Materials resitant to "Benfield" solution 1

[DesertEagle01]

Hi,

we have a CO2 Absorbing plant in Operation which uses "Benfield" lye as absorbant. Most parts of the System are made of Carbon steel. Nevertheless, we face some Problems with the few parts made of Nickelalloy and Chromium Carbide.

The Nickel alloy was completely desolved after 1y Service. The Chromium Carbide Shows some attack on the Surface but not as extreme as the Nickel hardfacing.

Is there some Information which alloys are / are not resistant to the Benfield solution?

 

[EdStainless]

Is this part a valve seat?
It looks like it sees some sliding wear. How is this material applied?
The first picture looks more like delamination (or lack of fusion) than corrosion attack.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[DesertEagle01]

Yes. It is the seat of a ball valve.

The method of application was HVOF (high velocity Oxygen fuel coating - Thermal spray). The ball was coated with Chromium Carbide which showed better resistance. The Nickel hardfacing turned "Black". It was a very weird failure. We are now concerned that such hardfacings are attacked by the Benfield lye and in search for indications which materials are resistant (except CS and SS, which we know are).

Any hardfacing you could recommend which is resistant?

 

[metengr]

I would look at Stellite 6 hardfacing for the seat versus HVOF.

 

[pradipgoswami]

There are few reports available in the web(

https://www.osti.gov)

with exhaustive description on corrosion in Benfield or Hot Potassium Carbonate solution. According to these reports: The Benfield plants are known to be subject to severe corrosion. Dissolved CO2 in Potassium Carbonate is the main contributor to such corrosion. Pure carbonate solutions without dissolved CO2 are not aggressive towards carbon and other steel.
I worked on design and shop fabrication of these equipment in the past which are extensively used in Ammonia-Urea Fertilizer Plants. Carbon, Austenitic stainless (304/316/316L) and clad( 304/316/316L on C.S) used to be mainstay of the static equipment.Corrosion was more for the plant personnel to look after and fix.
The following report from Sandvik is worth looking at

https://www.materials.sandvik/en/materials-center/corrosion-tables/potassium-carbonate/

Both Nickel alloys and Cr-Carbides should have good corrosion resistance against Benfield solution. It may be good to know which Nickel alloy was applied by HVOF process, as the composition stated here does not match the conventional Nickel alloys e.g. Alloy 400 600, 625 and on.
Whichever grade is used:- arc welding overlay Process SHALL always be the option in corrosive process fluid media.
Thanks.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
ca.linkedin.com/pub/pradip-goswami/5/985/299

 

[DesertEagle01]

Thanks for your Infos. I am checking your references and I find that process conditions are highly influencing the corrosion behaviour in this environment. Nevertheless there are no reports on failures as we experienced them.

The location in the process is in the "Lean" section where there is a minimum amount of CO2 in the Benfield lye. Temperature is around 120°C. We also found some pitting on the inside of the ball made of A351 Gr. CF8M. I am thinking of changing the valve to a carbon steel gate with standard stellite 6 hardfacing.

 

[EdStainless]

I suspect that the process fluids either attacked a binder phase in the coating, or the coating was not well adhered, or that you had corrosion under cutting the coating.
I would make the seats from a monolithic material, a cast Stellite insert or even ceramic valve trim might be an option.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube