Forms of Corrosion in Pumps

Corroserve offers customers a comprehensive pump service, which includes on and off site maintenance and repairs. We also offer the re-engineering of pumps, as well as coating services for corrosion protection on almost all types of pumps.  The bespoke nature of our expertise and services offered, enables Corroserve to respond to individual customer requirements promptly,  with the ability to provide solutions quickly and on budget.

Our clients include some of the world’s most respected pump companies, operating in fields as diverse as mining, oil and gas, chemicals, power generation, water and wastewater, pulp and paper, as well as the marine industries.

Our Pump / Engineering Manager, Simon Cappleman, is not only our technical representative, but is also responsible for all of the pumps and rotating equipment that come through our workshop, and assists the Corrosioneering Group globally with any technical issues. With over 20 years in the industry, Simon is our in-house pump expert. Here Simon provides insights in to the most common forms of corrosion we see in pumps, and how we repair and protect this type of equipment.

Cavitation 

Cavitation in a fluid occurs when a reduction in pressure, results in a lower pressure than the vapour pressure of the pumped fluid. The result of lowering the pressure below the vapour pressure of the fluid, is that a vapour bubble is formed in the fluid. The vapour bubble can only exist whilst the static pressure remains below the vapour pressure of the fluid. Once the static pressure increases,  the vapour bubble in the fluid can no longer exist. It reverts by rapid collapse to its liquid form. Cavitation is identified by the pitting on the substrate, caused by the shock wave as the vapour bubble collapses. As you will see in the above pictures, cavitation occurs in areas that see the pressure differential and apart from extreme cases, it is localised to these areas.

We repair numerous pumps each year, which have suffered from cavitation. Corrocoat EB is a popular coating system for this type of corrosion. This solvent-free, two pack epoxy coating provides excellent erosion resistance, toughness and outstanding anti-corrosive properties.

Uniform Corrosion

Uniform corrosion, also known as general corrosion, occurs in the atmosphere, in liquids and in soil, frequently under normal service conditions. Uniform corrosion commonly occurs on metal surfaces having homogeneity of chemical composition and of microstructure. Access to the metal by the attacking environment is generally unrestricted and uniform. In uniform corrosion, electrochemical reaction between adjacent closely spaced micro anode and micro cathode areas is involved; consequently, uniform corrosion might be considered as localised electrolytic attack, occurring consistently and evenly over the surface of a metal. In the above picture, you will see a volute casing used to pump salt water. This pump is not run continuously and can be left standing idle for days at a time.

Prior to coating and after the initial blast, the salt concentration of pump surface is always checked, internally and externally for porous substrates such as cast iron. If the salt levels are too high, we use Chlor*Rid solution to reduce the salt concentration to acceptable quantities. This ensures the coating does not suffer osmotic blistering in service.

Erosion Corrosion

Erosion corrosion is an acceleration in the rate of corrosion attack in metal, due to the relative motion of a corrosive fluid and a metal surface. The increased turbulence caused by pitting on the internal surfaces of a pump, can result in rapidly increasing erosion rates and eventually a leak. Erosion corrosion can also be aggravated by faulty workmanship. For example, burrs left at cut tube ends can upset smooth water flow, causing localised turbulence and high flow velocities, resulting in erosion corrosion. A combination of erosion and corrosion can lead to extremely high pitting rates. As you can see from the attached photograph, pumps can often suffer from vortices erosion, where the increased turbulence creates the swirling pattern of the erosion. It has also left a polished finish. This is the result from the fast moving fluid, sometimes containing fine suspended particles, creating multiple vortices, that are in turn dragged round by the spinning impeller.

For this type of corrosion, we use an abrasion resistant coating such as Plasmet HTE; a hardwearing, slip-free, three-pack, solvent-free polyamine cured epoxy screed, resistant to strong concentrations of sulphuric and other acids.

Simon says; “There are many companies that offer  pump repair, but only Corroserve has the best understanding of repairing pumps using our world class Glassflake products. We offer a really comprehensive service when it comes to pumps, including onsite maintenance service, repair or remanufacture, condition monitoring, certified testing, full strip and inspection reports, technical support and much more.”

Contact Simon to discuss how we can repair your pump.