Proposed 16 inch Main Steam Flange is Outside of B16.5 Class 2500 Table, Request Design Options 2

[racookpe1978]

Design conditions: Main Steam,
Service conditions: 450 psig at 905 degrees F.
Design conditions: 981 F at 1881 psig.
Pipe: 16 inch OD, 12.5 inch ID, 1.75 inch wall thickness to re-route and replace an existing main steam service pipe to a competitor's steam turbine that crashed.

One of my piping designers has proposed a "stretched" Class 2500 RFWN flange, scaled up from the B16.5 table for 12 inch 2500 class flanges, class 1500 16 inch flanges.
Flg OD = 32.50 inches
Flg thickness = 7.25 inch
Weld neck cone = 16 inch OD (at weld prep), 21.75 inch OD
(weld neck cone length ends 6.0 inch from the end of the weld prep)
Total Flg length = 1.5 in (weld prep) + 6.0 in (weld neck) + 7.25 (flg th) + 0.25 (RF) = 15.00 in.
BCD = 27.75 inches
Bolts = 16x (high strength studs)
RF = 18.5 inch OD, 12.50 inch ID.
Bolt holes = 16 x 2.625 inch dia
Flg Material = SA-182 F22

I'm skeptical, but could be convinced because his table of calculated stress values all are sat.

Do I have any options from a standard flange table for these conditions, perhaps API flanges or tongue and groove style faces?

 

[LittleInch]

First off what material are you planning to use?

I had a quick flick through 16.5 and at your design pressures and temperatures it's 1.5 upwards materials (e.g. A182) which gets close and not all of them. How you would weld that to your pipe might be an issue?

However some of the materials are so good at higher temperature all you would need is a class 1500 flange which comes in 16" size already?

Non mandatory appendix A to B 16.5 might be useful to check stresses etc.

API 6A only seems to go to 120C

You might find something like Vector compact flanges would design something for you, but analyzing flanges in FEA to ASME VIII always gets you very big flanges


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LittleInch]

Missed the A182 F22 material at the bottom of your OP. That won't quite make it into class 1500, but a different grade of A182 might.

Or if you could loose 30F from your design temp A182 F22 would be ok just at 1881 psi for class 1500.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MJCronin]

Why are the design conditions more than twice as high as the service conditions ?

How is this reasonable ???........ Or was an MBA somehow involved in selecting these values...

MJCronin
Sr. Process Engineer

 

[racookpe1978]

I cannot (logically) justify the large difference between operating and design conditions, but, it is the competitor's turbine the competotior's design spec's. We have at least been able to reduce the piping stresses to the turbine nozzle significantly by re-routing and improving support locations. That, with a much better disassembly process (added flanges, better location of flanges and spool pieces, and unitized support assemblies) should make outages shorter as well by reducing crane lifts and improving turbine and bearing access above and beside the splitline joint.

 

[keyen]

All: How economically feasible is it to get a small run of forgings made for these kind of flanges? Would you need custom forging dies? I assume you can't start with a block of forged A182 and just machine away until you're left with a WN?

OP: A design pressure four times higher than operating is weird. Is there a flange on the turbine you're tying into?

Sincerely,
A forging newb