mistakenly welded 25/35 Cr/Ni using a 25/35 high 5% tungsten wire

[dacf]

Hi, mistakenly welded 25/35 Cr/Ni tube using a 25/35 high 5% tungsten wire. Normally the wire would be 0.19% W. Anyone know the effect?? will the weld joint be too brittle??

appreiciate any comments

 

[metengr]

dacf;
The addition of this much tungsten could result in undesirable carbide formation along grain boundaries that will adversely affect mechanical properties and possibly corrosion resistance, depending on your application in service. I have seen literature that described alloy additions of tungsten behaving similar to alloy additions of molybdenum in Cr/Ni alloys.

I have attached the following article that describes the affects of various alloying elements in Ni-base alloys. Carefully review the section on carbide formation based on alloy additions of tungsten and other carbide formers.

http://www.key-to-metals.com/Article101.htm

For your unique situation, you should probably weld a coupon using the 5% W wire composition and perform the necessary mechanical tests to confirm affects. Otherwise, completely remove the weld metal and start over.

 

[stanweld]

We qualified procedures on HP Modified using the 5% W wires about 20 years ago per ASME B31.3 & IX. No reports of premature failure were ever recieved from the Owner/Operator. We have not used the procedure for reformer tubes for about 10 years, largely due to availability and one Client's preference for E/ERNiCrCoMo-1 filler metal for the service.

 

[dacf]

Cheers guys, I understand that we actually welded the root autogenously so I think we will grind off the cap and create a small v, then reweld with correct wire to dilute the effects of the W. This way we will not have to perform a complete cutout.

 

[VeryPicky]

What is it that you welded dacf?

Putting Human Factor Back in Engineering

 

[stanweld]

Just a footnote; the 5%W additions were common to HP modified cast alloys by ABEX and APV.

 

[metengr]

stanweld;
You have peaked my interest. Have you found a reason for the increase in tungsten to 5% for the modified HP alloys? Were they looking to offset 2% Si content by increasing tungsten?

I understand the benefit associated with increased creep rupture strength with minor alloy editions of tungsten. In fact, Oak Ridge National Laboratory was performing experiments on heat resistant (HK and HP) grades of austenitic stainless steel castings but no mention was made of increasing tungsten additions to 5%, versus the standard range of 0.2-0.5% W. Any ideas?

 

[stanweld]

metengr,
The W additions were reportedly made to increase resistance to carburization. In my review of the Creep properties of about 15-20 different HP mod alloys with and without W, I could see no real difference in Creep properties with the higher W additions.

 

[ijzer]

The 5W version of HP40 was indeed developed for cracking furnaces ,to improve the carburisation resistance. The disadvantage is that it is already very brittle in new (as cast) condition. After aging it becomes even worse.