Personnel training and qualification
In an effort to ensure fabrication would commence on a solid foundation, a dedicated group of experienced pipe welders were selected to undergo a period of training and qualification. The training encompassed both the handling practices and behavior characteristics associated with welding copper piping.
These welders had previous experience welding carbon & stainless steel with the gas tungsten arc (GTAW) welding process. They spent several weeks honing their skills at Welders qualification and training center, MFY. The extra training and experience gained from being in a totally different working environment provided fruitful results. Each welder successfully earned an ASME Sec IX 6G qualification. Each qualification was performed in the presence of an independent third party, namely Lloyds register of shipping and client (ONGC) representative. On completion of all testing, appropriate certificates were issued.
Welding procedure qualification
Following the training phase, a welding procedure was identified for qualification.
Qualification was performed in the 6G position on NPS 4" pipe diameter x 6.35 mm wall thickness.
To optimise efficiency and enhance productivity in welding this material, the GTAW process was selected in conjunction with a 2mm dia welding wire. Welding procedure was required to be qualified in accordance with ASME sec IX Code.
Helium was selected as a shielding gas because, risk of oxide entrapment in the weld pool is greatly reduced and provides deeper penetration.
Preheating of the base metal is typically required to maintain the base metal at welding temperatures without preheating, the high thermal conductivity of copper results in excessive loss of heat away from the weld zone.
Following mandatory period of familiarisation because of the differences in welding technique, operability and weld pool behavior commonly associated with welding Coppers. The resultant weld was then subjected to 100% visual, Dye Penetrant and Radiographic (x-ray) examination.
Following successful NDE, the weld was subjected to Tensile, Bend (180 deg) and Macro examination. All these tests were performed in the presence of an independent third party, LRS representative.
Safe welding
Copper alloys that contain appreciable amounts of beryllium, cadmium or chromium may present health hazards to the welder and others. Exposure to welding fumes containing these elements can produce adverse health defects. Fumes and dust of copper can cause irritation of the upper respiratory tract, nausea, metal-fume fever, skin irritation, and dermatitis and eye problems.
Precautions may include local exhaust ventilation, general areas exhaust ventilation etc.
---------------------------------B.Raghuram (MFY, QA & Welding Engg) January 2003---------------------------------------
No comments:
Post a Comment