Pumps are involved in every major industrial sector. The diversity of their functions is matched by the variety in their design. Keeping these vital pieces of equipment in optimum condition ensures continued efficiency and reliability. Sourcing spare parts and the remanufacturing of components is becoming quicker and easier with the increased availability of additive manufacturing services. This can minimize downtime and expedite repair times.
Dr. Yogiraj Pardhi, Global Lead for Additive Manufacturing for Sulzer, looks at the latest additive manufacturing techniques being used to create parts for pump equipment.
By Dr. Yogiraj Pardhi, Global Lead for Additive Manufacturing, Sulzer Services
In most critical operations, time is of the essence. There is a limited timeframe in which to complete repairs, even during planned outages. Replacing high-value assets may require long lead-times, making a remanufacturing project far more appealing. Furthermore, the need for significantly less energy, as well as new materials, make the renewal of existing parts far more sustainable. At the same time, the delivery of parts can be affected by many variables. Recent events have highlighted the fragility of some original equipment manufacturer (OEM) supply chains.
From the simplest seal in a submersible pump to a retrofit project on a boiler feed unit, carefully planned maintenance and repair is essential for continued reliability and efficiency. There are several techniques that are used to revitalize components depending on the materials, the type of repair, and the application of the part. In many cases, it is possible to improve on the original specification. This could mean increasing durability or tailoring the design better to the application, which may have changed over the service life of the pump. Today, repair specialists, such as Sulzer, are looking to use the latest available technology to cost-effectively create new components, even in small quantities.
The development of techniques such as additive manufacturing (AM) for industrial pumping applications have been championed by the oil and gas market, which is focused on absolute reliability due to the significant costs of unplanned downtime. As more operators are taking advantage of the service, it is becoming increasingly cost-effective and therefore more attractive to other sectors. Time and expense are not the only benefits. The decision to remanufacture an existing component also offers advantages for an operator’s sustainability and environmental goals. The whole process minimizes both the materials and the energy used for the repair, as opposed to a replacement.
Making the Best Choice
Direct AM can be achieved in several alloys such as 316L stainless steel and Inconel 625, using selective laser melting (SLM) to print complex components directly from 3D models. This area is expanding as the manufacturing processes for specialist alloys are further developed and provide fast turnaround times for specialist parts. This technique can be used with materials such as stainless steels and both nickel and cobalt based alloys which offer several benefits including high strength levels, good resistance to corrosion and excellent high-temperature performance.
Similarly, laser metal deposition (LMD) can be used with a range of materials including stainless steels, martensitic steels, corrosion resistant nickel-based alloys like INCONEL® and hard tungsten carbides and Stellite® coatings. LMD is also suited for delivering repairs
on Super Duplex stainless steel, commonly used for strength and corrosion resistance in many pump parts.
LMD is impressive due to its speed, versatility and quality of repair. It offers fast build rates and requires less heat input, which reduces the heat affected zone (HAZ) and minimizes any distortion. However, one of its greatest advantages is its superior strength due to the metallurgical bond and consistent material density. This ensures ultimate adhesion to the parent material.
For urgent part requirements on high value assets, such as those seen in the oil & gas or petrochemical industries, a hybrid process using laser metal deposition and five-axis milling now allows rapid manufacturing on a single, dedicated machine. For example, for an impeller, a forged core is machined using five-axis methods to establish the basic shape of the eye of the impeller. Next, a laser melts the powder and deposits a layer of metal onto the surface below.
Indirect AM uses technologies to print patterns and molds that are subsequently used in conventional casting processes. In one such application, AM prints patterns of the required part in polymers or wax. These are then encased in a ceramic shell, known as investment casting. The shell is heated to melt the wax/polymer and then heated further to fire the ceramic.
This produces a hollow mold that can be filled with a metal alloy. It is next allowed to cool before the ceramic shell is broken away to leave the final part. The detail and surface finish achieved through this process improves quality and greatly reduces the normally required time for tooling to create new parts.
Another indirect technique is to print the sand mold of a conventional sand process using binder jetting AM method. This eliminates the need to store conventional casing patterns and reduces the lead time as well as cost to produce new ones. In each case, the use of AM techniques offers significant time savings while maintaining or even improving the quality of finish of the part.
This allows large volumes of material to be built up quickly onto the core structure underneath. One of the many advantages of this process is that parts can be created from a small stock of forged bars in a few common materials. This enables the manufacturer to make an immediate start. Furthermore, the core of the impeller will have all the positive attributes associated with forged materials. This is then further built up using the laser metal deposition process which can be accomplished on the same machine.
Having created the basic internal structure, the milling function of the machine is used to finalize the surface finish of the internal passages. This is otherwise inaccessible to machine tools on the finished impeller. Then, the laser metal deposition process continues to add more material to the core, working towards the finished design.
Faster and Better
A clear benefit of the hybrid AM process is that an impeller with complex hydraulic geometry can be created on one machine, with no need to transfer it between different assets. This saves time and improves accuracy.
The flexibility of this manufacturing method also offers the opportunity to create components using different materials and allows specific alloys to be used in various areas of the design. This is an extension of technologies such as specialist coatings and hard-facings where optimized material properties can be incorporated into the design during the manufacturing process, rather than as an additional step.
A cooling water pump at a natural gas power station, which worked with seawater, was shipped to the company’s local service center for inspection. There, technicians discovered wear and corrosion on the impeller drive shaft.
A new shaft had a lead time of 20 weeks; however, the customer needed the pump to be back in operation more quickly as it was relying solely on its backup pump. Sulzer proposed its new LMD repair process as it offers exceptional durability while streamlining project completion.
Within six weeks, the most urgent repair was completed, and the pump returned to the power station for installation. Having identified a common issue with this design of pump, a preventative maintenance project was proposed to allow all similar equipment to be repaired during planned outages. This meant that the operator could schedule in the improvements to the pumps and avoid any disruption.
As each repair is completed, the process becomes leaner and more refined, minimizing the time that a pump is away from the power station. The proactive approach means that any damage is repaired before it develops into a problem. As a result, the power station operator can confidently continue to support energy users across Europe. While speed is of the essence, it is meaningless without quality and consistency. For this reason, additive manufacturing techniques must be delivered by skilled and experienced practitioners. The work required to develop the processes and complete the testing and verification is extensive.
However, the benefits for heavy industry are substantial. Additive manufacturing offers many advantages that will only be further expanded as more materials are qualified. Moving forward, greater flexibility in manufacturing location will be enabled and therefore streamline the process and minimize lead times.