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The Fluid Systems Engineering and Management Blog

by Swagelok Northern California

Improve Rotating Equipment Dry Gas Seal Reliability: 3 Common Problems to Avoid

by Paul Lesnau, on 11/10/20 7:45 AM

Swagelok-gas-seal

If you’re in the petrochemical industry you’re familiar with centrifugal compressors. They’re essential in many phases of the production cycle such as hydrocarbon processing, natural gas liquefaction, and pipeline transportation. Many compressors rely on dry gas seals (usually a dual seal arrangement) for reliable operation. Dry gas seals are machined with tolerances to allow a 3 to 10 µ gap between the rotating and stationary seal rings during compressor operations. Minute, integrated grooves in the rotating seal ring generate the gap that allows pressurized gas to infiltrate the space between the rings when the compressor is operating. 

Maintaining the required pressure and flow of clean, dry gas (typically nitrogen) to the dual seals is critical to reliable compressor functioning. The gas supply must be free of particulates that could clog the grooves or expand the seal gap. Without the proper gas flow, you’ll experience overheating and contamination that eventually leads to dry gas seal failure. When you’re dealing with hydrocarbons, seal failure can result in leakage that may subject you to sanctions from Cal/OSHA or BAAQMD. 

There are a few important steps that operations personnel can take to help ensure the reliability of rotating equipment that uses dry gas seals. Below I describe three common problems that jeopardize dry gas seal reliability, then explain how a properly configured seal support system such as API Plan 74 helps prevent these problems.

#1) Rotating Equipment: Dry Gas Seals Don’t Do Dirt

Problem: The minute grooves on dry seal faces force the pressurized nitrogen between the rotating and stationary faces to provide needed lubrication. With such close tolerances, microscopic particles (aka dirt) in the nitrogen supply can plug the grooves and damage seal faces

Solution: To avoid these contaminants, best practices recommend using supply line filters that can trap particulates 1 µ or larger that may be present in the nitrogen supply. 

Problem: Compressor casings can also be a source of dirt. If you can’t deliver the required gas pressure to a dual seal during compressor startup or shutdown dirty gas from the compressor casing can enter the seal chamber and foul the seal faces and seal components. 

Solution: You’ll avoid both of these problems with a seal support system that delivers clean, dry gas at constant pressure and flow regardless of the operating state of the compressor. 

#2) Seal Components: Must Be Compatible With Process Gas

Problem: Dry gas mechanical seals have components (O-rings, V-rings, U-rings) designed to contain process gas within the compressor casing. If these components are not compatible with process gas they’re exposed to, they’ll eventually deteriorate and lead to excessive leakage of nitrogen into the compressor. Without a careful diagnosis of the problem, you could easily confuse the leakage with mechanical seal face failure

Solution: When you’re selecting a dry gas mechanical seal for the process, or if there’s been a change in the process gas, make sure that components such as elastomers used in the dry gas seal are compatible with the process gas. 

#3) Lubrication: Nitrogen Gas Is Good, Oil Is Bad 

Problem: Lack of proper lubrication can accelerate the deterioration of many types of rotating equipment. But in the case of centrifugal compressors, oil-based lubrication needs to stay in its place. Upstream compressors (oil-flooded screw, oil-lubricated reciprocating, or oil-sealed turbo) can introduce oil into the process gas flow. When a seal support system fails to deliver the proper gas pressure in a dual seal the oil-tainted gas flow from an upstream compressor can infiltrate a downstream compressor’s mechanical seals and ruin their effectiveness. Friction, heat, and failure are likely outcomes. 

Solution: Oil-tainted process gas is really just another type of contaminant that dry gas seals cannot tolerate. A consistent, clean, pressurized flow of nitrogen to the dual seal is the most effective means to combat this problem. 

Rotating Equipment Dry Gas Seal Reliability Relies on the Proper Seal Support System

Rotating equipment dry gas seal reliability relies on the right seal support system configured for the specific process application. I’ll use API Plan 74 (Barrier Gas) to illustrate how a properly-configured system prevents dirt and oil contamination from degrading compressor performance.

Plan-74-render

API Plan 74 Control Panel delivers pressurized nitrogen to a dual mechanical seal to help ensure reliable centrifugal compressor operations. 

API Plan 74 delivers pressurized gas (usually nitrogen) from an external source to a dual mechanical seal. A properly-configured plan eliminates the problems mentioned above that could lead to dry gas mechanical seal failure in a compressor. The table below explains how these key features improve rotating equipment dry gas seal reliability.

 

API Plan 74 Features Reliability Benefit
Continuous supply of clean dry gas delivered at the proper temperature, pressure, and flow Maintains the proper seal chamber environment regardless of the compressor state (startup, running, shutdown, idle)
Pressure regulator ensures nitrogen supply is delivered at least 25 psi (1.7 bar) above the seal chamber pressure Lubricate seal faces and prevent process fluid particulates from entering between seal faces
Gas supply flowmeter with a transmitter on the gas supply panel Alert to an increased flow of nitrogen that could indicate mechanical seal failure
Coalescing filter on the nitrogen supply line Remove any particulates and moisture that may be present in the nitrogen supply

 

Adequate seal gas filtration, conditioning, and seal gas flow are the key factors to prevent this type of contamination from entering the seal. Whenever pressure is present in the compressor it’s critical to maintain the required pressure and flow of clean, dry gas.

Key Factors in Improving Rotating Equipment Dry Gas Seal Reliability 

When you consider the investments in centrifugal compressors and the critical role they play in transforming and moving volumes of hydrocarbons through production and distribution, it’s hard to believe that minute particles of dirt can lead to malfunction and failure. Any investment in a centrifugal compressor should be matched with a seal support system tailored to the specific needs of the compressor. 

Seal panel instrumentation, gas supply source and infrastructure, process gas, and mechanical seal components are key factors to consider when designing the solution to maintain the required seal chamber environment. For many organizations that can be a tall challenge, and in those instances, the guidance of an experienced mechanical seal support partner is the smartest way to solve the problem.

Swagelok: Local Support for Dry Gas Seal Reliability 

At Swagelok, we understand the criticality of rotating equipment that uses dry gas seals and have been designing and delivering seal support solutions for petrochemical industries in Northern California and Western Nevada for many years. Our experienced and certified Field Engineers are available for on-site or online consultation. We’ll invest the time to understand your unique seal support system concerns. With this detailed understanding, we’ll design, fabricate, and thoroughly test your dry gas seal support systems in our local facilities. The result? Improved rotating equipment dry gas seal reliability to keep your operations running smoothly.

To learn how Swagelok Northern California can help you improve the reliability of rotating equipment that uses dry gas seals, contact our team today by calling 510-933-6200.


Paul LesnauAbout Paul Lesnau | Sales Manager, Business Development Manager, and Field Engineer

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 focused within the pneumatic and hydraulic industry 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.

Topics:Assembly ServicesMission CriticalSeal Support Systems

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