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

Managers of petrochemical, refining, energy, offshore, pulp and paper and other services with intensive scorching processes and piping systems are regularly challenged with performing all the necessary coatings upkeep work only in periods of outages. Outages are required so that process tools 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 completed when the operations are shut down.
When coatings work needs to be carried out on areas where elevated temperatures are involved, many suppose that the ability has to be shut down. This is in all probability not the case.
A question incessantly posed by facility managers is, “Can I do upkeep painting work whereas the plant is operating?” As described under, the answer is, “Yes you can, however there are security and health points that have to be considered”.
Dangers to personnel must be managed no matter when or where work is carried out.
Safety and well being considerations
There is a spread of safety and health hazards that must be considered on each industrial upkeep painting venture, whether the coating material is being applied to hot steel or not. Some of those embrace correct materials dealing with and storage, fall protection, management of fireplace and explosion hazards, and exposure to noise, heavy metals, solvents and different well being risks.
These risks have to be properly evaluated and managed on each industrial upkeep portray challenge, no matter when or the place the work is carried out. While current on any job, when making use of specialty coatings to hot surfaces, some security and well being points ought to receive additional consideration.
เพรสเชอร์เกจวัดแรงดันน้ำ and flamable liquids in lots of coatings (solvents) can vaporize and form flammable mixtures in the air, particularly when atomized during spray software or heated. The degree of hazard depends on the next:
The auto ignition temperature (AIT) of the coating materials is the only most necessary issue when making use of coatings to hot working tools. 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 heat supply or contact with a heated surface with out the presence of an open spark or flame.”
The concept of flash level as defined by NFPA 30 is “the minimal temperature of a liquid at which adequate vapour is given off to type an ignitable combination with the air, near the surface of the liquid”. In different words, the flash level describes the temperature of the liquid that is high enough to generate sufficient vapour to create a flame if a source of ignition were introduced.
For vapours of flammable liquids, there’s a minimum concentration under which the unfold of the flame does not occur when in touch 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 spread of the flame doesn’t happen. This is the Upper Flammable Limit (UFL). The flammable vary is between the LFL and the UFL, when the focus of vapours can support combustion.
If security procedures are adopted, outages will not be required whereas upkeep is performed.
Implementing controls
Applying coatings to sizzling surfaces will increase the rate at which the solvents are driven off. When making use of solvent borne coatings to hot surfaces it should be assumed that the focus of vapours within the air could exceed the LFL (at least for a short time after application). As with coating application to ambient temperature metal, controls have to be carried out.
While the LFL is prone to be achieved over a shorter period of time throughout scorching application of coatings than coatings work performed at ambient conditions, the ensuing fireplace hazard exists in both applications. That is, the fireplace hazard and associated controls must be thought-about for the application of any solvent-borne flammable coating system, whatever the work environment. It have to be acknowledged that the fuel element of the fire tetrahedron might be present in each ‘hot’ and ‘ambient’ environments and primary steps have to be taken to minimize pointless solvent vapours within the work area. In addition, as outlined later, consideration should even be directed to eliminating the remaining factor of the tetrahedron – the source of ignition.
Controlling flammable vapours
The gas element of a fireplace can be lowered by implementing fundamental controls corresponding to dealing with and storing flammable liquids in accredited, self-closing containers, maintaining the number of flammable liquids containers in the work space and in storage areas to the minimum necessary and within allowable (regulatory) limits.
Alkaline detergents similar to tri-sodium phosphate could additionally be substituted, followed by surface washing with contemporary water or steam cleaning and pH testing of the floor, or non-combustible solvents corresponding to 1,1,1 trichloroethane) for pre-surface preparation solvent cleansing.
Combustible gasoline indicators should be used to verify that the concentration of flammable vapours is below the LFL. Combustible fuel indicators must be calibrated in accordance with the manufacturer’s recommendations and have to be permitted for use in flammable atmospheres. Operators of the equipment should be skilled in proper gear operation.
Readings must be taken in the common work area and the vicinity of the operator and in areas where there are potential sources of ignition. Typically, units are set to alarm at 10% of the LFL. If the alarm sounds, coatings utility work ought to instantly cease till the focus of flammable vapours is managed. The function of setting the alarm beneath the LFL is to supply a security factor that ends in management measures being applied before there is an imminent danger of fireplace or explosion.
Monitoring of the combustible vapour focus will be necessary as the effectiveness of pure ventilation could additionally be variable. If management of flammable vapours requires mechanical ventilation, an occupational security or health skilled or engineer with experience in industrial ventilation must be consulted.
At a minimal, mechanical ventilation methods should provide enough capacity to regulate flammable vapours to under 10% of the LFL by either exhaust air flow to remove contaminants from the work area or by dilution ventilation through introduction of contemporary air to dilute contaminants. As with combustible gas indicators, air flow gear should be permitted for protected use in flammable atmospheres. In addition, air flow gear have to be grounded and bonded.
Additional air flow, if wanted, must be continuous throughout coatings application as concentrations might enhance as more surfaces are coated in the course of the course of a work shift, and especially on scorching surfaces the place the speed of vaporization is higher.
Ventilation during coatings utility must be steady, particularly when working on hot surfaces.
Sources of Ignition
When making use of coatings to hot surfaces, the first source of ignition that readily involves mind is the warmth from the surface being painted. The AIT of the coating material is the only most important issue when applying coatings to scorching working equipment. 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, 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 below the AIT of the coatings being applied. While surface temperatures could also be known/available in lots of amenities, all floor areas of the process/piping being painted and/or any tools adjoining to the objects being painted where overspray might deposit must be measured for actual floor temperature. The outcomes must be compared to the AIT of the coating system.
While auto-ignition and open sources of ignition could additionally be readily apparent, a extra refined but nonetheless important source of ignition to manage on any industrial portray venture involving flammable solvents involves the production of static electrical energy. Equipment related to the spray-painting operation, similar to spray application gear and ventilation gear, can generate static electricity.
In addition to exterior 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 generation of warmth from oxidation of organic chemical substances such as paint solvents is accelerated till the ignition temperature of the gasoline is reached.
This situation is reached when the material is packed loosely allowing a big surface area to be exposed, there might be sufficient air circulating across the materials for oxidation to occur, but the pure air flow out there is insufficient to carry the heat away fast enough to forestall it from build up.
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