Introduction
Many businesses rely on industrial boilers and HVAC systems to provide heat, cooling, and process support year-round. But what happens when these systems are shut down for maintenance or during the off-season?
Without regular maintenance, the interior components of these systems can soon deteriorate due to corrosion and moisture exposure. This is where wet layup comes in.
What is a Wet Layup?
Wet layup is a protective preservation technique used to preserve boilers, chillers, and HVAC systems during temporary shutdowns. Wet layup differs from dry layup in that it keeps the system filled with treated water to avoid oxygen intrusion and corrosion.
It's especially handy when systems need to be back up and running quickly or after they've been down for short to medium lengths of time.
Why is Wet Layup Important?
When boilers or HVAC systems are turned off, they become susceptible to oxygen corrosion, especially if moisture and air are present within the system.
Over time, this can result in pitting, scale formation, microbiological growth, and expensive equipment damage.
Wet layup contributes by:
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Preventing rust on metal surfaces.
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Maintaining internal cleanliness during leisure times.
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Allows for speedier system restarts without the need for significant flushing or inspections.
How Wet Layup Works
Here's an overview of how the wet layup procedure is carried out for boilers or HVAC systems:
1. System Shutdown and Cleaning
Before beginning wet layup, the system is shut down and carefully cleaned to remove scale, sludge, and biological material.
2. Fill with treated water
The unit is filled with deoxygenated, chemically treated water that includes corrosion inhibitors such sodium sulfite, morpholine, and amines. This water is critical for keeping oxygen from damaging the metal surfaces.
3. Circulation and Monitoring
Some facilities maintain a minor recirculation system to ensure uniform chemical delivery. Regular monitoring ensures that the pH, inhibitor levels, and oxygen content remain within acceptable ranges.
4. Sealing the System
All vents and drains are carefully sealed to prevent air infiltration. A nitrogen blanket is sometimes placed on top of the water's surface to provide further protection.
Applications for Boiler and HVAC Systems
Boilers (Steam and Hot Water Systems)
Wet layup is appropriate for boilers that are shut down for less than 30 days to a few months. It is especially beneficial in seasonal activities like district heating or industrial boilers with variable demand.
HVAC Chillers and Cooling Systems
During the winter, chillers in large commercial buildings are frequently set to standby mode. Wet layup protects the system from corrosion and scale during this time. It also helps to preserve system integrity, ensuring that it is ready for summer.
Benefits of Wet Layup:
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Reduces corrosion dangers during idle periods.
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It extends the life of boilers and HVAC equipment.
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Reduces maintenance expenses by preventing unexpected breakdowns.
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Ensures a speedy startup and saves time during re-commissioning.
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