The Case of the Botched Welds on a 16" Pipeline
The contractor, welders and inspectors were not following the code or Welding Procedure Specification (WPS) for 7010 electrodes on butt welds of a 16” x 0.250” wall pipeline. While welding, the adverse effects of “arc blow” (magnetism) altered the arc characteristics and caused problems. The volt meters and ampere meters on the unitized welding power supply bank did not work. The x-ray processor was dirty and film was improperly interpreted as required by API 1104 standards. Weld x-ray interpretations for were unnecessarily rejected.
Welders, inspectors and x-ray film interpretors should always follow the guidelines described in API 1104 Standard. Slag should be completely removed after every pass. The WPS was re-qualified, each welder’s performance tested, and the essential welding variables consistently monitored by the inspector. The welder test coupons were positioned 12” above the ground, same as welding on the actual pipeline. Only newly certified welders were allowed to weld on the pipeline. A welder was allowed only 2 repairs per day. The x-ray film processor and tanks were dirty and film viewers needed light bulbs replaced.
The essential welding variables in the WPS must be followed, particularly heat input and slag removal. Otherwise, there was a good chance of defective welds and the cellulosic slag was difficult to remove with a brush and chipping hammer. Weld beads were cleaned by wire-brushing before occasional grind cleaning between passes. When slag was completely removed at the root and hot-pass, slag entrapment rejects were eliminated. Welds must be accepted by visual inspectors before x-ray. The welding ground clamp was relocated to near the actual joint being welded on the pipe to prevent arc blow. Larger diameter electrodes required higher volts and amps and smaller diameter electrodes were preferred.
The Lessons Learned:
Welders must adhere to a proven WPS for the job. When a wire brush techniques were implemented to remove slag between passes, more welds were accepted. When x-ray film processors and baths were cleaned, at proper temperatures, and viewer light bulbs were replaced, more welds passed x-ray.