Salt & Corrosion Considerations

Do you operate in a coastal or offshore site? Unfortunately, you probably have to deal with corrosion related issues such as irreversible damage to turbine blades, performance losses, early failures, and expensive repairs. You can, however, operate corrosion-free if you take measures to stop the process before it begins.

What is corrosion?

Gas Turbine engine performance degradation is classified as either recoverable or non-recoverable. Recoverable performance degradation is usually due to compressor fouling and can normally be overcome by online and offline water washing. Non-recoverable performance degradation is usually caused by rotating internal engine part wear, as well as plugging of cooling channels, erosion & corrosion due to contaminants in the air, fuel and / or water.

Ingested contaminants can result in corrosion of the compressor, combustor and turbine sections of a gas turbine engine. Hot corrosion is the most serious form of corrosion experienced in the turbine section. It is a form of accelerated oxidation that is produced between components and molten salts deposited on its surface. Sodium sulfate, (Na2SO4), is usually the primary deposit instigating hot corrosion, and becomes more severe as the gas turbine section temperature levels increase.

Hot Corrosion Image
Corrosion Triangle

What is the true impact of salt?

As the turbine firing temperature increases, sodium sulfate liquifies and attacks the coating of the turbine blades, causing irreversible damage and leading to performance loss, early failures and expensive repairs.

Upgrading the inlet system to EPA prevents the salt from entering the inlet, stopping the process of hot-end corrosion caused by sodium sulfate before it begins.

Salt Images
Salt Graph

How can you prevent corrosion?

Considering that 98% of a gas turbine’s input is air and 2% is fuel, you can prevent corrosion by removing the causes.

  1. Use cleaner fuel with low sulfur content
  2. Capture salt from the air before they reach the gas turbine by using an air inlet filter solution with specific design characteristics.
    • E12 efficiency according to EN1822: 2009 https://www.camfil.com/ps/Gas-turbine-filter-technology/Airborne-particles/Salt-and-corrossion/
    • Good water handling capabilities
    • Louvers & rain hoods will remove some water from the airflow before reaching the filters.
    • Coalescing pre-filters turn smaller droplets into larger droplets that can then fall out of the airflow before reaching the next stage filter. Good pre-filters drain large droplets at the front of the filter, keep a low pressure drop when wet, and coalesce small droplets into larger droplets at the back.
    • Hydrophobic (water resistant) final filters prevent any penetration of water and should have enough drainage to keep a low pressure drop.

You can take other measures to prevent corrosion by using corrosion-resistant blade material and coating your blades to add longer protection, however, they are temporary solutions since repeated Na2SO4 exposure will eventually take effect.

Identify the cause of corrosion at your site.

At some installations, the site conditions, package design, and / or maintenance procedures will contribute to an increased amount of contaminants ingested by the gas turbine engine. To help understand the ‘root cause’ of the issue, contact us and ask for the Hot Corrosion Root Cause Analysis tool.