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

Managers of petrochemical, refining, energy, offshore, pulp and paper and different facilities with in depth hot processes and piping methods are regularly challenged with performing all the mandatory coatings maintenance work solely during times of outages. Outages are required in order that process gear can be correctly maintained and repaired including cleaning of pipelines and vessels, maintenance and substitute of pumps, motors and valves, upkeep coating operations, and other work that may only be achieved when the operations are shut down.
When coatings work needs to be performed on areas the place elevated temperatures are involved, many suppose that the facility needs to be shut down. This may not be the case.
A question incessantly posed by facility managers is, “Can I do maintenance portray work while the plant is operating?” As described under, the reply is, “Yes you possibly can, however there are security and well being points that must be considered”.
Dangers to personnel should be managed no matter when or where work is performed.
Safety and well being concerns
There is a range of security and health hazards that must be thought-about on every industrial upkeep painting challenge, whether or not the coating materials is being utilized to sizzling steel or not. Some of those embrace correct material dealing with and storage, fall safety, management of fireplace and explosion hazards, and publicity to noise, heavy metals, solvents and other well being risks.
These dangers have to be correctly evaluated and controlled on each industrial upkeep portray venture, no matter when or the place the work is performed. While current on any job, when making use of specialty coatings to sizzling surfaces, some security and health points ought to receive extra consideration.
Flammable and flamable liquids in plenty of coatings (solvents) can vaporize and type flammable mixtures in the air, especially when atomized throughout spray application or heated. The diploma of hazard is dependent upon the following:
The auto ignition temperature (AIT) of the coating material is the one most necessary problem when applying coatings to sizzling operating tools. AIT is defined (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 combination will ignite from its personal heat source or contact with a heated surface without the presence of an open spark or flame.”
The concept of flash point as outlined by NFPA 30 is “the minimal temperature of a liquid at which sufficient vapour is given off to kind 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’s high sufficient to generate sufficient vapour to create a flame if a supply of ignition were introduced.
For vapours of flammable liquids, there is a minimal concentration below which the spread of the flame does not occur when involved with a source of ignition. This is the Lower Flammable Limit (LFL). There is a maximum concentration of vapour within the air above which the unfold of the flame doesn’t 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 security procedures are adopted, outages may not be required whereas upkeep is carried out.
Implementing เกจวัดแก๊สหุงต้ม
Applying coatings to hot surfaces increases the rate at which the solvents are pushed off. When making use of solvent borne coatings to scorching surfaces it must be assumed that the concentration of vapours within the air could exceed the LFL (at least for a brief while after application). As with coating utility to ambient temperature metal, controls should be implemented.
While the LFL is prone to be achieved over a shorter time frame throughout sizzling application of coatings than coatings work performed at ambient conditions, the resulting fire hazard exists in both functions. That is, the fire hazard and related controls should be considered for the applying of any solvent-borne flammable coating system, whatever the work surroundings. It have to be acknowledged that the gas part of the fireplace tetrahedron shall be present in both ‘hot’ and ‘ambient’ environments and primary steps have to be taken to reduce pointless solvent vapours within the work area. In addition, as outlined later, consideration must also be directed to eliminating the remaining factor of the tetrahedron – the source of ignition.
Controlling flammable vapours
The fuel component of a fireplace can be decreased by implementing fundamental controls such as handling and storing flammable liquids in permitted, self-closing containers, preserving the number of flammable liquids containers in the work space and in storage areas to the minimal essential and inside allowable (regulatory) limits.
Alkaline detergents similar to tri-sodium phosphate may be substituted, followed by floor washing with contemporary water or steam cleaning and pH testing of the floor, or non-combustible solvents such as 1,1,1 trichloroethane) for pre-surface preparation solvent cleaning.
Combustible gas indicators should be used to verify that the concentration of flammable vapours is under the LFL. Combustible fuel indicators have to be calibrated in accordance with the manufacturer’s suggestions and must be approved for use in flammable atmospheres. Operators of the tools should be skilled in proper equipment operation.
Readings ought to be taken within the common work area and the neighborhood of the operator and in areas the place there are potential sources of ignition. Typically, models are set to alarm at 10% of the LFL. If the alarm sounds, coatings application work ought to immediately stop until the focus of flammable vapours is controlled. The objective of setting the alarm beneath the LFL is to supply a security factor that ends in control measures being applied earlier than there is an imminent danger of fireplace or explosion.
Monitoring of the flammable vapour concentration might be necessary because the effectiveness of pure ventilation may be variable. If management of flammable vapours requires mechanical air flow, an occupational security or health skilled or engineer with experience in industrial air flow must be consulted.
At a minimal, mechanical air flow techniques ought to provide enough capacity to control flammable vapours to below 10% of the LFL by either exhaust air flow to take away contaminants from the work space or by dilution ventilation by way of introduction of contemporary air to dilute contaminants. As with flamable gasoline indicators, ventilation tools have to be permitted for protected use in flammable atmospheres. In addition, air flow gear must be grounded and bonded.
Additional air flow, if needed, ought to be continuous throughout coatings application as concentrations may increase as extra surfaces are coated during the course of a work shift, and particularly on hot surfaces where the rate of vaporization is greater.
Ventilation throughout coatings software should be continuous, particularly when engaged on hot surfaces.
Sources of Ignition
When applying coatings to scorching surfaces, the primary source of ignition that readily involves thoughts is the heat from the surface being painted. The AIT of the coating material is the single most essential issue when making use of coatings to sizzling operating tools. The AIT of a substance or combination is the minimal temperature at which a vapour-air mixture will ignite when in touch with a heated surface, with out the presence of any open spark or flame.
The key to controlling this supply of ignition is to confirm the surfaces being coated are below the AIT of the coatings being utilized. While surface temperatures may be known/available in many amenities, all floor areas of the process/piping being painted and/or any tools adjoining to the items being painted the place overspray may deposit ought to be measured for actual surface temperature. The outcomes must be compared to the AIT of the coating system.
While auto-ignition and open sources of ignition may be readily apparent, a extra subtle but nonetheless crucial source of ignition to manage on any industrial portray venture involving flammable solvents includes the production of static electricity. Equipment associated with the spray-painting operation, such as spray software equipment and ventilation gear, 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 era of warmth from oxidation of natural chemical substances similar to paint solvents is accelerated until the ignition temperature of the fuel is reached.
This situation is reached when the fabric is packed loosely allowing a big floor area to be uncovered, there is sufficient air circulating across the materials for oxidation to happen, but the pure air flow obtainable is insufficient to carry the heat away fast sufficient to stop it from build up.
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