A recent Coast Guard investigation highlighted safety issues related to condensate formation in air lines on a vessel. The investigation revealed that condensate was forming in the air lines supplying compressed air to the vessel's engine throttle and clutch control systems. In cold weather, the condensate could freeze, potentially blocking the flow of compressed air or causing the pneumatic engine controls to stick or freeze.
The reliable and uninterrupted flow of contaminant-free compressed air is crucial for various systems onboard ships, ensuring vessel and personnel safety. Equipment such as propulsion control systems, pneumatic engine starters, throttle controls, air-operated clutch systems, and air-blowers used in gas-freeing operations rely on the proper flow of compressed air.
Condensate forming within air lines indicates that the compressed air has not been adequately dried for the operating temperature. When compressed air is not adequately dried, the temperature of the air can drop below its pressure dew point, leading to condensation of water vapor in the air lines. This moisture contaminates the air lines, causing restrictions, blockages, corrosion, and failures of internal components. It can also create environmental hazards like increased static electricity generation when used with pneumatic blowers or tools.
To ensure the safe and reliable operation of air-operated equipment, it is critical to have a compressed air system designed for the specific operating environment. This includes installing an appropriate air dryer to remove moisture and reduce the pressure dew point of the compressed air below the ambient operating temperature. By doing so, condensation and contamination of the air lines can be prevented.
The Coast Guard strongly recommends that vessel owners and operators, inspectors, and third-party surveyors:
-Identify compressed air systems vital to the safety of the vessel and/or personnel. Such systems include but are not limited to:
engine starting, throttle control and clutch control,
pneumatic blowers or tools used by personnel working in or near flammable atmospheres,
compressed air systems supplying the ship’s horn,
other equipment for which the unexpected interruption of compressed air could jeopardize the safety of the vessel and/or persons on board.
-For vessels which may operate in cold temperatures: verify that control and ship’s service compressed air systems are properly equipped with air drying arrangements that will lower the pressure dew point (of the compressed air) below the operating temperature to which the air lines are exposed. This ensures that the temperature of the operating environment will not cause the temperature of the compressed air to reach its dew point and will prevent condensate and ice from forming within the air lines. For example, some desiccant and membrane dryers can reduce the pressure dew point of compressed air to minus 40° F below zero, which would prevent the formation of condensate and ice in air lines exposed to cold temperatures. Moisture removal may also involve equipment such as compressor intercoolers, aftercoolers, air filters, dryer desiccant, sensors, and automatic drain traps, all of which should be properly maintained to ensure a moisture-free air supply.