We are going to begin working on the qualification of a GTAW weld procedure for the welding of 1-1/2" thick Hastelloy plate. We will be attempting the flat position on 3/4" plate, using 1/16, 3/32 & 1/8" filler rod and 3/32" 2% thoriated tungsten electrode to accomplish this. The amperage range will be 75-130 and the voltage 10-16. The cover gas will be 100% Argon at 15-30 CFM. This will be done manually and we plan an interpass temp of 300deg F. Max.
My question is this:
Does this look adequate or are we headed for problems?
Sounds like alot of work.
Why not GMAW?
Because the parts get highly polished & then electro-polished to a mirror finish of 3-6Ra. This is an old standard method in pharmaceutical tank specification/fabrication.
We have had pretty good luck with SMAW on hastelloy with NiCrMo-10, passing X-ray and PT. It sounds like your main concern may be surface defects that ruin the polished surface? If so, what about doing the root & 1 or 2 more passes with GTAW, fill to within 1/8" or so of the surface with SMAW or GMAW as suggeted by others, then capping with GTAW to assure a good surface finish?
Our customer will not accept it, nor do we think it would be worth it as the joints to be welded are approx. 4" long & would require runoff tabs and repairs to cleanup both ends after scarfing them off.
these are some additional points you should consider :
1. cleanliness of the joint and the filler material is of utmost importance.
2. while shielding and purging, the level of oxygen content in the gas should 0.001% max.
3. the heat input to be kept to 1.5 kj/mm max.
hope the above would be helpful
Thanks. We consider the first (2) items as standard. The heat input control would usually not be an issue, however that is one of my main concerns for this material/posting. The production parts are to be in-process radiographed. This is on the customer drawing so I would guess they have had some cracking problems as small amounts & diameter porosity would be allowable per the ASME Section VIII code as long as they are scattered and not linear.
I with Lawrence why not GMAW, besides you will be there for hours just getting the puddle started, you may also want to consider Helium as a shielding gas.
Bill McBride
Quimby Welding
Logic does not always take precedence. I'm sure we all have seen the case where you would need 1/2 the time to do it your way but the customer wants it his/her way.
Brad,
You will find an excellent reference to your questions from Haynes International. Go to http://haynesintl.com/pdf/h2066.pdf
John Folk
Thanks. I've received several PDF downloads from their site. I'll check out what I have and get this one if I haven't downloaded it yet.
Brad,
Inch thick Hastelloy plate (I'm assuming a beveled groove weld, am I correct?) is going to take a long long time to weld even with 3/32 electrode and a 1/8 filler wire. A gtaw root with gmaw fill and cap sounds reasonable. To produce a fillet profile suitable for inch thick material your going to need a number of stringers with GTAW. While a spray transfer mig pass puts a bit of heat into the part it will be less cumulatively than all the passes necessary with gtaw. Either process should be fully able to meet your inspection criteria.
Fillet or Grove, distortion will also be a big factor with multiple gtaw passes.
If you do go the gtaw route, (assuming AMS 5798 filler) power wire wheel the weld surface between each pass at a minimum. Any oxide (even with good coverage there is some) can cause linear indications, poor sidewall fusion etc. Has-X is particularly sensitive in this regard (even thin sheet), welding over any visible discontinuity will be the cause of time consuming rework.
Brad,
Another thought occured to me but I just don't know enough about what your doing.
If your work is repair of wear areas and your qualification is a build up/fill in type, than GTAW is the best choice and there are a few specific process controls and techniques that can be brought to bear if your parent material is subject to lammelar tearing or underbead cracking in the HAZ. These process controls have been proven effective in Cast HIPPED Inco718 (hot isostatic processed) and Waspelloy castings.
If your situation is similar to the above let me know.
We are qualifying a GTAW weld procedure. The test plate will be 3/4" thick C-22. The filler wires will be 3/32 & 1/8". The bead type will be stringer. Interpass temp will be 300 deg F max. The cover gas will be 100% weld grade Argon. The parts we are welding cannot be done with the processes you all suggest. Our customer and the cost of the parts/rework don't justify the risk to them. They have to EP our welds. It's their material/reputation/product. They "drive our boat" so to speak.
Ok ok. I'll quit trying to talk you out of Tig :)
Sounds like your doing things right.
If your Tig torch is water cooled it will handle a 1/16 tungsten electrode up to your 130 amp max with a more concise and directional arc than the 3/32. This will help limit the HAZ. A big gas lens like this: http://store.weldingdepot.com/cgi/weldingdepot/45V24-29.html or maybe even a trailing shield is advisable. The big cup and collet body is heavy but not too heavy for a 4 inch weld. The big gas lens is nice for the extra big puddle and the fat 1/8 wire.
By the way, keeping that wire under the argon shield between each dip is really important too.
You know how much welders like to use a trailing gas shield, etc.? I will advocate a large cup and lens. Thanks for the help and interest. Also, I agree that a TIG root, MIG intermediate passes and TIG cover layers would be the best. The customer machines some of the cover off and makes a groove for a seal ring. All of those surfaces have to meet the defect free EP finish requirement. Great work. It is a slow process when working to achieve their requirements.
Thanks to you and all who responded.
Brad
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