Considerations for the appliance of high-temperature coatings – Part 1

Managers of petrochemical, refining, energy, offshore, pulp and paper and different services with extensive hot processes and piping techniques are regularly challenged with performing all the mandatory coatings maintenance work only in periods of outages. Outages are required in order that process gear could be correctly maintained and repaired including cleansing of pipelines and vessels, maintenance and alternative of pumps, motors and valves, maintenance coating operations, and different work that can only be accomplished when the operations are shut down.
When coatings work needs to be performed on areas the place elevated temperatures are concerned, many suppose that the ability needs to be shut down. This will not be the case.
A question frequently posed by facility managers is, “Can I do maintenance portray work whereas the plant is operating?” As described beneath, the answer is, “Yes you can, however there are safety and health points that have to be considered”.
Dangers to personnel must be managed no matter when or where work is performed.
Safety and health considerations
There is a range of safety and health hazards that have to be thought-about on every industrial maintenance painting venture, whether or not the coating materials is being utilized to sizzling steel or not. Some of those embrace correct material handling and storage, fall protection, control of fireplace and explosion hazards, and exposure to noise, heavy metals, solvents and different health risks.
These risks have to be properly evaluated and managed on each industrial maintenance portray project, no matter when or the place the work is carried out. While present on any job, when applying specialty coatings to sizzling surfaces, some safety and health points ought to obtain extra consideration.
Flammable and flamable liquids in plenty of coatings (solvents) can vaporize and form flammable mixtures within the air, particularly when atomized throughout spray software or heated. The diploma of hazard is determined by the following:
The auto ignition temperature (AIT) of the coating material is the one most important issue when applying coatings to sizzling operating gear. AIT is outlined (by the National Safety Council publication Accident Prevention Manual For Business and Industry: Engineering & Technology) as “…the minimum temperature at which a flammable gas-air or vapour-air mixture will ignite from its personal warmth supply or contact with a heated floor without the presence of an open spark or flame.”
The idea of flash point as outlined by NFPA 30 is “the minimal temperature of a liquid at which sufficient vapour is given off to form an ignitable mixture with the air, close to the surface of the liquid”. In different phrases, the flash point describes the temperature of the liquid that is high enough to generate sufficient vapour to create a flame if a source of ignition were launched.
For vapours of flammable liquids, there is a minimum concentration below which the unfold of the flame does not occur when in touch with a source of ignition. This is the Lower Flammable Limit (LFL). There is a most focus of vapour in the air above which the unfold of the flame does not occur. This is the Upper Flammable Limit (UFL). The flammable range is between the LFL and the UFL, when the focus of vapours can support combustion.
If safety procedures are followed, outages will not be required while maintenance is carried out.
Implementing controls
Applying coatings to scorching surfaces increases the speed at which the solvents are driven off. When applying solvent borne coatings to scorching surfaces it have to be assumed that the focus of vapours in the air could exceed the LFL (at least for a short while after application). As with coating software to ambient temperature metal, controls have to be carried out.
While the LFL is more likely to be achieved over a shorter period of time during hot utility of coatings than coatings work performed at ambient situations, the ensuing fire hazard exists in each purposes. That is, the fire hazard and associated controls should be thought of for the appliance of any solvent-borne flammable coating system, whatever the work environment. It must be recognized that the gasoline component of the hearth tetrahedron will be current in both ‘hot’ and ‘ambient’ environments and fundamental steps have to be taken to minimize pointless solvent vapours in the work space. In addition, as outlined later, attention must also be directed to eliminating the remaining component of the tetrahedron – the source of ignition.
Controlling flammable vapours
The gasoline component of a fireplace may be reduced by implementing fundamental controls similar to handling and storing flammable liquids in approved, self-closing containers, preserving the number of flammable liquids containers within the work space and in storage areas to the minimum needed and within allowable (regulatory) limits.
Alkaline detergents such as tri-sodium phosphate may be substituted, adopted by floor washing with fresh water or steam cleaning and pH testing of the surface, or non-combustible solvents such as 1,1,1 trichloroethane) for pre-surface preparation solvent cleaning.
Combustible gasoline indicators must be used to verify that the focus of flammable vapours is below the LFL. Combustible gasoline indicators have to be calibrated in accordance with the manufacturer’s suggestions and must be permitted for use in flammable atmospheres. Operators of the equipment must be skilled in proper gear operation.
Readings should be taken in the general work space and the vicinity of the operator and in areas the place there are potential sources of ignition. Typically, units are set to alarm at 10% of the LFL. If the alarm sounds, coatings software work ought to immediately stop till the concentration of flammable vapours is controlled. The function of setting the alarm below the LFL is to supply a security factor that results in management measures being applied earlier than there could be an imminent hazard of fire or explosion.
Monitoring of the flammable vapour concentration might be necessary as the effectiveness of natural air flow may be variable. If management of flammable vapours requires mechanical air flow, an occupational safety or well being skilled or engineer with expertise in industrial air flow should be consulted.
At a minimum, mechanical ventilation techniques should provide sufficient capability to manage flammable vapours to under 10% of the LFL by both exhaust air flow to remove contaminants from the work space or by dilution air flow through introduction of contemporary air to dilute contaminants. As with combustible fuel indicators, air flow tools must be approved for protected use in flammable atmospheres. In addition, air flow tools should be grounded and bonded.
เครื่องมือที่ใช้ในการวัดความดัน , if wanted, ought to be steady throughout coatings software as concentrations could improve as more surfaces are coated through the course of a work shift, and especially on scorching surfaces the place the rate of vaporization is higher.
Ventilation throughout coatings application should be steady, especially when engaged on sizzling surfaces.
Sources of Ignition
When making use of coatings to scorching surfaces, the primary supply of ignition that readily involves mind is the warmth from the floor being painted. The AIT of the coating materials is the only most necessary concern when applying coatings to hot operating tools. The AIT of a substance or combination is the minimal temperature at which a vapour-air combination will ignite when in touch with a heated surface, without the presence of any open spark or flame.
The key to controlling this supply of ignition is to verify the surfaces being coated are under the AIT of the coatings being utilized. While floor temperatures may be known/available in many services, all floor areas of the process/piping being painted and/or any equipment adjacent to the objects being painted where overspray could deposit ought to be measured for precise floor temperature. The results ought to be compared to the AIT of the coating system.
While auto-ignition and open sources of ignition may be readily apparent, a extra delicate but nonetheless important supply of ignition to manage on any industrial painting venture involving flammable solvents entails the production of static electricity. Equipment associated with the spray-painting operation, corresponding to spray software equipment and ventilation tools, can generate static electricity.
In addition to external sources of ignition, spontaneous ignition can occur when rags or wastes soaked with paint solvents are left in open containers. Spontaneous ignition happens when the sluggish technology of heat from oxidation of natural chemical substances corresponding to paint solvents is accelerated until the ignition temperature of the gas is reached.
This situation is reached when the material is packed loosely allowing a large floor area to be exposed, there’s sufficient air circulating around the materials for oxidation to happen, but the pure ventilation obtainable is inadequate to carry the heat away quick enough to forestall it from build up.
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