A friend ask me this question, it is  very vague, before I respond I would like to here the forum's chime-in on the subject. (in brackets are my initial thoughts)

The question I have for you is about cut & etching of a butt joint weld.

What is the AWS standard for 100% penetration on a butt joint that does not have any bevel groove in it? (what standard or code to be specific, or just general reference)
The only standard that I have found here is this:
Welds less then 300mm (12 inches) long, which is the case here. The minimum fused leg dimension shall not be less than .9t, where " t " is the thinnest gauge member being welded. ( sound like fillet weld leg size requirements- groove weld size is throat [depth of penetration into the joint])

I will also send you a picture of the weld to try to give you all the information and see what you could come up with.
(simple solution would be to bevel the thicker plate to assist achieving required penetration without undercutting the the edge of the vertical plate- or - add fillet weld to opposite side / other question I would ask are: what variation would be allowed?, butt the thinner piece into the thicker one, can the part be repositioned?, is CJP really required?,) 9t 0f 3.69 would = 3.32