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

Managers of petrochemical, refining, power, offshore, pulp and paper and other amenities with intensive hot processes and piping systems are regularly challenged with performing all the necessary coatings maintenance work only during periods of outages. Outages are required in order that process equipment could be correctly maintained and repaired together with cleansing of pipelines and vessels, upkeep and replacement of pumps, motors and valves, maintenance coating operations, and other 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 assume that the power has to be shut down. This is most likely not the case.
A query incessantly posed by facility managers is, “Can I do upkeep painting work while the plant is operating?” As described under, the answer is, “Yes you presumably can, however there are security and well being points that should be considered”.
Dangers to personnel must be managed no matter when or where work is performed.
Safety and well being considerations
There is a spread of security and health hazards that should be thought-about on every industrial maintenance portray venture, whether or not the coating material is being utilized to hot steel or not. Some of those include correct materials handling and storage, fall safety, management of fireside and explosion hazards, and publicity to noise, heavy metals, solvents and different health dangers.
These risks must be correctly evaluated and controlled on each industrial upkeep portray challenge, regardless of when or where the work is carried out. While current on any job, when making use of specialty coatings to scorching surfaces, some security and well being issues ought to obtain extra consideration.
Flammable and flamable liquids in many coatings (solvents) can vaporize and form flammable mixtures within the air, particularly when atomized during spray utility or heated. The diploma of hazard is dependent upon the next:
The auto ignition temperature (AIT) of the coating material is the only most essential problem when applying coatings to hot operating gear. 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 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 minimum temperature of a liquid at which sufficient vapour is given off to kind an ignitable combination with the air, close to the surface of the liquid”. In different words, the flash point describes the temperature of the liquid that’s high enough to generate enough vapour to create a flame if a source of ignition had been introduced.
For vapours of flammable liquids, there’s a minimum focus below which the spread of the flame does not occur 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 doesn’t occur. This is the Upper Flammable Limit (UFL). The flammable vary is between the LFL and the UFL, when the concentration of vapours can assist combustion.
If security procedures are followed, outages will not be required while upkeep is performed.
Implementing controls
Applying coatings to scorching surfaces increases the speed at which the solvents are driven off. When applying solvent borne coatings to sizzling surfaces it have to be assumed that the concentration of vapours within the air might exceed the LFL (at least for a brief time after application). As with coating software to ambient temperature steel, controls must be implemented.
While the LFL is likely to be achieved over a shorter time period during sizzling application of coatings than coatings work performed at ambient circumstances, the ensuing fireplace hazard exists in both functions. That is, the fire hazard and related controls have to be thought-about for the application of any solvent-borne flammable coating system, regardless of the work setting. It have to be acknowledged that the fuel component of the hearth tetrahedron will be current in both ‘hot’ and ‘ambient’ environments and fundamental steps should 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 component of the tetrahedron – the supply of ignition.
Controlling flammable vapours
The gasoline factor of a hearth may be lowered by implementing basic controls similar to dealing with and storing flammable liquids in accredited, self-closing containers, keeping the variety of flammable liquids containers in the work space and in storage areas to the minimum essential and inside allowable (regulatory) limits.
Alkaline detergents similar to 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 fuel indicators ought to be used to confirm that the focus of flammable vapours is below the LFL. Combustible gasoline indicators must be calibrated in accordance with the manufacturer’s recommendations and should be accredited for use in flammable atmospheres. Operators of the gear have to be educated in correct tools operation.
Readings should be taken in the common work area and the neighborhood of the operator and in areas where there are potential sources of ignition. Typically, models are set to alarm at 10% of the LFL. If the alarm sounds, coatings software work ought to instantly stop until the focus of flammable vapours is controlled. The purpose of setting the alarm under the LFL is to supply a safety issue that results in management measures being implemented before there’s an imminent hazard of fireside or explosion.
Monitoring of the flammable vapour concentration will be necessary as the effectiveness of natural air flow could additionally be variable. If control of flammable vapours requires mechanical air flow, an occupational security or health professional or engineer with expertise in industrial ventilation ought to be consulted.
At a minimum, mechanical ventilation systems ought to provide adequate capability to regulate flammable vapours to beneath 10% of the LFL by either exhaust ventilation to take away contaminants from the work area or by dilution air flow by way of introduction of recent air to dilute contaminants. As with combustible fuel indicators, air flow equipment have to be permitted for safe use in flammable atmospheres. In addition, air flow tools must be grounded and bonded.
Additional air flow, if wanted, should be continuous throughout coatings utility as concentrations may improve as extra surfaces are coated in the course of the course of a piece shift, and especially on sizzling surfaces the place the rate of vaporization is greater.
เครื่องมือวัดความดันคือ throughout coatings utility should be steady, especially when engaged on sizzling surfaces.
Sources of Ignition
When making use of coatings to scorching surfaces, the first supply of ignition that readily involves mind is the heat from the floor being painted. The AIT of the coating material is the one most important problem when making use of coatings to hot operating equipment. The AIT of a substance or combination is the minimum temperature at which a vapour-air combination will ignite when in contact with a heated surface, with out the presence of any open spark or flame.
The key to controlling this source of ignition is to confirm the surfaces being coated are under the AIT of the coatings being applied. While surface temperatures may be known/available in many facilities, all floor areas of the process/piping being painted and/or any tools adjoining to the gadgets being painted where overspray might deposit should be measured for actual surface temperature. The outcomes ought to be in comparability with the AIT of the coating system.
While auto-ignition and open sources of ignition could also be readily apparent, a extra subtle however nonetheless crucial source of ignition to regulate on any industrial portray project involving flammable solvents involves the manufacturing of static electricity. Equipment associated with the spray-painting operation, corresponding to spray utility tools 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 occurs when the slow generation of warmth from oxidation of organic chemicals corresponding to paint solvents is accelerated until the ignition temperature of the gasoline is reached.
เกจวัดแรงดันน้ำประปาราคา is reached when the material is packed loosely allowing a big surface space to be uncovered, there is sufficient air circulating around the materials for oxidation to occur, however the natural air flow obtainable is inadequate to carry the warmth away fast sufficient to prevent it from building up.
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