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

Managers of petrochemical, refining, energy, offshore, pulp and paper and different amenities with extensive hot processes and piping systems are frequently challenged with performing all the mandatory coatings upkeep work only during times of outages. Outages are required so that course of gear could be properly maintained and repaired including cleaning of pipelines and vessels, upkeep and replacement of pumps, motors and valves, maintenance coating operations, and other work that can only be completed when the operations are shut down.
When coatings work must be carried out on areas the place elevated temperatures are involved, many think 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 maintenance portray work while the plant is operating?” As described below, เกจแรงดันน้ำ is, “Yes you probably can, however there are security and health issues that have to be considered”.
Dangers to personnel have to be managed no matter when or where work is carried out.
Safety and well being concerns
There is a range of security and well being hazards that have to be thought of on every industrial upkeep painting project, whether or not the coating materials is being utilized to sizzling steel or not. Some of those embody correct material handling and storage, fall safety, control of fire and explosion hazards, and exposure to noise, heavy metals, solvents and different well being risks.
These dangers must be correctly evaluated and controlled on every industrial upkeep painting venture, regardless of when or where the work is performed. While present on any job, when making use of specialty coatings to sizzling surfaces, some safety and health points ought to obtain additional consideration.
Flammable and flamable liquids in plenty of coatings (solvents) can vaporize and form flammable mixtures in the air, especially when atomized during spray software or heated. The diploma of hazard depends on the following:
The auto ignition temperature (AIT) of the coating material is the only most essential issue when applying coatings to scorching operating tools. 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 idea 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, near the floor of the liquid”. In other 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 have been launched.
For vapours of flammable liquids, there is a minimal concentration below which the unfold of the flame doesn’t happen when involved with a source of ignition. This is the Lower Flammable Limit (LFL). There is a maximum focus of vapour within the air above which the spread of the flame doesn’t happen. This is the Upper Flammable Limit (UFL). The flammable vary is between the LFL and the UFL, when the focus of vapours can support combustion.
If security procedures are followed, outages is probably not required whereas maintenance is carried out.
Implementing controls
Applying coatings to sizzling surfaces will increase the speed at which the solvents are driven off. When making use of solvent borne coatings to hot surfaces it have to be assumed that the focus of vapours within the air might exceed the LFL (at least for a short time after application). As with coating software to ambient temperature metal, controls must be implemented.
While the LFL is prone to be achieved over a shorter time frame during scorching utility of coatings than coatings work performed at ambient situations, the resulting hearth hazard exists in both applications. That is, the fireplace hazard and related controls must be thought of for the appliance of any solvent-borne flammable coating system, regardless of the work surroundings. It have to be acknowledged that the gasoline part of the fireplace tetrahedron might be current in each ‘hot’ and ‘ambient’ environments and basic steps must be taken to attenuate pointless solvent vapours in the work area. In addition, as outlined later, attention must also be directed to eliminating the remaining factor of the tetrahedron – the supply of ignition.
Controlling flammable vapours
The fuel factor of a hearth may be lowered by implementing fundamental controls corresponding to dealing with and storing flammable liquids in permitted, self-closing containers, keeping the number of flammable liquids containers within the work space and in storage areas to the minimum necessary and inside allowable (regulatory) limits.
Alkaline detergents corresponding to tri-sodium phosphate could additionally be substituted, followed by surface washing with fresh water or steam cleaning and pH testing of the surface, or non-combustible solvents similar to 1,1,1 trichloroethane) for pre-surface preparation solvent cleaning.
Combustible fuel indicators must be used to verify that the focus of flammable vapours is beneath the LFL. Combustible gas indicators should be calibrated in accordance with the manufacturer’s recommendations and should be accredited to be used in flammable atmospheres. Operators of the equipment have to be educated in proper tools operation.
Readings should be taken in the basic work space and the neighborhood of the operator and in areas where there are potential sources of ignition. Typically, units are set to alarm at 10% of the LFL. If the alarm sounds, coatings software work ought to instantly cease till the concentration of flammable vapours is controlled. The objective of setting the alarm below the LFL is to provide a security issue that leads to control measures being implemented before there may be an imminent danger of fireplace or explosion.
Monitoring of the combustible vapour focus might be necessary as the effectiveness of pure ventilation could additionally be variable. If control of flammable vapours requires mechanical ventilation, an occupational safety or well being professional or engineer with expertise in industrial air flow should be consulted.
At a minimal, mechanical air flow techniques should present sufficient capacity to manage flammable vapours to below 10% of the LFL by either exhaust ventilation to take away contaminants from the work area or by dilution ventilation through introduction of contemporary air to dilute contaminants. As with flamable gasoline indicators, air flow equipment must be accredited for protected use in flammable atmospheres. In addition, ventilation equipment have to be grounded and bonded.
Additional ventilation, if needed, should be steady throughout coatings software as concentrations might improve as extra surfaces are coated in the course of the course of a work shift, and particularly on sizzling surfaces where the rate of vaporization is larger.
Ventilation during coatings utility should be steady, particularly when working on sizzling surfaces.
Sources of Ignition
When making use of coatings to scorching surfaces, the first supply of ignition that readily involves thoughts is the warmth from the surface being painted. The AIT of the coating materials is the one most necessary concern when making use of coatings to hot working tools. The AIT of a substance or mixture is the minimal temperature at which a vapour-air mixture will ignite when in contact with a heated surface, without 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 applied. While surface temperatures may be known/available in plenty of services, all floor areas of the process/piping being painted and/or any gear adjoining to the gadgets being painted where overspray could deposit ought to be measured for precise floor temperature. The outcomes must be compared to the AIT of the coating system.
While auto-ignition and open sources of ignition could also be readily apparent, a more delicate but nonetheless crucial source of ignition to control on any industrial painting challenge involving flammable solvents includes the production of static electrical energy. Equipment associated with the spray-painting operation, similar to spray application tools and air flow 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 gradual era of warmth from oxidation of organic chemical compounds corresponding to paint solvents is accelerated till the ignition temperature of the gas is reached.
This situation is reached when the fabric is packed loosely permitting a large floor space to be uncovered, there is sufficient air circulating around the materials for oxidation to occur, but the pure air flow available is inadequate to hold the warmth away quick enough to stop it from building up.
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