MoRe 160 tube corrosion

[abel2]

We have a customer's calciner tube that is experiencing spot corrosion and leading to holes throughout the tube (when I say throughout I specifically mean radially around zone 2). The composition of the alloy is unknown. The 'exact' chemical composition of the volatile calciner gases is unknown. What is known is that phosphates/phosphorous and ammonia gas are being released. The powder being calcined is carbon based. Product is calcined under nitrogen atmosphere and pressure washed periodically (every 4-5 runs). Calciner runs at 1050C.

My question was: Does anyone know some good lit on molybdenum/chromium/nickel alloy corrosion (specifically involving phosphates and ammonia)? I've done a bit of searching online and have not come up with much info on calciner/high temp furnace corrosion. Thanks in advance for your contribution!

 

[StoneCold]

My money is it is the washing step that is causing the bulk of the corrosion. Probably phosphoric acid being created when they wet down the phosphate containing material.

Regards
StoneCold

 

[EdStainless]

Or the washing could be forming salts that then are causing attack when heated.
Corrosion of high Mo alloys is a difficult field. Some of the Mo oxides are volitile at process temperatures leading to catastrophic attack.

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P.E. Metallurgy, Plymouth Tube

 

[abel2]

Update:

Did an analysis of some of the wash from the tube. Had high levels of nickel in the wash, indicating some form of denickelification. The only thing is.. the tube contains no copper, so I am not sure of the mechanism occurring.