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

Managers of petrochemical, refining, power, offshore, pulp and paper and different amenities with intensive hot processes and piping techniques are incessantly challenged with performing all the required coatings upkeep work only during times of outages. Outages are required in order that process gear could be properly maintained and repaired including cleaning of pipelines and vessels, upkeep and substitute of pumps, motors and valves, maintenance coating operations, and different work that may solely be accomplished when the operations are shut down.
When coatings work has to be carried out on areas where elevated temperatures are involved, many suppose that the facility must 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 under, the answer is, “Yes you can, however there are security and health points that have to 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 range of safety and health hazards that should be considered on each industrial maintenance portray project, whether or not the coating material is being applied to hot metal or not. Some of those embrace proper material dealing with and storage, fall protection, control of fireplace and explosion hazards, and exposure to noise, heavy metals, solvents and different health dangers.
These risks should be properly evaluated and managed on each industrial upkeep portray challenge, regardless of when or the place the work is performed. While current on any job, when applying specialty coatings to hot surfaces, some safety and health points should receive additional consideration.
Flammable and combustible liquids in plenty of coatings (solvents) can vaporize and kind flammable mixtures in the air, especially when atomized during spray application or heated. The diploma of hazard depends on the following:
The auto ignition temperature (AIT) of the coating materials is the single most essential problem when applying coatings to hot operating tools. 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 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 concept of flash point as outlined by NFPA 30 is “the minimal temperature of a liquid at which enough vapour is given off to type an ignitable mixture with the air, close to the surface of the liquid”. In different phrases, the flash point describes the temperature of the liquid that is excessive sufficient to generate enough vapour to create a flame if a source of ignition have been launched.
For vapours of flammable liquids, there is a minimal focus beneath which the spread of the flame does not occur when in touch with a source of ignition. This is the Lower Flammable Limit (LFL). There is a most focus of vapour in the air above which the spread of the flame does not happen. This is the Upper Flammable Limit (UFL). The flammable vary is between the LFL and the UFL, when the concentration of vapours can help combustion.
If safety procedures are followed, outages may not be required while maintenance is performed.
Implementing controls
Applying coatings to hot surfaces increases the speed at which the solvents are pushed off. When applying solvent borne coatings to scorching surfaces it have to be assumed that the concentration of vapours in the air could exceed the LFL (at least for a brief time after application). As with coating application to ambient temperature metal, controls must be carried out.
While the LFL is prone to be achieved over a shorter time frame throughout sizzling software of coatings than coatings work carried out at ambient circumstances, the ensuing fireplace hazard exists in both functions. That is, the fire hazard and associated controls must be thought-about for the appliance of any solvent-borne flammable coating system, regardless of the work surroundings. It must be recognized that the gasoline component of the fire tetrahedron might be present in both ‘hot’ and ‘ambient’ environments and fundamental steps must be taken to attenuate pointless solvent vapours within the work area. In addition, as outlined later, consideration should even be directed to eliminating the remaining element of the tetrahedron – the source of ignition.
Controlling เกจวัดแรงดันเชื้อเพลิง of a fireplace could be reduced by implementing primary controls such as handling and storing flammable liquids in approved, self-closing containers, preserving the variety of flammable liquids containers in the work space and in storage areas to the minimal necessary and inside allowable (regulatory) limits.
Alkaline detergents such as tri-sodium phosphate may be substituted, followed by surface washing with contemporary water or steam cleansing and pH testing of the surface, or non-combustible solvents similar to 1,1,1 trichloroethane) for pre-surface preparation solvent cleaning.
Combustible gasoline indicators ought to be used to confirm that the focus of flammable vapours is below the LFL. Combustible gas indicators have to be calibrated in accordance with the manufacturer’s suggestions and must be approved for use in flammable atmospheres. Operators of the tools have to be trained in proper tools operation.
Readings ought to be taken within the common work area and the vicinity of the operator and in areas where there are potential sources of ignition. Typically, models are set to alarm at 10% of the LFL. If the alarm sounds, coatings application work ought to instantly stop till the focus of flammable vapours is managed. The purpose of setting the alarm under the LFL is to provide a security issue that leads to management measures being applied before there’s an imminent hazard of fireside or explosion.
Monitoring of the flammable vapour focus might be necessary as the effectiveness of natural ventilation could also be variable. If control of flammable vapours requires mechanical ventilation, an occupational safety or health skilled or engineer with experience in industrial ventilation ought to be consulted.
At a minimum, mechanical air flow methods should provide adequate capability to manage flammable vapours to below 10% of the LFL by both exhaust ventilation to take away contaminants from the work space or by dilution ventilation via introduction of fresh air to dilute contaminants. As with flamable gas indicators, ventilation equipment should be approved for safe use in flammable atmospheres. In addition, ventilation equipment have to be grounded and bonded.
Additional air flow, if wanted, should be steady during coatings software as concentrations might increase as more surfaces are coated during the course of a piece shift, and particularly on sizzling surfaces the place the rate of vaporization is greater.
Ventilation throughout coatings utility must be continuous, especially when working on sizzling surfaces.
Sources of Ignition
When making use of coatings to sizzling surfaces, the primary supply of ignition that readily involves thoughts is the warmth from the surface being painted. The AIT of the coating material is the only most necessary problem when making use of coatings to scorching operating tools. The AIT of a substance or mixture is the minimal temperature at which a vapour-air combination will ignite when in touch 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 beneath the AIT of the coatings being applied. While floor temperatures could additionally be known/available in lots of amenities, all floor areas of the process/piping being painted and/or any equipment adjoining to the objects being painted where overspray may deposit must be measured for precise surface 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 more subtle however nonetheless crucial supply of ignition to regulate on any industrial painting project involving flammable solvents includes the manufacturing of static electrical energy. Equipment associated with the spray-painting operation, such as spray application equipment and ventilation 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. Spontaneous ignition occurs when the slow technology of heat from oxidation of natural chemical compounds similar to paint solvents is accelerated till the ignition temperature of the gas is reached.
This situation is reached when the material is packed loosely permitting a large floor space to be uncovered, there might be sufficient air circulating around the material for oxidation to occur, but the natural ventilation out there is insufficient to carry the heat away fast enough to prevent it from increase.
For extra data, go to