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

Managers of petrochemical, refining, energy, offshore, pulp and paper and other services with extensive hot processes and piping systems are incessantly challenged with performing all the required coatings maintenance work only in periods of outages. Outages are required so that process gear may be properly maintained and repaired including cleaning of pipelines and vessels, upkeep and substitute of pumps, motors and valves, maintenance coating operations, and other work that may solely be completed when the operations are shut down.
When coatings work has to be carried out on areas the place elevated temperatures are concerned, many think that the ability must be shut down. This will not be the case.
A query incessantly posed by facility managers is, “Can I do upkeep painting work whereas the plant is operating?” As described beneath, the reply is, “Yes you can, however there are security and well being points that should be considered”.
Dangers to personnel have to be managed regardless of when or where work is carried out.
Safety and health considerations
There is a range of security and well being hazards that must be thought-about on each industrial upkeep portray project, whether the coating material is being utilized to hot steel or not. Some of those include proper materials handling and storage, fall protection, control of fire and explosion hazards, and publicity to noise, heavy metals, solvents and other well being dangers.
These dangers should be correctly evaluated and managed on each industrial upkeep portray venture, regardless of when or where the work is performed. While current on any job, when applying specialty coatings to sizzling surfaces, some security and health issues should obtain further consideration.
Flammable and combustible liquids in plenty of coatings (solvents) can vaporize and type flammable mixtures in the air, especially when atomized throughout spray application or heated. The degree of hazard depends on the next:
The auto ignition temperature (AIT) of the coating material is the single most essential issue when making use of coatings to sizzling operating gear. AIT is outlined (by the National Safety Council publication Accident Prevention Manual For Business and Industry: Engineering & Technology) as “…the minimal temperature at which a flammable gas-air or vapour-air combination will ignite from its personal heat supply 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 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 words, the flash level describes the temperature of the liquid that’s high enough to generate enough vapour to create a flame if a supply of ignition were introduced.
For vapours of flammable liquids, there’s a minimum focus 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 spread of the flame doesn’t occur. This is the Upper Flammable Limit (UFL). The flammable vary is between the LFL and the UFL, when the focus of vapours can support combustion.
If security procedures are followed, outages is most likely not required while maintenance is carried out.
Implementing controls
Applying coatings to scorching surfaces increases the speed 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 might exceed the LFL (at least for a brief while after application). As with coating application to ambient temperature steel, controls should be implemented.
While the LFL is prone to be achieved over a shorter time frame throughout scorching software of coatings than coatings work carried out at ambient conditions, the ensuing hearth hazard exists in both purposes. That is, the hearth hazard and related controls must be thought-about for the appliance of any solvent-borne flammable coating system, regardless of the work environment. It must be acknowledged that the gasoline part of the fireplace tetrahedron will be current in each ‘hot’ and ‘ambient’ environments and fundamental steps must be taken to reduce unnecessary solvent vapours within the work space. In addition, as outlined later, attention should even be directed to eliminating the remaining element of the tetrahedron – the supply of ignition.
Controlling flammable vapours
The gas factor of a fire can be reduced by implementing primary controls corresponding to handling and storing flammable liquids in permitted, self-closing containers, maintaining the variety of flammable liquids containers within the work area and in storage areas to the minimal necessary and inside allowable (regulatory) limits.
Alkaline detergents such as 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 similar to 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 below the LFL. Combustible gas indicators have to be calibrated in accordance with the manufacturer’s recommendations and must be approved to be used in flammable atmospheres. Operators of the gear should be trained in correct equipment operation.
Readings must 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, units are set to alarm at 10% of the LFL. If the alarm sounds, coatings utility work ought to instantly stop till the focus of flammable vapours is managed. The objective of setting the alarm under the LFL is to supply a safety issue that results in management measures being carried out before there might be an imminent hazard of fireside or explosion.
Monitoring of the flammable vapour concentration will be essential as the effectiveness of natural ventilation may be variable. If control of flammable vapours requires mechanical air flow, an occupational safety or health skilled or engineer with expertise in industrial ventilation should be consulted.
At a minimal, mechanical air flow systems should present adequate capability to manage flammable vapours to under 10% of the LFL by both exhaust air flow to take away contaminants from the work area or by dilution ventilation by way of introduction of fresh air to dilute contaminants. As with flamable fuel indicators, ventilation gear should be accredited for safe use in flammable atmospheres. In addition, air flow tools must be grounded and bonded.
Additional ventilation, if needed, should be continuous during coatings application as concentrations may improve as more surfaces are coated through the course of a work shift, and especially on scorching surfaces the place the rate of vaporization is greater.
Ventilation during coatings utility must be steady, particularly when working on hot surfaces.
Sources of Ignition
When making use of coatings to hot surfaces, the first supply of ignition that readily involves mind is the heat from the surface being painted. pressure gauge 4 นิ้ว ราคา of the coating materials is the single most essential issue when making use of coatings to sizzling operating equipment. The AIT of a substance or combination is the minimum temperature at which a vapour-air combination will ignite when in touch with a heated floor, 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 may be known/available in many facilities, all surface areas of the process/piping being painted and/or any gear adjoining to the gadgets being painted the place overspray might deposit must be measured for actual floor 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 obvious, a extra refined but nonetheless crucial supply of ignition to manage on any industrial portray project involving flammable solvents involves the manufacturing of static electrical energy. Equipment associated with the spray-painting operation, corresponding to spray software tools 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 sluggish era of warmth from oxidation of natural chemicals corresponding to paint solvents is accelerated until the ignition temperature of the gasoline is reached.
This situation is reached when the material is packed loosely permitting a large surface area to be uncovered, there’s sufficient air circulating around the material for oxidation to happen, but the natural air flow available is insufficient to hold the warmth away quick sufficient to forestall it from increase.
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