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

Managers of petrochemical, refining, power, offshore, pulp and paper and different services with extensive scorching processes and piping techniques are regularly challenged with performing all the required coatings upkeep work only in periods of outages. Outages are required in order that process tools can be properly maintained and repaired including cleansing of pipelines and vessels, upkeep and alternative 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 has to be carried out on areas where elevated temperatures are concerned, many assume that the ability must be shut down. This may not be the case.
A query regularly posed by facility managers is, “Can I do upkeep painting work whereas the plant is operating?” As described below, the reply is, “Yes you can, but there are security and well being issues that have to be considered”.
Dangers to personnel should be managed no matter when or the place work is performed.
Safety and well being concerns
There is a spread of security and well being hazards that have to be thought-about on every industrial maintenance painting venture, whether or not the coating material is being applied to hot steel or not. Some of those include proper material dealing with and storage, fall safety, management of fire and explosion hazards, and publicity to noise, heavy metals, solvents and different well being risks.
These dangers should be properly evaluated and controlled on every industrial maintenance painting venture, regardless of when or where the work is performed. While current on any job, when making use of specialty coatings to hot surfaces, some security and well being points should receive further consideration.
Flammable and combustible liquids in lots of coatings (solvents) can vaporize and kind flammable mixtures in the air, especially when atomized throughout spray software or heated. The degree of hazard is determined by the following:
The auto ignition temperature (AIT) of the coating material is the only most essential concern when applying coatings to hot 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 mixture will ignite from its personal heat supply or contact with a heated surface with out the presence of an open spark or flame.”
The concept of flash level as outlined by NFPA 30 is “the minimal temperature of a liquid at which adequate vapour is given off to kind an ignitable mixture with the air, close to the surface of the liquid”. In other phrases, the flash point describes the temperature of the liquid that is high enough to generate sufficient vapour to create a flame if a source of ignition have been introduced.
For vapours of flammable liquids, there’s a minimal focus beneath which the spread of the flame doesn’t occur when in touch with a source of ignition. This is the Lower Flammable Limit (LFL). There is a most concentration of vapour within the air above which the unfold of the flame does not happen. This is the Upper Flammable Limit (UFL). The flammable vary is between the LFL and the UFL, when the focus of vapours can help combustion.
If safety procedures are adopted, outages will not be required whereas upkeep is carried out.
Implementing controls
Applying coatings to hot surfaces increases the speed at which the solvents are pushed off. When applying เกจวัดแรงดันเครื่องกรองน้ำ borne coatings to hot surfaces it must be assumed that the focus of vapours in the air may exceed the LFL (at least for a quick while after application). As with coating utility to ambient temperature metal, controls have to be implemented.
While the LFL is more doubtless to be achieved over a shorter time period during scorching application of coatings than coatings work carried out at ambient situations, the resulting fireplace hazard exists in both applications. That is, the fire hazard and related controls have to be considered for the appliance of any solvent-borne flammable coating system, whatever the work environment. It must be acknowledged that the gas element of the hearth tetrahedron will be current in both ‘hot’ and ‘ambient’ environments and basic steps should be taken to minimize unnecessary solvent vapours in the work space. In addition, as outlined later, consideration should also be directed to eliminating the remaining factor of the tetrahedron – the source of ignition.
Controlling flammable vapours
The gas element of a hearth may be decreased by implementing fundamental controls corresponding to dealing with and storing flammable liquids in approved, self-closing containers, keeping the number of flammable liquids containers in the work space and in storage areas to the minimal necessary and inside allowable (regulatory) limits.
Alkaline detergents similar to tri-sodium phosphate may be substituted, adopted by surface washing with contemporary 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 gas indicators must 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 recommendations and must be permitted to be used in flammable atmospheres. Operators of the equipment have to be trained in proper equipment operation.
Readings ought to be taken in the general work area and the neighborhood of the operator and in areas where there are potential sources of ignition. Typically, items are set to alarm at 10% of the LFL. If the alarm sounds, coatings software work ought to instantly cease till the concentration of flammable vapours is controlled. The objective of setting the alarm below the LFL is to provide a safety factor that ends in control measures being carried out earlier than there could be an imminent hazard of fireside or explosion.
Monitoring of the combustible vapour concentration might be necessary as the effectiveness of pure air flow could also be variable. If control of flammable vapours requires mechanical air flow, an occupational security or health skilled or engineer with experience in industrial ventilation ought to be consulted.
At a minimal, mechanical ventilation systems ought to provide adequate capability to control flammable vapours to below 10% of the LFL by both exhaust ventilation to remove contaminants from the work space or by dilution ventilation by way of introduction of contemporary air to dilute contaminants. As with combustible gas indicators, air flow tools should be permitted for protected use in flammable atmospheres. In addition, ventilation gear must be grounded and bonded.
Additional ventilation, if needed, should be continuous during coatings software as concentrations may improve as extra surfaces are coated during the course of a work shift, and particularly on sizzling surfaces the place the rate of vaporization is higher.
Ventilation throughout coatings software ought to be continuous, particularly when engaged on scorching surfaces.
Sources of Ignition
When making use of coatings to scorching surfaces, the first source of ignition that readily comes to mind is the warmth from the surface being painted. The AIT of the coating materials is the one most necessary problem when applying coatings to sizzling operating equipment. The AIT of a substance or mixture is the minimum temperature at which a vapour-air mixture will ignite when involved with a heated surface, without the presence of any open spark or flame.
The key to controlling this supply of ignition is to verify the surfaces being coated are under the AIT of the coatings being utilized. While surface temperatures could additionally be known/available in lots of facilities, all surface areas of the process/piping being painted and/or any tools adjacent to the items being painted the place overspray might deposit should be measured for actual floor temperature. The outcomes ought to be compared to the AIT of the coating system.
While auto-ignition and open sources of ignition could also be readily obvious, a more delicate however nonetheless crucial supply of ignition to regulate on any industrial painting project involving flammable solvents includes the manufacturing of static electricity. Equipment associated with the spray-painting operation, similar to spray software equipment and air flow tools, 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 occurs when the slow era of warmth from oxidation of natural chemical compounds similar to paint solvents is accelerated until the ignition temperature of the gas is reached.
This condition is reached when the material is packed loosely allowing a big floor space to be exposed, there is enough air circulating around the material for oxidation to happen, but the pure air flow out there is inadequate to hold the heat away quick enough to prevent it from building up.
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