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

Managers of petrochemical, refining, power, offshore, pulp and paper and different facilities with extensive sizzling processes and piping methods are frequently challenged with performing all the mandatory coatings upkeep work only during times of outages. Outages are required in order that course of equipment can be properly maintained and repaired including cleaning of pipelines and vessels, maintenance and alternative of pumps, motors and valves, upkeep coating operations, and different work that may only be achieved when the operations are shut down.
When coatings work must be performed on areas where elevated temperatures are concerned, many assume that the facility has to be shut down. This is in all probability not the case.
A question regularly posed by facility managers is, “Can I do maintenance painting work while the plant is operating?” As described below, the reply is, “Yes you’ll be able to, but there are safety and health issues that should be considered”.
Dangers to personnel must be managed regardless of when or where work is carried out.
Safety and health issues
There is a spread of safety and health hazards that have to be thought of on each industrial upkeep portray project, whether or not the coating material is being applied to sizzling steel or not. Some of these embrace correct material handling and storage, fall safety, control of fireplace and explosion hazards, and publicity to noise, heavy metals, solvents and other well being dangers.
These dangers must be properly evaluated and managed on each industrial upkeep portray venture, no matter when or the place the work is carried out. While present on any job, when making use of specialty coatings to scorching surfaces, some security and health issues ought to obtain further 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 depends on the next:
The auto ignition temperature (AIT) of the coating material is the only most necessary problem when making use of coatings to hot operating tools. 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 combination will ignite from its personal heat 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 minimum temperature of a liquid at which adequate vapour is given off to form an ignitable combination with the air, near the surface of the liquid”. In other phrases, the flash level describes the temperature of the liquid that’s high sufficient to generate enough vapour to create a flame if a source of ignition were launched.
For vapours of flammable liquids, there is a minimal focus beneath which the unfold of the flame does not occur when in contact with a source of ignition. เกจวัดแรงดันแก๊สหุงต้ม is the Lower Flammable Limit (LFL). There is a most focus of vapour in the air above which the unfold of the flame does not occur. This is the Upper Flammable Limit (UFL). The flammable range is between the LFL and the UFL, when the concentration of vapours can assist combustion.
If safety procedures are adopted, outages will not be required whereas upkeep is performed.
Implementing controls
Applying coatings to scorching surfaces increases the rate at which the solvents are driven off. When making use of solvent borne coatings to scorching surfaces it must be assumed that the concentration of vapours within the air may exceed the LFL (at least for a brief time after application). As with coating software to ambient temperature metal, controls must be applied.
While the LFL is likely to be achieved over a shorter period of time during hot utility of coatings than coatings work performed at ambient conditions, the ensuing fireplace hazard exists in each functions. That is, the fireplace hazard and associated controls have to be thought of for the appliance of any solvent-borne flammable coating system, regardless of the work surroundings. It must be acknowledged that the gasoline element of the fireplace tetrahedron shall be current in each ‘hot’ and ‘ambient’ environments and basic steps should be taken to attenuate pointless solvent vapours within the work area. In addition, as outlined later, consideration should also be directed to eliminating the remaining component of the tetrahedron – the supply of ignition.
Controlling flammable vapours
The gasoline component of a hearth can be lowered by implementing primary controls similar to dealing with and storing flammable liquids in permitted, self-closing containers, maintaining the variety of flammable liquids containers in the work space and in storage areas to the minimum necessary and within allowable (regulatory) limits.
Alkaline detergents corresponding to tri-sodium phosphate could additionally be substituted, followed by surface washing with recent 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 cleaning.
Combustible gasoline indicators must be used to confirm that the concentration of flammable vapours is beneath the LFL. Combustible fuel indicators must be calibrated in accordance with the manufacturer’s recommendations and have to be approved for use in flammable atmospheres. Operators of the equipment should be educated in proper gear operation.
Readings must be taken in the general work space 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 utility work should instantly cease until the concentration of flammable vapours is controlled. The objective of setting the alarm below the LFL is to provide a security factor that results in management measures being implemented before there could be an imminent hazard of fireplace or explosion.
Monitoring of the flammable vapour concentration will be necessary because the effectiveness of natural ventilation could also be variable. If management of flammable vapours requires mechanical air flow, an occupational security or health skilled or engineer with experience in industrial ventilation should be consulted.
At a minimum, mechanical air flow techniques should provide sufficient capability to regulate flammable vapours to under 10% of the LFL by both exhaust ventilation to remove contaminants from the work area or by dilution ventilation through introduction of recent air to dilute contaminants. As with combustible gas indicators, ventilation gear should be permitted for protected use in flammable atmospheres. In addition, air flow tools have to be grounded and bonded.
Additional air flow, if needed, should be continuous during coatings utility as concentrations might increase as more surfaces are coated through the course of a work shift, and especially on hot surfaces where the rate of vaporization is higher.
Ventilation throughout coatings utility should be continuous, particularly when engaged on scorching surfaces.
Sources of Ignition
When applying coatings to sizzling surfaces, the first supply of ignition that readily involves thoughts is the warmth from the surface being painted. The AIT of the coating material is the one most necessary concern when applying coatings to scorching operating tools. The AIT of a substance or combination is the minimum temperature at which a vapour-air mixture will ignite when involved with a heated floor, without the presence of any open spark or flame.
The key to controlling this supply of ignition is to confirm the surfaces being coated are under 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 equipment adjacent to the items being painted where overspray may deposit ought to be measured for precise floor temperature. The outcomes should be compared to the AIT of the coating system.
While auto-ignition and open sources of ignition may be readily apparent, a extra delicate but nonetheless critical source of ignition to control on any industrial portray project involving flammable solvents entails the production of static electricity. Equipment associated with the spray-painting operation, similar to spray utility equipment and ventilation gear, can generate static electrical energy.
In addition to external 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 sluggish era of heat from oxidation of organic chemical compounds corresponding to paint solvents is accelerated until the ignition temperature of the fuel is reached.
This condition is reached when the fabric is packed loosely permitting a large surface space to be uncovered, there is enough air circulating across the material for oxidation to occur, but the pure air flow obtainable is inadequate to hold the heat away quick sufficient to prevent it from building up.
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