Wash passes are made without filler metal additions. They can be used as above and to provide dimensional control. They are often misused to make a weld "pretty". Care must be taken in their implementation. Hot cracking, underbead cracking can occur in high alloy steels and nickel base alloys.
In a cross section they show as a wide partial penetration weld. IF they were done as part of the original process then the may be OK. If someone went back later to do one it would be suspect.
Welders may also use the technique to camoflauge poorly made welds. I had one case where the welder TIG washed a SMAW deposited weld in stainless steel to P91 to cover up almost 100% lack of fusion in the SMAW weld. The weld passed liquid penetrant examination but failed within 500 hours of service.
stanweld hit on the latest definition of of wash pass. It it used by "weld doctors" to beautify ugly or poorly made welds, mostly TIG. My last encounter was a 6" SS 300 lb NG line to a Frame 7 turbine. 21 of 21 welds in this line had to be cut out due to lack of fusion or penetration as well as porosity. All these welds had pretty cover passes. The contractor didn't read the pipe spec where it said 100% RT.
I think the term wash pass originated in the early days of TIG welding when it was being groomed for welding SS. In the early days Heliarc (He Shielding) it was almost a universal requirement to use only stringers. This was a carry over form SMAW weld procedures that only allowed stringers. It was almost given that a good welder would use a wash pass to even out the stingers in the cover. This practise ended when a figure 8 weave was allowed in TIG welding. This happened almost simultaneously with the change to Ar shielding.
The term wash pass was also used with SMAW welding of SS when stringers were the norm. The flux on the electrodes was normally Titania based which only made pretty welds in the hands of a very skilled welder. TIG welding of the root pass wasn't allowed so when you put in a root and hot pass it generally wasn't pretty so the weld availed himself of a TIG rig and smoothed out the existing weld.
A wash pass was also used to to correct the root of welds where one has access to the backside of the weld.
A wash pass normally means that the arc is used sans filler metal.
If they go back with filler I think of it as a cap pass.
In making heavy wall stainless pipe and tube we often weld with plasma (keyhole). This can leave a rougher weld than we want, so we use a 20-30% penetration TIG pass to re-melt the cap and smooth the weld.
The term "wash pass" goes back way further than that,unclesid.
My father in law said they used the term in the defense factories during WWII, in the '40's. Much the same reasons as you express as it was imperative that the welds 'looked good' for the inspectors...with all the implications that statement entails. I've worked a few gov't jobs and can attest to some of the tricks that I have seen.
I personally used the term for cleaning up open root welds when I was permitted to do so as far back as 1962, my Corp of Engineers test for the Atlas missile sites in NM. It's a crutch for bad welders, in most cases I am aware of, myself included. I was not very good when I started.
I had a colleague who'd worked with a Polish guy that had been forced labor in German Tank factories during WWII.
They got very good at 'wash passes'. They would basically do the minimum weld to hold the armour together and then make it look pretty. Idea being the welds would fail the first time it took a hit.
KENAT, probably the least qualified checker you'll ever meet...
Maybe I am missing something here, I thought a wash pass was to wave the torch at a long arc weaving the torch to preheat an area just prior to starting the weld without melting the metal.
This technique is used when welding brass or copper, to get enough heat into the part to start the weld, when you do not have a preheat torch.
B.E.
