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 systems are regularly challenged with performing all the necessary coatings maintenance work only during times of outages. Outages are required so that course of equipment could be correctly maintained and repaired including cleaning of pipelines and vessels, maintenance and replacement of pumps, motors and valves, maintenance coating operations, and different work that can only be completed when the operations are shut down.
When coatings work must be performed on areas where elevated temperatures are involved, many think that the power needs to be shut down. This is most likely not the case.
A question frequently posed by facility managers is, “Can I do upkeep portray work while the plant is operating?” As described below, the reply is, “Yes you can, but there are safety and health issues that should be considered”.
Dangers to personnel must be managed no matter when or where work is carried out.
Safety and health considerations
There is a spread of safety and health hazards that have to be thought of on each industrial maintenance painting project, whether or not the coating material is being utilized to hot metal or not. Some of those embrace correct materials handling and storage, fall safety, management of fireside and explosion hazards, and publicity to noise, heavy metals, solvents and different health risks.
These dangers should be correctly evaluated and controlled on each industrial upkeep painting project, regardless of when or the place the work is performed. While present on any job, when making use of specialty coatings to sizzling surfaces, some security and health issues should obtain further consideration.
Flammable and combustible liquids in many coatings (solvents) can vaporize and kind flammable mixtures within 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 material is the single most important problem when applying coatings to sizzling 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 mixture will ignite from its own heat source or contact with a heated surface with out the presence of an open spark or flame.”
The idea of flash point as outlined by NFPA 30 is “the minimal temperature of a liquid at which adequate vapour is given off to kind an ignitable combination with the air, near the surface of the liquid”. In different phrases, the flash level describes the temperature of the liquid that’s high sufficient to generate enough vapour to create a flame if a supply of ignition have been launched.
For vapours of flammable liquids, there’s a minimal concentration under which the unfold of the flame doesn’t happen when in touch with a supply of ignition. This is the Lower Flammable Limit (LFL). There is a maximum 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 range is between the LFL and the UFL, when the focus of vapours can support combustion.
If security procedures are followed, outages is probably not required while maintenance is carried out.
Implementing controls
Applying coatings to hot surfaces increases the speed at which the solvents are pushed off. When applying solvent borne coatings to sizzling surfaces it must be assumed that the focus of vapours within the air might exceed the LFL (at least for a brief while after application). As with coating application to ambient temperature metal, controls must be carried out.
While the LFL is more probably to be achieved over a shorter period of time throughout scorching application of coatings than coatings work performed at ambient circumstances, the ensuing hearth hazard exists in both functions. That is, the fireplace hazard and associated controls have to be considered for the appliance of any solvent-borne flammable coating system, regardless of the work surroundings. It must be acknowledged that the fuel component of the hearth tetrahedron will be current in each ‘hot’ and ‘ambient’ environments and fundamental steps have to be taken to reduce unnecessary solvent vapours within the work space. In addition, as outlined later, consideration should also be directed to eliminating the remaining element of the tetrahedron – the source of ignition.
Controlling flammable vapours
The fuel component of a fireplace may be decreased by implementing fundamental controls similar to dealing with and storing flammable liquids in permitted, self-closing containers, preserving 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, adopted by surface washing with contemporary water or steam cleaning and pH testing of the surface, or non-combustible solvents such as 1,1,1 trichloroethane) for pre-surface preparation solvent cleansing.
Combustible gasoline indicators should 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 recommendations and should be accredited for use in flammable atmospheres. Operators of the equipment must be trained in correct tools operation.
Readings should be taken within the general work area and the vicinity 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 application work should immediately stop until the concentration of flammable vapours is managed. เกจวัดแรงดันsumo of setting the alarm below the LFL is to offer a security factor that leads to control measures being carried out earlier than there is an imminent hazard of fireside or explosion.
Monitoring of the flammable vapour focus shall be necessary because the effectiveness of natural ventilation may be variable. If control of flammable vapours requires mechanical air flow, an occupational safety or health professional or engineer with experience in industrial ventilation should be consulted.
At a minimum, mechanical ventilation techniques should present adequate capacity to manage flammable vapours to below 10% of the LFL by either exhaust ventilation to remove contaminants from the work area or by dilution ventilation by way of introduction of fresh air to dilute contaminants. As with combustible gas indicators, air flow gear must be approved for safe use in flammable atmospheres. In addition, ventilation gear must be grounded and bonded.
Additional ventilation, if needed, must be continuous throughout coatings application as concentrations could enhance as extra surfaces are coated in the course of the course of a piece shift, and particularly on scorching surfaces the place the speed of vaporization is larger.
Ventilation during coatings application should be continuous, especially when engaged on hot surfaces.
Sources of Ignition
When making use of coatings to scorching surfaces, the primary source of ignition that readily comes to thoughts is the heat from the surface being painted. The AIT of the coating materials is the one most necessary concern when applying coatings to sizzling working gear. 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 below the AIT of the coatings being utilized. While surface temperatures could additionally be known/available in lots of services, all floor areas of the process/piping being painted and/or any tools adjoining to the items being painted the place overspray could deposit should be measured for actual floor temperature. The outcomes ought to be in comparison with the AIT of the coating system.
While auto-ignition and open sources of ignition may be readily obvious, a extra subtle but nonetheless crucial supply of ignition to control on any industrial portray venture involving flammable solvents entails the production of static electrical energy. Equipment associated with the spray-painting operation, similar to spray application equipment and ventilation gear, can generate static electricity.
In addition to external sources of ignition, spontaneous ignition can occur when rags or wastes soaked with paint solvents are left in open containers. Spontaneous ignition happens when the slow era of warmth from oxidation of natural chemicals such as paint solvents is accelerated until the ignition temperature of the gas is reached.
This condition is reached when the fabric is packed loosely permitting a large floor space to be uncovered, there might be sufficient air circulating across the materials for oxidation to happen, but the pure ventilation out there is insufficient to hold the warmth away fast enough to prevent it from build up.
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