Repair - Machining a Piston with inconel - Help!

[LucasVrV]

Our shop engennering/comercial/inspectors have some doubt in the situation bellow,

We have a piston that have Inconel coating and we need to repair it, so the scope is, Pre-machining the piston - Welding with inconel and Final-Machining.

The doubt are, in the Pre-Machining in normal situations how much we need to take it out, how much millimeters of coating we need to take it out ?

And about the Welding lay, how much we need to put, in consideration that we need to leave a range to machining in the last phase.

(We have some internal disagreement, inconel is a expensive material so each millimeters is essencial to know)

Thanks a lot!!

 

[racookpe1978]

No. The cost of the inconel metal (as weld rod, or weld wire for a GMAW machine) is near-trivial compared to the cost per hour of the welder and setup to prep the current cylinder (piston ??), overlay the current ground off metal to the thickness needed to re-machine it back to the original diameter.

You will not be able to consistently add metal beads so closely and so smoothly that the machinist can cut it smooth without over-laying it. So, assume your cuurent layer is depth 0.0 mm.
Your preparation will grind the current layer to 1-2 mm (at least!) to remove the corrosion layer, scars, and get a completely clean surface ready for welding. This will be -1.0 to -2.0 mmm.
Then your welder needs to add a layer - this will be a solid layer of new metal 1/16 to (maybe) 3/32 or so with manual GTAW above the old metal, plus a rough surface of the top of each weld. The welder's second layer adds more metal in between the "humps" of the first layer, hopefully consuming the first completely.
The machinist then cuts off the excess metal to return the surface back to 0.0 height datum.

 

[LucasVrV]

Thanks Racookpe1978.

In my country the price of Inconel is very high, we calculated near 120kg to repair this BOP cylinder/piston= BRL 37.200 our USD +- 12.000

So if we remove all the inconel layer to apply a new one would be much more expensive, we decide to remove 2mm our 3mm.

Thanks a lot for the help!