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

Managers of petrochemical, refining, energy, offshore, pulp and paper and different services with extensive hot 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 tools can be properly maintained and repaired including cleaning of pipelines and vessels, upkeep 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 carried out on areas where elevated temperatures are concerned, many think that the facility has to be shut down. This is probably not the case.
A question regularly posed by facility managers is, “Can I do upkeep painting work whereas the plant is operating?” As described beneath, the reply is, “Yes you’ll have the ability to, but there are security and well being points that should be considered”.
Dangers to personnel should be managed no matter when or where work is performed.
Safety and well being issues
There is a variety of safety and well being hazards that have to be considered on each industrial upkeep painting challenge, whether the coating material is being utilized to hot steel or not. Some of these embrace proper material dealing with and storage, fall protection, control of fireplace and explosion hazards, and publicity to noise, heavy metals, solvents and different well being risks.
These dangers must be correctly evaluated and controlled on every industrial upkeep painting venture, regardless of when or the place the work is performed. While current on any job, when applying specialty coatings to hot surfaces, some security and health points should obtain additional consideration.
Flammable and combustible liquids in many coatings (solvents) can vaporize and type flammable mixtures within the air, especially when atomized during spray application or heated. The degree of hazard is dependent upon the following:
The auto ignition temperature (AIT) of the coating material is the single most essential problem when applying coatings to hot operating gear. เกจวัดแรงดันน้ำดิจิตอล is defined (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 personal warmth supply 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, close to the surface of the liquid”. In different phrases, the flash level describes the temperature of the liquid that is excessive enough to generate sufficient vapour to create a flame if a supply of ignition had been introduced.
For vapours of flammable liquids, there’s a minimum concentration beneath which the unfold of the flame doesn’t happen when involved with a source of ignition. This is the Lower Flammable Limit (LFL). There is a most focus of vapour within the air above which the unfold of the flame doesn’t happen. This is the Upper Flammable Limit (UFL). เกจวัดแรงดันต่ำ is between the LFL and the UFL, when the focus of vapours can help combustion.
If security procedures are adopted, outages is probably not required whereas upkeep is carried out.
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 have to be assumed that the concentration of vapours within the air may exceed the LFL (at least for a quick while after application). As with coating utility to ambient temperature steel, controls must be implemented.
While the LFL is prone to be achieved over a shorter time period throughout scorching application of coatings than coatings work carried out at ambient circumstances, the resulting fire hazard exists in both purposes. That is, the hearth hazard and related controls have to be thought of for the appliance of any solvent-borne flammable coating system, regardless of the work surroundings. It should be recognized that the gas element of the fireplace tetrahedron will be present in both ‘hot’ and ‘ambient’ environments and fundamental steps have to be taken to minimize unnecessary solvent vapours in the work area. In addition, as outlined later, consideration must also be directed to eliminating the remaining element of the tetrahedron – the supply of ignition.
Controlling flammable vapours
The gasoline element of a fireplace can be decreased by implementing primary controls corresponding to handling and storing flammable liquids in accredited, self-closing containers, keeping the number of flammable liquids containers within the work area and in storage areas to the minimal needed and inside allowable (regulatory) limits.
Alkaline detergents similar to tri-sodium phosphate could also be substituted, adopted by surface 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 cleaning.
Combustible gasoline indicators must be used to verify that the concentration of flammable vapours is below the LFL. Combustible gas indicators should be calibrated in accordance with the manufacturer’s recommendations and have to be permitted to be used in flammable atmospheres. Operators of the tools have to be trained in proper equipment operation.
Readings must be taken in the basic work area and the neighborhood of the operator and in areas the place there are potential sources of ignition. Typically, items are set to alarm at 10% of the LFL. If the alarm sounds, coatings utility work ought to immediately stop till the focus of flammable vapours is managed. The purpose of setting the alarm under the LFL is to supply a security issue that ends in management measures being implemented before there’s an imminent danger of fireside or explosion.
Monitoring of the flammable vapour focus shall be needed as the effectiveness of pure air flow may be variable. If control of flammable vapours requires mechanical ventilation, an occupational safety or health professional or engineer with expertise in industrial air flow must be consulted.
At a minimal, mechanical air flow techniques should present sufficient capability to manage flammable vapours to under 10% of the LFL by either exhaust air flow to remove contaminants from the work area or by dilution air flow by way of introduction of contemporary air to dilute contaminants. As with combustible fuel indicators, air flow equipment should be permitted for secure use in flammable atmospheres. In addition, air flow tools should be grounded and bonded.
Additional air flow, if wanted, should be steady during coatings utility as concentrations could enhance as more surfaces are coated during the course of a work shift, and particularly on sizzling surfaces the place the speed of vaporization is greater.
Ventilation during coatings application should be steady, especially when engaged on sizzling surfaces.
Sources of Ignition
When applying coatings to scorching surfaces, the first source of ignition that readily comes to thoughts is the heat from the surface being painted. The AIT of the coating materials is the single most essential concern when making use of coatings to hot operating equipment. The AIT of a substance or mixture is the minimal temperature at which a vapour-air mixture will ignite when involved with a heated surface, with out 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 floor temperatures may be known/available in many amenities, all surface areas of the process/piping being painted and/or any gear adjoining to the objects being painted where overspray could deposit must 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 may be readily apparent, a extra subtle however nonetheless important source of ignition to control on any industrial painting challenge involving flammable solvents involves the production of static electrical energy. Equipment related to the spray-painting operation, such as spray software gear and ventilation equipment, 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 generation of warmth from oxidation of organic chemical substances such as paint solvents is accelerated until the ignition temperature of the gasoline is reached.
This situation is reached when the material is packed loosely permitting a big surface space to be uncovered, there’s sufficient air circulating around the material for oxidation to occur, but the pure ventilation out there is inadequate to hold the warmth away quick enough to forestall it from building up.
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