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

Managers of petrochemical, refining, power, offshore, pulp and paper and different facilities with intensive hot processes and piping systems are frequently challenged with performing all the mandatory coatings upkeep work only during periods of outages. Outages are required in order that process equipment may be properly maintained and repaired including cleansing 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 needs to be performed on areas where elevated temperatures are concerned, many think that the facility must be shut down. This will not be the case.
A query frequently posed by facility managers is, “Can I do upkeep painting work whereas the plant is operating?” As described beneath, the answer is, “Yes you can, but there are safety and health issues that have to be considered”.
Dangers to personnel must be managed no matter when or where work is carried out.
Safety and well being concerns
There is a variety of safety and well being hazards that must be considered on each industrial maintenance portray venture, whether or not the coating material is being applied to sizzling metal or not. Some of these include correct materials handling and storage, fall safety, management of fireplace and explosion hazards, and exposure to noise, heavy metals, solvents and other well being dangers.
These risks should be correctly evaluated and controlled on each industrial maintenance painting project, regardless of when or the place the work is carried out. While current on any job, when applying specialty coatings to sizzling surfaces, some security and well being points ought to obtain additional consideration.
Flammable and combustible liquids in many coatings (solvents) can vaporize and kind flammable mixtures in the air, especially when atomized throughout spray utility or heated. The diploma of hazard depends on the following:
The auto ignition temperature (AIT) of the coating material is the one most essential problem when applying coatings to scorching working equipment. 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 source or contact with a heated surface without the presence of an open spark or flame.”
The concept of flash level as defined by NFPA 30 is “the minimum temperature of a liquid at which adequate vapour is given off to type an ignitable combination with the air, close to the floor of the liquid”. In different phrases, the flash point describes the temperature of the liquid that is excessive sufficient to generate enough vapour to create a flame if a supply of ignition have been introduced.
For vapours of flammable liquids, there is a minimum concentration below which the spread of the flame does not happen when involved with a supply of ignition. This is the Lower Flammable Limit (LFL). There is a maximum focus of vapour within the air above which the spread of the flame doesn’t occur. This is the Upper Flammable Limit (UFL). The flammable range is between the LFL and the UFL, when the focus of vapours can help combustion.
If security procedures are adopted, outages may not be required while maintenance is carried out.
Implementing controls
Applying coatings to sizzling surfaces will increase the speed at which the solvents are pushed off. When applying solvent borne coatings to hot surfaces it must be assumed that the concentration of vapours within the air may exceed the LFL (at least for a brief time after application). As with coating utility to ambient temperature steel, controls should be implemented.
While the LFL is likely to be achieved over a shorter time period during scorching software of coatings than coatings work carried out at ambient situations, the ensuing hearth hazard exists in each functions. That is, the fire hazard and related controls must be considered for the appliance of any solvent-borne flammable coating system, whatever the work environment. เกจ์วัดแรงดันแก๊ส should be recognized that the gasoline element of the fire tetrahedron might be current in both ‘hot’ and ‘ambient’ environments and primary steps should be taken to reduce unnecessary solvent vapours in the work area. In addition, as outlined later, consideration should also be directed to eliminating the remaining component of the tetrahedron – the source of ignition.
Controlling flammable vapours
The fuel factor of a hearth can be reduced by implementing primary controls corresponding to dealing with and storing flammable liquids in accredited, self-closing containers, preserving the number of flammable liquids containers in the work area and in storage areas to the minimal needed and within allowable (regulatory) limits.
Alkaline detergents such as tri-sodium phosphate may be substituted, followed by surface washing with fresh 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 gasoline indicators ought to be used to verify that the focus of flammable vapours is beneath the LFL. Combustible fuel indicators have to be calibrated in accordance with the manufacturer’s recommendations and have to be approved to be used in flammable atmospheres. Operators of the equipment have to be educated in correct tools operation.
Readings must be taken within the basic work area and the vicinity of the operator and in areas the place there are potential sources of ignition. Typically, items are set to alarm at 10% of the LFL. If the alarm sounds, coatings utility work ought to immediately cease till the concentration of flammable vapours is managed. The purpose of setting the alarm beneath the LFL is to provide a safety issue that leads to control measures being carried out earlier than there is an imminent danger of fire or explosion.
Monitoring of the combustible vapour concentration shall be needed as the effectiveness of natural air flow may be variable. If management of flammable vapours requires mechanical air flow, an occupational safety or well being skilled or engineer with expertise in industrial air flow should be consulted.
At a minimal, mechanical air flow techniques should provide adequate capability to manage flammable vapours to below 10% of the LFL by both exhaust air flow to take away contaminants from the work space or by dilution ventilation via introduction of recent air to dilute contaminants. As with flamable gas indicators, ventilation gear must be accredited for safe use in flammable atmospheres. In addition, ventilation tools must be grounded and bonded.
Additional air flow, if wanted, ought to be continuous throughout coatings software as concentrations could improve as extra surfaces are coated in the course of the course of a piece shift, and particularly on sizzling surfaces the place the speed of vaporization is higher.
Ventilation during coatings utility should be continuous, especially when working on sizzling surfaces.
Sources of Ignition
When making use of coatings to hot surfaces, the first supply of ignition that readily involves mind is the warmth from the surface being painted. The AIT of the coating materials is the one most essential problem when applying coatings to hot working equipment. The AIT of a substance or combination is the minimum temperature at which a vapour-air combination will ignite when involved with a heated surface, without 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 could additionally be known/available in lots of facilities, all surface areas of the process/piping being painted and/or any gear adjoining to the gadgets being painted where overspray might deposit ought to be measured for precise surface temperature. The outcomes should be in comparability with the AIT of the coating system.
While auto-ignition and open sources of ignition may be readily obvious, a more delicate however nonetheless crucial supply of ignition to control on any industrial portray venture involving flammable solvents involves the production of static electrical energy. Equipment associated with the spray-painting operation, similar to spray application tools and air flow equipment, can generate static electricity.
In addition to exterior sources of ignition, spontaneous ignition can happen when rags or wastes soaked with paint solvents are left in open containers. Spontaneous ignition occurs when the sluggish technology of warmth from oxidation of organic chemical substances 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 permitting a large surface space to be uncovered, there could be sufficient air circulating around the material for oxidation to happen, however the pure air flow available is insufficient to hold the heat away quick sufficient to stop it from build up.
For more info, go to www.ppgpmc.com/Oil-Gas-Chemical.aspx
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