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

Managers of petrochemical, refining, power, offshore, pulp and paper and different amenities with in depth scorching processes and piping techniques are incessantly challenged with performing all the necessary coatings upkeep work solely during periods of outages. Outages are required so that process gear may be properly maintained and repaired including cleansing of pipelines and vessels, maintenance and replacement of pumps, motors and valves, upkeep coating operations, and different work that can solely be completed when the operations are shut down.
When coatings work must be performed on areas where elevated temperatures are involved, many suppose that the ability must be shut down. This will not be the case.
A question incessantly posed by facility managers is, “Can I do upkeep painting work while the plant is operating?” As described beneath, the reply is, “Yes you’ll be able to, but there are safety and well being points that should be considered”.
Dangers to personnel must be managed no matter when or the place work is performed.
Safety and well being issues
There is a spread of security and well being hazards that must be thought of on every industrial maintenance painting project, whether the coating materials is being utilized to sizzling metal or not. Some of these embody proper materials dealing with and storage, fall safety, control of fire and explosion hazards, and publicity to noise, heavy metals, solvents and other well being dangers.
These risks must be properly evaluated and managed on each industrial upkeep portray project, 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 safety and health points should receive extra consideration.
Flammable and flamable liquids in lots of coatings (solvents) can vaporize and kind flammable mixtures in the air, especially when atomized during spray application or heated. The degree of hazard is dependent upon the following:
The auto ignition temperature (AIT) of the coating material is the one most essential concern when making use of coatings to scorching working 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 combination will ignite from its own heat source or contact with a heated floor with out 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 type an ignitable combination with the air, close to the surface of the liquid”. In other words, the flash level 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 introduced.
For vapours of flammable liquids, there is a minimal focus below which the unfold of the flame doesn’t happen when in contact with a supply of ignition. This is the Lower Flammable Limit (LFL). There is a maximum 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 concentration of vapours can help combustion.
If safety procedures are followed, outages will not be required while maintenance is performed.
Implementing controls
Applying coatings to scorching surfaces increases the rate at which the solvents are pushed off. When applying solvent borne coatings to hot surfaces it must be assumed that the focus of vapours within the air might exceed the LFL (at least for a short while after application). As with coating application to ambient temperature metal, controls should be implemented.
While the LFL is more probably to be achieved over a shorter time period during scorching software of coatings than coatings work carried out at ambient situations, the ensuing fire hazard exists in each functions. That is, the hearth hazard and associated controls should be considered for the appliance of any solvent-borne flammable coating system, whatever the work setting. It have to be recognized that the fuel part of the fireplace tetrahedron will be current in each ‘hot’ and ‘ambient’ environments and primary steps must be taken to reduce pointless solvent vapours in the work space. In addition, as outlined later, attention should also be directed to eliminating the remaining factor of the tetrahedron – the supply of ignition.
Controlling flammable vapours
The gas component of a fire may be reduced by implementing fundamental controls such as dealing with and storing flammable liquids in approved, self-closing containers, preserving the variety of flammable liquids containers within the work space and in storage areas to the minimum needed and inside allowable (regulatory) limits.
Alkaline detergents such as tri-sodium phosphate could also be substituted, followed by surface washing with contemporary water or steam cleaning and pH testing of the floor, or non-combustible solvents corresponding to 1,1,1 trichloroethane) for pre-surface preparation solvent cleaning.
Combustible gas indicators must be used to confirm that the focus of flammable vapours is under the LFL. Combustible gas indicators should be calibrated in accordance with the manufacturer’s suggestions and have to be permitted for use in flammable atmospheres. Operators of the equipment should be skilled in correct equipment operation.
Readings should be taken within the basic work area and the neighborhood of the operator and in areas the place there are potential sources of ignition. Typically, เกจแรงดัน are set to alarm at 10% of the LFL. If the alarm sounds, coatings utility work should instantly cease until the concentration of flammable vapours is controlled. The function of setting the alarm under the LFL is to supply a safety factor that leads to management measures being carried out before there is an imminent danger of fire or explosion.
Monitoring of the combustible vapour focus will be necessary because the effectiveness of pure air flow could also be variable. If control of flammable vapours requires mechanical air flow, an occupational security or health professional or engineer with experience in industrial air flow must be consulted.
At a minimum, mechanical ventilation systems ought to present enough capability to manage flammable vapours to beneath 10% of the LFL by either exhaust ventilation to remove contaminants from the work area or by dilution ventilation through introduction of recent air to dilute contaminants. As with combustible fuel indicators, ventilation tools should be permitted for protected use in flammable atmospheres. In addition, ventilation tools have to be grounded and bonded.
Additional ventilation, if wanted, should be steady throughout coatings utility as concentrations could enhance as more surfaces are coated during the course of a work shift, and especially on scorching surfaces where the rate of vaporization is larger.
Ventilation throughout coatings software should be steady, especially when working on hot surfaces.
Sources of Ignition
When making use of coatings to scorching surfaces, the first supply of ignition that readily involves mind is the warmth from the floor being painted. The AIT of the coating material is the only most necessary issue when making use of coatings to scorching operating 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 floor, with out the presence of any open spark or flame.
pressure gauge หน้าปัด 2 นิ้ว to controlling this source of ignition is to confirm the surfaces being coated are beneath the AIT of the coatings being applied. While surface temperatures could also be known/available in many services, all floor areas of the process/piping being painted and/or any tools adjacent to the items being painted where overspray may deposit must be measured for actual floor temperature. The results must be in comparability with the AIT of the coating system.
While auto-ignition and open sources of ignition could additionally be readily obvious, a more refined but nonetheless critical supply of ignition to regulate on any industrial painting venture involving flammable solvents entails the production of static electrical energy. Equipment related to the spray-painting operation, such as spray software gear and air flow equipment, can generate static electricity.
In addition to exterior sources of ignition, spontaneous ignition can happen when rags or wastes soaked with paint solvents are left in open containers. Spontaneous ignition occurs when the slow generation of heat from oxidation of natural chemical compounds such as paint solvents is accelerated till the ignition temperature of the gas is reached.
This condition is reached when the fabric is packed loosely permitting a large floor area to be exposed, there’s enough air circulating around the material for oxidation to happen, however the pure air flow out there is insufficient to hold the heat away fast enough to forestall it from increase.
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