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

Managers of petrochemical, refining, power, offshore, pulp and paper and different amenities with in depth sizzling processes and piping techniques are incessantly challenged with performing all the required coatings maintenance work only in periods of outages. Outages are required so that process tools could be correctly maintained and repaired including cleaning of pipelines and vessels, maintenance and substitute of pumps, motors and valves, upkeep coating operations, and different work that may only be completed when the operations are shut down.
When coatings work needs to be carried out on areas where elevated temperatures are concerned, many assume that the facility needs to be shut down. This may not be the case.
A query regularly posed by facility managers is, “Can I do upkeep painting work while the plant is operating?” As described under, the reply is, “Yes you’ll find a way to, however there are safety and health points that should be considered”.
Dangers to personnel must be managed no matter when or where work is performed.
เกจวัดแรงดันsumo and well being concerns
There is a range of security and health hazards that have to be considered on every industrial maintenance painting venture, whether the coating material is being applied to scorching steel or not. Some of these embody proper material handling and storage, fall protection, management of fireplace and explosion hazards, and exposure to noise, heavy metals, solvents and different well being dangers.
These dangers should be properly evaluated and managed on each industrial maintenance portray venture, no matter when or the place the work is performed. While current on any job, when applying specialty coatings to sizzling surfaces, some safety and health issues should obtain additional consideration.
Flammable and flamable liquids in plenty of coatings (solvents) can vaporize and form flammable mixtures within the air, especially when atomized throughout spray application or heated. The diploma of hazard is determined by the following:
The auto ignition temperature (AIT) of the coating material is the only most necessary issue when applying coatings to sizzling working gear. AIT is outlined (by the National Safety Council publication Accident Prevention Manual For Business and Industry: Engineering & Technology) as “…the minimal temperature at which a flammable gas-air or vapour-air combination will ignite from its own warmth supply or contact with a heated surface 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, near the floor of the liquid”. In other phrases, the flash point describes the temperature of the liquid that’s excessive sufficient to generate sufficient vapour to create a flame if a supply of ignition have been launched.
For vapours of flammable liquids, there’s a minimum focus under which the spread of the flame does not happen when involved 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 unfold 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 safety procedures are adopted, outages is in all probability not required whereas maintenance is performed.
Implementing controls
Applying coatings to hot surfaces increases the rate at which the solvents are pushed off. When making use of solvent borne coatings to sizzling surfaces it must be assumed that the concentration of vapours within the air may exceed the LFL (at least for a brief while after application). As with coating application to ambient temperature steel, controls have to be carried out.
While the LFL is more doubtless to be achieved over a shorter period of time during sizzling application of coatings than coatings work performed at ambient circumstances, the resulting hearth hazard exists in each applications. That is, the hearth hazard and associated controls must be thought of for the application of any solvent-borne flammable coating system, regardless of the work setting. It must be acknowledged that the gas part of the fire tetrahedron will be current in both ‘hot’ and ‘ambient’ environments and basic steps must be taken to reduce pointless solvent vapours within the work area. In addition, as outlined later, attention must even be directed to eliminating the remaining factor of the tetrahedron – the source of ignition.
Controlling flammable vapours
The fuel component of a fire can be lowered by implementing basic controls such as handling and storing flammable liquids in permitted, self-closing containers, keeping the number of flammable liquids containers in the work area and in storage areas to the minimal essential and within allowable (regulatory) limits.
Alkaline detergents such as tri-sodium phosphate could additionally be substituted, followed by floor washing with recent water or steam cleaning and pH testing of the floor, or non-combustible solvents such as 1,1,1 trichloroethane) for pre-surface preparation solvent cleaning.
Combustible gasoline indicators should be used to verify that the focus of flammable vapours is under the LFL. Combustible gas indicators should be calibrated in accordance with the manufacturer’s suggestions and must be accredited to be used in flammable atmospheres. Operators of the equipment should be trained in correct gear 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, units are set to alarm at 10% of the LFL. If the alarm sounds, coatings application work should immediately cease until the concentration of flammable vapours is managed. The function of setting the alarm below the LFL is to offer a security issue that leads to management measures being applied before there might be an imminent hazard of fire or explosion.
Monitoring of the combustible vapour focus shall be essential as the effectiveness of natural ventilation may be variable. If control of flammable vapours requires mechanical air flow, an occupational safety or well being professional or engineer with experience in industrial ventilation must be consulted.
At a minimum, mechanical ventilation methods ought to present adequate capacity to regulate flammable vapours to below 10% of the LFL by both exhaust air flow to take away contaminants from the work space or by dilution ventilation by way of introduction of recent air to dilute contaminants. As with combustible fuel indicators, air flow gear should be approved for secure use in flammable atmospheres. In addition, ventilation tools must be grounded and bonded.
Additional ventilation, if wanted, should be steady throughout coatings application as concentrations could improve as extra surfaces are coated during the course of a piece shift, and especially on hot surfaces the place the speed of vaporization is higher.
Ventilation throughout coatings application ought to be continuous, particularly when engaged on hot surfaces.
Sources of Ignition
When applying coatings to hot surfaces, the primary supply of ignition that readily involves mind is the warmth from the surface being painted. The AIT of the coating material is the only most essential problem when applying coatings to hot working tools. The AIT of a substance or mixture is the minimal temperature at which a vapour-air combination will ignite when involved with a heated surface, with out the presence of any open spark or flame.
The key to controlling this source of ignition is to verify the surfaces being coated are beneath the AIT of the coatings being applied. While surface temperatures could additionally be known/available in many facilities, all surface areas of the process/piping being painted and/or any tools adjacent to the items being painted the place overspray could deposit ought to be measured for precise surface temperature. The outcomes ought to be in comparison with 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 regulate on any industrial painting project involving flammable solvents includes the production of static electrical energy. Equipment related to the spray-painting operation, corresponding to spray utility tools and air flow equipment, 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 sluggish generation of heat from oxidation of natural chemical substances similar to paint solvents is accelerated until the ignition temperature of the fuel is reached.
This situation is reached when the fabric is packed loosely permitting a big surface space to be exposed, there is sufficient air circulating around the materials for oxidation to occur, however the natural air flow available is inadequate to carry the warmth away fast enough to forestall it from increase.
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