Extending the Life of Pump Components

Pump components face a range of wear issues when in service.  Particularly in the oil & gas industry, pumps can be exposed to arduous service conditions which can affect both the service life and operational efficiency of the pump. Without the use of special alloys and coatings, parts have a very short lifespan.

• Read more about wear mechanisms in pumps
• Find out about our coating service in the UK and USA
• Request a quote for alloys, component manufacture, or coating services

Surfacing Alloys for Pumps

Wallex® 6,12, 21, 42

Cobalt-based alloys are the safe choice for high temperature applications and are often specified on drawings.

Wall Colmonoy cobalt-based Wallex® alloys offer excellent corrosion and resistance at elevated temperatures.  These alloys are widely used for the hard surfacing of pump components, and are commonly applied via PTA, thermal spray & HVOF. Several passes can be required, depending on the degree of dilution of the base material.  Increasingly these are applied by laser cladding, which typically requires thinner deposits.

Wallex 42 is designed for spray and fuse applications, particularly vacuum-fused.  Fused coatings form a metallurgical bond with the substrate providing inter-particle cohesive strength and substrate-to-coating adhesive strength with very low porosity. The coatings show good resistance to wear and impact.

Selector Charts (US | UK)

Colmonoy® 88, 62, 69, 72

These spray and fuse coatings offer excellent corrosion resistance and lower porosity versus a sprayed coating for typical applications within the Oil, Gas and Petrochemical industries.

Technical Data Sheets:

• Colmonoy® 88 (US | UK)
• Colmonoy® 62 (US | UK)
• Colmonoy® 69 (US | UK)
• Colmonoy® 72 (US | UK)

Comonoy® 7661-60 (Nickel matrix with spherical WC)

Although these types of coatings are sometimes used, they can prove problematic when the soft nickel matrix wears away, A slurry or silt erosion problem means that the surface is being attacked in many different directions, largely by very fine particles held loosely in a liquid which slowly destroys the NiCrSiB alloy which cements the tungsten carbide particles into place. Once that “matrix” is lost, the harder tungsten carbide particles or grit fall away which, in enclosed equipment, exasperates the problem. For a pump component, the coating should quickly take on a polish to avoid any adhesive wear from the slurry. Once the polished surface is achieved, adhesive wear will not be a problem.

Tungsten carbide based coatings 

A very hard coating with hardness maintained all the way through the coating. Most coatings achieve hardness of at least 1200 Vickers, whilst also offering excellent abrasion resistance.  Because it’s mechanically bonded, impact resistance can be a problem.

SoloCoat™ (840, 850 and 870) (Coldspray)

SoloCoat™ alloys are one-step self-bonding metallizing powders. SoloCoat™ alloys can be sprayed onto parts directly, without the need of an initial bond coat. Unlike most other one-step products, SoloCoat™ component powders are prealloyed. Prealloying produces a homogenous mix that does not separate during shipping or spraying; the result is a uniform coating. SoloCoat™ alloys are controlled to strict specification; are free flowing; and provide for uniform application and excellent results using many popular Thermal Spray processes and powder delivery systems, including the Spraywelder™ Model J-3 System.

Technical Data Sheet:

• SoloCoat™ One-Step Self-Bonding Thermal Spray Alloy Powders

Coating Technologies

Fusewelder™ (Thermal Spray )

The Fusewelder™ Torch is a special oxy-acetylene torch which preheats the base metal, sprays powdered alloy and fuses deposits to the workpiece – all with one integrated unit. 

Spraywelder™ (Spray and Fuse)

The Spraywelder™ System offers tight spray patterns and high spray rates to produce dense, low-porosity overlays. The Model J-3 is the culmination of more than 65 years of technical innovation following the invention of our first thermal spray gun.

The Sprayweld™ Process offers numerous advantages that favour its use in many applications:

• Adjustable equipment settings to suit your application
• High powder deposition efficiency minimizes powder loss
• Close tolerance control
• Reduced finishing time
• Wide range of system alloys

In the Sprayweld™ Process, a powdered alloy is thermal sprayed onto a part and subsequently fused to the base metal by a heat source. This creates a smooth, nonporous, metallurgically bonded overlay, producing a fused coating within 0.25 mm (0.01”) of the required finished dimension. The fusing stage can be done by induction, by the Fusewelder™ torch or by vacuum fusing.

HVOF (High Velocity Oxy Fuel)

Widely used in the pumps industry to spray tungsten carbide. This method is typically a high quality coating- typically less than 1% porosity. With high particle velocity and low heat input, it offers excellent wear and corrosion resistance.

Laser Cladding

Laser cladding offers an extremely precise method of applying a clad overlay with the lowest possible dilution of any conventional welding process. This means high first pass hardnesses are possible. Sound welds with virtually zero porosity can be made with precision control that minimizes the amount of finishing required.  Laser Cladding has become a cost effective process delivering high precision with minimal distortion and dilution, which results in less material being required.

PTA (Plasma Transferred Arc)

PTA is a conventional welding process, it produces a high quality weld overlay with no porosity or cracking.  With the correct parameters, dilution and penetration of the base material should be minimal, though several passes can be required.

Coldspray

Coldspray is a single spray process, where the material is sprayed-creating a mechanical bond, and then machined. There is no fusion required.  This is ideal for shaft repairs because the base material is never distorted.

Wallex® Cobalt-Based

Colmonoy® Nickel-Based

What type of wear happens in pumps?

The type of wear experienced depends on the type of pump and the conditions in which they are working.

Each type of pump has specific considerations:

• In a centrifugal pump, kinetic energy is transferred into the fluid using a rotating impellor. The type of wear experienced in this type of pump, depends heavily on the type of fluid being pumped.   For example, in a centrifugal pump moving water, the most significant wear experienced might be cavitation or corrosion. This type of wear would be very different to a centrifugal pump moving slurry which would have high levels of abrasion from hard particulates.  In a centrifugal pump, seal and bearing areas on the shaft, pump casing, impellors, and rings can all require wear protection. Cavitation is a particular problem at the impellor.
• Positive displacement pumps, though less commonly used, are subject to very different types of wear. In this type of pump, fluid is moved forward by trapping and pushing along a casing. Within the positive displacement category of pumps, there are two main types.

• • Reciprocating – these pumps contain a cylinder with a plunger or piston to deliver fluids. They are subject to metal on metal frictionIn the piston version, a removeable sleeve is often required to absorb the wear experienced by the piston rings as they move against the cylinder.

Simple Piston Pump (Reciprocating): As the piston is moved to the left, fluid is drawn in until the point where the chamber is full, increasing the pressure and forcing the outlet open. Then the piston then moves to the right, forcing the fluid into the outlet. Once the piston is fully extended, the direction of flow changes again as the piston is now moved to the left again and the inlet is now able to open once more.

• • Rotary-these pumps contain a fixed casing which contains vanes, gears or screws. They trap the liquid and push it through the casing to generate a smooth flow of fluid at the outlet. A gear pump, for example, often has issues with abrasion and corrosion of bushings that are in contact with the liquid. The wear mechanism of a  vane pump is very different.  In this type of pump, the risk of abrasion is very high  due to the vanes touching the casing wall. In a rotary gear pump, the movement of the gears allows fluid from the suction inlet to get trapped in-between the teeth of the gears and transported to the discharge outlet.

Another issues with positive displacement pumps is the wear caused by pulsing, an inherent characteristic of this type of pump.  The vibration and abrasion caused by pulsation, can require specific wear measures.

In any type of pump, the liquid that the pump is processing, will also play a large part in the type of wear experienced.  For example, the type of abrasive particle (uniform or irregular) is significant, as is particle size and the concentration in which they are found.  If the pump is moving corrosive liquids, the pump can suffer material loss leading to premature failure if parts are not protected.

Other factors to consider are temperature and pressure. Pumps operating in elevated temperatures will require an alloy that retains its properties in these conditions.  Also, pumps operating in high pressure environment will need good hardness to withstand the effects of abrasive particles.

The type of wear experienced by a pump can vary enormously and requires thorough understanding of the service conditions before recommending an alloy or wear-resistant coating.

Wall Colmonoy offers total manufacture of pumps components in cast, printed or coated form.