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

Managers of petrochemical, refining, power, offshore, pulp and paper and other facilities with extensive hot processes and piping systems are incessantly challenged with performing all the required coatings upkeep work only during periods of outages. Outages are required in order that process equipment could be correctly maintained and repaired together with cleaning of pipelines and vessels, maintenance and alternative of pumps, motors and valves, upkeep coating operations, and different work that can solely be achieved when the operations are shut down.
When coatings work has to be performed on areas the place elevated temperatures are involved, many assume that the facility must be shut down. This may not be the case.
A query regularly posed by facility managers is, “Can I do maintenance 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 health issues that have to be considered”.
Dangers to personnel should be managed no matter when or the place work is performed.
Safety and health concerns
There is a variety of safety and well being hazards that should be considered on every industrial upkeep painting project, whether the coating materials is being utilized to scorching metal or not. Some of those include proper materials dealing with and storage, fall safety, control of fireside and explosion hazards, and publicity to noise, heavy metals, solvents and other health dangers.
เกจวัดแรงดันไนโตรเจนราคา must be correctly evaluated and controlled on every industrial upkeep portray venture, regardless of when or where the work is carried out. While current on any job, when applying specialty coatings to scorching surfaces, some safety and health issues ought to obtain further consideration.
Flammable and combustible liquids in plenty of coatings (solvents) can vaporize and type flammable mixtures in the air, especially when atomized during spray software or heated. The diploma of hazard is dependent upon the next:
The auto ignition temperature (AIT) of the coating materials is the single most important issue when making use of coatings to scorching working equipment. 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 without the presence of an open spark or flame.”
The idea of flash point as defined by NFPA 30 is “the minimal temperature of a liquid at which sufficient 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 is excessive sufficient to generate enough vapour to create a flame if a source of ignition had been launched.
For vapours of flammable liquids, there’s a minimal focus below which the unfold of the flame does not occur when in contact with a supply of ignition. This is the Lower Flammable Limit (LFL). There is a maximum focus of vapour in the air above which the spread of the flame doesn’t occur. This is the Upper Flammable Limit (UFL). The flammable vary 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 while maintenance is performed.
Implementing controls
Applying coatings to sizzling surfaces increases the rate at which the solvents are driven off. When applying solvent borne coatings to hot surfaces it have to be assumed that the focus of vapours within the air might exceed the LFL (at least for a short time after application). As with coating software to ambient temperature steel, controls must be implemented.
While the LFL is prone to be achieved over a shorter time period throughout sizzling application of coatings than coatings work performed at ambient circumstances, the resulting fireplace hazard exists in both applications. That is, the fireplace hazard and associated controls must be considered for the applying of any solvent-borne flammable coating system, regardless of the work environment. It must be acknowledged that the fuel element of the fireplace tetrahedron might be present in both ‘hot’ and ‘ambient’ environments and basic steps must be taken to minimize unnecessary solvent vapours within the work area. In addition, as outlined later, consideration must even be directed to eliminating the remaining element of the tetrahedron – the source of ignition.
Controlling flammable vapours
The gasoline element of a fireplace may be lowered by implementing basic controls corresponding to handling and storing flammable liquids in approved, self-closing containers, maintaining the variety of flammable liquids containers within the work area and in storage areas to the minimum necessary and inside allowable (regulatory) limits.
Alkaline detergents similar to tri-sodium phosphate may be substituted, followed 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 cleansing.
Combustible gasoline indicators ought to be used to verify that the focus of flammable vapours is beneath the LFL. Combustible gasoline indicators have to be calibrated in accordance with the manufacturer’s recommendations and should be accredited for use in flammable atmospheres. Operators of the equipment must be skilled in correct tools operation.
Readings should be taken within the basic 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 immediately cease till the concentration of flammable vapours is controlled. The objective of setting the alarm below the LFL is to supply a security issue that results in control measures being carried out before there could be an imminent hazard of fireplace or explosion.
เครื่องมือใช้วัดความดัน of the flammable vapour focus shall be needed because the effectiveness of natural ventilation could additionally be variable. If control of flammable vapours requires mechanical air flow, an occupational safety or health skilled or engineer with expertise in industrial air flow should be consulted.
At a minimal, mechanical ventilation techniques should present enough capability to manage flammable vapours to under 10% of the LFL by both exhaust air flow to take away contaminants from the work space or by dilution air flow by way of introduction of recent air to dilute contaminants. As with combustible gasoline indicators, air flow equipment should be approved for protected use in flammable atmospheres. In addition, air flow equipment should be grounded and bonded.
Additional air flow, if wanted, ought to be continuous throughout coatings application as concentrations may improve as more surfaces are coated during the course of a piece shift, and particularly on sizzling surfaces where the speed of vaporization is higher.
Ventilation throughout coatings application must be steady, particularly when engaged on scorching surfaces.
Sources of Ignition
When applying coatings to scorching surfaces, the first source 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 scorching working gear. The AIT of a substance or mixture is the minimal temperature at which a vapour-air combination will ignite when in touch with a heated floor, 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 beneath the AIT of the coatings being applied. While surface temperatures could also be known/available in plenty of services, all surface areas of the process/piping being painted and/or any gear adjoining to the items being painted the place overspray may deposit ought to be measured for precise floor 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 delicate but nonetheless critical supply of ignition to manage on any industrial painting project involving flammable solvents includes the production of static electrical energy. Equipment associated with the spray-painting operation, corresponding to spray utility equipment and air flow 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 generation of warmth from oxidation of natural chemical compounds corresponding to paint solvents is accelerated till the ignition temperature of the gas is reached.
This condition is reached when the material is packed loosely permitting a big surface space to be uncovered, there is enough air circulating around the materials for oxidation to happen, however the natural air flow out there is inadequate to carry the heat away quick sufficient to prevent it from build up.
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