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

Managers of petrochemical, refining, energy, offshore, pulp and paper and other amenities with extensive sizzling processes and piping methods are incessantly challenged with performing all the necessary coatings upkeep work solely during times of outages. Outages are required in order that course of equipment could be correctly maintained and repaired together with cleansing of pipelines and vessels, maintenance and alternative of pumps, motors and valves, maintenance coating operations, and different work that can only be accomplished when the operations are shut down.
When coatings work has to be carried out on areas where elevated temperatures are involved, many suppose that the facility has to be shut down. This will not be the case.
A query incessantly posed by facility managers is, “Can I do maintenance portray work while the plant is operating?” As described below, the reply is, “Yes you’ll have the ability to, however there are security and well being points that should be considered”.
Dangers to personnel have to be managed no matter when or the place work is performed.
Safety and well being issues
There is a range of security and well being hazards that have to be considered on every industrial maintenance portray challenge, whether the coating material is being applied to hot metal or not. Some of these embrace proper material handling and storage, fall safety, control of fireplace and explosion hazards, and exposure to noise, heavy metals, solvents and different well being dangers.
These risks should be properly 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 scorching surfaces, some security and well being points ought to obtain additional consideration.
Flammable and flamable liquids in many coatings (solvents) can vaporize and type flammable mixtures in the air, especially when atomized during spray utility or heated. The degree of hazard depends on the next:
The auto ignition temperature (AIT) of the coating material is the single most essential concern when applying coatings to hot working 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 warmth supply or contact with a heated floor without the presence of an open spark or flame.”
The idea of flash point as defined by NFPA 30 is “the minimal temperature of a liquid at which adequate vapour is given off to kind an ignitable combination with the air, close to the surface of the liquid”. In other phrases, the flash point 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 is a minimal focus beneath which the unfold of the flame does not occur when in touch with a supply of ignition. This is the Lower Flammable Limit (LFL). There is a maximum 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 help combustion.
If safety procedures are followed, outages will not be required whereas maintenance is performed.
Implementing controls
Applying coatings to scorching surfaces will increase the rate at which the solvents are pushed off. When making use of solvent borne coatings to hot surfaces it have to be assumed that the focus of vapours in the air may exceed the LFL (at least for a quick time after application). As with coating software to ambient temperature metal, controls must be carried out.
While the LFL is likely to be achieved over a shorter time frame throughout scorching software of coatings than coatings work carried out at ambient circumstances, the resulting fire hazard exists in both applications. That is, the fire hazard and related controls should be considered for the appliance of any solvent-borne flammable coating system, regardless of the work setting. It should be recognized that the fuel part of the fireplace tetrahedron might be current in each ‘hot’ and ‘ambient’ environments and primary steps must be taken to attenuate unnecessary solvent vapours within the work space. In addition, as outlined later, consideration must even be directed to eliminating the remaining component of the tetrahedron – the supply of ignition.
Controlling เกจวัดแรงอัดกระบอกสูบ of a fire can be decreased by implementing fundamental controls similar to dealing with and storing flammable liquids in accredited, self-closing containers, maintaining the number of flammable liquids containers in the work area and in storage areas to the minimum needed and inside allowable (regulatory) limits.
Alkaline detergents corresponding to tri-sodium phosphate may be substituted, followed by floor washing with contemporary water or steam cleansing and pH testing of the floor, or non-combustible solvents similar to 1,1,1 trichloroethane) for pre-surface preparation solvent cleaning.
Combustible gas indicators ought to be used to confirm that the concentration of flammable vapours is below the LFL. Combustible gas indicators have to be calibrated in accordance with the manufacturer’s suggestions and have to be accredited to be used in flammable atmospheres. Operators of the equipment should be trained in proper gear operation.
Readings must 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 application work ought to instantly stop till the focus of flammable vapours is controlled. The objective of setting the alarm below the LFL is to supply a security issue that results in control measures being implemented earlier than there is an imminent danger of fireplace or explosion.
Monitoring of the combustible vapour focus will be needed because the effectiveness of natural air flow may be variable. If control of flammable vapours requires mechanical ventilation, an occupational security or health skilled or engineer with experience in industrial air flow ought to be consulted.
At a minimum, mechanical ventilation methods should present sufficient capability to manage flammable vapours to under 10% of the LFL by either exhaust ventilation to take away contaminants from the work area or by dilution air flow via introduction of fresh air to dilute contaminants. As with flamable fuel indicators, air flow gear must be permitted for secure use in flammable atmospheres. In addition, ventilation gear have to be grounded and bonded.
Additional ventilation, if wanted, ought to be continuous during coatings utility as concentrations could increase as more surfaces are coated through the course of a work shift, and particularly on sizzling surfaces the place the rate of vaporization is larger.
Ventilation throughout coatings utility ought to be steady, particularly when engaged on sizzling surfaces.
Sources of Ignition
When making use of coatings to scorching surfaces, the primary source of ignition that readily involves thoughts is the warmth from the surface being painted. The AIT of the coating materials is the one most necessary issue when applying coatings to scorching operating gear. 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 source of ignition is to confirm the surfaces being coated are beneath the AIT of the coatings being applied. While surface temperatures may be known/available in lots of facilities, all surface areas of the process/piping being painted and/or any tools adjacent to the objects being painted the place overspray might deposit ought to be measured for actual surface temperature. The results must be compared to the AIT of the coating system.
While auto-ignition and open sources of ignition could also be readily apparent, a extra delicate but nonetheless important source of ignition to manage on any industrial painting challenge involving flammable solvents entails the manufacturing of static electrical energy. Equipment associated with the spray-painting operation, corresponding to spray utility equipment and air flow gear, can generate static electrical energy.
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 gradual generation of heat from oxidation of natural chemical compounds such as paint solvents is accelerated until the ignition temperature of the gas is reached.
This condition is reached when the fabric is packed loosely allowing a large surface space to be uncovered, there could be enough air circulating around the material for oxidation to happen, but the pure ventilation obtainable is insufficient to carry the heat away quick enough to forestall it from build up.
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