Compressor fouling is the single largest recoverable cause of gas turbine performance loss, and most plants still fight it with one tool instead of two. Online washing runs while the unit stays on load. Offline washing needs the turbine stopped and cranked. Each recovers a different slice of lost performance, and mixing up when to use which one is where operators leave megawatts on the table. This guide breaks down both methods, water quality rules, and how to know which wash to run and when. Sign up to track wash events and performance recovery against your own turbine baseline.
Why It Exists
Airborne particles between 1 and 5 microns slip past inlet filters and stick to compressor blade surfaces, changing the airfoil shape and cutting mass flow, pressure ratio, and efficiency with every operating hour. A 5 percent drop in compressor efficiency on a 100 MW unit can burn an extra 1.2 million dollars in fuel a year, which is exactly the kind of loss a structured wash program exists to recover.
What Online And Offline Washing Actually Do
Online Washing
Water injected while the turbine runs at reduced load, slowing fouling buildup without taking the unit offline
Offline Washing
Water and detergent cycled through a stopped, cranking compressor to fully strip hardened deposits
Water Quality
Demineralized water with neutral pH protects hot-section blading from mineral deposits and corrosion
Detergent Use
OEM-approved detergent helps offline washing break down oily deposits water alone cannot remove
Deciding Which Wash To Run
Check Compressor Discharge Pressure
A gradual pressure drop against baseline is the earliest sign fouling is building on the blades
Compare Output Loss To Baseline
A small, steady output loss usually still responds to a scheduled online wash
Watch For Diminishing Recovery
When repeated online washes stop restoring performance, deposits have hardened past what water alone can lift
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Schedule An Offline Crank Wash
A detergent-assisted offline wash at the next planned outage resets the fouling curve back to near baseline
Stop Guessing When To Wash
Oxmaint tracks compressor discharge pressure, output, and efficiency trends against your unit's clean baseline, flagging the exact point where an online wash stops being enough. Sign up for a free trial to bring condition-based washing to your turbine, or book a demo to see it running on live performance data.
Online Wash vs Offline Wash
| Factor |
Online Wash |
Offline Wash |
| Turbine state |
Running at reduced load, no shutdown needed |
Stopped and rotated at cranking speed |
| Recovery level |
Slows fouling, partial performance hold |
Restores up to 80 to 95 percent of fouling losses |
| Typical frequency |
Daily to weekly, condition-dependent |
Tied to planned outages or major output drops |
| Best for |
Light, loose particulate buildup |
Hardened, oily, or long-accumulated deposits |
The Payoff
Fouling rates swing by up to 300 percent between seasons and sites, so a fixed calendar wash schedule either wastes wash cycles or misses the point where losses stack up. Running both methods on condition data, not a laminated schedule, means every wash actually earns back the megawatts it was meant to.
Frequently Asked Questions
Q
Can online washing replace offline washing entirely?
No, online washing only slows fouling buildup since the wash liquid boils off partway through the compressor and cannot reach every blade, so an offline wash is still needed to fully restore performance.
Q
Why does water quality matter so much for compressor washing?
Water carrying minerals or contaminants can leave deposits on hot-section blading during offline washing, which is why demineralized, neutral pH water is the standard across most OEM procedures.
Q
Can wash schedules be tracked digitally instead of on a calendar?
Yes, a CMMS can log every online and offline wash event against real-time performance data, turning each wash into a documented recovery record instead of a fixed date on a board.
Turn Every Wash Into A Measured Recovery
Oxmaint logs online and offline wash events against your turbine's performance baseline, so you know exactly what each wash recovered and when the next one is due. Sign up for a free trial to start tracking your compressor wash program, or book a demo to see it working on live turbine data.
