The Electrodes Left in the Feeder
A pressure-vessel shop is welding a 2-in.-thick A516 Grade 70 shell course with E7018-H4R electrodes. The electrodes arrive in hermetically sealed containers and are stored in a holding oven at 250 F. At 6:00 a.m. a welder takes approximately 50 lb from the oven, opens the container, and places the electrodes in an unheated wire feeder at the work station. The ambient temperature is 85 F and the relative humidity is 80%. At 4:00 p.m. the same electrodes are still in the feeder and are used to complete the root pass and part of the fill on a longitudinal seam. The welder says the electrodes feel dry and the shop's procedure does not state an exposure limit. The vessel is designed for wet H2S service and the customer specification requires low-hydrogen practice. The seam is scheduled for RT tomorrow.
1. Are the electrodes acceptable for use after 10 hours in the feeder?
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No. E7018-H4R is a low-hydrogen electrode, and the H4R designation applies to the product in its sealed condition or in proper storage, not after 10 hours in an open feeder at 85 F and 80% relative humidity. Low-hydrogen electrodes pick up moisture from the atmosphere, and the coating's moisture resistance delays but does not eliminate that pickup. Once the container is opened and the electrodes are exposed, the shop must follow a qualified exposure limit, typically a few hours at ambient conditions or continuous holding in a heated oven. Ten hours is well beyond normal ambient exposure limits. The welder's judgment that the electrodes feel dry is not a technical acceptance criterion. For a 2-in. A516 Grade 70 seam in wet H2S service, moisture pickup increases diffusible hydrogen and the risk of hydrogen-assisted cracking and sulfide stress cracking. The electrodes should be removed from service.
2. What records and immediate actions should you require?
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I would require the electrodes to be quarantined and not used for production. I would obtain the electrode lot number, the manufacturer's storage and redrying recommendations, the holding-oven chart, and the shop's exposure log, if one exists. If the electrodes are to be salvaged, they must be redried in accordance with the manufacturer's instructions, typically at an elevated temperature for a specified time, and then returned to a holding oven at the qualified temperature; redrying cycles should be limited as the manufacturer allows. If the electrodes have already been used in the seam, the seam becomes a nonconformance. I would require RT of the completed portion, and because the vessel is for wet H2S service, I would consider hardness testing and a hydrogen bake-out or other hydrogen-control measure recommended by the engineer. The NCR should state the exposure time, humidity, and disposition.
3. What should the welding procedure specify to prevent this in the future?
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The WPS should state the electrode classification, the required storage condition before opening, the maximum ambient exposure time after opening, the holding-oven temperature, the maximum number of redrying cycles, and the method for tracking exposure. It should also require that electrodes be returned to the holding oven at the end of the shift or after a defined period, and that partially used containers not be left in unheated feeders. The procedure should assign responsibility for recording the time electrodes leave and return to the oven. For wet H2S service, the procedure should include the low-hydrogen practice and any hardness or hydrogen-control requirements. The welder should be trained on why the exposure limit exists, not just told to keep electrodes dry. The inspector should verify the oven chart and exposure log at the start of each shift, not only after a problem is found.