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Weld overlay of SS clad CS plate

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ldav048

ldav048

Petroleum
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May 30, 2012
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NZ
We have a vacuum column that requires internal weld overlay for process reasons. It requires a overlay with 316 SS, and a Mo content greater than 2.5%. The column is designed to BS PD5500. The column already had a internal cladding - it's ASTM A263 explosion bonded plate (18mm ASTM A204-A plate with 3mm ASTM A240 TP410S cladding). The cladding is corroding in the current service, hence requiring the upgrade to 316. A weld overlay contractor has advised that they have had experience in applying SS weld overlay directly to a existing cladding with success.
Our concers is that with the large area of weld overlay required and the resultant shrinkage that I woud expect, it might be possible that the explosion bonded cladding with the additional weld overlay 'peels' off the base plate ie delaminates.
Our driver to leave the existing cladding in place and apply the weld overlay on top of this is due schedule constraints in an upcomming plant shutdown.
If anyone has had experience with this they are willing to share, please advise.
 
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I have seen welding done over existing clad, but not changing alloys.
In most locations they will actually be fusing through the existing clad layer.
If you are going to hit 2.5% min Mo with any weld dilution you may need to use 317L for the overlay. Just saying....

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Plymouth Tube
 
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I have seen more corrosion resistant alloys weld overlayed over the original "weld overlay". I have not seen it done on explosion bonded clad plate. If you attempt, a minimum of two layers will be required to meet the Mo requirement. The first layer with E/ER309LMo, the second layer with 317L as recommended by EdStainless.
 
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Or you might consider using a higher alloy material and doing it in one pass. Using a Ni based alloy (C22, 622, 59) would get you more corrosion resistance and also a lower thermal expansion than a 300 series SS. Cyclic thermal stresses can be very hard on overlay.

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Plymouth Tube
 
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Guys, thanks for the input. I understand that the process will likely involve the application of a 309L followed by either a 316 (if wire can be sourced with the correct Mo content) or 317. My greatest concern is the shrinkage as a result of this. We have had weld overlay done on other columns without a cladding and experienced significant shrinkage (ie the diameter of the column reduces). This signals to me that the cladding and weld overlay will be in a state of tension, and that will be opposed by the shell material which will be in compression. As mentioned earlier it's a vacuum column, which may exacerbate this.

The alternative to this is the removal of the cladding (by arc errosion) but will significantly add to the timeframe for the job.
 
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Shrinkage stress will be induced by weld overlaying over the 410S clad carbon steel or the carbon steel with the explosion bonded clad removed.

 
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I imagine that the explosion bonded cladding 'adhesion' to the shell material will not be as good as direct weld overlay to the shell material. If the tension was too great with the explosion bonded cladding on, i fear it could delaminate from the shell material. This is my main concern, and am not sure if this has been done before, and what the success of it's been.
 
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I would not attempt this repair option with clad substrate, period. You are correct in that the clad material will delaminate.
 
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In the explosion clad material that I have worked with the bond strength exceeds the yield strength of the CS.

Either way a trial is in order before you commit.

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Plymouth Tube
 
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If you do decide to weld overlay over the existing cladding, heed Edtainless regarding the trial. Also UT scan for disbonded cladding prior to weld overlay and again after.

 
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and,, residual stresses from welding can locally reach the yield strength of the CS substrate resulting in the previous mentioned distortion and lack of bond.

I do agree a trial should be performed. However, factoring the cost of performing 100% UT coverage to ensure adequate bond must be evaluated for the entire job. If anything goes wrong with this type of repair this could result in extended outage time.
 
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What I have done in the past is water cooling the outside area with a water heat sink using a small box and some plumbers putty. I know it sounds weird but the shrinkage will be cut to less than half. Rsweld

 
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