An industrial gas compressor—whether a large unit for natural gas processing or a smaller gas powered air compressor—isn’t just a piece of equipment; it's the heart of your operation. A compressor is a mechanical device that is critical for production. When it runs smoothly, your plant meets production targets. When it falters, the consequences ripple outwards, causing costly downtime, process upsets, and significant safety risks, especially when dealing with hydrogen and compressed natural gas. The silent, steady hum of a healthy compressor is the sound of profitability. Any deviation from that hum, whether from the main unit or a supporting combustion air compressor, is a direct threat to your bottom line.
This guide moves beyond basic definitions, as the selection of gas compressors requires expertise. It is written for the plant managers, reliability engineers, and maintenance supervisors who are responsible for the compressor performance of these critical assets. Drawing on over 20 years of field experience with compressor models from Cameron (TA-series, MSG), Ingersoll Rand, and Atlas Copco, we will dissect the practical realities of gas compression operation, a critical process in many industries from natural gas processing plants to manufacturing. These powerful natural gas compressors are industrial workhorses.
We will cover the foundational principles dictating the reliability of any type of compressor, from a rotary compressor to a reciprocating model, the subtle signs of impending failure, and a systematic process for diagnosing issues before they lead to catastrophic events.
Foundational Understanding: Dynamic vs. Positive Displacement Compressors for Gas and Air Compressor Systems
While any gas air compressor will increase pressure by compressing gas by reducing its volume, the mechanism they use fundamentally defines their operating characteristics, efficiency curves, and, most importantly, their failure modes. Understanding this distinction is the first step in effective management, as the wrong compressor type can be a costly mistake. This process is governed by the Ideal Gas Law, where the pressure of a gas, its volume, and temperature are interlinked (PV=nRT).
Positive Displacement Compressors: The High-Pressure Specialists for Natural Gas
These machines operate by trapping a fixed volume of gas in a chamber and mechanically reducing that chamber's volume. A positive displacement compressor can deliver a nearly constant flow regardless of discharge pressure, making them ideal for high-pressure, low-volume applications where a small gas volume of compressed gas is required.
Reciprocating Gas Compressors:
The classic piston-driven design, these are often called a conventional reciprocating compressor. They excel at reaching extremely high pressures, often exceeding 10,000 psi.
Operational Reality: Their design introduces pulsating flow, which can cause vibration in piping and downstream equipment. The most common failure points are the valves and piston rings, which are subject to high cyclical stress and must be designed to reciprocate for thousands of hours. Per API 618, valve life is a primary maintenance concern.
Rotary Screw Compressors and Other Types like Rotary Vane Compressors:
These screw compressors utilize two intermeshing helical screws to compress gas. They provide a continuous, pulsation-free flow. An air compressor is a specific type of this machine used for generating plant compressed air. For other processes, compressors are mainly used to move hydrocarbons or other chemicals.
Operational Reality: Efficiency is highly dependent on the tight clearances between the rotors. Bearing wear is a critical failure mode for this compressor is one that requires clean gas. Any particulate contamination in the gas flow can erode the screw profiles, permanently degrading performance.
Dynamic Compressors: The High-Volume Movers
These machines use rotating impellers or blades to force the gas to a higher velocity (kinetic energy), which is then converted into pressure. This type of flow compressor is common for moving a large gas volume. They are designed for high-volume, moderate-pressure applications.
Centrifugal Compressors:
A centrifugal compressor draws gas into the center of a spinning impeller and throws it outward by centrifugal force. A specific type of gas compressor like this is ideal for moving a large gas volume. In industries that rely on the pipeline transport of purified natural gas, centrifugal compressors are used extensively. Multi-stage units, like the Cameron TA-series, are the backbone of LNG, refining, gas storage, and large-scale chemical processing.
Operational Reality: These are high-speed, precision machines. Their greatest operational risk is aerodynamic surge—a condition of flow reversal that can cause violent pressure fluctuations and catastrophic damage to rotor bearings and seals, especially as the impeller accelerates the gas to the rim. The compressor is well suited for steady conditions, as its performance is highly sensitive to changes in gas composition, temperature, and pressure.
Axial Compressors:
In these units, gas flows parallel to the compressor's axis through a series of rotating blades and stationary vanes. Axial compressors are used in gas turbine engines. This compressor is a specific type that is unmatched for moving massive volumes of air, making them integral to medium to large gas turbine systems and large air separation units. The way the air is compressed allows for massive throughput.
Operational Reality: They have a narrower stable operating range compared to a centrifugal compressor. They are highly susceptible to fouling (buildup on blades), which degrades effectiveness and can lead to damaging vibrations. A study by the U.S. Department of Energy highlights that a 1% reduction in compressor efficiency due to fouling can increase fuel costs by over $300,000 per year for a large gas turbine. This is also a concern for large gas turbine engines and even the exhaust gas stream in some applications.
Early Warning Signs & Symptoms of Compressor Failure in Gas and Air Compressor Units
Catastrophic failures are rarely sudden. They are preceded by subtle symptoms that are often overlooked until it's too late. From our field experience, these are the critical indicators that demand immediate investigation.
Increased Vibration: This is the single most important leading indicator.
What to Look For: A sudden spike or a gradual upward trend in overall vibration readings. More specifically, look for changes in specific frequencies. For a centrifugal compressor, the appearance of sub-synchronous vibrations (vibrations below the main running speed) can be a precursor to oil whirl or whip in journal bearings. Even a portable truck mount air compressor can suffer from vibration issues.
Rising Discharge Temperature: Any deviation from the expected discharge temperature for a given pressure ratio signals inefficiency or a developing mechanical problem.
What to Look For: A 10-15°F increase above the normal baseline after accounting for ambient conditions. This can indicate internal recirculation, valve leakage (in units that reciprocate), or intercooler fouling. The goal is to avoid producing excessively hot high pressure air.
Unexplained Pressure Drops or Fluctuations: Stable pressure air is a sign of a healthy compressor.
What to Look For: In a centrifugal unit, an inability to meet required discharge pressure at a given speed points to fouling, internal seal wear, or a developing surge condition. In a reciprocating compressor unit, fluctuating suction or discharge pressure can indicate a failing valve.
Changes in Lube Oil Analysis: The oil is the lifeblood of the machine.
What to Look For: An increase in particle count, especially bearing-related metals like lead, tin, or copper. A change in viscosity or the presence of water can compromise the oil film, leading to bearing failure.
Abnormal Noises: An experienced operator can often "hear" a problem developing.
What to Look For: A high-pitched squeal could indicate a failing dry gas seal. A low-frequency rumble in a centrifugal compressor can be the sound of incipient surge. A distinct "knocking" points to a potential wrist pin or bearing issue. While not common in large industrial settings, a distinct noise in a typical diving compressor can mean something different entirely, highlighting the importance of knowing your specific machine.
Step-by-Step Diagnostic Process for your Gas Compressor
When a symptom appears, a structured diagnostic approach prevents guesswork and pinpoints the root cause efficiently.
Step 1: Baseline Data Collection & Verification
Before anything else, gather operational data from your plant's historian (e.g., PI System).
Action: Collect pressure, temperature, flow, speed, and driver amperage data for at least the last 72 hours. Compare current readings to the compressor's original OEM performance map. Is the machine operating where it should be on its curve?
Step 2: Performance Map Analysis
The OEM performance map is your most powerful diagnostic tool.
Action: Plot the current operating point (head vs. flow) on the map. This map is the key to understanding the machine's state, as compressors are designed for specific performance envelopes.
If the point is below the curve: This indicates an internal performance loss. Potential causes include fouling, impeller erosion, or internal recirculation, which can affect the entire area of the gas passage.
If the point has shifted left towards the surge line: The system resistance is higher than design. Look for downstream blockages, closed valves, or fouling in heat exchangers.
Step 3: Advanced Vibration Analysis
Overall vibration numbers are good, but a spectral analysis (FFT) is better.
Action: Capture vibration spectra. Look for peaks at specific frequencies.
1x RPM: Indicates imbalance.
2x RPM: Indicates misalignment.
Blade Pass Frequency: Indicates aerodynamic issues or diffuser problems.
Sub-synchronous Frequencies: Indicates oil-film instability in bearings. This requires immediate attention as per API 617 guidelines.
Step 4: Lube and Seal System Inspection
The support systems are often the source of the main equipment failure.
Action: Pull a lube oil sample for immediate analysis. Check seal gas supply pressures (and check if it's a breathing gas application, which has special requirements) and differential pressures. For a Cameron MSG compressor, verify pinion bearing and thrust-face temperatures are within the OEM's specified limits. A deviation here can indicate overload or alignment issues.
Step 5: Targeted Internal Inspection
If non-intrusive methods don't yield a clear cause, a planned internal inspection is necessary.
Action: Use a borescope to inspect centrifugal or axial compressor blades for fouling, erosion, or cracking. For larger reciprocating compressors, conduct a valve-cover inspection to check for broken springs or plates.
Common Causes & Proactive Prevention Strategies for your Compressor
Reactive maintenance is expensive. When it comes to industrial pumps and compressors, a proactive strategy focused on eliminating the root causes of failure is key to long-term reliability.
Common Cause | Affected Compressor Type(s) | Prevention Strategy |
Aerodynamic Surge | Centrifugal, Axial | Tune the anti-surge control system regularly. Ensure the anti-surge valve is fast-acting and sized correctly. Routinely test the valve's stroke time and verify its response against the control signal. |
Liquid Carryover | All Types | Install and maintain effective knockout drums and scrubbers upstream of the compressor. Implement automated drain cycles and ensure level instrumentation is functional and calibrated. Liquid can cause catastrophic failure in any compressor type. |
Bearing Failure | All Types (especially high-speed dynamic) | Maintain pristine lube oil cleanliness (targeting ISO 4406 code 16/14/11 or better). Implement a predictive oil analysis program that can even detect issues in a scroll compressor. Use vibration monitoring to detect bearing wear signatures before they become critical. |
Valve Failure | Piston-driven | Prevent liquid carryover and particulate contamination. Use materials of construction for valves and poppets that are appropriate for the specific gas service (e.g., fuel gas, hydrogen gas, or process gas) to avoid corrosion and erosion. This is crucial for any reciprocating natural gas compressor. |
Misalignment | All Coupled Machines | Perform laser alignment during installation. The compressor flywheel may drive accessories that also need alignment. Perform alignment checks after any maintenance that involves moving the driver or compressor. Thermal growth must be accounted for. According to a report by the Technical Association of the Pulp and Paper Industry (TAPPI), proper alignment can reduce vibration levels by over 50%. |
Fouling | Centrifugal, Axial | Implement an online and offline washing program. For critical applications, consider investing in advanced coatings for impellers and blades that resist deposit buildup. Monitor the compressor continuously; a gradual decay is a classic sign of fouling. The aim is to keep the process of air compression as effective as possible. |
Key Takeaways
Know Your Machine: The failure modes of a reciprocating compressor are fundamentally different from those of a centrifugal compressor or even a vane compressor. Tailor your maintenance strategy accordingly.
Vibration is the Best Messenger: Invest in and pay attention to vibration analysis. It provides the earliest and most specific warnings of mechanical degradation.
Data is Your Ally: Use your plant's historian data. Comparing real-time performance to the OEM map is the fastest way to diagnose efficiency losses and operational problems.
Control the Contaminants: Clean gas and clean oil are prerequisites for compressor reliability. Liquid carryover and particulate contamination are leading causes of premature failure in a gas compressor. It is important to treat the gas from the production site before it enters the machine.
Prevention Over Reaction: Proactive strategies like regular control system tuning, predictive analysis, and proper alignment are far more cost-effective than dealing with unplanned downtime. A good strategy for your gas compressor product is essential.
The Turbo Airtech Advantage
Diagnosing complex compressor issues, especially on multi-stage machinery like a Cameron MSG, an Ingersoll Rand Centac air compressor, or even a diaphragm compressor, which uses a flexible membrane and the compressor box to isolate the gas, requires deep, specialized expertise. We even have experience with smaller units found in refrigeration and air conditioner equipment. When your team has exhausted standard diagnostic procedures or when you need an independent, OEM-neutral analysis of a chronic problem, our experts are ready to assist.
We combine decades of hands-on experience with advanced diagnostic techniques to provide clear, actionable solutions that restore performance, improve uptime, and enhance the safety of your critical gas compression assets. As a leading service provider and not a gas compressor manufacturer, our advice is always OEM-neutral and focused solely on your plant's reliability.
Contact The Turbo Airtech Experts today for a data-driven consultation on your most challenging compressor reliability issues.
References
American Petroleum Institute. (2014). API Standard 617: Axial and Centrifugal Compressors and Expander-compressors for Petroleum, Chemical and Gas Industry Services (8th ed.).
American Petroleum Institute. (2007). API Standard 618: Reciprocating Compressors for Petroleum, Chemical, and Gas Industry Services (5th ed.).
U.S. Department of Energy. (2012). Improving Compressed Air System Performance: A Sourcebook for Industry.
Disclaimer: Turbo Airtech is an independent provider of parts and services for centrifugal compressors. We are not affiliated with OEMs such as Cameron Compression Systems, Ingersoll Rand, Atlas Copco, Hanwha Techwin, or IHI, though we service and provide parts for their machinery. All brand names and trademarks are the property of their respective owners and are used here for identification purposes only.
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