What Causes Heat Cracking or Checking of a Mechanical Seal

Heat cracking or checking is a common issue that can lead to premature failure of mechanical seals in various industrial applications. Understanding the causes behind this problem and implementing appropriate preventative measures are essential for ensuring reliable seal performance and extending equipment lifespan.

In this blog post, we will delve into the primary factors that contribute to heat cracking or checking of mechanical seals, including exceeding PV limits, dry running, excessive product heat, inadequate lubrication, and improper cooling.

Causes of Heat Cracking or Checking

Exceeded Pv Limits

Each mechanical seal is designed to operate within specific pressure and velocity (Pv) limits based on the seal material and operating conditions. If the mechanical seal is subjected to pressures or velocities that exceed its rated Pv limit, increased friction and heat generation will occur between the seal faces. This excessive heat can cause thermal expansion, stress, and eventually cracking or checking of the seal face material.

Dry Running

Mechanical seals require a thin fluid film between the seal faces for proper lubrication and cooling. If this fluid film is lost and the seal faces run dry against each other, rapid heat generation and thermal damage can occur. Dry running can happen due to issues like improper venting, fluid vaporization in the seal chamber, or operating with insufficient fluid levels.

Excessive Heat from Product

In some applications, the process fluid itself may be at a high temperature that can conduct excessive heat into the seal components. If this heat is not adequately dissipated, it can cause the seal faces to experience thermal expansion, increased wear, and heat-related damage like cracking. Careful seal selection and the use of cooling systems are important when dealing with high temperature process fluids.

Inadequate Lubrication

For mechanical seals to survive and operate properly, an adequate lubricating film must be maintained between the seal faces. Poor lubrication can occur if the sealed fluid has low viscosity, high temperatures cause the fluid film to vaporize, or the seal is running too slow to generate a sufficient hydrodynamic film. Without proper lubrication, increased friction, heat generation and thermal stresses will damage the seal faces.

Improper Cooling

Many mechanical seals, especially in high heat applications, require a cooling system to remove excess thermal energy and keep the seal faces at a safe operating temperature. If the cooling system is not properly designed, sized, or maintained, it may fail to provide adequate heat removal from the seal. This can allow heat to build up in the seal faces, eventually leading to thermal-related damage like heat checking or cracking.