Weld tests

[Welderpaul]

I want to show one of the young lads what we mean by weld penetration. He understands it at the moment that he is blowing a hole in the plate, then filling it up with wire, without leaving any gaps (Undercut), all happening while he moves the torch along.
Crude, but along the right lines. (albeit my exasperated way of describing it to him)

I was planning to get him to weld two plates together or whatever, cut it, then polish the cut end. Nitric acid on it to etch showing up the difference between the parent metal and the weld bead.

Will this do? What concentration should it be used at? I've seen some sources that say 5% nitric acid/95% water.

Will it work?

Ta

 

[TechnicAl]

Nitric is what you want..........god knows what Oxo doo dah is

5% Nitric in water will work, it will but it will soon rust, best using methanol

remember acid to water or methanol...........other way round can "explode" (it actually boils and spits)

 

[Paul.]

For a simple shop macro etch around 20% nitric acid in water preferably distilled will be ok, the weaker 5% mixture is usually used with micro etching, with a finer polish and a magnifying lense.
For a quick one off test you can use watered down pickling paste,

 

[Welderpaul]

One of the lads was talking about pickling paste but a couple of the others reckoned they had seen it tried and it would not work. Will try it anyway.
Where do you get nitric acid or methanol from?!

 

[hotrodder]

Google suggests oxoazinic is another (systematic?) name for nitric acid . Google shopping threw out several sources that sell 1 litre bottles (70% in water again), http://www.bonnymans.co.uk/products/product.php?productID=6424 also sell methanol FWIW. You can by nital ready mixed but it's 'kin expensive and iirc it doesn't work as well as fresh?

I would have thought (random guess) the HF acid in pickling paste would ruin the results but another suspect that sorta, kinda works is a drop of acid from a car battery- no detail but just about highlights the weld metal if you give it a while