E7018 Storage, Moisture Pickup and Delayed Cracking
A shop is fabricating moment connections for a four-story building. The WPS requires E7018 for every structural weld on 1 in thick A572 Gr. 50 plate. The 50 lb cans are opened on the bench, and the electrodes sit in an open tray beside the welder all day. The holding oven reads 110 °F. The shop is at 82 °F and 85% relative humidity, with the roll-up doors open to steady rain. The welder runs 3/8 in fillets with 1/8 in E7018 at 130 A, weaving about 1 in wide, and the plate has been sitting at 50 °F overnight. After a week, magnetic particle testing finds tight transverse cracks at the weld toes on several connections. The foreman had 'dried out' the damp electrodes by putting them in the shop's tempering oven at 500 °F for two hours and returning them to the tray.
1. List the deviations from correct low-hydrogen practice in this scenario and explain how each one feeds hydrogen into the joint.
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Low-hydrogen electrodes work only if the coating stays dry; every item here works against that.
- Holding oven at 110 °F instead of the 250–300 °F holding range, so electrodes are warm but not dry.
- Cans opened and left in an open tray all day: E7018 is normally limited to about four hours of exposure at ambient before reconditioning, and 85% RH with the doors open to rain is about the worst ambient available.
- Damp electrodes returned to the tray after a 500 °F bake that does not meet the reconditioning requirement, so they re-enter service still carrying moisture.
- Plate at 50 °F with no preheat: fast cooling produces a hard, crack-susceptible heat-affected zone, and hydrogen has nowhere to go.
- 1 in thick, highly restrained moment connections: thick sections and restraint concentrate diffusible hydrogen and triaxial stress at the toe, exactly where the cracks appeared.
- Wide 1 in weave: too wide for a single pass at 1/8 in diameter, giving poor fusion and slag entrapment and an inconsistent thermal cycle.
The cracks appearing a week later, at the toes, tight and transverse, are the classic signature of hydrogen-assisted cold cracking rather than a hot-cracking or overload problem.
2. Was the 500 °F re-drying adequate? Describe the correct conditioning regime and how you would verify it.
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No. Reconditioning temperatures for E7018 are typically on the order of 700–800 °F for a minimum of about one hour at temperature, per the electrode manufacturer; 500 °F for two hours does not drive off the moisture that has been absorbed into the coating, so the electrodes went back into production still wet. Overheating is also a risk - baking above the manufacturer's limit degrades the coating and can cause the coating to crack and spall.
The correct regime: keep unopened cans sealed and dry; hold opened electrodes in a holding oven at 250–300 °F; issue only what will be used in a short period and keep the rest in a portable oven at the point of use; observe the exposure limit (about four hours at ambient, per AWS D1.1 and the manufacturer); recondition only by the manufacturer's temperature/time, and do not recondition electrodes with damaged, rusty or oil-contaminated coating - scrap them.
Verification: a calibrated thermometer or thermocouple in the oven, not the dial; a written log of can number, date opened, oven in/out times and reconditioning cycles; and the electrodes are only as good as the record showing where they have been.
3. What must be done with the cracked welds and with the remaining electrodes in the tray?
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Cracked welds: hydrogen cracks are not repairable by welding over the top. The full weld and the crack must be removed by air-carbon-arc gouging or grinding back to sound base metal, past both crack tips, then inspected - magnetic particle or dye penetrant on the excavated area - before any repair weld is deposited. The repair is then made with the WPS preheat (typically 150–200 °F or more for 1 in Gr. 50 with high restraint), controlled interpass, stringer or narrow beads rather than a 1 in weave, and a hydrogen bake-out and slow cooling if the WPS calls for it. Because the cracking was delayed, the repaired region should be re-tested at least 48 hours after welding, not immediately.
Electrodes: electrodes that sat damp in the tray and went through an inadequate 500 °F bake should be scrapped, not reissued for structural work; the cost of a 50 lb can is trivial against the cost of rework. The rest of the stock should be reconditioned at the manufacturer's temperature, logged, and then held at 250–300 °F until issued. The shop should also re-examine its storage and issuance procedure, because the root cause was a system that allowed wet electrodes to reach a restrained 1 in joint.