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

Managers of petrochemical, refining, power, offshore, pulp and paper and other services with extensive hot processes and piping systems are regularly challenged with performing all the required coatings maintenance work only during times of outages. Outages are required in order that process equipment can be properly maintained and repaired together with cleansing of pipelines and vessels, upkeep and alternative of pumps, motors and valves, maintenance coating operations, and different work that may solely be achieved when the operations are shut down.
When coatings work must be performed on areas the place elevated temperatures are concerned, many think that the power has to be shut down. This will not be the case.
A query frequently posed by facility managers is, “Can I do upkeep portray work while the plant is operating?” As described beneath, the answer is, “Yes you can, however there are security and well being issues that have to be considered”.
Dangers to personnel have to be managed no matter when or the place work is performed.
Safety and health considerations

There is a range of security and well being hazards that have to be considered on every industrial maintenance painting venture, whether or not the coating materials is being utilized to sizzling steel or not. Some of these embrace correct materials dealing with and storage, fall safety, control of fireplace and explosion hazards, and publicity to noise, heavy metals, solvents and different health dangers.
These risks have to be properly evaluated and controlled on each industrial upkeep painting venture, no matter when or the place the work is performed. While present on any job, when making use of specialty coatings to hot surfaces, some security and health issues should receive further consideration.
Flammable and combustible liquids in lots of coatings (solvents) can vaporize and kind flammable mixtures within the air, especially when atomized throughout spray utility or heated. The degree of hazard is dependent upon the following:
The auto ignition temperature (AIT) of the coating materials is the single most necessary concern when making use of coatings to scorching working gear. 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 combination will ignite from its own warmth source or contact with a heated floor without the presence of an open spark or flame.”

The concept of flash point as outlined by NFPA 30 is “the minimum temperature of a liquid at which sufficient vapour is given off to kind an ignitable mixture with the air, near the surface of the liquid”. In different words, the flash point describes the temperature of the liquid that is excessive sufficient to generate enough vapour to create a flame if a source of ignition were launched.
For vapours of flammable liquids, there is a minimum focus below which the spread of the flame doesn’t happen when in touch with a supply of ignition. This is the Lower Flammable Limit (LFL). There is a maximum concentration of vapour within the air above which the spread 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 security procedures are adopted, outages is most likely not required whereas upkeep is performed.
Implementing controls

Applying coatings to sizzling surfaces will increase the speed at which the solvents are pushed off. When making use of solvent borne coatings to scorching surfaces it have to be assumed that the focus of vapours in the air may exceed the LFL (at least for a short 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 time period throughout scorching software of coatings than coatings work carried out at ambient circumstances, the resulting hearth hazard exists in each purposes. That is, the fireplace hazard and related controls have to be considered for the applying of any solvent-borne flammable coating system, whatever the work surroundings. It have to be recognized that the gas component of the fireplace tetrahedron might be present in each ‘hot’ and ‘ambient’ environments and fundamental steps have to be taken to minimize unnecessary solvent vapours in the work space. 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 gas factor of a hearth may be lowered by implementing fundamental controls similar to dealing with and storing flammable liquids in approved, self-closing containers, maintaining the number of flammable liquids containers within the work space and in storage areas to the minimal needed and inside allowable (regulatory) limits.
Alkaline detergents similar to tri-sodium phosphate could also 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 cleansing.
Combustible gasoline indicators ought to be used to verify that the focus of flammable vapours is beneath the LFL. Combustible fuel indicators must be calibrated in accordance with the manufacturer’s recommendations and should be permitted to be used in flammable atmospheres. Operators of the gear should be trained in proper tools operation.
Readings should be taken within the common work area and the neighborhood of the operator and in areas the place there are potential sources of ignition. Typically, units are set to alarm at 10% of the LFL. If the alarm sounds, coatings utility work should immediately cease till the focus of flammable vapours is controlled. The purpose of setting the alarm below the LFL is to provide a safety issue that results in control measures being implemented before there might be an imminent hazard of fireside or explosion.
Monitoring of the flammable vapour focus will be needed because the effectiveness of pure ventilation could additionally 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 must be consulted.
At a minimum, mechanical ventilation methods ought to present enough capacity to control flammable vapours to beneath 10% of the LFL by both exhaust ventilation to take away contaminants from the work area or by dilution ventilation by way of introduction of contemporary air to dilute contaminants. As with combustible gas indicators, ventilation gear should be accredited for secure use in flammable atmospheres. In addition, ventilation equipment have to be grounded and bonded.
Additional air flow, if needed, ought to be continuous throughout coatings software as concentrations could increase as extra surfaces are coated in the course of the course of a work shift, and especially on scorching surfaces the place the rate of vaporization is greater.
Ventilation during coatings software ought to be steady, especially when engaged on scorching surfaces.
weksler ea14 of Ignition

When making use of coatings to sizzling surfaces, the primary source of ignition that readily involves mind is the warmth from the floor being painted. The AIT of the coating material is the one most essential issue when making use of coatings to sizzling operating tools. 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, 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 under the AIT of the coatings being utilized. While surface temperatures may be known/available in lots of services, all floor areas of the process/piping being painted and/or any gear adjoining to the objects being painted the place overspray could deposit should be measured for actual floor temperature. The results must be in comparison with the AIT of the coating system.
While auto-ignition and open sources of ignition may be readily apparent, a extra delicate however nonetheless important supply of ignition to control on any industrial painting challenge involving flammable solvents includes the manufacturing of static electrical energy. Equipment associated with the spray-painting operation, corresponding to spray utility tools 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 happens when the sluggish era of warmth from oxidation of organic chemical substances corresponding to paint solvents is accelerated till the ignition temperature of the gas is reached.
This condition is reached when the fabric is packed loosely permitting a big surface space to be exposed, there’s enough air circulating around the material for oxidation to occur, but the pure ventilation available is inadequate to hold the heat away quick sufficient to prevent it from increase.
For more information, go to www.ppgpmc.com/Oil-Gas-Chemical.aspx

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