Pressure Design Thickness of Con or ECC Reducers

Option 1: Carry out a force balance along a theoretical section plane down the centre of the pipe at the two diameters either side of the reducer, and calculate the minimum wall thickness in each of the cases of the smaller and the larger diameter. Choose the greater wall thickness for the reducer, making sure that it matches the pipes either side of it. If it doesn't, go up in thickness until it does.

Option 2: telephone the local piping systems distributor and ask.

thanks

Rocco..

Read ASME B31.1/B31.3 and B16.9 carefully...

In essence, they state, if the straight piping wall thickness is carefully evaluated for the required design temperature and design pressure AND the matching reducer is constructed according to ASME B16.9.... THEN no detailed pressure evaluation of the component (reducer or elbow or whatever)is required.

Concentric or eccentic reduces.... makes no difference. If they match the wall thickness of the adjoing pipe AND the piping wall thickness was properly evaluated, then it is acceptable.

Why are you performing this evaluation ?

Do you have any piping "line specifications" fo the system in question ?

Thank you for your answer,

ASME B31.3 says "Some of the standards for components in Table 326.1 (e.g., ASME B16.9 and B16.11) state that pressure-temperature ratings are based on straight seamless pipe. Except as limited in the standard or else-where in this Code, such a component, made of a material having the same allowable stress as the pipe shall be rated using not more than 87.5% of the nominal thickness of seamless pipe corresponding to the schedule, weight, or pressure class of the fitting, less all allowances applied to the pipe (e.g., thread depth and/or corrosion allowance)."

My problem is, I have measured wall thickness of con and ecc reducers, which is 20 years in service, NPS 10 according ASME B16.9. I want know if measured thickness is still acceptable. So I must calculate the required pressure design thickness and compare it with measured thikness.

So my question is, can I used for calculation of required pressure thickness of these reducers the "Straight Pipe approach, eq. 3a", and evaluated required pressure thickness at both side of reducer (I mean start or run and end of reducer)?

Or what is the procedure? If you can write me example.

Thanks

Ahhhha ! We now understand your question.! ! You have an existing system !

The 87.5% mill tolerance rule only applies to new systems not yet constructed. The purchaser may get new piping that seems "light" on wall thickness, but meets the piping mill's contract requirements.

Since you have an existing system this does not apply to you.

I suggest that you use the existing methodologies available in many of the "fitness for service" programs available.

Review the paper on this site by Jaske - Shannon: www.fitness4services.com

API Recommended Practice #579 should be useful also.

Also see the services listed under www.carmagen.com

Thank you for interesting suggestions ,

in paper which you recommended to me, seems eq. (6a or 6b) for min. required wall thickness just like eq. for straight pipe (little diferences). So can I applied this eq. at any point of reducer's wall?

I ask because I saw in EN 13480-3 (Metal industrial piping. Design and calculation), eq. for required wall thck at any point is in principle same as for a straight pipe but multiplied by reducer's elevation.

e = (P.Di / 2.f.z - P) . (1/cos ALPHA) ..........eq. 6.4.4-1

e - required thck at any point

P - internal pressure

Di - internal diameter

f - allowable stress

z - weld factor

ALPHA - reducer's elevation

Please help me decided which approach may I use for calculation. I would only know how to calculated the required min. thck of new reducer, beacause I want compare measured thck and required thck in the middle, start and end of reducer.

Thanks