Have you ever noticed minute radial cracks that appear on metallic, tungsten carbide, or ceramic seal faces and shrugged them off as inconsequential? That’s a mistake you are going to need to get ahead of.
If you are not proactive about looking for the signs of mechanical seal heat checking, the results can be significant: component damage, unrepairable seal failure, and the associated downtime. These days, when margins are running even thinner than usual for many refineries, these are costs that you don’t want to add to your bottom line. It’s much easier—and less costly—to know the signs of heat checking and what to do about them.
Several factors, individually or collectively, contribute to thermal stress that leads to heat checking. Below, I’ve summarized the key factors to show there is often an interplay and demonstrate the value of a carefully configured mechanical seal support system to manage the problems. Sometimes your best solution is the most obvious.
Mechanical seal heat checking, caused by excessive thermal stress, is frequently found in high-temperature, high-pressure hydrocarbon processes such as those in California Bay Area refineries. Small cracks act as abrasives that may ruin seal face integrity and eventually lead to seal failure. And seal faces damaged by heat checking are typically unrepairable. Thermal stress can also damage other mechanical seal components—elastomers, bellows, and springs, requiring additional unplanned downtime to accommodate complete seal replacement.
Let’s take a look at some of the reasons these problems can occur:
Proper lubrication, whether it’s a process fluid flush, barrier fluids, or steam quench to prevent coking is critical to minimizing the seal face friction that creates heat and results in mechanical seal heat checking. Lubrication problems can be attributed to:
➢ Insufficient flow of process fluids, barrier fluids, or external quench to the seal chamber
➢ Barrier fluids that are incompatible with process fluids
➢ Dry pump startup caused by preventative maintenance flush of the seal chamber followed by improper venting that leaves an air pocket around the seal
➢ Running dry caused by the unexpected stoppage of flush fluids
➢ Excessive pressure between seal faces preventing adequate flow of lubricant across faces
Seal chamber temperature is closely tied to improper lubrication. Excessive seal face friction raises seal chamber temperature. Aside from inadequate lubrication, the other factors that contribute to increased seal chamber temperature and eventual mechanical seal heat checking are:
➢ Inadequate flow or volume of process, barrier, or quench flush to effectively dissipate heat from the seal chamber
➢ Disruption of flush caused by blockage in tube or filter, or unintended cessation of plant water or nitrogen flush delivered to mechanical seals
➢ Malfunction of seal support system pump that circulates barrier fluid
➢ Diminished capacity in heat exchanger as result of scaling on coils or inadequate flow of plant water through coils (Upgrading to a serviceable heat exchanger can mitigate this issue.)
➢ Change to higher-temperature process fluids that exceeds limits of the mechanical seal and/ or seal support system
Mechanical seals and support systems installed for specific processes years ago may no longer be adequate when process conditions change, such as processing higher-temperature (sour crude) hydrocarbons, increased process fluid viscosity, or higher processing volumes or throughput. The result of these process changes can be:
➢ Process fluid temperatures exceeding seal face design limits.
➢ Excessive seal face hydraulic loads that increase seal face friction.
➢ Process exceeds pressure-velocity (P-V) limits of seal face materials.
➢ Damaged thrust bearing or collar creating excessive seal face loads.
Any one or a combination of lubrication, cooling, or pressure factors can lead to mechanical seal heat checking and eventual seal failure. A proactive approach to preventing these issues requires a review of process conditions, seal design, and support systems, with the goal of ensuring mechanical seals and their support systems are properly configured for processing needs.
To determine the root cause of heat checking, you need to do a root cause analysis. This involves running through all the potential scenarios that may be contributing factors and identifying the bad actors. The questions below focus on conditions that need to be modified in order to prevent mechanical seal heat checking.
☐ Do significantly higher process fluid temperatures require modifications to mechanical seals and their seal support systems?
☐ Does pumping pressure exceed the design limit of the seal face materials?
☐ Are mechanical seals overloaded as a result of bearings, couplings, or drive malfunction?
Do significantly higher process fluid temperatures require modifications to mechanical seals and their seal support systems?
☐ Does pumping pressure exceed the design limit of the seal face materials?
☐ Are mechanical seals overloaded as a result of bearings, couplings, or drive malfunction?
☐ Is a different seal design, like a dual seal replacing process-side seal, needed for better temperature management?
☐ Do you need different face materials such as silicon-carbide to better resist the thermal stresses that cause mechanical seal heat checking?
☐ Would a different dimension of seal faces, like a larger diameter, help reduce the hydraulic load?
☐ Are new cooling coils, larger heat exchanger, increased plant water flow through the coils needed to better maintain seal chamber temperature?
☐ Will the addition of gauges, instrumentation, and transmitters provide better monitoring temperature, pressure, and flow of flush fluid conditions?
☐ Does the barrier fluid need to be changed to better match processing conditions?
☐ Is a more robust seal support system required? For example, replacing API Plan 52 (Buffer Fluid Seal Pot) with API Plan 54 (Barrier Fluid Pressurized by External System) to maintain fluid pressure via a pump and external reservoir?
Factors involving mechanical seals should be addressed with the assistance of your local mechanical seal support vendor. They can provide the latest information regarding the range of seal materials and designs now available to effectively contend with environments prone to thermal stress. Similarly, your seal support system vendor can provide expert guidance, helping you select and configure seal support systems to mitigate specific mechanical seal heat checking issues.
Component upgrades or complete replacements of current seal support systems are often the most effective means of mitigating mechanical seal heat checking issues. Seal support systems can be designed and configured with components tailored to address the specific mechanical seal lubrication and cooling concerns.
Swagelok offers local expertise for upgrading or replacing seal support systems to help eliminate factors that lead to mechanical seal checking. Our Field Engineers are available for on-site evaluation of your systems. Based on a thorough analysis, we can then propose the most cost-effective component upgrades or recommend seal support systems to enhance the reliability of mechanical seals.
Our certified technicians, employing ISO 9001, quality standards will then fabricate and thoroughly test your seal support systems in the Swagelok’s Fremont facility prior to delivery. Swagelok’s local presence ensures you have the availability of highest-quality parts after installation and ongoing technical support—all backed by the best Lifetime Warranty in the industry.
To find out more about how Swagelok Northern California can help you proactively avoid conditions that lead to mechanical seal heat checking using seal support systems specifically configured to your porcess requirements, contact our team today by calling 510-933-6200.
Paul holds a B.S. in Mechanical Engineering from North Dakota State University. Before joining Swagelok Northern California, he was the West Coast Regional Sales Manager for an organization based in Illinois involved in pneumatic and hydraulic applications where he supervised product distribution throughout the western United States, Canada, and Mexico. While in this role, he was able to help provide technical and application-specific expertise to customers and distribution to drive specifications.