Welding Monel to Carbon Steel

Date 07-13-2004 17:41

There is likely a variety of nickel based filler alloys that may be used to make the monel-to-CS dissimilar metal weld. The filller metal must be austenitic, and ferritic filler metals must not be used. Look at specialmetals.com and nidi.org to research this.

Weld cracking with copper-nickel alloys can easily occur if the base metals and filler metals are not ABSOLUTELY clean. The only thing that should be on the metals is the metal itself (watch those dirty gloves and tools). Do what you can to assure absolute cleanliness. Emphasize relative low heat input welding methods; say GTAW and small diameter SMAW rather than SAW. Small stringer beads are generally better.

If the monel base metal is cracking (never seen this), there are probably issues with the material quality/cleanliness and/or heat input is too high.

By ewpatnode Date 07-15-2004 14:19

I contacted specialmetals to verify that the filler that we are suing is correct and it is. The weld rod is "MONEL Welding Electrode 190".

The gentleman that I spoke with was very helpful and he indicated as you did that we may have a problem with cleanliness; or possibly impurities in the castings themselves.

By GRoberts (***)

Date 07-13-2004 19:10

A494 M30C can have weldability issues if it is not refined/heat treated correctly at the foundry. Do you know if that heat of material had the weldability test done per A494 S22?

By ewpatnode Date 07-14-2004 18:49

According to ASTM A 494 Table 2; weldable grades such as M-30C are left as as cast (No Heat Treat). We did not specify a weldability test per A494 S22 (maybe we need to do that from now on).

The material certification that we received with the cast pipe lists the tensile strength, yield strength and elongation as 78,910 psi, 34,910 psi and 28.2% respectively. These are all higher than the minumum values called for by the ASTM 494 Specification for M-30C.

By MBSims

Date 07-17-2004 04:27

What is the phosphorous and sulphur content of the Monel and CS base metals?

By ewpatnode Date 07-19-2004 15:48

For the Monel the P & S contents were 0.013 and 0.003 respectively.

For the carbon steel the P & S contents were both 0.033

By MBSims

Date 07-20-2004 00:44

It sounds like the P + S content on the CS side is a bit high for the nickel alloy weld deposit. You might try buttering the CS side of the joint with E7018 to provide a barrier layer, then finish the weld with ENiCu-7.

By Niekie3 (***)

Date 07-18-2004 17:35

Hi Ed

As indicated in some of the other posts, S & P contamination is a real problem for Ni based fillers. If you have high levels of these, then you are bound to have problems. Another potential problem, is dilution with Fe. Theoretically Monel 190 can take up to 30% Fe into solution before cracking. While this should generally not be reached, it is possible if the welder is getting a lot more penetration on the C/Steel than the Monel side of the joint.

Another option is to use pure Ni rods, as these can take up to 50% Fe before problems occur. They do however generally show lower strengths.

Regards
Niekie Jooste
Fabristruct Solutions

By ewpatnode Date 07-19-2004 15:52

Niekie,

Thank you for your response; though this leads me to another question.

We used carbon steel backing rings when making the welds. Should we have used Monel backing rings or doesn't this make a difference?

Thanks,

Ed Patnode

By Niekie3 (***)

Date 07-19-2004 16:05

Hi Ed

It will definately make a difference. With C/Steel backing, you will get a much higher dilution of the filler metal with Fe. With Monel backing rings, it will be much lower. With C/Steel backing rings, it will be very possible to get to the 30% level of Fe, if the welder is getting a lot of penetration into the backing ring. If this is the problem, then the cracking should only be limited to the root. By the time the second run is made, the dilution should be below the 30% level.

Just as a matter of interest, with TIG and MIG welding, the maximum Fe dilution that can be accomodated is only around 15 - 20%.

Regards
Niekie Jooste
Fabristruct Solutions