Preservation in tunnels – a damp challenge

Preserving electronic equipment in tunnels is a challenge – primarily due to extremely high humidity and long construction phases. Temperatures differ significantly from the surface, and groundwater is affected by the structures. We have gradually built up solid experience in protecting equipment for infrastructure projects in Norway. Here, you will find information on how to protect electrical cabinets and other electronic equipment in enclosures until the project is completed.

In tunnels, humidity is often up to 100% RH – both day and night, all year round. This makes preservation difficult, as equipment often stands for months before the power is turned on. In these cases, it is especially important to provide protection by controlling the atmosphere and using corrosion inhibitors.

Challenges

• Electronics are placed in an environment with nearly 100% RH
• Construction work generates moisture and alters the pH of the water
• It is not possible to activate heating or dehumidifiers
• Electronics remain without power for long periods
• It is difficult to seal cabinets that require frequent connections
• Equipment manufacturers require that the units be stored dry
• Measures must be carried out with discipline at planned intervals.

Solution

• The goal must be to develop a solution acceptable to both component suppliers and the developer. Storing electrical cabinets dry until startup—as often required by manufacturers' warranty terms—is challenging. In practice, "dry" means a relative humidity below 40-50% RH. When the surroundings are at 100% RH, it does not take much to exceed these levels. We often propose a multi-stage solution:
• Cabinets must be stored in a dry atmosphere until installation.
• Before cabinets are mounted, and preferably before they are transported into the damp area, install desiccant bags, flash rust inhibitors, and VCI capsules. The task of the desiccant bag is to remove moisture quickly and bring the air below 50% so that the inhibitors have a good, dry baseline to perform optimally. All three are necessary because, in practice, it is impossible to seal all cabinets well enough to keep moisture completely out. The inhibitors release a protective gas that attaches to all surfaces. The flash rust inhibitor develops protection extremely quickly, and the gas from the VCI capsule maintains the cabinet over the long term. A key advantage is that the inhibitors remain effective even if the cabinet becomes slightly damp over time.
• For monitoring, a humidity indicator card can be placed inside the cabinet.
• Basically, the cabinet is now protected against corrosion even if the indicator card shows levels well above 50% RH. However, it is useful to use the card to document how well-sealed the enclosure is and to ensure the desiccant is replaced before "free" water appears on the walls.
• The cabinet is closed, openings are sealed, and the entire enclosure is wrapped in 0.2mm moisture barrier film. Joints are taped.
• The cabinet is marked with the preservation date and "Do not open unnecessarily."
• If you open the cabinets briefly on a daily basis, new moisture will enter, and the desiccant bags will saturate more quickly. The two inhibitors will not be significantly affected by such inspections regardless.
• Silica gel should be replaced when indicators show approx. 70% RH or every three months.
• The flash rust inhibitor and the VCI capsule will last for 2 years under normal operation. Even if the inhibitor bag "crystallizes," it will still be effective. You will recognize a fruity scent when opening the cabinet, which indicates that the protective gas is being released.

Products

1. Fast-acting VCI
   
   
   
   Zerust AktivPak LS-35 is an extremely fast-acting VCI (Volatile Corrosion Inhibitor) and FCI (Volatile Flash Corrosion Inhibitor) that protects against issues such as flash rust. In environments as damp as tunnels, it is important to provide protection quickly so that metals are not exposed for too long. One bag is enough to protect up to one cubic meter in minutes. Furthermore, the effect lasts for one year from installation.

2. Desiccant
   An electrical cabinet must be packed tightly with plastic and sealed with tape. Gaskets must be tight, and conduit entries must be plugged. To remove moisture still present inside the cabinet and to keep it dry over time, 250-500g bags of silica gel are used. Use 0.5 kg of silica per 1m3; in damp environments, preferably five times that amount.
   
   It is important that the silica gel is stored correctly and not opened before use; otherwise, it will begin to absorb moisture from the air. If possible, the silica gel bag should be hung inside the cabinet. If that is not possible, place the bag in a safe spot, as high up as possible inside the cabinet.
   If inspections are to be carried out on the cabinets during the construction phase, it is important to have established routines for checking and replacing both the silica gel and the VCI.

3. Long-term corrosion inhibitors (VCI Capsules)
   To protect the cabinet over a long period, you must use VCI Capsules; these provide protection for 1-2 years depending on type and size. The capsules emit an invisible gas with VCI molecules that adhere as an invisible film to
   
   all metallic surfaces inside the closed container. This film prevents the electrolyte (moisture) from contacting the cathode/anode (metal), thus preventing corrosion. Cabinets and junction boxes are often installed years before a project is completed; it is therefore important to label the cabinets with the VCI capsule installation date and the replacement date.

Anything unclear? Please feel free to contact us, and we will tailor solutions for your project!