Considerations for the appliance 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 techniques are frequently challenged with performing all the necessary coatings upkeep work only during times of outages. Outages are required so that process gear may be properly maintained and repaired together with cleansing of pipelines and vessels, maintenance and replacement of pumps, motors and valves, upkeep coating operations, and different work that can only be achieved when the operations are shut down.
When coatings work must be performed on areas the place elevated temperatures are involved, many think that the ability needs to be shut down. This will not be the case.
A query frequently posed by facility managers is, “Can I do maintenance portray work while the plant is operating?” As described below, the reply is, “Yes you can, however there are safety and health points that have to be considered”.
Dangers to personnel should be managed regardless of when or the place work is performed.
Safety and health issues
There is a spread of safety and health hazards that should be considered on every industrial upkeep portray project, whether or not the coating material is being utilized to sizzling metal or not. Some of these embody correct material handling and storage, fall protection, control of fire and explosion hazards, and exposure to noise, heavy metals, solvents and different well being risks.
These risks must be correctly evaluated and managed on each industrial maintenance painting venture, regardless of when or where 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 many coatings (solvents) can vaporize and kind flammable mixtures in the air, especially when atomized during spray application or heated. The diploma of hazard is dependent upon the next:
The auto ignition temperature (AIT) of the coating materials is the single most necessary problem when making use of coatings to hot working gear. 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 personal heat supply or contact with a heated surface without the presence of an open spark or flame.”
The concept of flash level as outlined by NFPA 30 is “the minimal temperature of a liquid at which adequate vapour is given off to type an ignitable combination with the air, close to the floor of the liquid”. In different words, 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 were launched.
For vapours of flammable liquids, there is a minimal concentration beneath which the unfold of the flame does not occur when in contact 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 does not happen. This is the Upper Flammable Limit (UFL). The flammable range is between the LFL and the UFL, when the concentration of vapours can assist combustion.
If safety procedures are adopted, outages may not be required while upkeep is carried out.
Implementing controls
Applying coatings to sizzling surfaces will increase 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 in the air could exceed the LFL (at least for a brief while after application). As with coating utility to ambient temperature metal, controls must be carried out.
While the LFL is likely to be achieved over a shorter time period throughout sizzling utility of coatings than coatings work performed at ambient circumstances, the resulting hearth hazard exists in both functions. That is, the fire hazard and associated controls must be thought-about for the application of any solvent-borne flammable coating system, whatever the work surroundings. It have to be recognized that the gasoline component of the hearth tetrahedron shall be present in each ‘hot’ and ‘ambient’ environments and primary 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 fuel component of a hearth could be lowered by implementing basic controls such as 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 minimal needed and within allowable (regulatory) limits.
Alkaline detergents such as tri-sodium phosphate could additionally be substituted, followed by floor washing with contemporary water or steam cleansing and pH testing of the surface, or non-combustible solvents corresponding to 1,1,1 trichloroethane) for pre-surface preparation solvent cleansing.
Combustible gasoline indicators must 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 suggestions and should be accredited for use in flammable atmospheres. Operators of the equipment have to be trained in correct tools operation.
Readings ought to be taken in the basic work space and the neighborhood of the operator and in areas the place there are potential sources of ignition. Typically, items are set to alarm at 10% of the LFL. If the alarm sounds, coatings software work ought to instantly cease till the focus of flammable vapours is managed. The function of setting the alarm under the LFL is to supply a safety issue that ends in management measures being applied before there’s an imminent danger of fireplace or explosion.
Monitoring of the flammable vapour focus will be necessary as the effectiveness of pure ventilation could additionally be variable. If management of flammable vapours requires mechanical ventilation, an occupational safety or well being skilled or engineer with expertise in industrial ventilation ought to be consulted.
At a minimal, mechanical ventilation systems should provide sufficient capacity to control flammable vapours to beneath 10% of the LFL by either exhaust air flow to remove contaminants from the work area or by dilution air flow through introduction of recent air to dilute contaminants. As with flamable fuel indicators, air flow equipment must be approved for secure use in flammable atmospheres. In addition, air flow tools must be grounded and bonded.
Additional air flow, if needed, ought to be steady throughout coatings utility as concentrations could increase as more surfaces are coated in the course of the course of a piece shift, and especially on hot surfaces the place the speed of vaporization is larger.
Ventilation during coatings software ought to be continuous, particularly when working on scorching surfaces.
Sources of Ignition
When making use of coatings to hot surfaces, the first source of ignition that readily comes to thoughts is the heat from the floor being painted. The AIT of the coating materials is the only most essential concern when applying coatings to hot operating tools. เพรสเชอร์เกจวัดแรงดันน้ำ of a substance or combination is the minimal temperature at which a vapour-air mixture 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 below the AIT of the coatings being applied. While floor temperatures may be known/available in many facilities, all floor areas of the process/piping being painted and/or any equipment adjoining to the gadgets being painted the place overspray might deposit ought to be measured for precise surface temperature. The results must be in comparison with the AIT of the coating system.
While auto-ignition and open sources of ignition may be readily apparent, a more delicate however nonetheless critical source of ignition to manage on any industrial portray venture involving flammable solvents entails the manufacturing of static electrical energy. Equipment associated with the spray-painting operation, similar to spray application equipment and ventilation tools, can generate static electrical energy.
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 slow generation of warmth from oxidation of natural chemical compounds such as paint solvents is accelerated till the ignition temperature of the fuel is reached.
This condition is reached when the fabric is packed loosely permitting a large floor area to be uncovered, there is enough air circulating around the materials for oxidation to happen, however the pure ventilation out there is inadequate to carry the heat away quick sufficient to forestall it from build up.
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