Tungsten Carbide (TC)
Tungsten Carbide is a chemical compound. (specimen, a carbide) containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into shapes through a process called sintering for use in mechanical seals industrial, machinery, cutting tools, abrasives, armor and other tools and instruments.
Tungsten Carbide Seal Faces : A very versatile seal face like Silicon Carbide. It is very hard like silicon carbide however it is very heavy to the touch, making it easy to distinguish from silicon carbide. Ideal for high pressure applications due to a high modulus of elasticity which helps prevent face distortion. Tungsten carbide also can be re-lapped and polished to be re-used.
Sintered Silicon Carbide (SSIC)
Silicon Carbide : Is a bluish-black material created by fusing silica and coke. It is in the same family as Ceramic (due to the Silica), but has much better lubrication qualities and is harder. The most common is reaction-bonded silicon carbide. In Chemical applications however, Alpha Sintered Silicon Carbide may be recommended. Alpha Sintered Silicon carbide does however sacrifice the Pressure Velocity ratios due to the lack of un-reacted free carbon. Either grade of SIC can usually be re-lapped and polished to be reused. Sintered (alpha) silicon carbide (SSIC) is produced by initially mixing fine (sub-micron) and pure silicon carbide powder with non-oxide sintering aids. The powdered material is formed or compacted by using most of the conventional ceramic forming processes such as die pressing, isostatic pressing and injection molding. Following the forming stage, the material is sintered in an inert atmosphere at temperatures above 2000°C. The sintered silicon carbide can then be machined to precise tolerances using a range of precision diamond grinding or lapping techniques. As with most advanced ceramics the cost of the component is reduced if the amount of diamond grinding is reduced i.e. either the material manufacturer can achieve the required tolerances "as sintered" or the designer removes unnecessary tolerances.
Why Silicon Carbide Seal Face : Sintered Silicon Carbide offers a high-performance seal face material that has proven successful in such diverse pumping applications as chemical processing, refining, mining and pulp and paper processing. The material provides superior corrosion and abrasion resistance; shock resistance; and low sliding friction against a wide range of mating materials. Either grade of SIC can usually be re-lapped and polished to be reused.
Reaction Bounded Silicon Carbide (RBSIC)
Although silicon carbide can be densified with high temperature and pressure, the process is not a viable commercial process. Reaction bonded silicon carbide is made by infiltrating compacts made of mixtures of SIC and carbon with liquid silicon. The silicon reacts with the carbon forming silicon carbide. The reaction product bonds the silicon carbide particles. Any excess silicon fills the remaining pores in the body and produces a dense SiC-Si composite. The ratio of SiC to carbon and particle size distribution varies widely in practice. Articles are produced with a wide range of compositions and properties. At one extreme, carbon fibre felt or cloth can be infiltrated with liquid silicon, whilst at the other extreme, an impervious silicon carbide body can be made with a small amount of carbon. Most reaction bonded silicon carbide is made with formulations that contain an organic plasticizers, carbon and silicon carbide particles. This mixture is ideally suited to near net formation by pressing, injection moulding or extruding. Further, since the reaction process typically gives a dimensional change of <1%, manufacturers have excellent control of component tolerances.
To enhance the properties of carbon-graphite grades, they are typically impregnated with various substances in order to achieve the required chemical and physical properties. These adders are typically resins, ceramics, and metals. Metal impregnated carbons offer the highest strength and antimony is commonly used; Antimony impregnated carbon is the default carbon identified in API 682 when considering use in a light hydrocarbon service. Antimony carbon is commonly used in various services in midstream pipelines. Specialized Nickel impregnated grades have also been used widely with go&1 success, although lead times and costs of those materials make them less desirable options. Although antimony filled carbon-graphite primary ring can produce the best performance and lowest leakage, the relatively soft nature of the material in abrasive or viscous services can present limitations. In practice, two hard faces are usually necessary in order to prevent mechanical and/or abrasive face damage in crude oil service. Additionally, in pressures beyond 1200 PSIG (82 BARG), evaluation of the carbon material is required to assure sufficient margin of safety against mechanical failure of the material and also deficiencies in the seal performance from excessive distortion due to pressure. The majority of the carbon seal faces utilized in midstream pipeline applications.