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

Managers of petrochemical, refining, energy, offshore, pulp and paper and other facilities with in depth hot processes and piping techniques are incessantly challenged with performing all the necessary coatings upkeep work solely 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, maintenance and alternative of pumps, motors and valves, maintenance coating operations, and different work that may only be completed when the operations are shut down.
When coatings work needs to be carried out on areas the place elevated temperatures are concerned, many think that the ability needs 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 under, the reply is, “Yes you’ll be able to, however there are security and well being issues that should be considered”.
Dangers to personnel must be managed no matter when or the place work is performed.
Safety and well being considerations
There is a spread of safety and health hazards that must be considered on every industrial upkeep portray venture, whether or not the coating material is being utilized to sizzling steel or not. Some of these embody correct material dealing with and storage, fall protection, control of fireplace and explosion hazards, and exposure to noise, heavy metals, solvents and other health risks.
These dangers have to be correctly evaluated and controlled on every industrial maintenance portray project, regardless of when or the place the work is performed. While present on any job, when applying specialty coatings to scorching surfaces, some safety and well being issues ought to receive further consideration.
Flammable and combustible liquids in lots of coatings (solvents) can vaporize and form flammable mixtures in the air, especially when atomized during spray software or heated. The degree of hazard depends on the next:
The auto ignition temperature (AIT) of the coating material is the only most important problem when applying 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 mixture will ignite from its own heat supply or contact with a heated floor with out 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 sufficient vapour is given off to type an ignitable combination with the air, near the surface of the liquid”. In other phrases, the flash point describes the temperature of the liquid that’s high sufficient to generate sufficient vapour to create a flame if a supply of ignition have been launched.
For vapours of flammable liquids, there’s a minimal concentration below which the unfold of the flame doesn’t occur when involved with a source of ignition. This is the Lower Flammable Limit (LFL). There is a most focus of vapour within 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 adopted, outages will not be required while upkeep is carried out.
Implementing controls
Applying coatings to hot surfaces increases the rate at which the solvents are driven 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 quick time after application). As with coating application to ambient temperature metal, controls should be implemented.
While the LFL is prone to be achieved over a shorter time period during sizzling utility of coatings than coatings work carried out at ambient circumstances, the ensuing hearth hazard exists in each purposes. That is, the fireplace hazard and associated controls should be thought of for the applying of any solvent-borne flammable coating system, regardless of the work setting. It must be recognized that the gas component of the fire tetrahedron shall be present in each ‘hot’ and ‘ambient’ environments and fundamental steps must be taken to minimize pointless solvent vapours within the work area. In addition, as outlined later, consideration must 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 primary controls corresponding to dealing with and storing flammable liquids in accredited, self-closing containers, maintaining the number of flammable liquids containers within the work space and in storage areas to the minimal essential and inside allowable (regulatory) limits.
Alkaline detergents corresponding to tri-sodium phosphate could also be substituted, adopted by surface washing with fresh water or steam cleaning and pH testing of the floor, or non-combustible solvents similar to 1,1,1 trichloroethane) for pre-surface preparation solvent cleaning.
Combustible gas indicators must be used to verify that the concentration of flammable vapours is beneath the LFL. Combustible gas indicators have to be calibrated in accordance with the manufacturer’s suggestions and must be accredited to be used in flammable atmospheres. Operators of the tools should be trained in proper tools 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, items are set to alarm at 10% of the LFL. If the alarm sounds, coatings utility work should immediately stop until the focus 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 earlier than there’s an imminent danger of fireside 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 air flow, an occupational security or health professional or engineer with experience in industrial air flow ought to be consulted.
At a minimum, mechanical air flow methods ought to provide enough capability to regulate flammable vapours to below 10% of the LFL by both exhaust ventilation to remove contaminants from the work area or by dilution air flow via introduction of fresh air to dilute contaminants. As with flamable gasoline indicators, air flow gear should be accredited for secure use in flammable atmospheres. In addition, air flow tools should be grounded and bonded.
Additional air flow, if needed, should be steady throughout coatings application as concentrations may increase as extra surfaces are coated through the course of a work shift, and especially on scorching surfaces the place the speed of vaporization is greater.
Ventilation during coatings application should be steady, particularly when working on hot surfaces.
Sources of Ignition
When making use of coatings to hot surfaces, the primary source of ignition that readily comes to mind is the warmth from the surface being painted. The AIT of the coating material is the one most necessary problem when applying coatings to hot working tools. Mere of a substance or mixture is the minimal temperature at which a vapour-air combination will ignite when in touch with a heated floor, with out the presence of any open spark or flame.
The key to controlling this source of ignition is to verify the surfaces being coated are beneath the AIT of the coatings being utilized. While surface temperatures may be known/available in plenty of services, all floor areas of the process/piping being painted and/or any equipment adjoining to the items being painted where overspray could deposit must be measured for precise floor temperature. The outcomes should be compared to the AIT of the coating system.
While auto-ignition and open sources of ignition may be readily obvious, a extra subtle but nonetheless important source of ignition to manage on any industrial painting challenge involving flammable solvents involves the manufacturing of static electricity. Equipment related to the spray-painting operation, similar to spray application gear and ventilation 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 happens when the gradual technology of heat from oxidation of organic chemicals corresponding to paint solvents is accelerated until the ignition temperature of the gasoline is reached.
This condition is reached when the material is packed loosely permitting a big floor area to be exposed, there could be enough air circulating across the material for oxidation to occur, but the natural air flow obtainable is insufficient to carry the heat away quick sufficient to stop it from increase.
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