Experience: Repair ofSplit Case Pump Corrosion and Erosion Damage

For some applications, corrosion and/or erosion damage is unavoidable. Whensplit casepumps receive repairs and are badly damaged, they may look like scrap metal, but with proper restoration techniques, they can often be restored to their original performance or better. Damage from corrosion and/or erosion can occur on stationary pump components as well as on rotating impellers.

NOTE: Cavitation damage is a form of erosion damage.

1. Coating Repair

Common repair methods for metal parts damage are divided into three categories: coating repair, machining repair and welding repair. Of course, many repairs involve a combination of all three. Of the three methods, coating repair is the most straightforward and often the easiest to implement. There are many suppliers and various restoration materials designed specifically for this purpose.

2. Mechanical repair

Machining repairs are most common when the seam surfaces of split case pump parts are damaged. Since the alignment of the pump components can be affected by the seam finish, proper design is required to ensure the pump fits back together properly. Of course, maintaining the concentricity and perpendicularity of the surfaces is critical. In addition, when a spigot face is machined to eliminate damage, it changes the axial position of the mating and related components.

If the axial position of bearings, seals, wear rings or other precision parts is affected, it may be necessary to adjust the position of the relevant parts, such as adjusting the position of the shoulder of the locating bearing on the shaft. If the impeller of the vertical turbine pump is equipped with a ring shaft key, machining the seam face of the fixed part may require machining a new shaft with an adjusted ring key position.

3. Welding Repair

Welding repair is the least desirable method. Cast pump components (impellers and stationary parts) can be difficult to repair by welding. Brazing may be successful, but the parts must be heated evenly, and even this can cause distortion. Extensive weld repairs to components may require rework of all machined surfaces to ensure that the effects of distortion are removed.

An example is the repair of mating surfaces on splitcasepump casings used in common water systems. If the mating pump housing surface is damaged, a few thousandths (microns) can be machined off to obtain a new flat surface. To achieve a proper fit after machining, a thicker pump case gasket can be fitted to compensate for the removed material. However, this is not suitable for maintenance of high energy pumps. The repair of these high energy pumps is beyond the scope of this article.

Repairing corrosion and/or erosion damage inherent in many pump applications is an important part of pump repair. If the damaged surface is left unrepaired, the damage process will be accelerated due to increased turbulence over the rough surface. The method described here should help resolve most common corruption situations.