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

Managers of petrochemical, refining, power, offshore, pulp and paper and other services with intensive scorching processes and piping systems are frequently challenged with performing all the mandatory coatings maintenance work only during times of outages. Outages are required in order that course of gear could be properly maintained and repaired including cleansing of pipelines and vessels, upkeep and alternative of pumps, motors and valves, maintenance coating operations, and other work that can solely be accomplished when the operations are shut down.
When coatings work must be carried out on areas the place elevated temperatures are involved, many assume that the power needs to be shut down. This will not be the case.
A query incessantly posed by facility managers is, “Can I do upkeep portray work whereas the plant is operating?” As described beneath, the answer is, “Yes you’ll have the ability to, however there are safety and health issues that must be considered”.
Dangers to personnel should be managed no matter when or the place work is performed.
Safety and well being concerns
There is a spread of safety and well being hazards that have to be thought of on each industrial upkeep painting challenge, whether or not the coating materials is being utilized to hot metal or not. Some of these include correct materials handling and storage, fall protection, control of fireplace and explosion hazards, and publicity to noise, heavy metals, solvents and different health risks.
These risks should be properly evaluated and managed on every industrial maintenance portray challenge, no matter when or the place the work is carried out. While present on any job, when making use of specialty coatings to hot surfaces, some safety and well being points ought to receive further consideration.
Flammable and flamable liquids in lots of coatings (solvents) can vaporize and form flammable mixtures in the air, especially when atomized during spray software or heated. The diploma of hazard is dependent upon the next:
The auto ignition temperature (AIT) of the coating materials is the only most important problem when applying coatings to scorching working 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 mixture 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 outlined by NFPA 30 is “the minimum temperature of a liquid at which adequate vapour is given off to kind an ignitable mixture with the air, near the surface of the liquid”. In other phrases, the flash level 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 introduced.
For vapours of flammable liquids, there’s a minimum focus beneath which the spread of the flame doesn’t happen when in touch with a source of ignition. This is the Lower Flammable Limit (LFL). There is a most concentration of vapour in the air above which the unfold of the flame does not occur. This is the Upper Flammable Limit (UFL). The flammable range is between the LFL and the UFL, when the focus of vapours can assist combustion.
If security procedures are adopted, outages is in all probability not required whereas upkeep 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 must be assumed that the focus of vapours within the air may exceed the LFL (at least for a brief time after application). As with coating application to ambient temperature metal, controls should be carried out.
While the LFL is prone to be achieved over a shorter time frame throughout scorching utility of coatings than coatings work performed at ambient situations, the resulting hearth hazard exists in each applications. That is, the hearth hazard and associated controls should be thought of for the applying of any solvent-borne flammable coating system, regardless of the work environment. It should be acknowledged that the gas part of the fireplace tetrahedron shall be current in both ‘hot’ and ‘ambient’ environments and fundamental steps should be taken to attenuate pointless solvent vapours within 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 gas component of a fire could be decreased by implementing primary controls corresponding to dealing with and storing flammable liquids in approved, self-closing containers, maintaining the variety of flammable liquids containers in the work space and in storage areas to the minimum needed and inside allowable (regulatory) limits.
Alkaline detergents corresponding to tri-sodium phosphate may be substituted, followed by surface washing with recent water or steam cleansing and pH testing of the floor, or non-combustible solvents such as 1,1,1 trichloroethane) for pre-surface preparation solvent cleaning.
Combustible gasoline indicators ought to be used to confirm that the concentration of flammable vapours is below the LFL. Combustible fuel indicators must be calibrated in accordance with the manufacturer’s suggestions and must be approved for use in flammable atmospheres. Operators of the equipment must be skilled in proper equipment operation.
Readings ought to be taken in the general work space and the vicinity of the operator and in areas the place there are potential sources of ignition. Typically, models are set to alarm at 10% of the LFL. If the alarm sounds, coatings utility work ought to instantly stop until the focus of flammable vapours is managed. เกจวัดแรงดัน300psi of setting the alarm beneath the LFL is to offer a safety issue that leads to control measures being implemented before there is an imminent hazard of fire or explosion.
Monitoring of the combustible vapour concentration might be needed as the effectiveness of pure ventilation could also be variable. If control of flammable vapours requires mechanical ventilation, an occupational security or health professional or engineer with expertise in industrial ventilation ought to be consulted.
At a minimal, mechanical air flow systems should provide sufficient capacity to manage flammable vapours to beneath 10% of the LFL by both exhaust ventilation to remove contaminants from the work space or by dilution air flow by way of introduction of fresh air to dilute contaminants. As with flamable gas indicators, air flow gear should be approved for secure use in flammable atmospheres. In addition, ventilation tools must be grounded and bonded.
Additional air flow, if wanted, should be continuous during coatings application as concentrations could improve as extra surfaces are coated during the course of a piece shift, and particularly on sizzling surfaces the place the speed of vaporization is higher.
Ventilation during coatings utility ought to be continuous, especially when working on sizzling surfaces.
Sources of Ignition
When applying coatings to scorching surfaces, the first supply of ignition that readily comes to thoughts is the warmth from the floor being painted. The AIT of the coating material is the only most necessary concern when applying coatings to sizzling operating tools. The AIT of a substance or mixture is the minimum temperature at which a vapour-air combination will ignite when in contact with a heated surface, without 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 plenty of amenities, all floor areas of the process/piping being painted and/or any gear adjacent to the gadgets being painted where overspray may deposit should 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 may be readily obvious, a more subtle but nonetheless important source of ignition to manage on any industrial painting challenge involving flammable solvents entails the manufacturing of static electricity. Equipment related to the spray-painting operation, such as spray software gear and ventilation equipment, can generate static electrical energy.
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 slow generation of heat from oxidation of organic chemical compounds corresponding to paint solvents is accelerated till the ignition temperature of the gasoline is reached.
This condition is reached when the material is packed loosely permitting a big floor space to be exposed, there’s enough air circulating around the materials for oxidation to occur, but the natural ventilation out there is insufficient to carry the warmth away fast sufficient to forestall it from build up.
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