M.A.P.NC is Governed by a Flange !

[rkdpv]

What should we do when MAPNC is governed by a standrad flange.
Why mawap or mapnc should not governed by flange and what should we do in that case?

Regards

 

[SnTMan]

rkdpv, your situation is not that uncommon, and unless a customer spec or something prohibits the flange limiting, there is no practical reason it can't. Something has to limit, after all.

If, on the other hand, it is not permitted to limit, and since is the N&C, you have few options. You can change the flange rating or the material.

Regards,

Mike

 

[jte]

I don't recall ever seeing a spec in which the limiting component on MAP was restricted (note to self: check draft revision of spec on desk). MAWP restrictions - yes, as discussed extensively in previous threads (rkdpv - do some searching in this forum and forum292 for those threads).

I'd be curious as to what the difference in MAP is between the flange(s) and the next limiting non-standard flange component. Let's keep in mind that MAP is essentially used only for setting a hydrotest pressure.

Presuming that "standard flange" refers to an ASME B16.5 flange and that the vessel code is ASME VIII Div. 1, the hydrotest (adjusted for temperature...) is going to be 1.3*MAP. I would suspect that if you use the MAP of the next limiting component to set the hydrotest pressure, that pressure will still be below the 1.5*(flange rating) which is allowed for a B16.5 flange.

So... avoid an issue with the client and just set the hydrotest pressure based on the next limiting component. What percent increase in hydrotest pressure are we talking about anyway?

jt

 

[rkdpv]

Thanks all..

Jt: thanks, good option, can we set hydrotest pressure based on the next limiting component? Is this permitted in ASME code?

Regards

 

[jte]

ASME VIII does not place an upper limit on hydrotest pressure. You should, however, check on the stresses during hydrotest - as, depending on which Division, these may be limited. As long as you're below 1.5* flange rating, don't bother checking the flanges.

Can you confirm which code you are working to, and which flavor flanges you are using?

jt

 

[rkdpv]

jt
I am using ASME sec. VIII div 1.
and flanges are standard ASME B 16.5.

Thanks

 

[curtis2004]

Hi everyone,
In my opinion if your limiting item is standard flange, then this will be MAWP of your vessel, IMHO.
For hydro-test pressure you have to calculate by the following formula: Pht=1.3 X Pmax70
where Pmax70 is max pressure of your flange at 70 degree F.
Please correct if I'm wrong.
Thank you,

Curtis

 

[jte]

Curtis-

I believe you're confusing MAP and MAWP. Do you see anything technically wrong with the path I suggested above?

jt

 

[pvessel]

curtis2004,

You forgot to include the temp correction factor for the reduction in allowable stress @ higher temps.

So you need to multiply 1.3*(Sa@RT/Sa@MAWT)*MAWP.NOTE: Use the lowest ratio for vessels constructed of multiple materials, so as to not overstress the weaker materials of construction. This causes the hydrotest pressure to remain the same or increase & stress the PV @ RT at the same levels as @ the MAWT. UG-99 (2)(b)

I do mostly Div2 & Div3 designs @ temps up to 1300°F & pressures up to 200,000 psig, but this should always be accounted for even though for most people the fraction =1 & doesn't make any difference.

 

[curtis2004]

Hi everyone,

In case of standard flange we do not have "S" but only "Pmax" at certain temperatures (It's already given maximum pressure flange can accept at diff. temperatures). I also had a flange limiting MAWP for a vessel. What I did is I used Pmax of flange as a MAWP. I calculated hydrotest pressure by multiplaying Pmax for a flange at 70 F. That is how I dealt with this issue.

Curtis

 

[vesselfab]

if you are using ug-99(c) to base your hydro you use
1.3 time map new & cold (no need for the stress factor) as you have already used lower temp stress to figure map

if you are using a standard hydro 1.3 times mawp hot & corroded time ( stress at room temp / stress at hot temp)