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Modern radiators are only slightly protected against mechanical damage and corrosion. Precautions are taken in each production phase, from fabrication until operation. This limitation does not have a negative effect on the proper functioning of such heating systems. This article’s main objective is to give recommendations in order to increase the life span of plate steel radiators or at least to prevent premature damage. Tips for the proper placing and maintenance of radiators are also given. The advice is to be taken into account for all parties involved: manufacturers, wholesalers, installers, study agencies, architects and users.
1.2. Mechanical damage
2. PRECAUTIONS AGAINST MECHANICAL DAMAGE
2.1. Handling, transport and installation
3. PROTECTION AGAINST EXTERNAL CORROSION
3.1. Precautionary protection
3.2. Radiators with damaged paint coat
3.3. Radiators in use
4. PROTECTION AGAINST INTERNAL CORROSION
4.1. Expansion tanks
4.2. Disconnection possibilities
4.3. Use of various metals
4.4. Use of PVC pipes
6.1. Rational energy consumption
6.2. Water quality
6.3. Drawing off and filling up
6.4. Precautions against frost
6.5. Working pressure
The two main causes of premature damage to steel panel radiators are:
- On the one hand, mechanical damage during handling, transport, installation and use
- On the other hand, internal as well as external corrosion, caused by aggressive molecules of the environment and/or the water inside the radiators. Remark that the difference between the consequences of the mechanical damage and of the corrosion are not as clear as one may think.
1.2. Mechanical damage
Mechanical damage has to be avoided as soon as the radiator is produced and especially after the waterproof and pressure check in the factory. Throughout all the different production phases and storage in the factory, all possible measures have to be taken to keep the radiator in excellent condition. Especially bumping, denting, carving, bending, perforating or damaging of the radiator by way of friction with other materials or tools must be avoided. The preceding measures should be taken into account when loading and unloading, during transport, during storage in the workshop or at the construction site and when installing the radiator itself. Damaged radiators may not be installed. They have to be repaired or replaced by faultless specimens when reparation is not possible. The users and the maintenance engineers, in short everyone who handles steel radiators should ensure that the radiators are not exposed to abnormal mechanical damage.
Steel corrosion is especially due to the combined operation of water and oxygen and/or the presence of other corrosive molecules. Steel radiators are no exception, corrosion can develop internally as well as externally. In particular circumstances, this phenomenon can develop so quickly the steel is being corroded in no time at all over the entire thickness, and at least locally (pitting). Deposition of sediment, oxides and salts can considerably accelerate the corrosion process where the deposition takes place.
2. PRECAUTIONS AGAINST MECHANICAL DAMAGE
2.1 Handling, transport and installation
Precautions have to be taken during transport of large quantities to avoid sliding. If the radiators cannot be transported in a properly closed lorry, they have to be protected by a canvas against rain and dust. In special cases, they have to be specially packed. Handle the radiators very carefully and do not place them on sharp edges, especially not on hard edges. The following recommendations should also be considered:
- Always carry the radiators and do not slide them over the ground, otherwise corrosion can occur on the bare metal
- Do not drop the radiator on a sharp edge when unloading
- Radiators with multiple panels should always be rested on all panels, do not put down the radiator abruptly on one of the panels; this can cause a fracture in the coating, resulting in corrosion around the connection boxes; the radiator can also be deformed
- Always carry panel radiators at the bottom or with special plastic grasps which fit the collector boxes
- When assembling the radiator, ensure that no damage is inflicted on the paintwork when fastening taps and joints
- When installing the radiator, the number of supports has to be sufficient to complement the length of the radiator. The supports or consoles have to allow expansion and shrinkage of the radiator. When bumping into the radiator, the cramping on the top of the radiator has to prevent any kind of fluctuation.
As well as in the workshop as on the construction site, the radiators must be stored in a dry and covered place, protected against falling objects, mortar, lime, plaster, etc. They have to be placed in their normal position, top up. They have to rest on horizontally placed wooden beams of at least 10 cm wide. The best protection is to separate each radiator by means of soft pieces of wood or a similar material. Heavy, cutting or sharp objects may never be placed on the radiator.
3. PROTECTION AGAINST EXTERNAL CORROSION
3.1 Precautionary protection
External corrosion can be prevented by applying a special paint which resists the corroding environment, or even better, which possesses anti-corrosive properties. This is mostly used for the external protection of radiators. The protective paint is applied in multiple coats, from which the first or first two coats are anti-corrosive. These coats are directly applied on the cleaned metal. The time the anti-corrosion coat can stay unprotected depends on its composition and exposure. A further top coat is then applied onto the anti-corrosive coats, specially designed to resist high temperatures and thermic shocks. Moreover, this paint has the benefit of being resistant to sanding, preventing paint loosening and offering an esthetic view. Lately, paints that have an anti-corrosive effect as well as a coating function are also used. Taking into account the applying properties and characteristics of the factory paint (simple primer or full system), the manufacturer decides on the effectiveness of the radiator’s protection. The radiators have to remain in their original packaging until the final installation. An ideal solution is to let the radiator in the packaging during the installation and to remove it afterwards.
3.2 Radiators with damaged paint coat
The handling of radiators can bring about scratching which can cause surface corrosion. You have to apply the protective coat as soon as possible after the anti-corrosive coat has been restored.
3.3 Radiators in use
When using radiators, take the following into account:
- Each damage of the paint system of radiators in a humid atmosphere (bathroom, kitchen, laundry room, toilet) irrevocably leads to external corrosion. Any possible damage has to be repaired from the beginning. Avoid contact with soap or other cleaning products, because water with soap is very corrosive. We do not advise installing radiators above bath tubs or in or next to showers.
- The toilet calls for special attention, because urine drops are strongly corrosive. We suggest not to place a radiator on less than 80 cm next to the toilet. The radiator should be placed opposite from the toilet.
- Do not hang damp linen over the radiator and especially not during summer; use towel dryers instead. In a specially corrosive environment, such as in laboratories, swimming pools etc., we recommend a special and sufficient protection of the radiator from the beginning. This has to be reported to the manufacturer when the order is delivered, mentioning the kind of atmosphere where the radiators will be installed.
4. PROTECTION AGAINST INTERNAL CORROSION
In order to prevent internal corrosion in radiators, penetration of air inside the installation has to be avoided. The oxygen reacts instantly with the metal components of the installation and starts a corrosion process, which lasts as long as there is oxygen present or keeps penetrating into the installation. This principle has to be considered when assembling and using the installation. It is useful to know that present or penetrating air piles up easily at the top of radiators. This air has to be drained off as soon as possible on regular times and especially when concluded water has to be added regularly. The manufacturer of the radiator has to ensure the ventilation can occur properly, in other words, it has to be placed on the highest point of the radiator. In addition, we mention that plate steel radiators are intended for central heating installations on warm water. The use of plate steel radiators for steam installations is strongly dissuaded.
4.1 Expansion tanks
In general, open expansion tanks make the internal corrosion risk very high because of the permanent penetration of oxygen in the radiator water. Existing open expansion tanks should be replaced by closed expansion tanks with a membrane, which do not have this disadvantage. The now popular closed expansion tanks have to be installed correctly, this means as close to the boiler as possible, on the suction side of the pump and in the drain pipe. Moreover, the expansion tank has to be large enough and the pressure has to be adjusted correctly; only then the installation avoids low pressure when cooling off.
4.2 Disconnection possibilities
To avoid draining the whole water volume when replacing or moving a radiator, it is possible to provide each radiator with the necessary draw-off taps. In those cases, the drawing-off can be limited to the volume of the radiator itself. When the individual disconnection of each radiator is normally not possible (e.g. installations with one pipe) or not desired (financial reasons), it is useful to provide draw-off taps for each cycle or group of radiators. When enlargements are provided, draw-off taps have to be installed starting from the first assembling for the future cycles.
4.3 Use of various metals
The use of various metals in the same installation has to be limited as much as possible, as well as during the construction of the radiators as when assembling the installation. The combination and order of occurrence of different metals can cause prematurely internal corrosion by way of electrolysis, where the water of the installation causes a transfer of electrical current. This kind of corrosion is often even strengthened or accelerated when air penetrates the installation or when untreated aggressive water flows in the installation.
4.4 Use of PVC pipes
The distribution of heat when using heating systems with radiators is more and more realized with the help of PVC pipes. A disadvantage of these PVC pipes is that they are not fully airtight, despite the fact that the current pipes are provided with an anti-oxygen layer. Because of the permanent supply of oxygen in the installation, a corrosion process will take place, which will grow stronger as the water temperature rises. Because installations with plate steel radiators normally function on high water temperatures, the danger of corrosion damage is realistic. That is why it is recommended to offer the installations a maximally preventive protection. The permanent penetration of oxygen can be fought against by means of a water treatment, by which a product (inhibitor) is added to the water, creating a protective layer on the metal parts or neutralizing the oxygen with a chemical process.
As soon as the installation is filled up with fresh, rich in oxygen water, the corrosion process commences. This first corrosion is rather minimal, because it stops after the water runs out of oxygen.
Take the following advice into account in order to exclude or limit further corrosion:
- Once filled up, the installation has to be permanently filled with water. The cycles have to be designed and kept in a way that limits the drainage time during watertight tests and the installation. The periods when the radiator is being emptied have a high corrosion risk.
- When filling up the radiator, the water has to be brought to the maximum temperature immediately. When this temperature is reached, the installation with shut down pump and all taps open has to be drained off completely.
- Only tap water or specially treated anti-corrosive water can be used; the use of anti-corrosive products is absolutely recommended in the case of installations with PVC pipes.
6.1 Rational energy use
When exploiting a heating system, the energy use is an important and sensitive evaluation criterion, which can be estimated on the basis of the installation’s output. This can be formulated as a product of a number of partial outputs (heat production, heat distribution, heat output and adjustment). One of the partial outputs who plays an important role is the heat output of the radiators. In order to keep the heat output of the radiator as high as possible, it is necessary to reduce the heat loss to the minimum, considering the following points of interest:
- The radiators are preferably placed against an outside wall and when possible underneath a window. They may never be placed directly in front of a glazing (e.g. door with a large window). It is recommended to provide the wall behind the radiator with extra heat-insulation and a heat reflecting foil.
- The placing of the radiators should correspond the normal placing, at 5 cm from the wall and 10 cm above the floor surface. Each obstruction of the heat output by way of built-in niches, window-sills, casings, screenings, curtains, etc. should be avoided. In case it does occur, a larger radiator has to be chosen considering a lower heat output.
- The radiators have to be well-maintained, especially avoid dust deposition between the panels and convection fins. No objects can be placed or hanged on top of the radiators and the free space underneath the radiators has to remain clear.
- The visible front of the radiators cannot be painted with a metallic paint, because this decreases the heat output by radiation. Unlike the front panel, the back panel of the radiator can be painted with a metallic finish, because the loss of radiation to the outside wall will decrease.
6.2 Water quality
Only tap water can be used to fill up the radiator. When demineralized water is being used, it has to be verified no chlorides have been added during the demineralization process. When using anti-corrosive products in the installation’s water, verification against which metals the product gives protection is needed. Moreover, the combination with other products present (e.g. antifreeze) or with demineralized water may not cause aggressive reactions. The presence and the concentration of the anti-corrosive products have to be controlled regularly and kept up to the mark.
6.3 Drawing off and filling up
A well designed and executed installation requires little or no fill-ups. When determined the installation consumes water regularly, the cause should be investigated (tap or pump leaks, boiler leaks, pipe leaks, drawing off water from the radiators, low pressure) and solved as soon as possible. In order to be aware of possible leaks, an automatic fill-up of the installation is not recommended. In every case, the installation has to be designed in such a way the user can easily verify the working pressure in function of the specific data of the installation (water content of the installation, characteristics of the closed expansion tanks, static height).
6.4 Precautions against frost
Precautions have to be taken against frost damage when a building is not occupied during winter and the installation has to be permanently filled up with water to avoid corrosion. These precautions against frost include:
- Using the thermostatic valve bodies in such a way the temperature stays above freezing;
- Provide an adapted adjustment system, allowing the installation to operate on the lowest level.
6.5 Working pressure
The manufacturer’s guaranteed working pressure may never be exceeded.
Electrical appliances may never be earthed to pipes and radiators. Radiators placed in humid rooms have to be earthed (A.R.G.I.), paying attention to electrolysis as a consequence of small leak currents.