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

Managers of petrochemical, refining, power, offshore, pulp and paper and different amenities with extensive hot processes and piping systems are incessantly challenged with performing all the necessary coatings maintenance work only during periods of outages. Outages are required so that process tools can be properly maintained and repaired including cleaning of pipelines and vessels, maintenance and substitute of pumps, motors and valves, upkeep coating operations, and other work that may solely be completed when the operations are shut down.
When เกจวัดแรงดันเครื่องกรองน้ำ needs to be carried out on areas the place elevated temperatures are concerned, many suppose that the ability needs to be shut down. This may not be the case.
A question frequently posed by facility managers is, “Can I do maintenance painting work while the plant is operating?” As described beneath, the answer is, “Yes you can, however there are security and health points that have to be considered”.
Dangers to personnel should be managed regardless of when or where work is performed.
Safety and health considerations
There is a spread of security and well being hazards that should be thought of on every industrial maintenance portray venture, whether the coating materials is being applied to hot metal or not. Some of these embody correct materials dealing with and storage, fall protection, control of fire and explosion hazards, and publicity to noise, heavy metals, solvents and other well being risks.
These dangers have to be correctly evaluated and controlled on every industrial maintenance painting project, no matter when or the place the work is performed. While current on any job, when applying specialty coatings to hot surfaces, some security and well being points should receive additional consideration.
Flammable and combustible liquids in plenty of coatings (solvents) can vaporize and type 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 materials is the single most essential concern when making use of coatings to scorching operating gear. 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 mixture will ignite from its own warmth source or contact with a heated floor without the presence of an open spark or flame.”
The idea of flash point as outlined by NFPA 30 is “the minimum temperature of a liquid at which enough vapour is given off to form an ignitable combination with the air, close to the surface of the liquid”. In other phrases, the flash level describes the temperature of the liquid that’s high sufficient to generate sufficient vapour to create a flame if a source of ignition were introduced.
For vapours of flammable liquids, there’s a minimal 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 most concentration of vapour within 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 concentration of vapours can assist combustion.
If security procedures are followed, outages may not be required whereas upkeep is carried out.
Implementing controls
Applying coatings to sizzling surfaces increases the speed at which the solvents are driven off. When making use of solvent borne coatings to sizzling surfaces it must be assumed that the focus of vapours in the air could exceed the LFL (at least for a brief time after application). As with coating utility to ambient temperature steel, controls should be applied.
While the LFL is more likely to be achieved over a shorter time frame throughout hot software of coatings than coatings work performed at ambient conditions, the resulting hearth hazard exists in both applications. That is, the hearth hazard and associated controls should be thought of for the application of any solvent-borne flammable coating system, regardless of the work setting. It must be recognized that the gasoline component of the fire tetrahedron might be current in each ‘hot’ and ‘ambient’ environments and primary steps have to be taken to minimize pointless solvent vapours within the work area. In addition, as outlined later, attention must also be directed to eliminating the remaining element of the tetrahedron – the source of ignition.
Controlling flammable vapours
The gasoline element of a fire could be decreased by implementing basic controls such as dealing with and storing flammable liquids in accredited, self-closing containers, maintaining the number of flammable liquids containers within the work space and in storage areas to the minimal essential and inside allowable (regulatory) limits.
Alkaline detergents similar to tri-sodium phosphate could also be substituted, adopted by floor washing with fresh 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.
Combustible fuel indicators ought to be used to verify that the concentration of flammable vapours is below the LFL. Combustible gas indicators have to be calibrated in accordance with the manufacturer’s recommendations and have to be accredited to be used in flammable atmospheres. Operators of the tools should be educated in correct tools operation.
Readings ought to be taken in the basic work space and the vicinity of the operator and in areas where there are potential sources of ignition. Typically, units 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 function of setting the alarm under the LFL is to provide a security factor that ends in management measures being implemented earlier than there may be an imminent danger of fire or explosion.
Monitoring of the flammable vapour concentration will be needed as the effectiveness of pure air flow may be variable. If management of flammable vapours requires mechanical ventilation, an occupational safety or well being professional or engineer with expertise in industrial air flow ought to be consulted.
At a minimal, mechanical air flow systems ought to present enough capacity to manage flammable vapours to below 10% of the LFL by both exhaust ventilation to remove contaminants from the work space or by dilution air flow via introduction of fresh air to dilute contaminants. As with combustible fuel indicators, air flow gear have to be accredited for protected use in flammable atmospheres. In addition, ventilation tools have to be grounded and bonded.
Additional ventilation, if needed, must be steady throughout coatings software as concentrations might increase as extra 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 should be continuous, particularly when working on sizzling surfaces.
Sources of Ignition
When making use of coatings to sizzling surfaces, the first source of ignition that readily involves thoughts is the warmth from the floor being painted. The AIT of the coating materials is the one most essential concern when making use of coatings to hot operating gear. The AIT of a substance or combination is the minimum temperature at which a vapour-air mixture will ignite when in contact with a heated floor, with out the presence of any open spark or flame.
The key to controlling this source of ignition is to verify the surfaces being coated are beneath the AIT of the coatings being applied. While surface temperatures could also be known/available in lots of services, all floor areas of the process/piping being painted and/or any gear adjoining to the items being painted where overspray might deposit must be measured for precise surface temperature. The results should be in comparison with the AIT of the coating system.
While auto-ignition and open sources of ignition could additionally be readily apparent, a extra subtle but nonetheless important supply of ignition to regulate on any industrial portray challenge involving flammable solvents entails the production of static electrical energy. Equipment related to the spray-painting operation, such as spray utility tools and ventilation equipment, 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 occurs when the slow era of warmth from oxidation of natural chemicals similar to paint solvents is accelerated till the ignition temperature of the fuel is reached.
This situation is reached when the material is packed loosely allowing a large floor space to be exposed, there is enough air circulating around the material for oxidation to occur, but the pure ventilation obtainable is insufficient to carry the warmth away quick sufficient to prevent it from increase.
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