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

Managers of petrochemical, refining, power, offshore, pulp and paper and different amenities with extensive hot processes and piping methods are incessantly challenged with performing all the mandatory coatings maintenance work solely during periods of outages. Outages are required in order that course of equipment may be correctly maintained and repaired together with cleansing of pipelines and vessels, upkeep and alternative of pumps, motors and valves, upkeep coating operations, and different work that may only be completed when the operations are shut down.
When Restricted has to be carried out on areas the place elevated temperatures are involved, many suppose that the facility has to be shut down. This is probably not the case.
A question incessantly posed by facility managers is, “Can I do upkeep portray work while the plant is operating?” As described below, the answer is, “Yes you’ll have the ability to, however there are security and well being issues that have to be considered”.
Dangers to personnel should be managed no matter when or where work is carried out.
Safety and health considerations
There is a variety of security and health hazards that should be thought-about on every industrial maintenance painting project, whether or not the coating materials is being applied to hot metal or not. Some of these embody proper material dealing with and storage, fall safety, management of fire and explosion hazards, and exposure to noise, heavy metals, solvents and different health dangers.
These risks have to be correctly evaluated and managed on every industrial upkeep portray project, regardless of when or where the work is performed. While present on any job, when applying specialty coatings to scorching surfaces, some security and well being points ought to obtain further consideration.
Flammable and combustible liquids in many coatings (solvents) can vaporize and type flammable mixtures within the air, particularly when atomized throughout spray utility or heated. The diploma of hazard depends on the next:
The auto ignition temperature (AIT) of the coating material is the single most essential problem when making use of coatings to hot operating 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 own warmth source or contact with a heated floor with out the presence of an open spark or flame.”
The concept of flash point 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 words, the flash level describes the temperature of the liquid that’s excessive sufficient to generate enough vapour to create a flame if a supply of ignition had been launched.
For vapours of flammable liquids, there is a minimum concentration beneath which the spread 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 spread of the flame doesn’t 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 followed, outages may not be required whereas maintenance is carried out.
Implementing controls
Applying coatings to scorching surfaces increases the speed at which the solvents are pushed off. When applying solvent borne coatings to sizzling surfaces it have to be assumed that the concentration of vapours in the air may exceed the LFL (at least for a quick while after application). As with coating utility to ambient temperature steel, controls must be implemented.
While the LFL is likely to be achieved over a shorter time period during hot application of coatings than coatings work carried out at ambient conditions, the ensuing fire hazard exists in both functions. That is, the hearth hazard and related controls have to be thought-about for the applying of any solvent-borne flammable coating system, whatever the work setting. It must be acknowledged that the gas component of the fireplace tetrahedron shall be present in each ‘hot’ and ‘ambient’ environments and fundamental steps should be taken to attenuate unnecessary solvent vapours in the work space. In addition, as outlined later, attention should also be directed to eliminating the remaining element of the tetrahedron – the supply of ignition.
Controlling flammable vapours
The fuel element of a fireplace could be lowered by implementing fundamental controls such as handling and storing flammable liquids in permitted, 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 may be substituted, followed by floor washing with contemporary water or steam cleansing and pH testing of the floor, or non-combustible solvents similar to 1,1,1 trichloroethane) for pre-surface preparation solvent cleansing.
Combustible gas indicators must be used to confirm that the focus of flammable vapours is under the LFL. Combustible gas indicators have to be calibrated in accordance with the manufacturer’s suggestions and must be permitted to be used in flammable atmospheres. Operators of the gear should be skilled in proper tools operation.
Readings should be taken within the general work space and the neighborhood 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 software work ought to immediately stop until the focus of flammable vapours is controlled. The objective of setting the alarm beneath the LFL is to supply a security issue that results in management measures being applied earlier than there’s an imminent danger of fireplace or explosion.
Monitoring of the combustible vapour focus shall be needed as the effectiveness of pure air flow may be variable. If control of flammable vapours requires mechanical ventilation, an occupational safety or health professional or engineer with expertise in industrial air flow ought to be consulted.
At a minimum, mechanical ventilation methods should present sufficient capability to manage flammable vapours to below 10% of the LFL by both exhaust air flow to take away contaminants from the work area or by dilution ventilation by way of introduction of recent air to dilute contaminants. As with combustible gas indicators, air flow tools should be accredited for safe use in flammable atmospheres. In addition, ventilation tools must be grounded and bonded.
Additional ventilation, if needed, must be steady throughout coatings software as concentrations could increase as more surfaces are coated through the course of a work shift, and especially on scorching surfaces where the speed of vaporization is greater.
Ventilation during coatings utility ought to be steady, particularly when engaged on hot surfaces.
Sources of Ignition
When making use of coatings to scorching surfaces, the primary supply of ignition that readily comes to mind is the heat from the floor being painted. The AIT of the coating material is the only most essential problem when applying coatings to scorching 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 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 below the AIT of the coatings being utilized. While surface temperatures may be known/available in many facilities, all floor areas of the process/piping being painted and/or any gear adjacent to the gadgets being painted the place overspray may deposit must be measured for precise surface temperature. The outcomes ought to be compared to the AIT of the coating system.
While auto-ignition and open sources of ignition may be readily apparent, a more delicate but nonetheless critical source of ignition to manage on any industrial portray project involving flammable solvents entails the manufacturing of static electrical energy. Equipment related to the spray-painting operation, similar to spray software gear and air flow gear, 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 slow generation of warmth from oxidation of natural chemicals corresponding to paint solvents is accelerated until the ignition temperature of the gasoline is reached.
This situation is reached when the material is packed loosely allowing a big floor area to be uncovered, there may be sufficient air circulating around the material for oxidation to happen, but the natural air flow out there is insufficient to carry the warmth away quick enough to prevent it from build up.
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