Preservation in tunnels – a moist challenge

Preserving electronic equipment in tunnels is a challenge - primarily because of the extremely high humidity and the long construction phase. The temperatures are quite different from up on the ground, and the groundwater is affected by the constructions. We have gradually built up good experience in protecting equipment for transport projects in Norway. Here you get information on how to protect electrical cabinets and other electronic equipment in cabinets until the project is finished.

In tunnels, the humidity is often up to 100% RH - both day and night, all year round. This makes preservation difficult, as the equipment often sits for months before the power is switched on. It is then particularly important to protect by controlling the atmosphere and using corrosion inhibitors.

Challenges

• The electronics are in an environment with close to 100% RH
• Construction work is taking place which develops moisture and changes the pH of the water
• It is not possible to turn on heat or dehumidifiers
• The electronics are without power for a long period
• It is difficult to seal cabinets that you have to constantly connect
• The electrical manufacturer requires that the equipment be stored dry
• Actions must be carried out with discipline at planned intervals.

Solution

The goal must be to develop a solution that can be accepted by the component suppliers and the client. It is challenging to store electrical cabinets dry until start-up, as is often stated in the warranty requirements from the manufacturer. In practice, dry means relative humidity below 40-50% RH. When the surroundings have 100% RH, it doesn't take much before this is passed. Our proposal is often a multi-step solution:

• The cabinets must be stored in a dry atmosphere until installation.
• Before the cabinets are assembled, and most preferably before they are transported into the humid area, desiccant bags, flash rust inhibitor and VCI capsules are installed. The desiccant bag's task is to remove moisture quickly and bring the air below 50% so that the inhibitors get a good, dry starting point to work as best as possible. All 3 are necessary because in practice it is not possible to seal all cupboards well enough to keep the moisture out completely. The inhibitors emit a protective gas that sticks to all surfaces. The Flashrust inhibitor develops the protection lightning fast and the gas from the VCI capsule takes care of the cabinet in the long term. The good thing is that the inhibitors are effective even if the cupboard gets a little damp over time.
• For control, a moisture 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 good to use the card to document how tight the packaging is and ensure that the desiccant is replaced before "free" water appears on the walls.
• The cabinet is closed, openings are sealed and the entire cabinet is lined with a 0.2 mm moisture barrier. Joints are taped.
• The cabinet is marked with the preservation date and "Do not open unnecessarily"
• If you now open the cupboards for a short time each day, new moisture will be let in, and the desiccant bags will be saturated more quickly. In any case, the two inhibitors will not be significantly affected by the inspection.
• Silica gel should be changed when the indicators show about 70% RH or every three months.
• The flashrust inhibitor and VCI capsule will last for 2 years under normal operation. Even if the inhibitor bag "crystallises", it will still be effective. You will recognize a fruity scent when you open the cabinet indicating that the protective gas is being released.

The 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, among other things, flash rust. In such humid environments as tunnels, it is important to protect quickly, so that metals are not exposed for too long. One bag is enough to protect up to one cubic meter in minutes. Moreover, the effect lasts for one year from installation.

2. Desiccant
   An electrical cabinet must be packed tightly with plastic and taped tightly. Gaskets must be tight and penetrations must be blinded. To remove moisture that is still 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 humid environments preferably 5 times as much silica.
   
   It is important that the silica gel is stored correctly and not opened before use, otherwise it will start to absorb moisture from the air. If possible, the bag of silica gel should be hung up inside the cupboard. If that is not possible, put the bag in a safe place, as high up as possible inside the cupboard.
   If checks are to be carried out on the cabinets during the construction phase, it is important to have fixed routines for checking and changing both silica gel and VCI.
   
   

3. Long-acting corrosion inhibitors (VCI Capsules)
   To protect the cabinet over a long period of time, you must use VCI Capsules , these provide protection for 1-2 years depending on the type and size. The capsules secrete one
   invisible gas with VCI molecules that stick like an invisible film on it
   
   all metallic surfaces inside the closed container. This membrane prevents the electrolyte (moisture) from coming into contact with the cathode/anode (metal) – thus corrosion cannot occur. The cabinets and junction boxes are often installed years before the project is completed, that is
   it is therefore important to mark the cabinets with the installation date of the VCI capsules and the date of replacement. .

Something unclear? Feel free to get in touch, and we will tailor solutions to your project!