This article discusses technological advancements in plant maintenance aimed at reducing costs and improving mechanical seal efficiency. It highlights innovations such as non-contact mechanical end face sealing with grooves, which reduces friction and wear by using inert gas instead of liquid barriers. New materials like silicon carbide with self-lubricating properties and diamond-coated sealing surfaces enhance durability and performance. Standardization through EN 12756 and API 682 ensures interchangeability and cost reduction. These advancements significantly improve sealing reliability, energy savings, and service life, especially in critical applications like oil and gas, petrochemicals, and pharmaceuticals.
In plant maintenance can reduce costs. To achieve this, there are two important factors:
Technological development
A mechanical seal consists of a rotating component (dynamic ring) and a fixed component (static ring). The moving ring is usually connected to the rotating part of the equipment (such as the shaft), while the stationary ring is connected to the fixed part of the machine (such as the packing box of the rotary pump). In order to ensure effective sealing performance, the sealing surface must be absolutely flat and the surface roughness must be extremely low. The precisely matched dynamic and static rings can fit tightly, effectively preventing leakage of process fluids.
The interaction between the two sealing surfaces determines the hydraulic equilibrium state of the mechanical seal. Under normal working conditions, the formed liquid film can achieve hydraulic equilibrium between the opening and closing forces generated by the pressure of the sealing fluid, thereby limiting physical leakage. The API 682 standard provides detailed guidance and specifications on how to calculate the correct size parameters.
However, during operation, the sealing ring may deform due to mechanical and thermal stresses, which can affect the performance of the mechanical seal. This deformation will break the original hydraulic balance, making the liquid film between the sealing surfaces unstable and leading to excessive leakage.
Therefore, engineers are constantly exploring new technological methods to reduce friction, especially under critical application conditions, with a special focus on the development of new materials and the application of new sealing technologies. These innovations have significantly improved the sealing efficiency and reliability in modern production processes.
Non contact technology - sliding end face with grooves
The non-contact mechanical end face sealing system consists of a moving ring and a stationary ring. The end face of the moving ring is specially processed to have a specific geometric shape (such as spiral or stepped), which can generate fluid dynamic effects between the two end faces, thereby forming a stable small gap between them (refer to Figure 1). This design utilizes the principle of fluid dynamic lifting, allowing the sealing surface to maintain an effective sealing state without direct contact.
Unlike traditional contact seals, this non-contact design does not rely on liquid barriers and their related support systems. On the contrary, it achieves sealing effect by supplying inert gas to the sealing interface. The selection of inert gases is usually based on their chemical stability and adaptability to the working environment to avoid reactions with the sealed medium. In addition, the pressure and flow rate of the inert gas can be precisely controlled through a simple control panel to ensure the stability and reliability of the sealing performance.
Due to the effective reduction of friction coefficient and wear of seals to near zero, this solution is very suitable for applications that require significant energy savings, especially in the oil and gas, petrochemical, and pharmaceutical industries that require zero emissions.
New generation materials
Silicon carbide materials with self-lubricating properties are widely used in mechanical seals. In the selection of matching for moving parts, materials of different hardness are usually used to minimize friction as much as possible. The selection of sealing ring combination is particularly crucial, among which the most commonly used combination is carbon ring and silicon carbide ring (see Figure 2, pressure x cycle velocity PxV coefficient for common surface combinations). This combination not only has excellent thermal conductivity and chemical resistance, but also effectively resists wear caused by abrasive particles in the fluid.
When graphite rings and silicon carbide rings deform due to various reasons, they exhibit excellent mutual adaptability, thereby maintaining good sealing performance. However, in situations where the working pressure is very high or the fluid contains a large amount of dirt, two high hardness rings must be used to ensure the sealing effect. Although these materials have a high coefficient of friction, this can result in the generation of more heat during rotation, which may cause liquid film evaporation, leading to dry running, ring deformation or fracture, and affecting the performance of auxiliary gaskets.
A recently developed manufacturing process involves adding self-lubricating material particles to a sintered silicon carbide matrix through immersion method (silicon carbide immersion method). The fixed and rotating rings made using this method can achieve extremely high performance limits. Specifically, mechanical seals using this material can limit the absorbed torque value, significantly reducing friction and heat generation. This not only improves the durability and reliability of the sealing components, but also extends their service life, especially suitable for applications under extreme working conditions.
Diamond coated sealing surface
Silicon carbide rings are typically coated with a thin layer of diamond coating through chemical vapor deposition (CVD) process to enhance their tribological properties and chemical compatibility. In hot water applications in power plants and petroleum and petrochemical facilities, liquid gases are prone to evaporation, leading to loss of lubrication performance, while diamond coatings can significantly improve the wear resistance and corrosion resistance of seals.
In the pharmaceutical industry, traditional seals often cannot meet strict requirements due to the need to avoid any contamination, while diamond coated seals exhibit excellent chemical inertness and purity, fully meeting these high standard requirements.
In addition, mechanical seals using diamond coated rings can withstand brief operation under dry operating conditions of dual sealing and non-contact sealing, further expanding their application range.
Engineering machinery seals
During the design phase, maintaining consistency in the cross-sectional area of the sealing ring is a major challenge (see Figure 3). This consistency is crucial for ensuring the driving stability of the sealing ring and preventing reversal. This type of seal is currently widely used in boiler feed pumps, pipelines, water injection systems, multiphase pumps, and other high-pressure applications with working pressures exceeding 100 bar. Accurately controlling the size and shape of the sealing ring not only helps maintain sealing performance, but also effectively reduces wear and extends service life.
Standardization and interchangeability
Mechanical seal components, like other industrial accessories, have a reference standard that specifies their installation dimensions, allowing for the use of seals produced by other manufacturers for replacement. This not only improves the service quality for end-users, but also reduces factory operating costs.
EN 12756 standard
The EN 12756 standard specifies the main installation dimensions for single mechanical seals and double mechanical seals when used as components, excluding flanges and sleeves covering rotating and fixed components. In the early post-war period, the first batch of mechanical seals were introduced from the United States to Europe, with the unit of measurement being inches.
The DIN 24960 standard later evolved into the EN 12756 standard, bringing significant benefits to manufacturers who produce pumps according to ISO standards, especially for end users who are no longer limited to seal suppliers providing non standardized products. The price of seals and their related maintenance costs have therefore significantly decreased.
API standards
Pumps in oil and gas equipment are typically manufactured according to API 610 standards, while mechanical seals are typically manufactured according to API 682 standards. According to this standard, seals must be provided in the form of cylindrical components, equipped with flanges and bushings, to simplify installation and allow for testing before delivery. The API standard provides recommendations for determining the size of mechanical seals based on the packing box specifications of different API pumps on the market.
This standardization is not only technically feasible, but can also standardize the overall dimensions of the components inside the stuffing box, thereby achieving medium scale mass production and reducing manufacturing and warehouse management costs.
Importantly, this standardization allows end-users to choose different 'qualified mechanical seal manufacturers', thereby eliminating interchangeability issues. Through this method, users can flexibly choose suitable seals and ensure their smooth replacement, reducing downtime and maintenance costs caused by mismatched seals.
