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

Managers of petrochemical, refining, power, offshore, pulp and paper and other amenities with extensive sizzling processes and piping techniques are frequently challenged with performing all the required coatings maintenance work solely during times of outages. Outages are required so that course of gear could 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 completed when the operations are shut down.
When coatings work must be performed on areas where elevated temperatures are involved, many suppose that the power has to be shut down. This will not be the case.
A question frequently posed by facility managers is, “Can I do upkeep painting work while the plant is operating?” As described beneath, the reply is, “Yes you’ll find a way to, but there are security and health points that must be considered”.
Dangers to personnel must be managed no matter when or the place work is carried out.
Safety and well being considerations
There is a range of safety and health hazards that must be considered on each industrial upkeep painting project, whether or not the coating material is being utilized to scorching metal or not. Some of those embody proper materials dealing with and storage, fall safety, control of fireplace and explosion hazards, and exposure to noise, heavy metals, solvents and different health risks.
These risks should be properly evaluated and controlled on every industrial maintenance portray project, no matter when or the place the work is carried out. While present on any job, when making use of specialty coatings to sizzling surfaces, some safety and well being points should obtain extra consideration.
Flammable and flamable liquids in lots of coatings (solvents) can vaporize and form flammable mixtures within the air, particularly when atomized during spray utility or heated. The diploma of hazard is dependent upon the following:
The auto ignition temperature (AIT) of the coating materials is the single most essential concern when making use of coatings to hot operating 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 personal heat supply or contact with a heated floor without the presence of an open spark or flame.”
The idea of flash level as defined by NFPA 30 is “the minimal temperature of a liquid at which enough vapour is given off to form an ignitable combination with the air, close to the surface of the liquid”. In other phrases, the flash point describes the temperature of the liquid that’s excessive enough to generate enough vapour to create a flame if a supply of ignition have been introduced.
For vapours of flammable liquids, there is a minimal concentration under which the unfold of the flame doesn’t occur when in touch with a supply of ignition. This is the Lower Flammable Limit (LFL). There is a most concentration 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 security procedures are followed, outages is most likely not required while upkeep is carried out.
Implementing controls
Applying coatings to hot surfaces increases the rate at which the solvents are pushed off. When applying solvent borne coatings to hot surfaces it should be assumed that the concentration of vapours in the air could exceed the LFL (at least for a quick time after application). As with coating utility to ambient temperature steel, controls should be implemented.
While the LFL is more likely to be achieved over a shorter time frame during sizzling software of coatings than coatings work performed at ambient circumstances, the resulting fire hazard exists in both functions. That is, the fireplace hazard and associated controls should be thought-about for the applying of any solvent-borne flammable coating system, regardless of the work environment. It should be recognized that the fuel component of the fire tetrahedron will be present in both ‘hot’ and ‘ambient’ environments and basic steps must be taken to reduce unnecessary solvent vapours within the work area. 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 fire may be reduced by implementing primary controls similar to dealing with and storing flammable liquids in accredited, self-closing containers, maintaining the number of flammable liquids containers in the work area and in storage areas to the minimal necessary and within allowable (regulatory) limits.
เครื่องมือที่ใช้วัดความดันเลือด corresponding to tri-sodium phosphate may be substituted, adopted by surface washing with contemporary water or steam cleansing and pH testing of the surface, or non-combustible solvents such as 1,1,1 trichloroethane) for pre-surface preparation solvent cleaning.
Combustible fuel indicators must be used to verify that the focus of flammable vapours is below the LFL. Combustible gasoline indicators should be calibrated in accordance with the manufacturer’s suggestions and must be accredited for use in flammable atmospheres. Operators of the tools must be skilled in correct equipment operation.
Readings ought to be taken within the general 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 should instantly stop until the concentration of flammable vapours is controlled. The purpose of setting the alarm beneath the LFL is to offer a security factor that results in control measures being carried out earlier than there is an imminent hazard of fire or explosion.
Monitoring of the combustible vapour concentration will be essential because the effectiveness of natural ventilation could additionally be variable. If control of flammable vapours requires mechanical ventilation, an occupational safety or well being skilled or engineer with expertise in industrial ventilation ought to be consulted.
At a minimum, mechanical ventilation systems should provide adequate capacity to control flammable vapours to under 10% of the LFL by either exhaust air flow to remove contaminants from the work space or by dilution ventilation via introduction of recent air to dilute contaminants. As with flamable fuel indicators, ventilation equipment have to be permitted for protected use in flammable atmospheres. In addition, air flow equipment must be grounded and bonded.
Additional air flow, if wanted, should be continuous during coatings software as concentrations could improve as more surfaces are coated in the course of the course of a work shift, and particularly on sizzling surfaces where the rate of vaporization is higher.
Ventilation throughout coatings application must be continuous, particularly when engaged on sizzling surfaces.
Sources of Ignition
When applying coatings to scorching surfaces, the first supply of ignition that readily comes to mind 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 equipment. The AIT of a substance or mixture is the minimal 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 verify the surfaces being coated are under the AIT of the coatings being applied. While surface temperatures may be known/available in plenty of facilities, all surface areas of the process/piping being painted and/or any gear adjacent to the items being painted the place overspray could deposit ought to be measured for actual surface temperature. The outcomes must be compared to the AIT of the coating system.
While auto-ignition and open sources of ignition could also be readily apparent, a extra delicate but nonetheless important supply of ignition to manage on any industrial painting venture involving flammable solvents entails the manufacturing of static electricity. Equipment associated with the spray-painting operation, similar to spray utility equipment and air flow gear, can generate static electricity.
In addition to exterior 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 organic chemical compounds corresponding to paint solvents is accelerated till the ignition temperature of the gasoline is reached.
This situation is reached when the fabric is packed loosely permitting a big surface space to be exposed, there’s sufficient air circulating around the material for oxidation to happen, however the pure air flow out there is insufficient to carry the heat away quick enough to forestall it from increase.
For extra info, go to www.ppgpmc.com/Oil-Gas-Chemical.aspx
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