Impellers are critical components in any pumping or turbo-machinery equipment. Their balance, precision of form, consistency from one to another and surface finish are the primary determinants of pump efficiency. A 1% improvement in pumping performance can reduce pump operating costs by 50%. However, production of impellers with the attributes required for pumps with high performance specifications is difficult, and exposes the limitations of even the most advanced casting manufacturing techniques.
Impellers are geometrically complex components and are produced in corrosion, erosion and cavitation-resistant alloys which are difficult to cast, especially in the thin sections of the vane profile. Moreover, high specification pumps are typically made in very low volume – a ‘one off’ is quite common – so the cost of utilising these techniques, setting to one side their shortcomings, becomes prohibitive because of the high tooling cost.
Cti has been well-aware of this gap in market provision and has long-sought a solution. The breakthrough came with the support provided through the Advanced Manufacturing Technology Initiative, which facilitated the acquisition of key items of equipment and allowed focussed, product-specific development effort to take place. Having arrived at a prospective solution, Cti approached Sulzer Pumps (UK) Ltd to establish their interest in evaluating the new approach.
Sulzer Pumps (UK) Ltd is a subsidiary of Sulzer AG, Switzerland, and is one of 14 Sulzer Pump Division factories across the world. Its business is focussed on the oil and gas, hydrocarbon processing, and power generation sectors. Some of the world’s largest and most powerful pumps have been designed, manufactured, packaged and tested at their Leeds operation for customers on all continents. The most demanding requirements from these customers is in the field of ‘sea-water injection pumps’ which are used on production platforms to assist in raising oil to the surface. As oil reserves become more difficult to access, i.e. deeper, it is becoming more common for higher pressure impellers to be specified. It is, therefore, imperative that a cost-effective and functional solution be found to satisfy the market need for improved impeller performance, so Sulzer were keen to evaluate Cti’s proposition. The outcome of the early tests were so encouraging that a directive was issued at Sulzer that impellers for their new range of high pressure pumps must only be produced by the Cti technique.
According to John Chorlton, Engineering Director: “there is no other viable option, or viable route, of producing impellers to the standard required for these pumps”.
Dimensional accuracy and consistency have been verified using state-of-the-art metrology at Leeds College of Technology who advised that ‘they were the best impellers they have ever measured’. The tolerances on key dimensions were almost an order of magnitude better than the best values achieved by investment casting.
The benefits to Sulzer are:
- Pattern costs and lead-times are eliminated, castings being produced directly from 3D CAD files e-mailed to Cti;
- Lead-time is reduced, with the potential for even faster response once certain process refinements are concluded;
- The cost and time of ‘detailing’ – manual finishing and polishing – is eliminated. Hydraulic testing has proven that the quality of surface finish is high enough to use the impellers in the ‘as received’ condition;
- The risk of a pump not achieving the design specification is much reduced, so the cost and time of stripping down, detailing of impellers, rebuild and re-testing is much lower. Not only will this save approximately £15k each time a problem is avoided, but it will also save the financial penalties and loss of goodwill associated with late deliveries.
Steve Richards, Design Engineer at Sulzer, adds: ”This process has eliminated the dependency on manual patternmaking skills which, at their best, cannot deliver the consistency and accuracy that we require. It has allowed us to bring the control of product quality in-house by developing the required 3D geometry ourselves, which eliminates risks of design interpretation. It has justified our investment in 3D modelling software and training, which for our two operators totals £30,000. In addition, we estimate that we have spent approximately £17.5k evaluating the impellers produced by Cti, to which we contributed £52,000 to this development and exploratory phase. However, this activity has safeguarded 5 jobs and created 10 posts because the new process has been exploited in four projects requiring high pressure sea water injection pumps in:
- Amenam, Nigeria
- Enfield, Western Australia
- Clyde Talisman, North Sea
- Aramco Haradh, Saudi Arabia
The value of these sales is £5.5m and it is a reflection of the confidence in Cti that Sulzer were willing to risk projects of this magnitude by using impellers manufactured by their new technique. We are now looking at other critical components such as diffusers to evaluate what additional benefits we may realise from their technology. They are keen to set up an operation dedicated to impeller manufacture, and we would commend such an initiative because the focus this would bring to the supply chain would yield even greater benefits”.