Substitue Material for SA 234 for Boiler U-Bends 1

[Metcorr]

We are evaluating the use of SA 106 Gr C in place of SA 234 WPC for a boilers U-bend application. The SA 234 WPC and SA 106 Gr C have almost identical chemical composition and often used in u-bends for boilers also. In our case, as per the original design application, the boiler tubes are of SA 106 Gr C but the U-bends are of SA 234 WPC. Due to non-availability of SA 234 WPC in the market, we are evaluating the alternate SA 106 Gr C for u-bends.

During our internal discussions, it was mentioned that SA 106 Gr C have some grain growth issues when the pipe is bend during subsequent heat-treatment.

Would appreciate sharing of any concerns if you may have regarding the use of SA 106 Gr C in place of SA 234 WPC. Any input regarding the use of SA 106 Gr C in U-bends for boiler application would be greatly welcomed. Also, if someone can enlighten us as to why SA 234 WPC was specified for U-bends while boilers tubes are of SA-106 Gr C. Thanks

Best regards,
Metcorr

 

[metengr]

There should be no issues with grain growth because the bending should be done hot to achieve a 180 degree hairpin bend with no post bend thermal treatment. I doubt the bending would be done cold because of wall thickness concerns. Second, SA 234 is for welded fittings, which is applicable for a u-bend shape.

 

[Metcorr]

Thanks Metengr.

The SA 106 Gr C, a possible alternative to SA234 WPC U-bend, is also to be welded to the tubes which are of SA 106 too. Do you see any concern using SA 106 Gr C instead of SA 234 WPC for U-bend application. Thanks.

 

[metengr]

No. Have the u-bends formed hot and not cold. If cold bent, the tubes should be subjected to a thermal stress relief to remove cold work.

 

[Metcorr]

Hi Metengr,

The tubes are formed in hot state. Would appreciate if you could share what are the specific reasons that SA 234- WPC are preferred choice for u-bend compared to SA 106 grade C. They both have similar composition and in application where tube metal temperature is not above 400C, their hardness which is an important parameter from erosion prospective are also the same. Thanks.

 

[metengr]

SA 234 specification is for fittings, of which a hairpin bend would be considered as such and enables a clam shell welded design for hair pin bends versus bending seamless pipe material into a hairpin bend. I am not sure I agree that it is a preferred choice rather an option.