RFWN vs RFLWN Cost of manufacture

[CuMo]

I was designing a replacement vessel where
the flanges of the existing vessel were RFSO which allowed some compact design.
For the new vessel however the client has specified that RFSO are no longer acceptable and only RFWN or RFLWN are acceptable.
If I tried to substitute two of the main 20"NB flanges with WN the proximity of the flange to neck and neck to shell welds became too small.
So I thought I'd save us the hassle and opt for RFLWN flanges instead.
Now project engineers reported that RFLWN flanges will cost as much as 5 times more to buy in comparison to standard ASME B16.5 RFWN.
Flange material is ASTM A350-LF2-1.

I appreciate the fact that RFLWN is twice heavy and twice long compared to RFWN but there's no way I can justify
such great difference in cost in my mind. Especially for something that involves similar repetitive forging process,
similar machining and drilling process...
I'd think that 2 times or 3 times should sound reasonable but 5 times?

Is there such great difference in manufacturing process that would justify 5 times higher cost of a RFLWN flange?

Thanks!

 

[XL83NL]

Have you tried getting quotes from different suppliers for both flange types, to determine the actual price factor?

 

[LittleInch]

It would also suggest that RFLWN are not as popular as RFWN and hence need a special production run?

If they need to specially make only 2 of them I'm not too surprised at x5. If you asked for 20 or 200 then the unit price would tumble.

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

 

[XL83NL]

Have you factored in the cost savings you get for the added wall thickness of the LWNRF compared to the standard WNRF? Not saying that, for that reason, a LWNRF will always be more overall cost effective, but if youre talking cost savings, look at the whole picture (which would then also include 1 circ weld less, as you dont need to weld the nozzle pipe to the flange, and thus potentially 1 Xray picture less).
At smaller sizes (say up to 4" or 6") I can imagine LWNRF could still be stock items for standard materials (like 316(L), A105N, 350-LF2-1). If you go up in size I imagine they're custom order made.

 

[r6155]

If the proximity of the flange to neck and neck to shell welds became too small, what is the problem?

Regards
r6155

 

[CuMo]

Yes. We do usually get quotes from at least several suppliers.
And I bet I can beat our project engineers in finding a better deal but that shouldn't be my job neither I have the time to do it.
This is why I needed an external opinion.

Even if they were custom made - I can't imagine the company making them to start from scratch.
They will have the equipment to do it. But yes. I agree. Some variables can bring the price up dramatically.

Regarding the X-ray. Yes. This was one of the reasons I preferred LWN rather than WN.
The vessel has to be X-Rayed before and after PWHT.
And yet project engineers tell me that price for 2 OFF WN + X-ray before & after PWHT costs (let's call them) 1500 units vs 3000 units for a single LWN...

Anyway I have gone back to WN which will be more cost effective but less practical from my point of view...

Regarding the proximity of welds. From my experience - although it's not forbidden, it isn't the best practice out there
and if possible - should be avoided.

Thank you all for the input.

 

[XL83NL]

The issue with this, is that there isnt any such factor. It depends on too much things that can (significantly) impact the ratio, such as;
- material
- size
- timing; lead times and prices may vary from day to day
- stock items or not
- alloy surcharge
- location
- vendor

Only years of experience will tell you which solution (WNRF or LWNRF) is best for your application, taking into account all things that play a role (not only economics play a role here). Even when you have mastered that experience, I doubt if factors can be given to these ratio's.

What's the background of your project engineers, and what track record do they have to have credibility when it comes to assigning such factors?