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

Managers of petrochemical, refining, power, offshore, pulp and paper and other facilities with in depth sizzling processes and piping methods are frequently challenged with performing all the necessary coatings upkeep work only during periods of outages. Unlock are required in order that process equipment could be properly maintained and repaired together with cleansing of pipelines and vessels, upkeep and alternative of pumps, motors and valves, maintenance coating operations, and other work that may only be achieved 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 power has to be shut down. This may not be the case.
A question frequently posed by facility managers is, “Can I do upkeep portray work whereas the plant is operating?” As described beneath, the reply is, “Yes you can, however there are safety and well being issues that should be considered”.
Dangers to personnel have to be managed regardless of when or the place work is carried out.
Safety and well being considerations
There is a range of safety and well being hazards that must be considered on each industrial upkeep painting challenge, whether the coating material is being applied to scorching metal or not. Some of those include correct material handling and storage, fall protection, control of fireside and explosion hazards, and publicity to noise, heavy metals, solvents and other health dangers.
These risks have to be correctly evaluated and controlled on every industrial maintenance portray challenge, regardless of when or where the work is carried out. While current on any job, when making use of specialty coatings to sizzling surfaces, some security and well being issues ought to receive further consideration.
Flammable and flamable liquids in plenty of coatings (solvents) can vaporize and kind flammable mixtures in 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 only most essential problem when making use of coatings to hot operating gear. AIT 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 own heat supply or contact with a heated floor with out the presence of an open spark or flame.”
The idea of flash point as defined by NFPA 30 is “the minimum temperature of a liquid at which adequate vapour is given off to type an ignitable mixture with the air, near the floor of the liquid”. In different words, the flash level describes the temperature of the liquid that’s high sufficient to generate sufficient vapour to create a flame if a supply of ignition have been introduced.
For vapours of flammable liquids, there is a minimal concentration under which the spread of the flame doesn’t happen when in touch with a source 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 doesn’t happen. This is the Upper Flammable Limit (UFL). The flammable range is between the LFL and the UFL, when the focus of vapours can help combustion.
If security procedures are followed, outages is most likely not required while 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 hot surfaces it should be assumed that the focus of vapours in the air might exceed the LFL (at least for a brief while after application). As with coating application to ambient temperature metal, controls have to be implemented.
While the LFL is more doubtless to be achieved over a shorter time period throughout hot software of coatings than coatings work carried out at ambient situations, the ensuing fireplace hazard exists in both purposes. That is, the fireplace hazard and related controls must be thought-about for the applying of any solvent-borne flammable coating system, regardless of the work setting. It have to be acknowledged that the fuel part of the fireplace tetrahedron shall be current in both ‘hot’ and ‘ambient’ environments and basic steps should be taken to attenuate pointless solvent vapours in the work space. In addition, as outlined later, attention must even be directed to eliminating the remaining component of the tetrahedron – the source of ignition.
Controlling flammable vapours
The fuel factor of a fireplace could be lowered by implementing basic controls similar to dealing with and storing flammable liquids in approved, self-closing containers, preserving the variety 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 fresh water or steam cleansing and pH testing of the surface, or non-combustible solvents such as 1,1,1 trichloroethane) for pre-surface preparation solvent cleansing.
Combustible fuel indicators must be used to confirm that the concentration of flammable vapours is beneath the LFL. Combustible gasoline indicators must be calibrated in accordance with the manufacturer’s suggestions and must be permitted to be used in flammable atmospheres. Operators of the tools have to be trained in correct tools operation.
Readings should be taken in the general work area and the neighborhood 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 software work ought to instantly stop until the concentration of flammable vapours is controlled. The purpose of setting the alarm below the LFL is to supply a security issue that leads to control measures being applied earlier than there’s an imminent hazard of fire or explosion.
Monitoring of the combustible vapour focus shall be needed because the effectiveness of pure air flow could additionally be variable. If control of flammable vapours requires mechanical ventilation, an occupational safety or health professional or engineer with experience in industrial air flow should be consulted.
At a minimal, mechanical ventilation methods ought to provide adequate capacity to regulate flammable vapours to under 10% of the LFL by either exhaust air flow to take away contaminants from the work area or by dilution air flow via introduction of fresh air to dilute contaminants. As with combustible fuel indicators, air flow tools should be permitted for protected use in flammable atmospheres. In addition, ventilation equipment should be grounded and bonded.
Additional air flow, if needed, ought to be steady throughout coatings utility as concentrations might increase as extra surfaces are coated through the course of a work shift, and particularly on sizzling surfaces where the rate of vaporization is larger.
Ventilation during coatings application should be continuous, 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 floor being painted. The AIT of the coating material is the only most essential problem when applying coatings to scorching working gear. The AIT of a substance or combination is the minimal temperature at which a vapour-air combination 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 verify the surfaces being coated are under the AIT of the coatings being utilized. While floor temperatures may be known/available in many services, all floor areas of the process/piping being painted and/or any equipment adjoining to the objects being painted the place overspray could deposit ought to be measured for precise surface temperature. The results must be compared to the AIT of the coating system.
While auto-ignition and open sources of ignition may be readily obvious, a extra subtle but nonetheless crucial supply of ignition to manage on any industrial portray challenge involving flammable solvents involves the production of static electricity. Equipment associated with the spray-painting operation, similar to spray utility tools 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 happens when the sluggish era of heat from oxidation of organic chemical compounds corresponding to paint solvents is accelerated until the ignition temperature of the fuel is reached.
This situation is reached when the fabric is packed loosely allowing a big surface area to be uncovered, there is enough air circulating around the material for oxidation to occur, however the pure air flow available is inadequate to carry the warmth away quick enough to prevent it from building up.
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