316L with CA6NM 3

[chtimi]

I have to weld a pipe ( vent, drain, flushing ) in 316L on a pump casing in martensitic steel CA6NM.
What do you suggest for filler métal. I don't want to do a postweld heat treatment, because my pump casing is machined.
Thank you for your help.

JL

 

[Carburize]

What kind of service conditions will this be used in?

Typically the as-welded heat affected zone in CA6NM is very hard and this is unaffected by the choice of consumable.

 

[metengr]

Depending on service conditions, have you looked at a threaded connection versus welded?

 

[GRoberts]

The most common practice is to have the bosses where pipe attachments will take place overlayed with 309L at the foundry, then given a PWHT. Subsequent welding of a pipe to the overlay will not require PWHT. However, it is a little to late for that now. Besides the risk of cracking or service failure depending on your environment, it may be prohibited by code, so check that out also. If you have to weld without PWHT, which is not recommended, but is sometimes done under certain circumstances, you would want to use an austenitic filler metal like 309L, or nickel based like Inco 82 or Incoweld A (NiCrFe-2) so that even though you will have a hard HAZ, less hydrogen will diffuse into the HAZ, thus reducing the likelihood of cracking. It would also be beneficial to weld with a temper bead technique. Deposit a layer of 309L/Inco over the area to be attached to, then grind half of it off, and weld another layer of 309/Inco over the first layer so that the HAZ of the first weld will be tempered by the second one. (This technique is described further in ASME Section III) Then attach the pipe to the 309L/Inco overlay. The lower the carbon in the pump case, the better off you are also.

 

[unclesyd]

Check out this thread.
thread725-31486

Also this alloy is used to weld your material.
409t1-1/4a
UNS W40931
Specifications
AWS: A5.22 PWHT required

If possible I would use a straight thread nipple/fitting and then a small seal weld with an alloy that would satisfy your requirements. You can weld a couple of small test tabs in inconspicious spots around the periphery of the flanges and see how the behave. We had very good results welding with a proprietary alloy similar to 312 SS on our 410 SS equipment. This was used only for strength not corrosion resistance.

If your casting has been HT previously I wouldn't think that an 1100°F PWHT would affect the dimensions.

What type and how big is your pump?

 

[chtimi]

thank you for your answers. In fact it's a centrifugal pump, and liquid pumped is hydrocarbon @ 57°C/85°C with H2S.
Nace is applicable.

JLuc

 

[GRoberts]

If you are required to comply with NACE, (23 max HRC), I don't think you will get there without a full double temper of 1250/1125 (temperatures may vary slightly). Occasionally, you will even have a hard time getting there with even the double temper.

 

[metengr]

As mentioned earlier and what unclesyd alluded to, could you thread a nipple into the pump case using straight pipe threads and instead of a seal weld, use some type of chemical resistant Teflon tape or other suitable joint compound that would provide a leak tight seal at these operating temperatures? You did not mention if this will be installed on the suction or discharge side of the pump case.