to a bigger force (bigger inner radius)

I added the 2 types of formulas i dont know which one is right.

B31.3 adds the corrosion to the radius (Formula trD1) but ASME VIII D1 not.

Im confused

Dont find a similar question here

And year it is about pressure vessels the area im working in

Regards Stefan

 

[prex]

UG-16(b)(5)(e) Corrosion Allowance in Design Formulas. The dimensional symbols used in all design formulas throughout this Division represent dimensions in the corroded condition.

prex
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[SnTMan]

soletto, make your life simple, see Appendix 1 for OD formulae.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[soletto]

thx.... so than asme is not consistent in my eyes because according note 19 R stands for nominal inner radius.

What is nominal inner radius

yea that would be a solution but who wants to have an easy life

 

[racookpe1978]

What did your boss/supervisor say when you asked him?

YOUR company should have specific guidelines for THEIR industry and THEIR specifications for the pipe material, fluid/pressure/temperature/class of service THEY have bid for in their price estimates.

What is your background and number of months of engineering experience? it will make it easier to discuss things and details if we know how to address "basic" issues like actual diameter, nominal diameter, minimum diameter, mill tolerances, etc.