There are certainly many answers for what exactly does HOT PASS means in welding terminology and from where it actually evolved. Different people had a different opinion and they are as below mentioned.
- It is to fill the weld bevel.
- It is to melt and float out the wagon tracks left after the root pass.
- To release trapped gases, hydrogen entrapment at root weld to minimize the risk of Hydrogen induction cracking (HIC).
- A significant other is that a large majority of pipeline welds are done in a clamp and under some sort of stress. A root bead and hot pass are generally the minimum amounts of weld that must be done before the crane/side boom etc can be released and the weld can then be left to completely cool and be filled and capped at a later time/date.
But actually, it’s a kind of a misnomer that second pass after root pass, for example, TIG joints is hot pass, even though it is sometimes run colder than the root.
Then what exactly it is?
A hot pass is a term used in stove-pipe welding when the bead is complete it is given a quick clean up with a grinder then the hot pass follows, it burns out the slag that is trapped at the junction between the bead and the pipe wall, the slag is often called wagon tracks.
The hot pass got the name from 6010 pipe joints where the second pass had to be “hot” enough to burn out any leftover slag from the root. The one thing you can probably count on is that the term “hot pass” is always referring to the pass after the root pass usually on pipe welds.