Welding Titanium Sheet, Plate, and Tubing by GTAW Process
1. Scope
1.1 This standard provides procedures for gas tungsten arc welding titanium sheet, plate, and tubing.
4. Safety
4.2 Titanium is explosive and may ignite spontaneously if dispersed in air. Sawing or fine machining operations ignite titanium easily and it burns with brilliant incandescence. Coarse turnings and chips of the order of 0.8 by 4.8 mm (
1/32 by 3/16 inch) and larger are difficult to ignite and present only slight fire hazard. Take precautions when machining, grinding, or otherwise preparing titanium for welding or fabrication operations to assure that fine titanium chips or dusts do not accumulate. Carbon dioxide, foam, dry chemical, and vaporizing liquid type extinguishers are not effective on titanium fires. Good results can be obtained with extinguishers containing agents developed specifically for use on combustible metal fires. Also take care when oxy-fuel cutting steel in the vicinity of titanium and its alloys5.1 The materials shall be as following:
a. Sheet and Plate: ASTM B265, Grades 1 to 4.
b. Pipe: ASTM B337, Grades 1 to 7.
c. Tubing: ASTM B338, Grades 1 to 4.
d. Filler Rod: AWS A5.16, ERTi-1.
e. Shielding Gas: Welding grade argon of 99.95 percent minimum purity.
6. Cleaning
6.1 Degrease the titanium joint to be welded along with the adjacent area to be heated, to a 51 mm (2 in) minimum distance from weld on both sides, and the filler rod, after shearing, machining, or draw filing. Remove all scale and other foreign material. Lint free gloves are recommended to eliminate oil and moisture from handling. Dust and fingerprints on the material will result in unsatisfactory welds.
6.1.1 Titanium has the ability to dissolve in its own oxide, therefore, clean the surface where weld metal will flow or surfaces that are to be melted, to a bright shiny metal prior to welding. Clean titanium exposed to normal atmospheric conditions develops a tightly adherent scale that has a slightly milky cast. Remove this material.
6.2 Use nontoxic and nonresidue forming solvents. Trichlorethylene or other chlorinated solvents shall not be used. Acetone, alcohol, or methyl ethyl ketone are acceptable but their flammability requires caution. Degrease jigs, fixtures, clamps, and other equipment.
6.3 Cleaning by alkaline wash or dip in lieu of solvent is permissible; careful and complete rinsing and drying shall be required. Dilute sodium hydroxide or proprietary alkaline cleaners may be used.
6.4 Clean and brighten welding rods before use, using the same solvents used to clean the base metal.
6.5 Where grinding is employed for weld preparation, keep the titanium surface temperature below 316
°C (600°F) (oxidation temperature); otherwise a brittle surface will result. It is desirable to use a wet air and water mist grindingtechnique. Grinder surface shall be steel free.7. Equipment
Direct current straight polarity (dcsp), supplied either by a constant current motor generator set or a rectifier unit, is most suitable for welding titanium. The power source shall be capable of maintaining the current within narrow limits. In addition, the machine shall have good control adjustment in the lower current ranges. Superimposed high frequency (hf) current is recommended for starting the arc. A foot pedal operated contact and current control is most useful. Make provision for torch gas flow before initiating arc (pre-purge) and after breaking the arc (post-purge).
8. Welding Technique
8.1 Standard GTAW welding techniques with direct current straight polarity (dcsp) are used to weld titanium. Pay attention to the protection of weld pool, weld bead, heat-affected zone (HAZ), and weld rod from contamination. Figures 9 to 15 in SES W13-F01 provide several designs of welding chambers, trailing shields with diffusers, cross draft baffles and weld cooling fixtures. It is sometimes difficult for welders to manipulate a GTAW torch with trailing shield attached. It may be easier to utilize a helper to provide gas diffusion over the hot metal using a diffuser. SeeFigure 1 for typical joint preparation. 8.2 Extreme care is required to keep the filler rod in the gas shield. The 'dip and dap' technique shall not be used as the hot end of the rod could become contaminated. If it does, cut off the contaminated rod.
9. Weld Quality and Inspection
9.1 The visual appearance of weld beads after cooling to room temperature is the best evidence of the quality of gas shield protection. A bright silver like metallic luster indicates a good coverage and no degradation. A straw color (light yellow) or light blue color indicates the weld was adequately shielded down to about 427
°C (800°F). Any embrittlement will be very slight. Dark blue, gray blue, gray, bright yellow, or white (scale) indicates sufficient contamination to warrant removal of weld and adjacent base metal. Progressively, remove the undesirable weld by wet grinding as indicated byreduction in hardness.10. Repair and Field Welding
10.1 Conform to the cleanliness and gas coverage requirements described above for repair and field welding of titanium.
10.2 Repair work on used titanium requires complete removal of corrosion products, or other extraneous matter from all areas and surfaces that will be heated during welding.
10.3 Repair work on defective welds necessitates complete removal of such welds and complete replacement of all damaged areas. Field welding requires extensive study and planning for inert-gas coverage.
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Dear All,
I have already post this question to you all, again I am making a remainder. I am in need of a sample WPS and PQR for Titanium welding . Consider the tube material SB 338 and grade 2 and the tube sheet is SB 265. I want to weld seal welding (tube to tubesheet) in GTAW process. Please if anyone have it please forward , it will be very much useful to me. Thanks .
Regards,
J.C.Andrews,
QA/QC Engineer,
Doha-Qatar.
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