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

Managers of petrochemical, refining, energy, offshore, pulp and paper and other services with in depth scorching processes and piping systems are incessantly challenged with performing all the mandatory coatings upkeep work only during times of outages. Outages are required so that course of tools could be correctly maintained and repaired together with cleansing of pipelines and vessels, maintenance and substitute of pumps, motors and valves, upkeep coating operations, and different work that may solely be achieved when the operations are shut down.
When coatings work has to be performed on areas the place elevated temperatures are involved, many think that the power has to be shut down. This will not be the case.
A question frequently posed by facility managers is, “Can I do maintenance painting work whereas the plant is operating?” As described below, the reply is, “Yes you can, however there are security and health points that have to be considered”.
Dangers to personnel should be managed no matter when or where work is carried out.
Safety and health considerations
There is a variety of security and well being hazards that should be thought-about on every industrial upkeep painting venture, whether the coating material is being utilized to scorching steel or not. Some of those embrace correct material dealing with and storage, fall safety, management of fireplace and explosion hazards, and exposure to noise, heavy metals, solvents and other well being dangers.
These risks should be properly evaluated and controlled on each industrial upkeep painting project, no matter when or the place the work is performed. While present on any job, when making use of specialty coatings to sizzling surfaces, some security and health points ought to obtain further 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 degree of hazard is determined by the next:
The auto ignition temperature (AIT) of the coating materials is the single most essential concern when making use of coatings to sizzling operating tools. AIT is outlined (by the National Safety Council publication Accident Prevention Manual For Business and Industry: Engineering & Technology) as “…the minimal temperature at which a flammable gas-air or vapour-air combination will ignite from its own heat supply or contact with a heated surface with out the presence of an open spark or flame.”
The concept of flash level as defined 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, near the floor of the liquid”. In different phrases, the flash point describes the temperature of the liquid that is high sufficient to generate enough vapour to create a flame if a supply of ignition have been launched.
For vapours of flammable liquids, there is a minimal focus beneath which the spread of the flame does not occur when involved with a supply of ignition. This is the Lower Flammable Limit (LFL). There is a most concentration of vapour within the air above which the spread of the flame doesn’t occur. This is the Upper Flammable Limit (UFL). The flammable vary is between the LFL and the UFL, when the focus of vapours can assist combustion.
If security procedures are followed, outages is most likely not required whereas upkeep is carried out.
Implementing controls
Applying coatings to hot surfaces will increase the speed at which the solvents are driven off. When making use of solvent borne coatings to hot surfaces it should be assumed that the focus of vapours in the air could exceed the LFL (at least for a short time after application). As with coating utility to ambient temperature steel, controls have to be carried out.
While the LFL is prone to be achieved over a shorter period of time throughout scorching application of coatings than coatings work carried out at ambient conditions, the ensuing fireplace hazard exists in both functions. That is, the hearth hazard and associated controls should be considered for the appliance of any solvent-borne flammable coating system, regardless of the work setting. It must be acknowledged that the gasoline component of the hearth tetrahedron might be present in both ‘hot’ and ‘ambient’ environments and basic steps must be taken to reduce unnecessary solvent vapours in the work area. In addition, as outlined later, consideration should even be directed to eliminating the remaining component of the tetrahedron – the supply of ignition.
Controlling flammable vapours
The gasoline factor of a hearth could be lowered by implementing primary controls such as handling and storing flammable liquids in approved, self-closing containers, keeping the number of flammable liquids containers within the work area and in storage areas to the minimal necessary and within allowable (regulatory) limits.
Alkaline detergents similar to tri-sodium phosphate could additionally be substituted, adopted by floor washing with contemporary water or steam cleansing and pH testing of the surface, or non-combustible solvents such as 1,1,1 trichloroethane) for pre-surface preparation solvent cleansing.
Combustible fuel indicators ought to be used to confirm that the concentration of flammable vapours is below the LFL. Combustible gasoline indicators must be calibrated in accordance with the manufacturer’s recommendations and must be permitted for use in flammable atmospheres. Operators of the gear have to be educated in proper tools operation.
Readings ought to be taken within the general work area and the neighborhood of the operator and in areas where there are potential sources of ignition. Typically, items are set to alarm at 10% of the LFL. If the alarm sounds, coatings application work ought to instantly cease till the concentration of flammable vapours is managed. The objective of setting the alarm beneath the LFL is to provide a security factor that leads to control measures being implemented earlier than there is an imminent danger of fireplace or explosion.
Monitoring of the combustible vapour focus will be necessary because the effectiveness of pure ventilation may be variable. If management of flammable vapours requires mechanical ventilation, an occupational security or health skilled or engineer with expertise in industrial ventilation must be consulted.
At a minimal, mechanical ventilation techniques ought to provide sufficient capability to control flammable vapours to below 10% of the LFL by both exhaust ventilation to remove contaminants from the work space or by dilution air flow by way of introduction of contemporary air to dilute contaminants. As with combustible gasoline indicators, ventilation tools have to be approved for protected use in flammable atmospheres. In addition, ventilation gear should be grounded and bonded.
Additional ventilation, if wanted, must be continuous during coatings utility as concentrations may enhance as extra surfaces are coated through the course of a piece shift, and particularly on scorching surfaces the place the speed of vaporization is higher.
เกจวัดแรงดันแก๊สlpg during coatings software must be continuous, especially when engaged on sizzling surfaces.
Sources of Ignition
When applying coatings to hot surfaces, the first source of ignition that readily involves thoughts is the heat from the floor being painted. The AIT of the coating material is the single most essential issue when making use of coatings to hot working equipment. The AIT of a substance or mixture is the minimum temperature at which a vapour-air mixture will ignite when in touch with a heated surface, without the presence of any open spark or flame.
The key to controlling this source of ignition is to verify the surfaces being coated are under the AIT of the coatings being applied. While surface temperatures may be known/available in many facilities, all surface areas of the process/piping being painted and/or any equipment adjoining to the gadgets being painted where overspray could deposit must be measured for actual floor temperature. The results must be compared to the AIT of the coating system.
While auto-ignition and open sources of ignition could additionally be readily obvious, a extra subtle however nonetheless critical source of ignition to manage on any industrial painting venture involving flammable solvents involves the production of static electricity. Equipment associated with the spray-painting operation, corresponding to spray application gear and air flow tools, can generate static electrical energy.
In addition to exterior sources of ignition, spontaneous ignition can occur when rags or wastes soaked with paint solvents are left in open containers. Spontaneous ignition occurs when the sluggish era of warmth from oxidation of organic chemical compounds similar to paint solvents is accelerated until the ignition temperature of the fuel is reached.
This condition is reached when the material is packed loosely permitting a big floor area to be uncovered, there is sufficient air circulating around the materials for oxidation to happen, however the natural air flow available is inadequate to carry the warmth away quick sufficient to prevent it from building up.
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