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

Managers of petrochemical, refining, energy, offshore, pulp and paper and different facilities with extensive hot processes and piping systems are frequently challenged with performing all the mandatory coatings upkeep work solely in periods of outages. Outages are required so that process gear may be properly maintained and repaired together with cleaning of pipelines and vessels, maintenance and alternative of pumps, motors and valves, upkeep coating operations, and other work that may only be completed when the operations are shut down.
When coatings work must be performed on areas the place elevated temperatures are concerned, many suppose that the facility has to be shut down. This is in all probability not the case.
A query incessantly posed by facility managers is, “Can I do upkeep portray work while the plant is operating?” As described beneath, the answer is, “Yes you’ll find a way to, however there are safety and well being issues that should be considered”.
Dangers to personnel have to be managed regardless of when or where work is carried out.
Safety and health issues

There is a variety of safety and well being hazards that should be thought-about on every industrial maintenance portray venture, whether or not the coating materials is being utilized to hot steel or not. Some of these embody correct material dealing with and storage, fall safety, control of fire and explosion hazards, and publicity to noise, heavy metals, solvents and different well being risks.
These dangers must be properly evaluated and controlled on each industrial upkeep painting challenge, regardless of when or the place the work is performed. While current on any job, when applying specialty coatings to sizzling surfaces, some security and well being issues should obtain additional consideration.
Flammable and flamable liquids in many coatings (solvents) can vaporize and kind flammable mixtures in the air, especially when atomized during spray software or heated. The degree of hazard is dependent upon the next:
The auto ignition temperature (AIT) of the coating materials is the one most necessary issue when making use of coatings to scorching working equipment. 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 own warmth supply or contact with a heated floor with out the presence of an open spark or flame.”

The concept of flash point as outlined by NFPA 30 is “the minimal temperature of a liquid at which enough 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 is excessive sufficient to generate sufficient vapour to create a flame if a source of ignition have been launched.
For vapours of flammable liquids, there’s a minimal concentration below which the unfold of the flame does not occur when in contact with a supply of ignition. This is the Lower Flammable Limit (LFL). There is a maximum concentration of vapour in the air above which the unfold of the flame doesn’t happen. This is the Upper Flammable Limit (UFL). The flammable vary is between the LFL and the UFL, when the concentration of vapours can assist combustion.
If safety procedures are followed, outages will not be required while upkeep is performed.
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 within the air may exceed the LFL (at least for a brief while after application). As with coating utility to ambient temperature metal, controls must be applied.
While the LFL is prone to be achieved over a shorter time period throughout scorching software of coatings than coatings work performed at ambient conditions, the ensuing fireplace hazard exists in each functions. That is, the hearth hazard and associated controls must be thought of for the applying of any solvent-borne flammable coating system, whatever the work setting. It should be acknowledged that the gas part of the hearth tetrahedron shall be current in both ‘hot’ and ‘ambient’ environments and primary steps must be taken to attenuate unnecessary solvent vapours within the work area. In addition, as outlined later, consideration should even be directed to eliminating the remaining element of the tetrahedron – the source of ignition.
Controlling flammable vapours

The gasoline element of a fire may be decreased by implementing primary controls similar to handling and storing flammable liquids in permitted, self-closing containers, keeping the number of flammable liquids containers within the work space and in storage areas to the minimum needed and inside allowable (regulatory) limits.
Alkaline detergents similar to tri-sodium phosphate could additionally be substituted, followed by surface washing with recent water or steam cleansing and pH testing of the floor, or non-combustible solvents corresponding to 1,1,1 trichloroethane) for pre-surface preparation solvent cleansing.
เกจวัดแรงดัน ought to be used to verify that the concentration of flammable vapours is under the LFL. Combustible gas indicators have to be calibrated in accordance with the manufacturer’s suggestions and should be permitted to be used in flammable atmospheres. Operators of the tools must be educated in correct tools operation.
Readings should be taken in the basic work space and the vicinity of the operator and in areas where there are potential sources of ignition. Typically, items are set to alarm at 10% of the LFL. If the alarm sounds, coatings application work ought to instantly stop until the focus of flammable vapours is managed. The objective of setting the alarm under the LFL is to supply a safety issue that leads to control measures being implemented earlier than there is an imminent hazard of fire or explosion.
Monitoring of the combustible vapour focus will be necessary because the effectiveness of pure air flow could additionally be variable. If management of flammable vapours requires mechanical air flow, an occupational security or well being professional or engineer with experience in industrial air flow ought to be consulted.
At a minimum, mechanical air flow systems ought to present enough capacity to manage flammable vapours to beneath 10% of the LFL by both exhaust air flow to take away contaminants from the work area or by dilution air flow by way of introduction of contemporary air to dilute contaminants. As with combustible fuel indicators, air flow equipment must be approved for protected use in flammable atmospheres. In addition, air flow tools should be grounded and bonded.
Additional air flow, if needed, ought to be steady during coatings utility as concentrations may increase as extra surfaces are coated through the course of a piece shift, and particularly on sizzling surfaces the place the speed of vaporization is higher.
Ventilation throughout coatings software should be continuous, especially when working on hot surfaces.
Sources of Ignition

When applying coatings to scorching surfaces, the primary source of ignition that readily comes to thoughts is the warmth from the floor being painted. The AIT of the coating material is the one most essential problem when making use of coatings to sizzling operating equipment. The AIT of a substance or combination is the minimal temperature at which a vapour-air mixture will ignite when in contact 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 applied. While floor temperatures could also be known/available in many amenities, all surface areas of the process/piping being painted and/or any gear adjacent to the items being painted the place overspray might deposit ought to be measured for actual surface temperature. The results should be in comparison with the AIT of the coating system.
While auto-ignition and open sources of ignition could also be readily apparent, a extra delicate but nonetheless crucial supply of ignition to control on any industrial painting project involving flammable solvents includes the production of static electricity. Equipment associated with the spray-painting operation, corresponding to spray software gear and ventilation tools, can generate static electricity.
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 occurs when the gradual generation of warmth from oxidation of organic chemicals such as paint solvents is accelerated until the ignition temperature of the gasoline is reached.
This situation is reached when the material is packed loosely allowing a large floor area to be uncovered, there’s sufficient air circulating across the material for oxidation to happen, but the natural ventilation available is insufficient to carry the heat away fast enough to prevent it from increase.
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