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> Hydrogen controlled rods
ih100
post Jan 18 2018, 06:17 PM
Joined: 2-Jan 10



Perhaps one of our more technicAl contributors can answer this one for me, or put it to bed as an urban myth. I read on an American forum someone's stated opinion that unbaked 7018's are actually more prone to hydrogen embrittlement and cracking than 6013's. Sounds a bit questionable to me, and I can't find any other reference to this.
Technic Al
post Jan 18 2018, 06:58 PM
Joined: 14-Oct 03



There are 3 factors that combine to produce a hydrogen crack, a susceptible structure, high stresses and hydrogen. If any one of them is high enough the other two can be lower. The susceptible structure usually means hardness. If the weld is harder than the plate the crack is more likely to be in the weld, If its the other way and the plate is harder then its usually the HAZ that cracks.

7018 weld metal is usually slightly harder than 6013 weld metal, but wet 7018s are still likely to be lower in hydrogen than 6013s. Both are more than likely to be softer than the plate.

So as a general statement I would say 6013s are the most prone but there can be circumstances where 7018s can be more prone.

Hydrogen cracking is often talked about and considered in Standards and Procedure but in my experience its very rare. Ive seen lots of cracks over the years and by far the most common arent cracks at all but lack of fusion thats been mistaken as a crack.
ih100
post Jan 19 2018, 07:21 AM
Joined: 2-Jan 10



Thanks, Al. I'm pleased you picked this one up. I think I can see where this one has come from, as a poor restart can cause a small crack or porosity., I suppose if you don't know what you're looking at you could think it's hydrogen inclusions.
Technic Al
post Jan 19 2018, 09:39 AM
Joined: 14-Oct 03



Crater cracks will be hot cracks. shrinkage pulls the molten centre apart..the faces are dark.......Hydrogen cracks usually happen hours after welding so are cold cracks ...the faces are shiny......
try_some_welding
post Feb 3 2018, 10:12 AM
Joined: 14-Jan 07



You've heard from Technical Al - take his word as authoritative.

It is commonly said that Basics - limestone-based - 7016's, 7018's, etc - will "suck up" water until they contain about the same as 6013's. They'll do that quite rapidly. Giving about 30ml of H2 per 100g of deposited metal.

Observations support this. I once kept an "emergency stock" of 7018's on the concrete floor in my office in a factory building and when I put them in a small drying oven, when I first opened the door there was a visible rising cloud of steam.

Structural steels from good manufacturers are incredibly hydrogen-resistant. Western European steels from Basic Oxygen Converters are very homogenous and accurately formulated to just make the strength guarantee - eg. S275, S355 - so are very soft. As I had it explained to me by some folk from a steelmaker with whom our paths crossed.

Bolts and so on are another world - there is frequent chaos. Galv. for corrosion resistance and you trap the hydrogen in and even in warm climates like refitting the Golden Gate Bridge in San Francisco things can go horribly wrong. I had to completely recalibrate what hydrogen levels can cause trouble in alloyed hardened steels, compared to modern structural weldable steels which are so immune / resilient to hydrogen.

Anyway, to recap. If you have that frequent rejoinder "You mean Lo-Hi's" when you say "7018" - they suck up moisture to quite high levels but weld just fine in that state for most applications. These levels of hydrogen do increase the penetration of the rod. Can't so easily prove it for SMAW, but for mechanised FCAW, going from 5ml H2 per 100g of deposit to double (both still low hydrogen) increases penno.

Try Some.
try_some_welding
post Feb 3 2018, 10:23 AM
Joined: 14-Jan 07



In summary,
and correct me if I am mistaken...
Yes 7018's do suck up moisture until they have about the same as 6013's, but for general fabrication of structural steels welding SMAW, that has absolutely no consequence.
Because none of the 7018 weld metal, good structural steel, and any reasonable heat-affected zone from general welding practice, have much susceptibility to hydrogen.
Problems occur way way up the scale of frozen-in-stress from large thickness plus hardness due to carbon and other hardening alloying elements, etc. - way clear far further up the scale from general steel fab.
Technic Al
post Feb 5 2018, 02:24 AM
Joined: 14-Oct 03



To be honest "try some" Low Hy coatings vary quite a lot. Modern ones will never reach the moisture content of a 6013 and some of the old ones wont either but more by luck than judgement. The trick is the binders. It was discovered that getting the right balance between Sodium and Potassiun could result in reduced moisture absorption. Lithium could also be used but too much reduces shelf life....the costing pits and the packet is full of little bits of coating.
We tried hundreds and even those that had bee treated badly rarely exceeded 15mls HDM....we made one which was always below 3 mls...whatever happened to it....and we didnt know for donleys years....until a customer asked and we tried it.
try_some_welding
post Feb 7 2018, 09:14 PM
Joined: 14-Jan 07



thanks Technical Al - that knowledge and experience is interesting - Try Some
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