Many millions are spent in the oil sands industry providing new plants for the production of oil from tar sands. Oil sands pumps are a key component in these expansions.
The cost of non-conformance can be enormous so ensuring specified pump performance and reliability is of paramount importance. Subsequently, testing by the manufacturer prior to shipment has become more common as part of any purchase. Manufacturers are expected to offer various testing options aimed at providing confidence that equipment will meet expectations upon field installation. It is also understood that early identification of non-conformance enables more expedient corrective action measures and minimizes overall schedule impact.
It is generally not possible to test the pumps at the manufacturer's facility on the actual oil sands media because of environmental, cost, schedule requirements and other concerns. Consequently, testing one of each size bare-shaft pump on clear water via the manufacturer's standard test stands is considered satisfactory. Tests that actually can be completed and their limitations are of particular interest.
Background and Standards
Compared to the water pump industry, few slurry pumps intended for mining and other associated industries are subjected to acceptance tests before shipment to the customer. Experience over the past 10 years indicates that Flue Gas Desulphurization (FGD) pumps for the power industry and pumps supplied to the oil sands industry are the exceptions. A picture of a large oil sands hydrotransport pump is shown in Figure 1.
Figure 1. Hydrotransport pump set up for lab test
These industries typically require complete pump testing that includes: hydrostatic, hydraulic performance, net positive suction head (NPSH) requirement, mechanical (functional), bearing temperature stabilization, sound level and vibration. In general, centrifugal slurry pump manufacturers design their equipment to adhere to the American National Standards (ANSI) Hydraulic Institute (HI) standards, which include sections that provide guidelines and acceptance criteria for the above stated testing (References 1 -5).
Hydrostatic testing (Reference 2) of the pump wet-end assembly demonstrates that the product has been designed and manufactured to handle the pressure it will experience with an acceptable safety margin. Wetted parts experience wear while operating on slurry, thus the 25 to 50 percent pressure test margins are intended to ensure the product operates safely and to account for the reduction in pressure carrying capacity over time.
The American National Standards for Rotodynamic (Centrifugal) Slurry Pumps for Nomenclature, Definitions, Applications, and Operation (Reference 1) requires performance tests in accordance with ANSI/HI 1.6-2000 (Reference 2) using only clear water. Hydraulic performance testing enables verification that the pump can produce the required total dynamic head while operating at the rated duty flow for a specified shaft speed. The pump's efficiency and shaft power requirements are also verified.
This standard provides two acceptance levels having varying tolerances. Typically test costs increase as performance tolerances decrease to account for extra preparation required in producing and testing the pumps to tighter specifications. The standard acknowledges that if the facility cannot test at rated speed because of limitations in power, electrical frequency or available speed changers, the pump may be tested at between 80 to 120 percent of rated speed. For pumps greater than 225-kW, test speeds may be between 60 to 140 percent of rated speed. Scaling of test data is performed by use of the pump affinity laws back to rated speed for performance evaluation. Correction rules are provided that allow for the effect of variations in temperatures, fluid specific weight and (Newtonian only) viscosity.
Net Positive Suction Head requirement (NPSHr) testing per Reference 2 can be performed on the pump and compared to the NPSH availability of the application to ensure that an acceptable margin is maintained in accordance with Reference 6, which states slurry pumps should be 10 percent or 0.6-m, whichever is greater. The primary purpose of this testing is to confirm that the pump will operate stably without cavitating when placed into service. Reference 6 also indicates that the noise, vibration and possibly the reliability of a centrifugal pump and mechanical seal (if applicable) may be significantly affected if an appropriate NPSH margin is not provided by the system above the NPSH required by the pump.
Mechanical (functional) testing can be performed per Reference 2 to demonstrate satisfactory mechanical operation of a pump at the rated condition, including vibration levels; lack of leakage from shaft seals, gaskets and lubricated areas; and free running operation of rotating parts. When specified, bearing temperature stabilization will also be performed and recorded per Reference 3, which can require pump operation up to eight or more hours. For this test, the standard does not make provision for operation at a reduced speed.