Kermetico HVAF and HVOF thermal spray equipment

Equipment and Coatings for Wear and Erosion Protection of Slurry Pump Impellers, Backing Plates and Casings

Kermetico HVAF equipment is utilized by the largest American corporations to protect slurry pumps’ wet parts from erosion and abrasion by hard solid particles — extending component life, enabling longer mean time between failures and significantly reducing maintenance costs.

Kermetico HVAF thermal spray systems deposit ductile, high-bond tungsten carbide coatings harder than 1,600 HV300.

We would like to share our experience in wear protection and repair of slurry pump impellers, casings, liners and housings.

Abrasive Wear, Erosion and Corrosion of Slurry Pumps

A slurry is a mineral feedstock to be processed in a mining concentrator plant or a waste stream of tailings including hard particles. In oil and gas refining, slurries are usually catalyst streams, including limestone or zeolites. Under unfavorable circumstances of corrosive media, the combined effect of corrosion and erosion can lead to dramatically increased wear rates.

The mechanical and chemical forces are extremely demanding for the material integrity of pump parts — especially when temperature, pressure or flow volume increases.

Kermetico HVAF tungsten carbide coatings combine high hardness, corrosion resistance and ductility to protect slurry pump volutes, liners and impellers.

Surface Treatments to Protect Slurry Pump Parts from Wear

Carbide coatings deposited by using different high velocity technologies (HVOF, HVAF, Detonation), are extremely wear-resistant. Tungsten carbide in combination with cobalt, nickel or cobalt-chrome matrices is used preferably.

The erosion and corrosion behavior of thermal spray coatings are important factors for the assessment of the coating application.

We use our HVAF equipment to apply tungsten carbide coatings that are wear-resistant and tough enough to be used at all angles of impingement.

Only 100 microns (0.004”) of our WCCoCr coating is gas-tight, protecting an impeller base metal from corrosive agents as a barrier layer.

1,5 mm (0.06″) of our HVAF tungsten carbide shows the same performance as 25.5 mm (1″) of wear resistant high chrome iron usual for the slurry backing plates.

We recommend WC-Co-Cr-bound powders because they exhibit the highest wear resistance coupled with an adequate corrosion resistance in any environment except very high pH environments or hydrofluoric acid.

Since 2006 we have sprayed numerous different slurry pump parts for both new and repair work.

Our customers and partners in the USA, Europe and China spray a lot of pump spares.

A Case of a Slurry Pump Coating

Background: we were asked to coat a slurry pump backing plate to protect it from the abrasive slurry passing through the pump.

The impeller came from the manufacturer already coated with tungsten carbide presumably by an HVOF process.

The pump housing was uncoated, and the customer didn’t want the housing coated as in previous experience with this pump in this application the backing plate was the only part adversely affected by the pumped slurry.

Results: Here is the backing plate with the as applied Kermetico HVAF tungsten carbide coating after one year of service.

The Slurry Pump Backing Plate with the Kermetico HVAF Wear Resistant Coating After a Year of Service

The Slurry Pump Backing Plate with the Kermetico HVAF WCCoCr Coating After a Year of Service

Measuring the coating thickness we found that the thickness after a year of service was identical to the initially applied coating thickness.

As we began to examine the backing plate we found an interesting area seen below.

The backing plate seal to the housing wasn’t absolute, and some erodent made it past the coated surface of the backing plate and eroded material from under the coating.  It is hard to see in the photo, but the coating is undercut and is still intact forming a sharp overhang of the coating.  Here is a close up of the eroded area.

The pump liner eroded area under the HVAF Tungsten Carbide Coating

The Eroded Area Under the HVAF Tungsten Carbide Coating

The other main parts of this slurry pump didn’t fare as well.  The impeller shown below lost much of the applied coating and the blades were wearing away fast.

If the pump hadn’t begun leaking, the impeller would have failed after little additional service.

HVOF-coated Slurry Pump Impeller After a Year of Service

The HVOF-Coated Slurry Pump Impeller After a Year of Service

In the close-up view, you can see where the HVOF coating is completely gone.

Worn Slurry Pump Impeller

The Worn Slurry Pump Impeller

In those areas where the coating is worn away the metal is being worn away quickly as those blades are significantly shorter than the adjacent blades that still have coating remaining on the surface. This can be seen using a straight edge and a little backlighting.

A Failed Slurry pump Impeller

The Failed Slurry Pump Impeller

Wear of the Unprotected Slurry Pump Casing

The pump case didn’t do well either.  Here is a look at it as received.

The damage is readily apparent.

A Failed Slurry Pump Casing

The Failed Slurry Pump Casing

Our customer has decided that the best course of action is to line everything with Kermetico’s HVAF WC-10Co-4Cr tungsten carbide coating.  We wholeheartedly agree with his decision.

Is it something extraordinary?

Not really.

A Comparison of Abrasive Wear and Erosion Protection Properties of HVOF and Kermetico HVAF Coatings

Slurry erosion test, courtesy of Schlumberger.


This test has compared a Kermetico HVAF tungsten carbide coating to the coatings of the same material deposited by industry-leading HVOF and detonation systems.

The two following charts are courtesy of the Central Power Research Institute of India.

A Comparison of Hardness and its Deviation of an HVOF and Kermetico HVAF Coatings

A Comparison of Hardness and its Deviation of an HVOF and Kermetico HVAF Coatings


A Comparison of Young's Modulus of HVOF and Kermetico HVAF Coatings

A Comparison of Young’s Modulus of HVOF and Kermetico HVAF Coatings

Could the reason for this result be that we are comparing ourselves to less than the best available coating equipment?

You may also be interested in a comparison of Kermetico HVAF WCCoCr coatings with one of the most advanced HVOF systems on the market.

A Comparison of HVAF WCCoCr Coatings with HVOF and Ultra-HVOF Specimens

A Comparison of Our HVAF WCCoCr Coatings with HVOF and Ultra-HVOF Specimens

Are you interested in how our HVAF Balanced and Ultra modes provide such outstanding results?

A Research of Kermetico HVAF WCCoCr Wear and Corrosion Protection Features

As Prof. Wang has shown in his article “Wear and corrosion performance of WC-10Co-4Cr coatings deposited by different HVOF and HVAF spraying processes”:

“Three WC-10Co4Cr coatings were deposited by HVOF and HVAF processes, and their microstructure and properties were investigated in this study. The following conclusions were drawn as a result.

(1) The WC-10Co4Cr coating deposited by the HVAF spraying process exhibited nearly the same phase composition as its initial feedstock powder, which included mainly the WC and some Co3W3C and crystal Co phases with nearly no decarburization. The JK coating sprayed with Jet Kote III-HVOF equipment exhibited the most severe decarburisation with high-intensity W2C and even metallic W phase. The phase composition of the JP coating deposited by the JP8000-HVOF system was composed of main WC and minor W2C peaks and exhibited a light degree of decarburisation.

(2) The wear resistance and mechanism of the HVOF/HVAF-sprayed coatings were influenced not only by their hardness but also by their fracture toughness. The high hardness of carbide coating could effectively hinder the cuts caused by the abrasives, and their high toughness could make the binder absorb some of the energy caused by abrasive attacks with some degree of plastic deformation.

(3) The WC-10Co4Cr coatings, which had different degrees of decarburisation, exhibited different dominant wear mechanisms.

(4) The electrochemical corrosion resistances and mechanisms of HVAF- and HVOF-sprayed WC-10Co4Cr coatings were influenced by their phase compositions and microstructures.”

Scientists tell us that HVAF provides better wear and erosion resistance than HVOF. But a lot of companies still use other methods to protect pumps and other equipment.

Why is that?

Maybe HVAF is too expensive?

The Economic Aspects of Kermetico HVAF Coatings

The list price of our HVAF equipment is lower than the price of good HVOF equipment.

And the operating expenses are much lower.

A Comparison of HVAF and HVOF cost per kilogram of deposited WC-10Co-4Cr (prices in Texas, USA, the price of tungsten carbide is $81 per kg).

A Comparison of Kermetico HVAF and HVOF Cost per Kg of Deposited WC-10Co-4Cr (Prices in Texas, USA).

With Kermetico HVAF thermal spray systems we are not limited to the “best coating possible.”

We can choose how to spray a tungsten carbide coating:

  • save money spraying in HVAF economy mode, getting HVOF quality with lower costs;
  • spray the highest coating quality in HVAF Ultra mode to achieve high hardness, ductile, non-porous, abrasion and cavitation resistant coatings;
  • or choose HVAF Balanced mode to gain a competitive edge in both cost and quality.

But it’s not the end of the story.

Blast and Spray Slurry Pump Parts with Kermetico HVOF Equipment

Usually, we deposit coatings onto slurry pumps impellers and plates using robotic blast and spray operations.

We blast a surface with a Kermetico HVAF gun (it is extremely fast and uniform) and spray with the same gun after switching the powder feed hose and perhaps changing the nozzle

It is much faster, more accurate and consumes much less grit than manual blasting.

Hot grit blasting also produces very even surface preparation and induces less stress into the base metal.

Kermetico HVAF Thermal Spray Coating Equipment

Kermetico designs and manufactures three families of HVAF thermal spray equipment.

  • Convertible HVOF and HVAF equipment:
    • C7 – an HVAF/HVOF gun for large parts
    • C6 – a general purpose HVAF-HVOF gun
  • Multi-purpose HVAF AK systems, with a variety of spray guns:
    • AK7 – a high-power gun for the thermal spray of large parts
    • AK6 – a universal gun to spray a balanced mix of parts in a job shop
    • AK5 – a compact gun to spray smaller parts, thin walls and complex surfaces
    • AK-ID – an 80 mm (3.15”) and larger internal diameter spray gun
    • AK-IDR – a rotating ID gun to spray 4” (100 mm) and larger bores
    • AK-HH – a handheld gun for on-site coating
  • Specialized HVAF S equipment:
    • SL – a specialized gun for spraying low melting point metals
    • SP – a dedicated gun for the most efficient precious metals’ deposition
    • STi – a specialized system for the deposition of titanium and Ti-alloy coatings

Kermetico, Inc. – Material Science Excellence, HVAF and HVOF Equipment Manufacturing and Thermal Spray Coating Services Since 2006

We create equipment that helps material scientists, engineers and business managers achieve their goals.

We have installed more than 60 Kermetico HVAF and HVOF systems in the USA, Europe, Japan, and China.

Some of the systems are at work in Universities and National Labs, but most of them are used in production thermal spray shops.

We proudly design and produce our HVAF thermal spray equipment in California and install it all over the world.

You can visit our R&D center in Benicia to meet our designers and see our HVAF and HVOF equipment in action.

We also provide HVAF and HVOF thermal spray coating services to customers in North America – ourselves and through our network of partners.

Equipment and Coatings for Wear and Erosion Protection of Slurry Pump Impellers, Backing Plates and Casings
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Equipment and Coatings for Wear and Erosion Protection of Slurry Pump Impellers, Backing Plates and Casings