Currently, I am working on a small project where the mixer paddle of a fertilizer factory is facing severe corrosion and abrasion problems. working environment contain 99% concentration of Ammonia Nitrate and work at 175 Deg C. Mixing all the raw material in the mixer in slurry condition. The paddle wear in very fast and the current life span is approximately 6-7 weeks. Base metal used currently are 304 stainless steel and hard faced with Chromium Carbide. The welded CrC seem to have intergranular corrosion attack and break out rather than wear in. I suspect the CrC wear due to Corrosion and assist by abrasion as secondary wear. My current suggestion is to coat the mixer paddle with nickel base hard facing materials (40% NiCrBSi matrix with 60% Tungsten Carbide). Is this a good procedure to weld the paddle surface with this Nickel base hard facing materials as the price is very very much higher compare to CrC hard facing? Anyone has come across the better solution to solve this working environment. Yours advise and comment is highly appreciated. Look towards your advise. Thanks & Regards, KK Chiong.
Your question sounds more like a corrosion problem than a welding issue. I don't know if anyone on this forum will be able to answer your question. I know I certainly can not. But if you don't get anywhere here you might try the discussion group at nace.org or even
corrosion-doctors.org If you navigate those sites you will find how to access the discussion groups.
I forgot to mention that you need to look for the "List Servers" link in the left hand column at the nace.org site.
Thanks a lot for your advise and I will search thru the relevant web site for my answer. Bye. KK Chiong
Very few industries, if any, face the corrosion problems the fertilizer industry does. Apart from the attack produced by highly aggressive agentes, there is also abrasion produced by undissolved solids, which aggravates the problem.
I know it quite well because years ago I've been deeply involved in design of fertilizer plants. 304 stainless steel and chromium carbide are DEFINETELY NOT suitable materials for this kind of industry, and hence the corrosion they show.
I don't know the details of your particular case but, just to start with, I'd suggest you to consider two cases:
a) soft rubber (neoprene) lined carbon steel mixer. Soft rubber (Shore hardness not exceeding 40) withstands perfectly the corrosive materials from a fertilizer plant and also withstands abrasion. However, it doesn't withstand high rotational speed. What's the speed of your mixer? From this point of view, Hypalon plastic is somewhat better, although more expensive, than rubber.
b) highly sophisticated metallic materials which, unfortunately, are very expensive. Metallic materials don't withstand corrosion and abrasion as well as rubber but they withstand mechanical stresses much better.
There are a few metallic alloys which have developed specifically for the fertilizer industry. Among them I remember:
2RK65, made by Sandvik of Sweden
Sanicro 28, also made by Sandvik
Ferralium, made by Langley Alloys of Great Britain.
Not knowing the details of your particular case, I can't give you any valid suggestion. What I do suggest you is to get in contact with a highly reputable rubber lining applier in your country and with Sandvik's and Langley's representatives. Call them for a meeting (not at the same time, of course), explain them your problem, let them visit your plant and look personally at the mixer, answer their questions and listen to their recommendations. Don't forget to ask for references: have they already dealt with similar problems? When? Where? Do they mind if you check personally the references?
After this, you'll be in a position to make up your mind and chose what appears to be the best solution.
Giovanni S. Crisi
Sao Paulo - Brazil
Dear G.S. Crisi,
Thanks for your advise and I will look into your suggestion seriously. anwersing to your earlier Q, the rotation speed is about 30-40 RPM. I think it is quite slow as compare to other mixer RPM. Hope that you can assist me thru this corrosion and abrasion problem in fertilizers plant. Thanks. KK Chiong
I am currently experimenting with this material. It's too early to tell if the material is worth the cost. Out of the gate, it seems to be performing really well.
I work for an OEM that produces aggregate (rock/stone) processing equipment.
My focus with this material is primarily with wear (mode: sliding abrasion) on our mixing paddles. However, it has been pointed out to us that corrosion (a very slight case) could be aggravating the wear. I know this is NOT close to the same application but here is my experience for whatever it is worth.
As you mentioned the material cost is expensive, ball park $23/pound, unfortunately the manufacturing costs are also expensive.
The WC material (as in my case) was a cored wire and it was applied by a method similar to brazing. Brazing this material requires a clean fluxed surface. The flux is a powder ($35/ pound) and it is crucial for bonding the WC-material to the base metal. The flux is applied through a special torch onto the surface of a pre-heated component. The component's contact surfaces MUST be thoroughly cleaned before and after the flux is applied. Poorly prepped surfaces will keep WC material from bonding to the base metal.
Applying the WC
The challenge is the brazing-technique. The heated WC cored wire becomes a semi-solid over a small distance and it tends to easily break away from the solid portion of WC cored wire. This decreases the craftsman’s ability to manipulate the WC cored wire and causes the brazing process to slow down and manufacturing cost to increase. The manufacturer has put a thin gauge wire in the center of the WC cored wire to help with this problem but it still exists. Also note: depending on the mass of your component, pre-heating the component to 500F for an hour is possible (soaking) before the brazing process can begin. It’s a slow and hot job.
The key measurable is between the wear/ corrosion life and costs. If you experiment with this material, I recommend comparing the material and manufacturing costs with maintenance downtime, production downtime, and accidents (that could be attributed with maintenance) during the lifecycle of the material. You should come up with a cost per processing volume or mass ($/ ft^3 or $/ ton). This is a better indicator than just material cost alone.
Sorry for the long email.
Thanks for your advise and I will look into them seroiusly. Bye.
Thanks again for your advise and I would like to share with you regarding my earlier involment in Batching Plant Mixer Paddle (SIMEX from Italy) and I had use 3 difference type of hard facing materials in this research. (CrC, Complex Carbide and WC). The hardness increase from CrC to WC. But, the results show not much improvement with WC as compare to CrC. I suspect two wear mode exist namely abrasion and compression. WC seem to be break off due to high compression while CrC show good polishing properties in this working condition. I don't know what type of mixer you are working on now but if you want to share with me, maybe some of my past experience is useful to you. But please bear in mind that every working condition is vary depend on aggregate size and their moisture content. KK Chiong
Hello Mr. Chiong,
I wonder if you have considered a themal spray solution. The company I am associated with provides solutions for wear and corrosion via thermal spray coatings consisting of ceramics or polymers. Some thermal spray wires/powders can be useful for surface engineering. The application and all specifics dictate the proper choice of course. We also provide polymers that can be trowled on or alloys that can be furnace or torch fused. I would be glad to take this up with my colleagues if it would be useful to you.
ceramics doesn't work in the fertilizer industry. Ceramics usually contain silica and the fertilizer industry releases a lot of hydrofluoric acid, nº one enemy to silica. HF eats silica in matter of hours.
Giovanni S. Crisi
Sao Paulo - Brazil
Thank you Giovanni,
The Ni/Cr B/Si/WC material that Mr. Chiong speaks of sounds very similar to the spray and fuse powder chemistry. Given your extensive involvement with fertilizer plant design and your considerable experience with it's inherent problems, what would your opinion be of a fused coating using a Ni/Cr/B/Si powder w/o the addition of WC? The material cost would be about half that of the WC blend. It would seem that maximum deposit hardness would be achieved using the S/F process as the dilution rate of the base material with the sprayed deposit would be very low. As deposited, the S/F coating would also be very smooth and dense. The material could fused as it is deposited, (leaving the surface less than perfectly smooth) or deposited, then furnace fused if practical.
Thanks Steve 3884 & G.S. Crisi,
Both of you have provide valuable input for my analysis and as discuss by Steve if the WC is withdraw from NiCrBSi. What will be the effect? From my finding, NiCrBSi is a very tough and very corrosion resistance alloy but the problem is that it is a bit soft. So, if in my case, paddle coated with NiCrBSi materials (either powder-by thermal spray, Tig rod-by TIG welding, Stick Electrode-by Arc Welding, Flux Core Wire-by FCAW) is very resistance against Corrosion problems only and the another problem (abrasion and erosion wear due to hard particle entering the mixer will cause plastic deformation and wash off of the NiCrBSi coating). Another concern is the thermal spray normally applicable for thin layer surfacing (below 2mm). If there is any better alloy than about, please advise?
I have another idea of using Titanium plate and treat the wear surface with Nitriding process. Is there anyone have experience on the application of Titanium and it's alloy for corrosion and abrasion problem. Any constructive suggestion is most welcome for discussion.
I also receive some recommendation to coat the surface with treated rubber e.g. Bromobutyl-base rubber. Is there anyone who know further about this rubber. Your suggestion and advise is most welcome. Thank you.
Hello Mr Chiong,
The coating thickness of the spray material need not be over .794mm in thickness. The coating can be as thin as .010" or as heavy as required. For S/F, a coating thickness that is below 1.5mm is common. Heavier coatings are applied using self fluxing materials.
I propose that the spray process will yield a higher hardness than an electric arc process due to the lack of penetration into the base material. Thinner coatings are possible with the spray process largely due to this fact. Typicall hardness should range from the high 50's to the low 60's on the rockwell 'C' scale.
I am also researching the possibility of using a Zirconia base ceramic. I wonder if Mr. Crisi can shed any light on that subject. The person I need to consult with is not available until after the holiday.
I am back after sometimes working with the corrosion and abrasion resistance materials. I found that Tungsten Carbide embeded in NiCrSiB matrix is a good solution and this materials does survive that tough working environment.
If anyone of you who have experience with other materials in the same working environment is most welcome to share your experiences. Look towards somebody to reply this mail.
I don't know about your specific chemical, but another alloy family that claims to resist abrasion and corrosion are the cobalt based alloys commonly called Stellite. Try contacting Deloro Stellite (canada), or Weartech (California) about you specific application. The alloys are available as welding wire/rod and wrought/cast material.
Thanks for your advice and I wish to inform that the chemical mentioned here are the Fertilizer raw materials. And the type of wear exist are corrosion plus abrasion. I heard about Stellite materials but so far have not try them yet. (Various Stellite grade are available e.g. Stellite1, 6, 12, 21, F etc...) I heard that some of these stellite materials will exhibit crack on their weld bead. Do you think would this initial the stress corrosion problems.
Please advice whether you have any practical experience using the stellite material in coating the mixer paddle for the fertilizer application. Have you conduct any relevant study between the life span of Ni base hard facing materials against Cobalt base hard facing materials in this application. If another who have such experience, please share with me.
I know that Sellite 6 & 21 can be welded without exhibiting cross checking, or craking if welded properly. Since we make equipment, I unfortunately rarely get to see the results of thier applications, so I do not know about your particular situation, but the people either at Deloro Stellite, or Weartech should.
As you mention earliere that you are manufacturing some equipment or component with Stellite coating, may I know where is your application and how good is this materials performance in your particular application. Concerning my case, the main application would be as a protective layer on mixer blade in the fertlizer plant. My intended coating thickness is approximately 2mm on front surface an about 10mm the the sliding edges which may rub against the fertilizer and the wall liner during mixing process. I heard about the stellite product and my only knowledge in the stellite application is for coating on the bandsaw tip and grinding them to the intended shape and size.
That's all I can tell from my current experience.