Repair welding Titanium

Date 11-21-2007 16:31

Try the "kings" of titanium: Titanium Metals Corp. (www.timet.com)
They're very kind people (or at least they were with me), willing to help people who has doubts about handling titanium.
Giovanni S. Crisi
Sao Paulo - Brazil

By Lawrence (*****)

Date 11-21-2007 19:38

Professor Crisi is right

You need expert consultation for a project of the magnitude you describe.

Some investigation to discover why these very substantial joints cracked in the first place might have an influence on repair design.

By ssbn727 (*****)

Date 11-22-2007 07:20

Hi Larry, Giovanni!

I believe that you both have given sound advice to this gentleman but, one company that comes mind that handles these type of repairs worldwide: Titanium Fabrication Corporation of Fairfield, NJ.

Here's their website:
http://www.tifab.com/

They're the best in the business hand down!!! Check them out!!!

Respectfully,
Henry

By 803056

Date 11-22-2007 15:13 Edited 11-27-2007 14:38

I have some ideas on the subject, but I agree with the others. Go to a manufacturer of the material and ask for their input. The root cause of the cracks need to be determined to see what can be done to prevent them from reoccurring. Simply repairing the existing cracks will only result in more cracks in the future. A redesign can eliminate the reason why the cracks developed to begin with.

A structure as large as the one you described needs to be supported in a manner that won't introduce additional problems while the repairs are being made.

The welding of the crack is only a small part of the overall fix.

1) The vessel wall as well as the fillet welds to the supports will be repaired by welding.
   Retain the services of an engineer to determine the method and means of supporting the vessel during repairs.

2) How should the channels be removed from the shell? Best method for the field.
   You should be able to remove them with a cutting disk. Oxy-acetylene will cut titanium, but do you want to introduce fire, flame, and sparks into your working environment? Plus there is a lot of smoke generated.

3) How should the wall of the vessel be prepared for welding? Mechanical? plasma? etc.
   Use mechanical means of preparation to eliminate any surface oxidization from the plasma or oxy-acetylene. The material isn't that thick to begin with. I suggest the use of rotary files using an electric power tool rather than a compressed air powered tool. Compressed air has oil and moisture in it (contamination).

4) Chemical cleaning in the field? what product?
   Can't help you much with the chemical cleaning other than to warn you not to use anything that contains chlorine or other halides. Once the inside and outside surfaces are cleaned, don't touch them and wire brush them with a clean stainless steel bristled brush that has be completely cleaned with 90% isopropyl alcohol just before welding. The filler metal should also be cleaned with alcohol.

5)   Manufacture of trailing gas fixtures for GTAW?
   Make your own trailing cup. Use plastic to "tent" the inside of the vessel so that the root side can be purged with argon. You can also use a "tent" on the outside of the vessel to purge the area to be welded. The GTAW torches can be taped to wood dowels an placed inside the "tent" while the wood handles extend to the outside where the welder can manipulate them. Any openings the dowels pass through have to be sealed with tape.

6)   Any good practices to reduce oxidization of base material.
   See item 5. By the way, if the tent method is used, no trailing cups are necessary. The tent material should be clear plastic (like they sell for storm windows).

Titanium welds very nicely if it is properly cleaned and purged. Any contamination by materials that are vaporized by the heat of welding (dirt, oils, grease, finger prints, paint, etc.) will freely enter the molten weld puddle and contaminate the weld and base metal. Remember that the titanium is a reactive metal and will react with nearly any gas or surface contaminant. Once contaminated, the repair involves removing the weld and any unprotected metal surrounding the weld affected by the contamination. The major problem I've had with titanium is cleaning it and then keeping it clean while welding it. Welding is easy, cleaning is hard. A sure indication that your weld and base metal is contaminated and is when a piece of "scrap" used as a getter has any coloration other than silver to very light straw color on the surface of the weld or adjacent base metal.

Any advice given is only worth the price you paid for it. ;)

Best regards - Al

By canuckweld Date 11-22-2007 14:56

Thanks for the contacts.

By 803056

Date 11-27-2007 04:56 Edited 11-27-2007 14:35

I just received the December edition of the Welding Journal. There are two articles on arc welding titanium that may be of interest to you. I haven't read them yet, but I will. I did give them a quick scan and notice one listed a number of pointers such as cleaning, purging, and repairs.

I just read one of the articles. It is very basic and likely to be applicable to your project. There are three items I would question.
One is the use of an IR thermometer for checking interpass temperature and to ensure the shielding gas is being properly maintained until the welds have cooled sufficiently. IR thermometers can give erroneous readings from reflective (non-black) surfaces. I've seen errors in excess of 150 degrees F from the surface of nickel components.
The second issue is the maintenance of the shielding gas until the weld has cooled to 800 degrees F. My experience is that the shielding gas is maintained until the welded part has cooled to 450 degrees F or lower.
The last issue is the "purity" of the shielding gas environment. The article stated the purity of the gas has to be 99.995% pure (if I remember correctly) and I have no problem with that, but it appeared that that was also the "purity" of the purge or welding environment. I don't believe that was the intent. The quality of the purge has to be such that the oxygen content is reduced to less than 0.5% if memory serves me correctly. In any event, the article mentions welding on a piece of material before welding the actual part. That is sometimes referred to as a "Getter" and is used when welding in an envelop or chamber. Always a good idea to verify everything is working correctly. If all is well, the weld will have a shiny silver surface with no discoloration.

Lawrence is an experienced aerospace welder/instructor and can provide some excellent information on this subject or he may even take issue with some of my comments. On issues relating to titanium, I defer to his opinions.

Best regards - Al

By canuckweld Date 11-28-2007 11:42

Thanks for the information. I have not recieved the December issue yet. I have contacted the manufacture and received some good information but the field experience and advice from others is invaluable. We have also tasked our Mechanical department to analyze the reasons for the cracks and to design a better bracket. Thanks.