Solid CRA Nozzle Welded to CS Vessel
Solid CRA Nozzle Welded to CS Vessel
(OP)
Code: ASME
Mat'l: Predominantly A516 Gr 70 + 3mm 316L
Location: Offshore Platform
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Due to wet CO2 corrosion, most of the vessels require 316L internal cladding. The reservoir temperatures are high and in some cases up to 140 deg C.
After speaking to some vessel fabricators, they admitted that when it comes to smaller nozzles, it is almost impossible to get a less than 8% ferrite content at the weld overlay fusion line. Thus these smaller nozzles will fail the chemical analysis required.
The best and easiest solution to this problem will be to use solid CRA.
If solid CRA nozzles are used, the temperature then becomes an important factor in selecting the right material. As the reservoir temperature is high, the temperature could vary between 40-140 deg C depending upon the service this vessel is in. The CRA material could be a choice between stainless steel, duplex and superduplex.
Question:
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Is there any problem welding stainless steel, duplex or super duplex nozzles onto a internally cladded carbon steel vessel? Is welding a concern? Is there anyting else regarding welding of dismilar material that I need understand before taking this approach?
Mat'l: Predominantly A516 Gr 70 + 3mm 316L
Location: Offshore Platform
========================================================
Due to wet CO2 corrosion, most of the vessels require 316L internal cladding. The reservoir temperatures are high and in some cases up to 140 deg C.
After speaking to some vessel fabricators, they admitted that when it comes to smaller nozzles, it is almost impossible to get a less than 8% ferrite content at the weld overlay fusion line. Thus these smaller nozzles will fail the chemical analysis required.
The best and easiest solution to this problem will be to use solid CRA.
If solid CRA nozzles are used, the temperature then becomes an important factor in selecting the right material. As the reservoir temperature is high, the temperature could vary between 40-140 deg C depending upon the service this vessel is in. The CRA material could be a choice between stainless steel, duplex and superduplex.
Question:
=========
Is there any problem welding stainless steel, duplex or super duplex nozzles onto a internally cladded carbon steel vessel? Is welding a concern? Is there anyting else regarding welding of dismilar material that I need understand before taking this approach?





RE: Solid CRA Nozzle Welded to CS Vessel
Regarding DMW, the cladding will need to be stripped back on the carbon steel substrate to facilitate DMW along with a proper selection of filler metal. The filler metal could be 309L or 309MoL for joining either an austenitic stainless steel or duplex stainless steel nozzle to the carbon steel vessel wall.
Post weld heat treatment (PWHT) requirement per the Code of Construction needs to be reviewed and will only apply to the carbon steel vessel wall. If you elect to use duplex ss as the nozzle material, PWHT should NOT be performed. In this case, the carbon steel weld prep along the opening of the nozzle penetration would need to be buttered first using 309L and locally subjected to post weld heat treatment before welding in the duplex ss nozzle. This is why I would use a 316L nozzle material in lieu of a duplex or superduplex ss. Once this DMW operation is completed, a weld overlay of 309L will be necessary to protect the nozzle attachment weld up to the solid CRA nozzle and surrounding exposed base metal that was stripped of cladding.
RE: Solid CRA Nozzle Welded to CS Vessel
RE: Solid CRA Nozzle Welded to CS Vessel
We have 14, 100,000 gal 304/316 SS clad reactors and all nozzles are solid CRA alloys. There are no clad nozzles in these vessels.
When we have to replace or increase a nozzle in size we use essentially the same procedure as described by metengr. We stay with the 309LMo if the clad is 316/316L SS.
RE: Solid CRA Nozzle Welded to CS Vessel
Another silly question. Why should the chemical composition at 1mm above fusion line matter when the other 2mm has the right composition (i.e 316L)?
Thanks.
RE: Solid CRA Nozzle Welded to CS Vessel
Regarding your second question, I agree. Dilution of the weld overlay with the base metal will be a factor at 1mm from the weld fusion line.
RE: Solid CRA Nozzle Welded to CS Vessel