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

Managers of petrochemical, refining, power, offshore, pulp and paper and different amenities with intensive hot processes and piping systems are incessantly challenged with performing all the required coatings upkeep work only during periods of outages. Outages are required so that course of equipment can be properly maintained and repaired including cleaning of pipelines and vessels, maintenance and replacement of pumps, motors and valves, upkeep coating operations, and different work that can only be accomplished when the operations are shut down.
When coatings work needs to be performed on areas the place elevated temperatures are involved, many suppose that the facility must be shut down. This is most likely not the case.
A question incessantly posed by facility managers is, “Can I do upkeep portray work whereas the plant is operating?” As described under, the reply is, “Yes you’ll find a way to, but there are security and health issues that have to be considered”.
Dangers to personnel have to be managed no matter when or the place work is carried out.
Safety and health concerns
There is a range of security and well being hazards that have to be thought of on every industrial upkeep portray project, whether the coating materials is being applied to sizzling steel or not. Some of those embody proper materials dealing with and storage, fall protection, control of fire and explosion hazards, and publicity to noise, heavy metals, solvents and other well being risks.
These risks should be correctly evaluated and managed on every industrial upkeep painting project, regardless of when or the place the work is carried out. While เครื่องมือที่ใช้ในการวัดความดัน on any job, when making use of specialty coatings to hot surfaces, some safety and well being issues should obtain extra consideration.
Flammable and combustible liquids in many coatings (solvents) can vaporize and form flammable mixtures within the air, especially when atomized throughout spray software or heated. The degree of hazard is dependent upon the following:
The auto ignition temperature (AIT) of the coating material is the one most necessary problem when making use of 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 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 minimum temperature of a liquid at which adequate vapour is given off to kind an ignitable mixture with the air, close to the surface of the liquid”. In other phrases, the flash point describes the temperature of the liquid that’s high enough to generate enough vapour to create a flame if a supply of ignition were launched.
For vapours of flammable liquids, there is a minimal concentration beneath which the unfold of the flame doesn’t happen when in touch with a source of ignition. This is the Lower Flammable Limit (LFL). There is a maximum focus of vapour within the air above which the spread of the flame doesn’t happen. This is the Upper Flammable Limit (UFL). The flammable vary is between the LFL and the UFL, when the concentration of vapours can support combustion.
If safety procedures are adopted, outages may not be required while upkeep is carried out.
Implementing controls
Applying coatings to hot surfaces increases the speed at which the solvents are pushed off. When making use of 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 short while after application). As with coating application to ambient temperature metal, controls have to be implemented.
While the LFL is more probably to be achieved over a shorter period of time throughout hot application of coatings than coatings work carried out at ambient circumstances, the resulting fireplace hazard exists in both purposes. That is, the hearth hazard and related controls should be thought of for the application of any solvent-borne flammable coating system, whatever the work surroundings. It must be acknowledged that the gasoline part of the fireplace tetrahedron will be current in each ‘hot’ and ‘ambient’ environments and primary steps have to be taken to reduce pointless 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 supply of ignition.
Controlling flammable vapours
The gas component of a hearth may be reduced by implementing fundamental controls corresponding to handling and storing flammable liquids in permitted, self-closing containers, preserving the number of flammable liquids containers within the work space and in storage areas to the minimal needed and within allowable (regulatory) limits.
Alkaline detergents corresponding to tri-sodium phosphate could additionally be substituted, followed by floor washing with fresh 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 fuel indicators ought to be used to confirm that the focus of flammable vapours is under the LFL. Combustible fuel indicators should be calibrated in accordance with the manufacturer’s suggestions and should be permitted for use in flammable atmospheres. Operators of the tools should be skilled in proper tools operation.
Readings should be taken within the common work area and the vicinity of the operator and in areas where there are potential sources of ignition. Typically, items are set to alarm at 10% of the LFL. If the alarm sounds, coatings software work ought to immediately cease till the focus of flammable vapours is managed. The purpose of setting the alarm under the LFL is to provide a safety issue that results in management measures being applied before there is an imminent danger of fireplace or explosion.
Monitoring of the flammable vapour concentration will be necessary as the effectiveness of pure air flow may be variable. If control of flammable vapours requires mechanical air flow, an occupational security or health professional or engineer with expertise in industrial ventilation must be consulted.
At a minimum, mechanical ventilation techniques should provide sufficient capacity to manage flammable vapours to under 10% of the LFL by both exhaust ventilation to take away contaminants from the work area or by dilution ventilation via introduction of recent air to dilute contaminants. As with combustible gasoline indicators, ventilation tools should be accredited for secure use in flammable atmospheres. In addition, air flow gear have to be grounded and bonded.
Additional ventilation, if wanted, ought to be steady throughout coatings application as concentrations may improve as extra surfaces are coated through the course of a piece shift, and especially on scorching surfaces the place the speed of vaporization is higher.
Ventilation throughout coatings utility ought to be steady, especially when engaged on hot surfaces.
Sources of Ignition
When making use of coatings to sizzling surfaces, the first supply of ignition that readily involves thoughts is the heat from the floor being painted. The AIT of the coating materials is the one most important problem when applying coatings to hot working tools. The AIT of a substance or mixture is the minimum temperature at which a vapour-air mixture will ignite when in contact with a heated floor, without the presence of any open spark or flame.
The key to controlling this source of ignition is to verify the surfaces being coated are below the AIT of the coatings being utilized. While surface temperatures could also be known/available in lots of facilities, all surface areas of the process/piping being painted and/or any gear adjoining to the objects being painted where overspray could deposit ought to be measured for precise surface temperature. The results ought to be in comparison with the AIT of the coating system.
While auto-ignition and open sources of ignition could additionally be readily obvious, a more refined but nonetheless important source of ignition to manage on any industrial portray challenge involving flammable solvents involves the production of static electricity. Equipment associated with the spray-painting operation, corresponding to spray utility 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 occurs when the slow era of warmth from oxidation of natural chemical compounds such as paint solvents is accelerated till the ignition temperature of the fuel is reached.
This situation is reached when the material is packed loosely permitting a large surface area to be exposed, there might be sufficient air circulating around the material for oxidation to occur, however the natural air flow available is inadequate to hold the warmth away fast enough to forestall it from building up.
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