Acid Etch & Penetration

[TechnicAl]

Im amazed this is possible........copyright laws etc..........but there is a downloadable copy of EN1011 here
http://www.125books.com/move-other-bk?file=BS EN 1011-2.pdf

Hopefully it works.

I dont have all the details so I cant be 100% sure but I believe that S275 needs to be over 100mm combined thickness (ie 2 x 50mm pl;ates) before it needs preheat
However as Dimitri suggested it does depend on the %CE..........I would expect European sourced steel to be less than 0.43 but some of the imported stuff Im not so sure........I saw some Vietnamese steel that was close..

 

[Bede]

It's 275JR and the weld throat spec is 12mm with no prep specified.

Lifting lugs are 40mm, welded to the centre of the flange of 254 x 254 x 167kg/m UC. Flange thickness is 30mm

 

[Dimitri De Spiegeleer]

When checking the graphs in the EN1011-2 (as TechnicalAl linked to above),
you see (figure C.7) that a CE of .3x needs a preheat of at least 100°C, whereas a CE of .4x already needs 200°C.

I know this is not completely correct ( I use the CE in place of the CET, there is a difference) and I guessed the HI , but I'd say this is a fair indication of where you need to be. see also my previous post where I mentioned a range, now I actually took the standard and narrowed it down a little finer. The more info, the smaller the tolerance. But in practice, it isn't feasable to say a preheat of e.g. 173°C, as preheat isn't controllable upto a few grade celsius correct.

@TechnicAl : if conditions are worse enough, you'll need preheat starting from 10mm of combined thickness.

edit: if 12mm throat is specced, and fatigue isn't the controlling factor, the moment you have positive penetration (the actual "corner" is fused) AND you have 12mm throat, you're good. deeper penetration alows you to lessen the external throat (but you still need a complete throat of 12mm) ONLY if you can document you always have a certain amount of penetration. Depending on the codes you work according to, this can be a real hassle as there's no way they can take a sample from the actual workpiece without "destroying" it.

 

[TechnicAl]

Dimitri........its MIG so the Hydrogen level should be E

 

[Dimitri De Spiegeleer]

I took H5 as 5ppm is the lowest ppm you can actually measure correctly. None of the test facilities can measure 2 or 3 ppm correctly. You're correct though, MIG and TIG are the lowest H2 class.
But all you need is a hole the size of a hair in your gas hose to dramatically up the ppm H2 in your weld.

Anyway, if you take the theoretical approach, your tolerance band lies withing 100 and 180°C.
But with this thick a steel, and as Bede mentioned (JR) it's certainly not Z-quality, and is thus prone to lamellar tearing, and as the combined thickness is 100mm, the additional 20°C won't break the bank and will certainly have a positive influence on the stresses in the weld afterwards.

 

[TechnicAl]

I dont know where youre having tests done but Ive had tests done that are less than 1ml/100g. TWI can do it. I think its Gas Chromatography method.
We had Lincoln Supramig tested by Swinden Labs in Rotherham (Tata or Corus or British Steel) and they found 1ml as welded and Zero after 24 hours. This allowed us to agree to a shorter waiting period before NDT.
I also had a foreign wire tested. It was very heavily lubricated. You could feel the lube with your fingers. That one gave a result of 6ml/100g.

 

[TechnicAl]

I took H5 as 5ppm is the lowest ppm you can actually measure correctly. None of the test facilities can measure 2 or 3 ppm correctly. You're correct though, MIG and TIG are the lowest H2 class.
But all you need is a hole the size of a hair in your gas hose to dramatically up the ppm H2 in your weld.
.

Do you know there is hardly any Hydrogen in the atmosphere. At ground level the Hydrogen averages 0.6ppm. Gas contamination would more likely result in Nitorgen, Oxygen contamination. There is Moisture but whether or not that will crack and introduce Hydrogen is a big question. It helps oxidisation.

 

[Bede]

So will my lifting beam break and kill loads of folk or am I good to go?!

 

[TechnicAl]

Id say good to go........but dont stand underneath it

 

[Kent]

So will my lifting beam break and kill loads of folk or am I good to go?!

Ah, just use the glue and save the 'lectic

 

[Bede]

I've today taken delivery of an ESAB 400 amp all singing Synergic this that and the other.

Had a play but don't want to fanny about with all the unfamiliar fancy Dan settings so cancelled everything and set it all manually on basic and will run some test pieces later.

Got a tempil stick of 146 degrees for the preheat. That's it now. Three run prep, bit of a warm and it's having it.

 

[Richard.]

Put up some more etched samples of the welds produced with the Esab if pos. would be great to see the comparison to the first ones you did. Best of luck mate.

 

[Kent]

And compare them with the glue

 

[Bede]

Will do.

I'm trying around 300 amp, about 28.5 volts and about 13.5m/min feed if I remember correctly (just at home stuffing my face)

Similar set up to my last test piece but I won't be at the top of my duty cycle on a bigger machine so should be a bit more consistent through the job.

I've got about 200 metres of weld to slap down in total.

Why do I never get these heavy welding jobs deep in winter?!

 

[Bede]

Hmmm, just ran a three run test piece, 28.5 volts was kicking out around 260 amps but running a long arc. If I up the wire feed the weld is looking a tad cold and convex. Up the lot and I'm getting a little sag on the weld. This is on 1.2 wire.

This ESAB is clearer to weld and more responsive but I'm eager to see the results on an acid etch. Fairly happy with how the weld felt but a longer arc than I'd like. If the etch comes out half decent though I'm good to go. The weld looks 'ok' on a visual.

 

[Bede]

If it doesn't im upping the lot to 300 - 320 amps and moving a fair bit faster to get less weld build up.

 

[TechnicAl]

Longer Arc = lower current = less penetration

no matter what it says on the tin the parameters you set are WFS and Voltage.........the current sets automatically to melt the wire.....a long stick out preheats the wire (called I2R heating....like resistance heating in an electric fire) and therefore you need less current to melt it.

The voltage spreads the bead

 

[Bede]

So up the wire feed for a shorter arc and travel faster?

 

[Richard.]

Stick out varies current which varies penetration depths as does wire speed so increasing wire speed will increase penetration but if you increased the stick out along with it you'll decrease the penetration

 

[Richard.]

You'll know already what stickout you need so if you want more pen keep the stickout the same and increase wire speed. Then as you'll already know match the wire speed with the volts. Then you can travel at the speed you need for your desired bead size