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Full Pen Weld Accessible from One Side Only 2
- Thread starter kslee1000
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2
- #2
kslee1000;
There is no simple answer, it is really application specific. If the plate contains a through-wall crack, weld repair can be performed from only one side. The crack would be removed by local excavation, similar to a V-shaped cavity.
Crack removal needs to be carefully performed to avoid having too large of an opening once you have reached the full thickness of the plate.
There are several approaches to weld restoring a cracked plate from having access to only one side. One method uses an open root butt, which means after the crack has been completely removed by reaching the other side of the plate you close the opening using the GTAW process. This requires great welder skill because you are essentially using single passes of weld metal to bridge the opening left behind when you removed the through-wall crack.
A second approach is to remove the crack until about 1/8" of ligament thickness is remaining at the base of the excavation. The GTAW process would be used to consume the crack within the 1/8" thick ligament, and fill the remaining excavation with weld metal.
A third approach is to open the base of the excavation large enough to insert a backing strip. Tack weld into position, and weld restore the excavation using the backing material.
The problem with all three methods above is that you cannot back grind the weld on the side of the plate that is not accessible. In reality, you might not achieve a full penetration weld joint with these methods.
There is no simple answer, it is really application specific. If the plate contains a through-wall crack, weld repair can be performed from only one side. The crack would be removed by local excavation, similar to a V-shaped cavity.
Crack removal needs to be carefully performed to avoid having too large of an opening once you have reached the full thickness of the plate.
There are several approaches to weld restoring a cracked plate from having access to only one side. One method uses an open root butt, which means after the crack has been completely removed by reaching the other side of the plate you close the opening using the GTAW process. This requires great welder skill because you are essentially using single passes of weld metal to bridge the opening left behind when you removed the through-wall crack.
A second approach is to remove the crack until about 1/8" of ligament thickness is remaining at the base of the excavation. The GTAW process would be used to consume the crack within the 1/8" thick ligament, and fill the remaining excavation with weld metal.
A third approach is to open the base of the excavation large enough to insert a backing strip. Tack weld into position, and weld restore the excavation using the backing material.
The problem with all three methods above is that you cannot back grind the weld on the side of the plate that is not accessible. In reality, you might not achieve a full penetration weld joint with these methods.
metengr,
You state... "A second approach is to remove the crack until about 1/8" of ligament thickness is remaining at the base of the excavation. The GTAW process would be used to consume the crack within the 1/8" thick ligament, and fill the remaining excavation with weld metal."
Wouldn't there be a serious problem with the crack extending beyound the weld pool? I have seen a number of instances wherein welders fail to grind deep enough to remove the crack and the crack propogated during welding operation. In these cases it was the SMAW process, not GTAW.
Joe Tank
You state... "A second approach is to remove the crack until about 1/8" of ligament thickness is remaining at the base of the excavation. The GTAW process would be used to consume the crack within the 1/8" thick ligament, and fill the remaining excavation with weld metal."
Wouldn't there be a serious problem with the crack extending beyound the weld pool? I have seen a number of instances wherein welders fail to grind deep enough to remove the crack and the crack propogated during welding operation. In these cases it was the SMAW process, not GTAW.
Joe Tank
Joe Tank;
The 1/8" thick ligament would only apply if the crack is entirely through-wall on the side of the plate you cannot reach. It is presumed that the side of the plate that could not be reached contained a crack. If the crack was on the accessible side of the plate, it could be entirely removed and the excavation weld restored
The reason I suggested using the GTAW process is that the heat is more localized with this welding process and what you are attempting to so is to consume the crack with no filler metal within the 1/8" thick ligament section. Yes, this is risky because depending on the contaminants along the crack surfaces, problems could occur.
The 1/8" thick ligament would only apply if the crack is entirely through-wall on the side of the plate you cannot reach. It is presumed that the side of the plate that could not be reached contained a crack. If the crack was on the accessible side of the plate, it could be entirely removed and the excavation weld restored
The reason I suggested using the GTAW process is that the heat is more localized with this welding process and what you are attempting to so is to consume the crack with no filler metal within the 1/8" thick ligament section. Yes, this is risky because depending on the contaminants along the crack surfaces, problems could occur.
- Thread starter
- #7
I would like to add one caveat to the post by metengr[/].
If the crack is emanating from the ID a vessel or component that is sees cyclic service there should be a concerted effort to establish the ends of the crack. Assuming this is a fatigue failure the aspect ration of the inside length to outside length could be large, 3::1 isn't uncommon. It is also not uncommon for this type cracking not to be continuous toward the ends.
If the crack is emanating from the ID a vessel or component that is sees cyclic service there should be a concerted effort to establish the ends of the crack. Assuming this is a fatigue failure the aspect ration of the inside length to outside length could be large, 3::1 isn't uncommon. It is also not uncommon for this type cracking not to be continuous toward the ends.
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