Nickel overlay on stainless pipe 1

[rfitts]

I need some help in predicting shrinkage of pipe that has been clad with nickel. I have a 30" piece of 6" sch80 304ss pipe. If it is overlayed with nickel how much will it shrink? Bob

 

[metengr]

What is the actual weld metal composition (Ni-rod 99)? Depending on the thickness of the overlay, you may not notice or measure any appreciable shrinkage of the stainless substrate. Most of the Ni-rod weld metals have low strength and high ductility, which would allow them to absorb residual stresses from weld metal shrinkage.

 

[rfitts]

It is NI 99 0.125" thick. The 6" pipe is part of a spray lance. The 6" pipe section is welded to a 8" 600# flange. The other end (spray end) has a 6 x3 conical reducer and a 3 x 2 conical reducer ending with a small air atomizing nozzle. the 30" 6" pipe section along with the conical reducers will all get overlayed. A group in here that have had similiar lances done told me that the ended up with 4" of shrinkage from end to end? I find that hard to believe so the reason for this post. Are you talking about diameter shrinkage or as I mentioned longitudinal shrinkage. Bob

 

[metengr]

I was initially referring about the pipe diameter but the following explanation applies to the axial length of the pipe as well. For a 1/8" thick weld overlay that is applied uniformly over 304L stainless steel using Ni-rod 99, you should have some minor change in length dimension because the Ni-rod 99 has relatively comparable strength to the 304L (I would not believe 4”). Also, the weld shrinkage stresses will be balanced in the radial direction because the overlay is applied in a circumferential orientation, while a large part of the axial stresses from weld metal shrinkage will be absorbed by the Ni-rod 99 overlay and 304L substrate.

If you were to weld with an over-matching strength filler metal (ie, the weld metal strength is greater than the base metal strength) that is also much thicker you will have more measurable distortion in the axial direction.

How do I know this, because we have weld overlayed boiler tubes with no measurable change in the axial direction – Inconel cladding/carbon steel tube.