Investment cast parts for down-hole oil and gas exploration operations
Oil & Gas
Oil is a finite resource and it is important that the process of extraction be carried out economically and efficiently. Various components of the drilling hammers used in oil extraction experience abrasion from mud, metal-to-metal wear and erosion. To combat excessive wear drilling hammers are hardfaced with composite alloys of tungsten carbide dispersed in a nickel or cobalt based matrix. Plasma transferred arc deposits of Ni-Cr-B-Si alloys are used to combat wear on plungers, sleeves, sucker rods and seals of mud pumps and submersible pumps.
In the refining sector, cobalt based alloys applied by PTA are used extensively to combat wear, erosion, abrasion and corrosion.
The hardfacing of engine valve seats, which is a high volume process, was originally done using Oxyfuel welding (OFW) and gas tungsten arc welding (GTAW) processes. However since the 1980’s hardfacing of engine valves has gone steadily toward PTA due to its consistently repeatable quality, productivity and enhanced deposit characteristics.
Engine valve seats experience a variety of wear modes such as erosion, adhesion, galling, corrosion and fatigue. Demands like fuel efficiency, power-to-volume rating increase, and fuel quality impose further strains on the valves. Cobalt-based alloys, such as Stellite® F and Stellite® 6, have proven to be effective under such circumstances and a host of cobalt based alloys are now used in the automotive industry for wear resistance.
Internal combustion engine valve manufacturers are big consumer’s of cobalt alloys for hardfacing applications. Precise control of the hardfacing alloys that go into each valve is of paramount importance from a cost standpoint. The metering of the alloy must be controlled to a fraction of a gram, and PTA offers the advantage of precise feed stock delivery, consistent hard face quality, and low rejection rates.
In addition to cobalt-based alloys, several nickel-based alloys that depend on borides and carbides for hardness are also used for hardfacing engine valves.
The steam cycle of power generators contains steam generators, turbines, and pumps that handle steam and water. This requires a variety of control, safety, and shut off systems. The main area of wear is in steam and water valves, which experience high-pressure steam, high temperatures, and metal-to-metal wear at seating areas. The valve seats and spindles also need to inhibit oxidation on the surface, which otherwise can cause sticking. PTA deposits of cobalt based alloys are used extensively on valve seats and faces to take advantage of their high resistance to metal-to-metal adhesive and erosive wear. Cobalt alloys also retain their hardness at temperatures in the range of 550°C or higher, which is the temperature of super heated steam. Cobalt alloys are deposited on the leading edges of turbine blades to combat the effects of liquid droplet erosion due to condensing steam. Cobalt based alloys also are reported to perform well on high-pressure steam turbine nozzles and induced draft fan blades.
Additional PTA Information:
To view product relevant to this process, please view our PTA Laser Powder product page
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