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

Managers of petrochemical, refining, power, offshore, pulp and paper and other amenities with in depth sizzling processes and piping techniques are incessantly challenged with performing all the necessary coatings upkeep work only during periods of outages. Outages are required so that course of gear can be properly maintained and repaired including cleaning of pipelines and vessels, upkeep and substitute 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 needs to be performed on areas the place elevated temperatures are involved, many assume that the facility must be shut down. This may not be the case.
A question frequently posed by facility managers is, “Can I do maintenance painting work whereas the plant is operating?” As described under, the answer is, “Yes you presumably can, however there are security and well being issues that must be considered”.
Dangers to personnel should be managed no matter when or the place work is performed.
Safety and well being considerations
There is a range of security and well being hazards that have to be thought of on every industrial maintenance portray project, whether the coating materials is being applied to sizzling steel or not. Some of these embody correct materials handling and storage, fall protection, control of fireside and explosion hazards, and publicity to noise, heavy metals, solvents and other well being dangers.
These dangers must be properly evaluated and managed on each industrial upkeep painting venture, regardless of when or where the work is carried out. While current on any job, when applying specialty coatings to hot surfaces, some security and well being issues should obtain further consideration.
Flammable and flamable liquids in plenty of coatings (solvents) can vaporize and type flammable mixtures within the air, especially when atomized during spray utility or heated. The degree of hazard is dependent upon the next:
The auto ignition temperature (AIT) of the coating materials is the one most necessary concern when applying coatings to hot operating 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 mixture will ignite from its own warmth supply or contact with a heated surface without the presence of an open spark or flame.”
The idea of flash level as defined by NFPA 30 is “the minimum temperature of a liquid at which enough 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 sufficient vapour to create a flame if a source of ignition have been introduced.
For vapours of flammable liquids, there’s a minimal focus beneath which the spread of the flame does not happen when in contact with a source of ignition. This is the Lower Flammable Limit (LFL). There is a most concentration of vapour within the air above which the spread 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 focus of vapours can assist combustion.
If safety procedures are adopted, outages is probably not required whereas maintenance is performed.
Implementing controls
Applying coatings to scorching surfaces increases the speed at which the solvents are pushed off. When making use of solvent borne coatings to sizzling surfaces it must be assumed that the concentration of vapours within the air may exceed the LFL (at least for a short time after application). As with coating software to ambient temperature metal, controls must be carried out.
While the LFL is more likely to be achieved over a shorter period of time during sizzling software of coatings than coatings work performed at ambient situations, the ensuing hearth hazard exists in both purposes. That is, the fire hazard and associated controls have to be thought of for the appliance of any solvent-borne flammable coating system, whatever the work environment. It must be recognized that the fuel element of the fireplace tetrahedron might be current in each ‘hot’ and ‘ambient’ environments and primary steps must be taken to reduce unnecessary solvent vapours in the work space. In addition, as outlined later, consideration should even be directed to eliminating the remaining element of the tetrahedron – the supply of ignition.
Controlling flammable vapours
The fuel component of a fireplace can be reduced by implementing primary controls such as handling and storing flammable liquids in approved, self-closing containers, keeping the variety of flammable liquids containers in the work space and in storage areas to the minimal essential and within allowable (regulatory) limits.
Alkaline detergents similar to tri-sodium phosphate could additionally be substituted, adopted 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 cleansing.
Combustible fuel indicators must be used to verify that the concentration of flammable vapours is under the LFL. Combustible gasoline indicators should be calibrated in accordance with the manufacturer’s suggestions and have to be approved to be used in flammable atmospheres. Operators of the equipment should be trained in proper gear operation.
Readings must be taken in the common work space and the neighborhood of the operator and in areas the place there are potential sources of ignition. Typically, units are set to alarm at 10% of the LFL. If the alarm sounds, coatings utility work ought to instantly cease until the focus of flammable vapours is controlled. The objective of setting the alarm beneath the LFL is to supply a security issue that ends in control measures being applied before there is an imminent hazard of fireside or explosion.
Monitoring of the combustible vapour focus will be necessary as the effectiveness of pure ventilation may be variable. If control of flammable vapours requires mechanical ventilation, an occupational safety or well being professional or engineer with expertise in industrial ventilation must be consulted.
At a minimal, mechanical ventilation methods should provide adequate capability to manage flammable vapours to beneath 10% of the LFL by both exhaust air flow to remove contaminants from the work area or by dilution air flow via introduction of fresh air to dilute contaminants. As with combustible fuel indicators, ventilation equipment must be permitted for secure use in flammable atmospheres. In addition, air flow tools should be grounded and bonded.
Additional ventilation, if needed, should be steady throughout coatings application as concentrations might increase as more surfaces are coated through the course of a work shift, and particularly on hot surfaces the place the rate of vaporization is greater.
Ventilation throughout coatings utility ought to be steady, particularly when engaged on scorching surfaces.
Sources of Ignition
When applying coatings to hot surfaces, the first source of ignition that readily involves mind is the warmth from the surface being painted. The AIT of the coating materials is the one most necessary problem when applying coatings to sizzling working equipment. The AIT of a substance or combination is the minimal temperature at which a vapour-air combination will ignite when involved with a heated floor, with out the presence of any open spark or flame.
The key to controlling this supply of ignition is to verify the surfaces being coated are under the AIT of the coatings being utilized. While floor temperatures may be known/available in many facilities, all floor areas of the process/piping being painted and/or any tools adjacent to the objects being painted where overspray could deposit must be measured for actual floor 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 obvious, a extra refined but nonetheless critical source of ignition to regulate on any industrial painting venture involving flammable solvents entails the production of static electricity. Equipment associated with the spray-painting operation, such as spray software equipment and air flow equipment, can generate static electrical energy.
In addition to external sources of ignition, spontaneous ignition can happen when rags or wastes soaked with paint solvents are left in open containers. เกจวัดแรงดันดิจิตอล occurs when the sluggish generation of warmth from oxidation of natural chemicals corresponding to paint solvents is accelerated till the ignition temperature of the gas is reached.
This condition is reached when the material is packed loosely allowing a large floor space to be exposed, there is enough air circulating across the material for oxidation to happen, however the natural air flow available is inadequate to hold the warmth away fast sufficient to stop it from build up.
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