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

Managers of petrochemical, refining, power, offshore, pulp and paper and other services with in depth sizzling processes and piping methods are frequently challenged with performing all the mandatory coatings maintenance work only in periods of outages. Outages are required in order that course of gear can be properly maintained and repaired including cleaning of pipelines and vessels, maintenance and substitute of pumps, motors and valves, maintenance 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 involved, many suppose that the power must be shut down. This may not be the case.
A query incessantly posed by facility managers is, “Can I do maintenance painting work while the plant is operating?” As described beneath, the reply is, “Yes you’ll be able to, however there are safety and well being issues that should be considered”.
Dangers to personnel should be managed no matter when or where work is performed.
Safety and health concerns
There is a spread of safety and well being hazards that should be thought-about on every industrial maintenance painting venture, whether the coating material is being utilized to scorching metal or not. Some of those include correct materials handling and storage, fall protection, control of fire and explosion hazards, and exposure to noise, heavy metals, solvents and other well being dangers.
These dangers have to be correctly evaluated and managed on each industrial maintenance painting venture, no matter when or the place the work is performed. While current on any job, when applying specialty coatings to sizzling surfaces, some security and well being issues ought to obtain further consideration.
Flammable and flamable liquids in lots of coatings (solvents) can vaporize and type flammable mixtures within the air, particularly when atomized throughout spray software or heated. The degree of hazard is dependent upon the following:
The auto ignition temperature (AIT) of the coating materials is the only most important problem when making use of coatings to scorching operating tools. AIT is defined (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 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 defined by NFPA 30 is “the minimal temperature of a liquid at which sufficient vapour is given off to kind an ignitable combination with the air, close to the surface of the liquid”. In other words, the flash level describes the temperature of the liquid that’s excessive enough to generate enough vapour to create a flame if a source of ignition had been introduced.
For vapours of flammable liquids, there’s a minimum focus under which the unfold of the flame doesn’t happen when in contact with a supply of ignition. This 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 happen. 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 followed, outages will not be required whereas upkeep is carried out.
Implementing controls
Applying coatings to scorching surfaces will increase the rate at which the solvents are pushed off. When applying solvent borne coatings to scorching surfaces it should be assumed that the focus of vapours within the air could exceed the LFL (at least for a short while after application). As with coating utility to ambient temperature metal, controls should be implemented.
While the LFL is more probably to be achieved over a shorter time frame throughout scorching utility of coatings than coatings work carried out at ambient situations, the resulting fire hazard exists in each functions. That is, the fire hazard and associated controls must be thought-about for the applying of any solvent-borne flammable coating system, regardless of the work environment. It should be acknowledged that the gasoline component of the fire tetrahedron might be present in both ‘hot’ and ‘ambient’ environments and fundamental steps must be taken to reduce pointless solvent vapours in the work area. In addition, as outlined later, consideration should even be directed to eliminating the remaining element of the tetrahedron – the source of ignition.
Controlling flammable vapours
The gasoline factor of a hearth may be lowered by implementing basic controls corresponding to dealing with and storing flammable liquids in permitted, self-closing containers, preserving the variety of flammable liquids containers in the work area and in storage areas to the minimal essential and within allowable (regulatory) limits.
Alkaline detergents such as tri-sodium phosphate could additionally be substituted, adopted by surface washing with recent 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 cleaning.
เกจวัดแก๊สหุงต้ม should be used to confirm that the concentration of flammable vapours is beneath the LFL. Combustible gas indicators should be calibrated in accordance with the manufacturer’s recommendations and should be accredited for use in flammable atmospheres. Operators of the gear should be trained in correct equipment operation.
Readings ought to be taken in the common work area and the vicinity of the operator and in areas the place there are potential sources of ignition. Typically, models are set to alarm at 10% of the LFL. If the alarm sounds, coatings application work ought to immediately cease until the focus of flammable vapours is controlled. The purpose of setting the alarm below the LFL is to supply a security issue that leads to management measures being applied earlier than there’s an imminent hazard of fireplace or explosion.
Monitoring of the combustible vapour concentration will be essential because the effectiveness of natural air flow could additionally be variable. If control of flammable vapours requires mechanical ventilation, an occupational security or well being professional or engineer with expertise in industrial ventilation must be consulted.
At a minimum, mechanical air flow techniques ought to provide enough capability to control flammable vapours to beneath 10% of the LFL by both exhaust air flow to take away contaminants from the work area or by dilution ventilation via introduction of contemporary air to dilute contaminants. As with combustible gas indicators, air flow tools have to be accredited for protected use in flammable atmospheres. In addition, ventilation equipment should be grounded and bonded.
Additional ventilation, if wanted, should be continuous throughout coatings software as concentrations might improve as more surfaces are coated in the course of the course of a piece shift, and particularly on sizzling surfaces where the rate of vaporization is higher.
Ventilation throughout coatings application should be steady, particularly when working on hot surfaces.
Sources of Ignition
When applying coatings to scorching surfaces, the first supply of ignition that readily involves thoughts is the warmth from the floor being painted. The AIT of the coating materials is the only most necessary problem when making use of coatings to scorching operating tools. The AIT of a substance or mixture is the minimal temperature at which a vapour-air combination will ignite when in contact with a heated floor, without the presence of any open spark or flame.
The key to controlling this source of ignition is to confirm the surfaces being coated are below the AIT of the coatings being utilized. While surface temperatures may be known/available in plenty of amenities, all floor areas of the process/piping being painted and/or any tools adjacent to the items being painted the place overspray could deposit ought to be measured for precise floor temperature. The outcomes should be in comparability with the AIT of the coating system.
While auto-ignition and open sources of ignition could also be readily apparent, a more delicate but nonetheless crucial source of ignition to control on any industrial painting project involving flammable solvents involves the manufacturing of static electrical energy. Equipment related to the spray-painting operation, corresponding to spray utility equipment and air flow equipment, can generate static electrical energy.
In addition to exterior 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 similar to paint solvents is accelerated until the ignition temperature of the gas is reached.
This situation is reached when the fabric is packed loosely allowing a large surface area to be uncovered, there is enough air circulating around the materials for oxidation to occur, but the pure air flow obtainable is insufficient to carry the heat away quick sufficient to prevent it from building up.
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