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

Managers of petrochemical, refining, energy, offshore, pulp and paper and different amenities with in depth sizzling processes and piping systems are frequently challenged with performing all the required coatings upkeep work solely in periods of outages. Outages are required in order that course of equipment can be correctly maintained and repaired together with cleansing of pipelines and vessels, maintenance and substitute of pumps, motors and valves, upkeep coating operations, and other work that can solely be accomplished when the operations are shut down.
When coatings work needs to be carried out on areas the place elevated temperatures are concerned, many suppose that the facility must be shut down. This will not be the case.
A query frequently posed by facility managers is, “Can I do maintenance painting work whereas the plant is operating?” As described under, the answer is, “Yes you probably can, however there are safety and well being points that must be considered”.
Dangers to personnel should be managed regardless of when or the place work is carried out.
Safety and well being issues
There is a spread of security and health hazards that should be considered on each industrial maintenance painting challenge, whether the coating materials is being applied to hot steel or not. Some of these include proper material handling and storage, fall protection, control of fire and explosion hazards, and exposure to noise, heavy metals, solvents and different well being dangers.
These dangers must be properly evaluated and managed on each industrial upkeep painting challenge, regardless of when or the place the work is carried out. While current on any job, when making use of specialty coatings to scorching surfaces, some safety and health points ought to receive further consideration.
Flammable and flamable liquids in lots of coatings (solvents) can vaporize and type flammable mixtures within the air, particularly when atomized during spray software or heated. The degree of hazard depends on the following:
The auto ignition temperature (AIT) of the coating material is the one most important problem when making use of coatings to hot operating 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 combination will ignite from its own warmth supply or contact with a heated surface with out the presence of an open spark or flame.”
The idea of flash point as outlined by NFPA 30 is “the minimal temperature of a liquid at which enough vapour is given off to form an ignitable combination with the air, close to the floor of the liquid”. In เกจวัดแรงดันน้ำมันเครื่อง , the flash level describes the temperature of the liquid that’s high sufficient to generate enough vapour to create a flame if a supply of ignition were launched.
For vapours of flammable liquids, there’s a minimal concentration below which the spread of the flame doesn’t happen when in contact with a source of ignition. This is the Lower Flammable Limit (LFL). There is a most concentration 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 support combustion.
If safety procedures are adopted, outages is probably not required whereas maintenance is performed.
Implementing controls
Applying coatings to hot surfaces will increase the rate at which the solvents are pushed off. When making use of solvent borne coatings to scorching surfaces it must be assumed that the focus of vapours within the air could exceed the LFL (at least for a brief while after application). As with coating utility to ambient temperature metal, controls have to be applied.
While the LFL is likely to be achieved over a shorter period of time during sizzling utility of coatings than coatings work carried out at ambient circumstances, the resulting fire hazard exists in each purposes. That is, the fire hazard and associated controls must be considered for the applying of any solvent-borne flammable coating system, whatever the work surroundings. It have to be acknowledged that the fuel component of the hearth tetrahedron shall be present in both ‘hot’ and ‘ambient’ environments and primary steps should be taken to minimize pointless solvent vapours within the work area. In addition, as outlined later, attention must even be directed to eliminating the remaining element of the tetrahedron – the supply of ignition.
Controlling flammable vapours
The fuel element of a hearth could be decreased by implementing fundamental controls such as handling and storing flammable liquids in approved, self-closing containers, preserving the number of flammable liquids containers in the work space and in storage areas to the minimum essential and inside allowable (regulatory) limits.
Alkaline detergents such as tri-sodium phosphate may be substituted, adopted by floor washing with fresh water or steam cleaning and pH testing of the surface, or non-combustible solvents corresponding to 1,1,1 trichloroethane) for pre-surface preparation solvent cleansing.
Combustible fuel indicators should be used to confirm that the focus of flammable vapours is beneath the LFL. Combustible gasoline indicators must be calibrated in accordance with the manufacturer’s recommendations and should be accredited for use in flammable atmospheres. Operators of the tools have to be skilled in proper tools operation.
Readings should be taken in the common work space and the neighborhood of the operator and in areas the place there are potential sources of ignition. Typically, items are set to alarm at 10% of the LFL. If the alarm sounds, coatings software work should instantly cease till the focus of flammable vapours is managed. The function of setting the alarm below the LFL is to supply a security factor that ends in management measures being applied earlier than there might be an imminent danger of fireplace or explosion.
Monitoring of the combustible vapour focus might be needed because the effectiveness of natural ventilation may be variable. If management of flammable vapours requires mechanical air flow, an occupational security or well being skilled or engineer with expertise in industrial ventilation should be consulted.
At a minimal, mechanical air flow systems ought to provide enough capacity to control flammable vapours to under 10% of the LFL by either exhaust air flow to take away contaminants from the work space or by dilution ventilation by way of introduction of recent air to dilute contaminants. As with flamable fuel indicators, air flow tools should be approved for secure use in flammable atmospheres. In addition, air flow tools have to be grounded and bonded.
Additional air flow, if needed, must be steady throughout coatings application as concentrations might improve as extra surfaces are coated through the course of a piece shift, and especially on hot surfaces where the speed of vaporization is larger.
Ventilation throughout coatings utility ought to be continuous, particularly when engaged on scorching surfaces.
Sources of Ignition
When making use of coatings to sizzling surfaces, the primary source of ignition that readily comes to thoughts is the heat from the surface being painted. The AIT of the coating materials is the only most important issue when making use of coatings to scorching working equipment. The AIT of a substance or mixture is the minimum temperature at which a vapour-air combination will ignite when involved with a heated surface, without the presence of any open spark or flame.
The key to controlling this source of ignition is to verify the surfaces being coated are under the AIT of the coatings being applied. While floor temperatures may be known/available in plenty of amenities, all floor areas of the process/piping being painted and/or any gear adjacent to the objects being painted the place overspray might deposit ought to be measured for precise surface 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 subtle however nonetheless critical source of ignition to manage on any industrial portray challenge involving flammable solvents involves the manufacturing of static electricity. Equipment related to the spray-painting operation, such as spray application gear and air flow gear, 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 happens when the sluggish era of heat from oxidation of organic chemical substances such as paint solvents is accelerated till the ignition temperature of the gasoline is reached.
This condition is reached when the material is packed loosely allowing a big floor space to be exposed, there’s sufficient air circulating across the material for oxidation to happen, but the natural ventilation obtainable is inadequate to hold the warmth away fast sufficient to stop it from increase.
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