Mick, for the sake of this discussion let's assume you are using the correct wire for whatever project you are on (EXXT-G is a multiple pass FCAW electrode and should be adequate). Full strength on a groove weld denotes full penetration. Full strength on a fillet weld is a leg length equal to at least 3/4 of the of the thickness of the thinnest plate being welded. In a perfect world full strength may equal gas tight, in reality it means no such thing. Gas tight means that the weld is good enough to be pressurized to some predetermined pressure. I have had jobs come into my shop like this and what the customer really wants is a good weld that will hold as much pressure as the A-36 and do the job it was designed to do for life expected of it.

Respectfully,
Mike Sherman
Shermans Welding

There is no way to assure the welds are gas tight just because they are full strength as Mr. Sherman indicated above. One thing that you could do to verify the welds are gas tight is to perform vacuum box leak testing. In some ductwork specifications I have worked with customers specify this or some other form of leak testing.

Another method that is used by one of the fabricators I am currently inspecting products in is dieisel fuel leak testing. Diesel fuel is applied to one side of the joint and allowed to remain. After an adequate dwell time, the other side is inspected for bleed through. It works pretty well.

The fabricator is responsible for providing welds that are gas tight. This contractual requirement could be brought up if a duct were to leak in service. If no requiremnts exist for leak testing doesn't mean you shouldn't perform any. If I were the fabricator I would leak test since I am bound by the contract to provide such weld and diesel fuel testing is cheap. If I were the customer inspector (current position) I could not require NDE if not specified in the contract unless the option existed if I deemed it necessary and the cobtract allowed for optional testing.

Full strength and full penetration are not the same. Variables such as joint type (Butt, Lap, edge, corner, tee), filler metal strength, base metal thicknesses can help evaluate if a full strength weld can be achieved without a ful penetration weld. A butt joint with equal thickess pieces is assumed to be full strength if welded full penetration with filler metal equal in strength to the base metal.

The depth of bevel/groove, included angle, root opening, backgouging/backing method all are contributing factors to achieving full penetration.

Have a nice day


Gerald Austin
Iuka Mississippi.