General Tank Coating Code of Practice for New Constructions and Refurbishments Issue April 2008 FOREWORD The intention of this Code of Practice is to highlight the vital factors regarding planning and execution of work by the use of protective coatings in aggressive tank environments. Valuable, and in theory sufficient, information regarding this can be found in the technical data sheets for the products to be used. However, it has been found required to present some more background information to secure that the personnel involved understand and practise the requirements set forth in tank projects. In order to obtain maximum coating performance, factors like surface cleanliness and profile, a continuous paint film of appropriate thickness and proper curing of the coating system are all of high importance. We would also mention the maintenance of a safe working environment. This will provide good working conditions and thereby form a sound basis for achievement of the required final quality. Jotun will underline that a coating system’s performance is determined by the skill and knowledge of personnel involved in the work procedures. One cannot take for granted that a painting contractor, although well reputed, possesses the special competence required for the surface preparation, coating application or other operations involved in tank coating. Furthermore, most coating failures are the result of simple omissions and application errors. Coating successes, on the other hand, are the result of thorough planning and skilled craftsmanship. This Code of Practice addresses critical factors of special importance to obtain the maximum protective lifetime of Jotun’s coatings. It does not contain detailed descriptions of various procedures in the coating process. Its intention is rather to pinpoint the individual elements that may have great impact on the coating’s performance in the long run. Following these guidelines will help the smooth running of any coating project. However, because local conditions differ around the world, discussion with Jotun’s local Technical Sales Support department is recommended on any contentious subjects. General Tank Coating Code of Practice Issue April 2008 Page 2 of 24 CONTENTS Foreword Contents Scope and field of application General 2 3 4 5 The Painting Contractor The Coating Advisor The Owner’s representative The Contractor (shipyard or construction company) Jotun Technical Sales Support department Rules for cooperation Planning Pre-project meeting Follow-up meetings 5 5 5 5 5 5 6 6 6 Tank condition prior to work start-up Scaffolding 7 8 4.1 4.2 4.3 General Access Dismantling and removal 8 8 8 Basic work sequence for tank coating 9 5.1 5.2 New constructions Refurbishment 9 10 Surface preparation 11 6.1 6.2 6.3 6.4 6.4.1 6.4.2 6.5 6.5.1 6.5.2 6.5.3 6.5.4 6.6 6.7 General Pre-blasting welds (for tanks in block sections) Steel preparation work Degreasing and cleaning General recommendations Washing procedures Abrasive blast cleaning Ambient conditions, ventilation and protection from rain Abrasives Air supply Removal of dust and abrasives Steel surface assessment prior to coating application Boiler suits etc 11 11 11 12 12 12 13 13 13 14 14 14 15 Coating application 16 7.1 7.2 7.3 7.4 General Film thickness, types and number of coats Ambient conditions Ventilation and dehumidification 16 16 17 17 Health and Safety 19 8.1 8.2 8.3 8.4 8.5 8.5.1 8.5.2 8.5.3 8.5.4 General Safety preparations Scaffolding safety Elimination of ignition sources Management of solvent vapour concentration General advice Ventilation and air exchange Finding the required ventilation rate Monitoring the ventilation system 19 19 19 20 21 21 21 22 24 1 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3 4 5 6 7 8 General Tank Coating Code of Practice Issue April 2008 Click on Chapter/Sub-chapter in Contents to go to relevant page. To return to Contents page click on bottom left heading ‘General Tank Coating Code of Practice.’ Page 3 of 24 1. Scope and field of application This Code of Practice deals with various aspects related to protection of steel, exposed to aggressive water or cargo of different kinds, by use of specialized coatings. It lays down a set of rules required to obtain optimal service life of coatings in corrosive environments. The document treats tanks both at the new building / block stage and at the refurbishment stage. This Code of Practice is intended both for marine, offshore and land based tanks. The principles are the same, although choice of products and practical arrangements may differ. Requirements that are found in each product’s technical or safety data sheet are not included in the present document. General Tank Coating Code of Practice Issue April 2008 Page 4 of 24 2 General 2.1 The Painting Contractor The Painting Contractor is responsible for carrying out the work in accordance with the relevant technical data sheets and coating specification. He shall take corrective action in the case of non-compliance with specifications. The Painting Contractor is the party employed to carry out the part of the project that includes surface preparation and application of the coating system. The Painting Contractor selected for surface preparation and application of the coating system should be an organisation approved by Owner, Contractor (i.e. the company constructing the tank) and Jotun. 2.2 The Coating Advisor The Coating Advisor acts on behalf of Jotun to secure and record that all work is carried out in accordance with the agreed specifications; cooperating with the Contractor’s and Owner’s coating representatives. 2.3 The Owner’s representative The Owner’s Representative is authorised to represent the Owner in matters related to the coating operation. In particular, he is responsible for providing written confirmation to the Contractor and Jotun of all intended use of the tanks to be coated. 2.4 The Contractor (shipyard or construction company) The Contractor is responsible for all repairs of damage to the coating system caused by welding, burning, mechanical impact etc. 2.5 Jotun Technical Sales Support department The Technical Sales Support department of Jotun shall assist in technical matters regarding special circumstances that might occur during the coating operation and afterwards. 2.6 Rules for cooperation All work should be performed in accordance with this Code of Practice, Jotun’s Technical Data Sheets and the coating specification. Proposed alterations to the specification or work procedures must be approved by all parties before a written alteration to the relevant document is issued and distributed. General Tank Coating Code of Practice Issue April 2008 Page 5 of 24 2.7 Planning A proper planning of the entire operation is absolutely critical for successful work performance, which in turn is a prerequisite for obtaining optimal protection by the applied coating system. Planning must cover all phases of the coating operation and its intention shall be to secure the correct quality of work and a safe working environment. A detailed work plan should include the scheduling of all operations to be carried out before, during and after application of the coating system. The work plan should be available to the Coating Advisor prior to the start of any work related to the coating operation. 2.8 Pre-project meeting A pre-project preliminary meeting shall be arranged before any coating-related work starts. Representation from all involved parties; Owner, Contractor, Painting Contractor and Jotun is compulsory. The pre-project meeting must settle all matters of importance to the scope of work, and make available all documentation necessary to carry out the work in accordance with the requirements and specifications. The Coating Advisor and/or other Jotun Representatives shall use this meeting to ensure that the other parties are familiar with the products to be used, the coating specification, safety data sheets etc. Furthermore, responsibilities are to be stressed, i.e. possible consequences of any non-conformances, and the Painting Contractor’s obligation to follow up his own work during the whole operation, including compliance with Jotun’s specifications. 2.9 Follow-up meetings Decisions about regular follow-up meetings are also to be made in the preproject preliminary meeting. Meeting frequency and participation shall be agreed upon. The follow-up meetings should be set to discuss or review the following points: • Unpredictable difficulties hindering the ordinary work progress • Deviations from specifications • Elements to add to, or delete from, the work schedule • Conditions effecting compliance with specification General Tank Coating Code of Practice Issue April 2008 Page 6 of 24 3 Tank condition prior to work start-up Before starting the work it is essential that the tanks are in a suitable condition. All vulnerable fittings should be masked off with a suitable protective material to avoid possible damage. All hot work within the tank and at its outside must be completed before grit blasting takes place (in order to avoid formation of mill scale and weld fumes, which is not easily removed by grit blasting). It shall be understood by all parties that illumination will be a critical prerequisite to achieve the correct coating quality, safely and in good time. Adequate electrically safe illumination by means of both spotlights and background lights must be available, and accepted by the coating inspector. General Tank Coating Code of Practice Issue April 2008 Page 7 of 24 4 Scaffolding 4.1 General A suitable and safe system for temporary scaffolding is to be provided. The construction shall permit easy cleaning operations. It should be possible to conveniently ‘turn’ all boards so that grit and dust can be easily removed. Scaffolding tubes are to be capped at open ends using wooden or hard rubber stoppers. Taping the ends is not recommended. 4.2 Access The scaffolds must provide free access to all surfaces to be treated without having to move planks or erect temporary ladders. It must also provide adequate working space and support for the maximum numbers of workers. The scaffold design must not hinder ventilation in any way. The scaffolds shall have a minimum distance of 30 cm to surfaces to be treated, and about 2 m between each level. Sufficient space should be available, allowing the operator to do his work properly, and to move from level to level fast and efficiently. 4.3 Dismantling and removal The scaffolds shall not be dismantled before the upper areas of the tank have been fully coated and accepted. The utmost care not to destroy the coating must be taken during dismantling and removal. Any damage to the coating should be repaired in accordance with the original specification. General Tank Coating Code of Practice Issue April 2008 Page 8 of 24 5 Basic work sequence for tank coating 5.1 New constructions There are a few internationally accepted principles that apply for all coatings work. For a specific project these principles must be kept in mind even if the situation seems difficult and not ideal for coating work. The general sequence is: • Steel repair work (if required), removal of weld spatter and sharp edges etc • Solvent washing, in order to remove fat and oil (i.e. dirt that is solvent soluble) • Water washing, to remove dirt that is water soluble. (This includes weld fumes and salts.) Use of an alkaline detergent will also remove minor amounts of oil and fat. • Blast cleaning to obtain a suitable roughness for the coating to adhere well. • Dust and grit removal • Paint application The order is important. If, for instance, blast cleaning is done prior to washing, the contaminants will be smeared into the surface, and the subsequent washing will probably not remove them adequately. For ships where the ballast tanks are constructed as integral parts of block sections, coating work will take place both at the block stage and at the assembly stage. Hence, one may find it required to repeat some of the steps above. For all new building projects it may be difficult to obtain a satisfactory steel surface roughness at all places. In particular, the erection joint welding seams and plate edges that have been made by flame cutting may not have the desired roughness. If possible, manual grinding should be undertaken if no other means are acceptable. As soon as possible after the surface pre treatment, the first coat of paint should be applied all over the tank. In this way one avoids that bare steel areas are left uncoated for prolonged times, possibly resulting in contamination and rusting. After a first coat the normal procedure will be to apply two stripe coats, each in a contrasting colour, before the next full coat. For a tank coating job the tank may be split is sections, where the work is finished section wise. A typical situation may be that the upper part of the tank is being coated while leaving the lower part untreated or partly coated and protected by a temporary shield. General Tank Coating Code of Practice Issue April 2008 Page 9 of 24 After the coating work is done one may require a test to check for holidays. For ships the tank is filled with seawater for a day or two, and inspected after drainage. Touch up at spots revealing rust is then to be undertaken. Alternatively, high or low voltage holiday detection may be employed for the same purpose. There also exist specially pigmented coatings where holidays may be detected by shining ultra violet light onto the surface. 5.2 Refurbishment For refurbishment blast cleaning may not be permitted, and water jetting with or without abrasives may be an alternative. In this case it must be ensured that the water is sufficiently clean, and the pressure at the nozzle high enough to ensure an adequate cleaning result. A thorough water removal (as well as removal of the abrasives, if employed) and drying must be made as soon as the water jetting is finished, in order to avoid flash rust. A drawback associated with water jetting is that it does not produce roughness. Insufficient steel work at the new building stage may thus have consequences for the coating work at subsequent refurbishment jobs. As can be concluded from the considerations above, wet abrasive blasting will be efficient both with regard to removing dirt and salts, produce roughness and maintain a good working environment (without the blast cleaning dust problem), all in one operation. However, the practical arrangements required in order to remove wet grit from a tank may prevent widespread use of the wet abrasive blasting method. The existing tank coating must be assessed with regard to type and present condition. Its compatibility with the new system must be verified. Care should also be taken to obtain a smooth overlap between the old coating and bare steel areas resulting from paint damage. It may be necessary to sweep blast or in other ways roughen the surface, as well as cleaning it. General Tank Coating Code of Practice Issue April 2008 Page 10 of 24 6 Surface preparation 6.1 General The cleanliness and surface roughness shall be assessed according to the ISO 8501 and 8503-2 standards, respectively, unless otherwise specified in the technical data sheets. Some coatings may be applied onto surfaces that are cleaned by way of Water Jetting or Wet Abrasive Blast Cleaning. For these surfaces reference is made to SSPC-VIS 4 / NACE VIS 7 and SSPC-VIS 5 / NACE VIS 9, respectively. For a tank where a previous coating is not being removed (e.g. a shop primer, or at refurbishment), special care must be taken not to damage this coating. On the other hand, the old coating must be made thoroughly clean. Fresh water washing, when required also with solvent borne or water borne detergents should be employed as required. Similarly, sweep blasting or other means of creating a rough surface may be required to obtain sufficient adhesion. Likewise, sweep blasting must be done when an old glossy and hard coating, typically a coal tar epoxy coating, is to be re-coated. Instead of sweep blasting sand paper (or emery paper) may be employed in order to obtain sufficient surface roughness of old paint. 6.2 Pre-blasting welds (for tanks in block sections) Prior to the steel preparation work all welds should be blast cleaned to visual cleanliness standard Sa 2½ ISO 8501:1 1988. This is in order to open any hidden weld blowholes, and to facilitate fast and efficient detection of steel surface defects thereafter. Grit and dust must be removed after the pre-blasting. 6.3 Steel preparation work The steel should be prepared so that a smooth surface contour is obtained. This is a prerequisite for obtaining a continuous coating of appropriate thickness. Sharp edges should be rounded by using a grinder or disc sander to get approximately 2 mm radius as a minimum (r =2 mm). Practically this can be obtained by way of three passes with a grinding tool on the edges. Weld spatter must be thoroughly removed. Undercuts and surface indentations with a depth exceeding 0.8 mm and a width less than its depth should be repaired by welding and grinding. Weld blowholes shall be repaired by welding and grinding. General Tank Coating Code of Practice Issue April 2008 Page 11 of 24 Rough weld seams are to be smoothed by grinding. The surface irregularities should not exceed 2 mm. Overlap welding beads with sharp notches are to be repaired by welding and grinding. Gas cut surfaces must be smoothed by grinding. Air driven tools for steel repair and cleaning are commonly oil lubricated, and oil may come out of the exhaust pipe within the tank. Special care should be taken to avoid this. Any oil contamination must be thoroughly removed by use of a suitable solvent after steel repair and smoothing / cleaning work. If the steel repair work will not be succeeded by blast cleaning, steps should be taken to produce some roughness at this stage. Grinding roundels, fibre discs with particles (‘Scotch-Brite Clean N Strip’ wheels, or equivalents) and sand paper should be considered. Wire brushes should be avoided, as the wires will tend to polish the steel surface rather than create roughness. 6.4 Degreasing and cleaning 6.4.1 General recommendations Degreasing and cleaning shall be carried out prior to grit blasting in order to prevent contamination of the steel during blasting. Both organic (grease and oil) and inorganic (particularly salts) contaminations should be removed before blast cleaning. If blasting is done prior to cleaning; grease, oil, salt and dirt may be smeared into the roughened steel surface thus making subsequent cleaning difficult and time consuming. For this reason it is, in case of refurbishment jobs, important to break any intact blisters before washing is performed, so that the blister contents may be removed. Verification that the steel surface is sufficiently clean should, however, be done after grit blasting (or water jetting) has taken place. This is in order to ensure that the blasting / jetting process has not contaminated the surface after the degreasing and cleaning operations. 6.4.2 Washing procedures Remove oil and grease deposits using scrubbing brushes and a water-based alkaline degreasing detergent. Repeat this process until water no longer ‘snakes’ or ‘beads’ when poured down the surface. After degreasing, all tank surfaces must be high-pressure fresh water washed to remove traces of detergent and contaminations such as acidic weld smoke residues and traces of sea water salts. These species will, beneath a coating, lead to blistering by an osmotic effect. General Tank Coating Code of Practice Issue April 2008 Page 12 of 24 For large areas, apply the detergent through airless spray equipment. Start at the bottom of the tank and work upwards. After the detergent has been on the surface for 20-30 minutes, it should be rinsed off by steam-cleaning (preferably) or by high-pressure water washing. The water used for steam cleaning or water washing must be of a suitable quality and approved by Jotun in advance. The rinsing should start at the bottom of the tank and go upwards, following the course taken when applying the detergent. All detergent should be thoroughly removed so that no foaming occurs when water is applied to the surface. Note: Why start cleaning at the bottom, moving upwards? Because this will make the surface more evenly clean. If one starts at the top the dirt will tend to accumulate on the lower areas. 6.5 Abrasive blast cleaning 6.5.1 Ambient conditions, ventilation and protection from rain and dust Condensation of water onto the steel surface must be avoided during blast cleaning. Hence the steel temperature must be kept at least 3ºC above the dew point of air. The relative humidity must be kept sufficiently low throughout the blasting operation until immediately prior to application of the first coat. If required, this must be accomplished by way of dehumidification equipment. Care should be taken to produce a positive pressure inside the tank, so that no moist air from the outside will get into the tank. During the grit blasting operation, forced ventilation may be required to give adequate visibility for the operator. A flexible ventilation system should be used to get dusty air out, and fresh air in. In connection with manholes, ladders and tank entrances adequate covering must be provided to prevent water, dust or other contaminants from entering the work areas during grit blasting and thereafter. In the case of wet abrasive blasting the relative humidity requirements become irrelevant. However, to suppress the tendency to flash rusting, the tank should be dried to max 85% relative humidity as soon as possible after blasting. 6.5.2 Abrasives The selected abrasive medium must be compatible with both the surface to be blast cleaned and the specified coating system. The abrasives shall meet relevant specifications as per ISO 11124-2 & 3 (metallic abrasives), or ISO 11126-2 to 8 (non-metallic abrasives). Sampling for check should be done according to ISO 11125-1 (metallic) or ISO 11127-1 (non-metallic), and tested according to ISO 11125-2 to 7 or ISO 11127-2 to 7 as appropriate. General Tank Coating Code of Practice Issue April 2008 Page 13 of 24 The abrasives and the blasting equipment should be stored in a dry place in order to prevent moisture pickup thus resulting in clogging. Recycling of used abrasives is prohibited unless approved by Jotun. 6.5.3 Air supply A minimum air pressure of 7 bar at the nozzle is required to obtain acceptable surface cleanliness and profile within an acceptable time frame. The supply of clean air to the blasting pots must be secured to avoid contamination of the abrasives and thereby the blast cleaned surfaces. Compressors must be fitted with sufficient traps for oil and water. It is also recommended to fit two water separators in succession at the blasting machine to ensure a supply of moisturefree air to the abrasive chamber. 6.5.4 Removal of dust and abrasives Surface preparation shall not be considered complete until the blast cleaned surface is free of dust and particles that may remain on the surface. Vacuum cleaning will be required. A recommended practice is to employ stiff fibre brushing followed by vacuum cleaning, or to attach a stiff brush around the vacuum nozzle orifice in order to agitate dust away from the surface. The operation shall start at the top of the tank and proceed downwards, finishing with the removal of dust from the tank floor. This procedure is applicable for the scaffolds as well. Scaffolding planks must be vacuum cleaned, turned, and vacuum cleaned again. Any ends of tubular parts of scaffolding that have accidentally been opened shall be vacuum cleaned at the entrance and then closed with wooden or hard rubber plugs. 6.6 Steel surface assessment prior to coating application There are no standardised methods for the quantitative determination of grease or oil on cleaned surfaces. This should raise caution (rather than neglect) during the cleaning operation. As described in section 6.4.2 Washing procedures, washing should continue until the wash water no longer ‘snakes’ or ‘beads’ when poured down the steel surface. (A rough test, used extensively in the old days, is to draw a piece of chalk across the steel. Where the chalk does not adhere to the steel, fatty compounds are present.) General Tank Coating Code of Practice Issue April 2008 Page 14 of 24 Contrary to this there are several methods for a quantitative determination of soluble salts on a steel surface. A practical field method is the ISO 8502-6 Bresle sampling method for conductivity testing. The measured conductivity value is converted to milligram salt per square metre steel surface by way of a simple calculation. The water-soluble salts (particularly sodium chloride, NaCl) remaining on a blast-cleaned surface immediately prior to a coating application should not exceed 80 mg/m2 (8 µg/cm2). (taking only the chloride part of the salts this is equivalent to 48 mg/m2 or 4.8 µg/cm2.) These limits are for ship’s ballast tanks. For ship’s other tanks the limit is 50 mg/m2 (30mg/m2 as chloride). The limits are based on Jotun’s experience with ship’s tank coating. For other objects there may be other limits. The NORSOK standard M-501 ‘ Surface preparation and protective coating’ specifies max 20 mg/m2 NaCl for ‘ offshore installations and associated facilities’. The NORSOK specification is limited to new steel constructions. For ‘old’ steel (i.e. refurbishment) one has experienced that it is difficult to obtain as low salt levels as for new steel, due to the surface degradation. Salt determination shall be done by the ISO 8502-6 method using the Bresle sampling equipment . Bresle sampling and testing should be carried out randomly, but with an emphasis on places that typically have higher salt levels: flat horizontal surfaces, corners and the tank floor. The number of tests per tank should be discussed and agreed in the pre-project meeting. Depending on the size of the tank, a suitable number of tests could be one test for every 150-300 m². If the tank is found to have too high surface salt levels, re-washing must be done. Dust remaining on the steel surface may give poor coating adhesion. The dust level can be determined by way of ISO 8502-3:1992 ‘Assessment of dust on steel surfaces prepared for painting (pressure-sensitive tape method)’. 6.7 Boiler suits etc When the tank has been cleaned and is ready for further treatment it is important to avoid steel surface contamination by way of dirty boiler suits and shoes etc. All efforts should also be made to avoid human sweat falling onto the clean steel or painted surfaces which are due to be painted again. Personnel entering the tank after grit blasting must wear foot covers. General Tank Coating Code of Practice Issue April 2008 Page 15 of 24 7 Coating application 7.1 General All work in adjacent areas, which may negatively affect the quality of the coating application, or imply safety hazards, should be completed or stopped before starting the coating application. It is vitally important that sufficient ventilation, dehumidification, heating equipment and lighting is provided to meet conditions as described in the technical data sheets, this Code of Practice, and regulations given by relevant authorities. For additional information on how to provide a safe environment for tank coating application reference is made to section 8 of this Code of Practice. The steel surface conditions must be as described in the previous section, and following the agreed specifications for the project. 7.2 Film thickness, types and number of coats It is considered important to avoid excessively thick coatings. Too thick coatings are more prone to cracking and blistering due to mechanical stress and solvent entrapment. Therefore the recommendations in the technical data sheets shall be strictly adhered to. Stripe coating should be made by use of a brush. Use of a spray gun for stripe coating will easily lead to too high film thickness. Further, brush application is considered more efficient in getting the paint into all narrow crevices etc. Roller application is only permitted in scallops and rat holes where even a brush would not be suitable. Consequently the following application sequence is recommended: • 1st full primer coat applied by spray • 1st stripe coat applied by brush • 2nd stripe coat applied by brush • 2nd ordinary primer coat applied by spray • Touch up, if required The 1st full coat should be applied before stripe coating so that most of the steel is coated in its best condition – as soon as possible after grit blasting. Delaying the first full coat application leads to increased possibility for contamination of the steel with dirt, dust and human sweat. The 1st stripe coat should have the same colour as the 2nd full coat. General Tank Coating Code of Practice Issue April 2008 Page 16 of 24 The purpose of the 1st stripe coat is to cover plate edges, bare spots etc after the 1st coat application. The 2nd stripe coat should be applied where the coating thickness may be not sufficient. Typically this will be on top of the 1st stripe coat, but it can also be applied to areas where a DFT measurement has shown insufficient first coat thickness. For ease of inspection – and for ease of application, the 2nd stripe coat should have the same colour as the 1st full coat. By doing this the 2nd full coat will be applied to a surface of uniform colour. When a three-coat system is specified, the last coat should preferably have a colour different from the 2nd coat, in order to secure that all areas receive the last coat as well. 7.3 Ambient conditions The steel temperature must be kept at least 3ºC above the dew point when the paint is applied. Requirements to the air relative humidity (RH) are given in the relevant technical data sheets. The temperature must also be sufficiently high for the paint to cure within the required time, as given in the technical data sheet. 7.4 Ventilation and dehumidification Good ventilation, meaning sufficient air supply and air exchange in all parts of the coated object is required to remove solvent vapours and thereby promote solvent evaporation and coating cure. Ventilation must be maintained during the paint application and continue throughout the drying period as long as solvents are released from the paint film. When the ventilation is so arranged that fresh air is blown into the tank (i.e., a positive pressure is obtained), dust and other contaminants may be prevented from entering the tank. General Tank Coating Code of Practice Issue April 2008 Page 17 of 24 Examples of good ventilation arrangements General Tank Coating Code of Practice Issue April 2008 Page 18 of 24 8 Health and Safety 8.1 General Safety is the overriding consideration for all tank coating work, and the responsible Contractor’s Safety Officer must be made fully aware of all aspects of the operation, and all potential dangers. Detailed attention must be given to the following dangers: • Explosion or fire • Lack of oxygen in the tank atmosphere • Asphyxiation / suffocation by solvent fumes • Falling down from the scaffolds • Skin damage from toxic coating materials 8.2 Safety preparations Safety matters shall be on the agenda in the preliminary pre-project meeting. All safety requirements and rules shall be agreed upon and made available for all parties involved. The Painting Contractor should be pre-qualified, and his operational staff certified through a safety programme to ensure that the staff is familiar with safety and operational procedures. The personnel must also be trained in the Contractor’s emergency procedures. Before the coating work starts, authorised personnel from the Contractor shall review the work arrangements of the Painting Contractor to ensure that no procedure that could endanger any person’s health will take place. The Coating Advisor shall be provided with safety regulations valid for the Contractor’s plant. The Contractor and Painting Contractor must be provided with Jotun’s safety data sheets. 8.3 Scaffolding safety A suitable and safe system for scaffolding must be provided. The scaffolds must provide free access to all surfaces to be treated without replacing planks or erecting temporary ladders. It must also provide adequate working space and support for the maximum number of workers. The scaffolds must not hinder ventilation in any way. Enough space should be available, allowing the operator to execute his work properly, and to move from level to level fast and efficiently. General Tank Coating Code of Practice Issue April 2008 Page 19 of 24 Waist-high safety rails (scaffolding tubes) must be erected between all uprights on the inner perimeter of the scaffold construction above the first level. The same applies for any other dangerous places. This is required to hinder personnel fall down. 8.4 Elimination of ignition sources Welding, cutting or grinding inside the tank shall be completed before grit blasting. By the time of coating application, this rule shall apply to all areas within a 20-metre radius of the tank and its outlets. Areas where work is in progress must be clearly identified and sectioned off. Hazard warnings showing ‘EXPLOSION RISK’ and ‘NO SMOKING’ must be placed clearly visible around all tank entrances during the coating operation and shall not be removed before the concentration of flammable vapours is too low to cause a fire hazard. Such hazard warnings should be placed at 10 metres distance from the tank entrance(s). Lights, including hand torches, must be no more than 24-Volt and certified by the manufacturer as flash proof or suitable for use in a solvent-laden atmosphere. All electrically powered equipment in use must be earthed properly. This includes, but is not limited to, compressors, blasting equipment and spraying equipment. Explosion- and spark-certified equipment should be used during the coating application. Electric cables, motors and illumination systems must be typeapproved. Extension cables with internal connectors should never be used. No electrical junction boxes should be allowed in tanks. Personnel working in confined spaces during paint application and curing must wear rubber-soled shoes. If heating is required in order to satisfy the painting specification, it should be by means of a heat exchange system. Hot exhaust gas from a combustion process should not be used for heating, because it will contain carbon dioxide which is undesirable inside a tank. Mobile telephones and battery operated cameras must not be used inside or near tanks or ventilation outlets until paint fumes are totally dispersed. General Tank Coating Code of Practice Issue April 2008 Page 20 of 24 8.5 Management of solvent vapour concentration 8.5.1 General advice The solvent content of the paint, as well as added thinner, may present limitations when it comes to the application process, both with regard to fire hazards and the paint applicators’ health. Any organic solvent-based coating can give off sufficient solvent vapour to produce an explosive mixture in a tank. This can not be tolerated, as one can never be 100% sure that a spark or other form of ignition will occur. The solvent (and thinner) may also produce an atmosphere which is dangerous to the health of personnel in the tank. Either of these circumstances will dictate a minimum forced ventilation to be arranged. However, nowadays paint applicators always use fresh air masks, and are not dependent on the tank atmosphere for breathing. Therefore, it is the fire and explosion risk that will have to be assessed and controlled in ballast tank coating projects. Mixtures of organic solvents (or thinners) and air are explosive in a wide concentration range; usually from about 1% up to about 10%. These limits are called the Upper and Lower Explosive Limits, abbreviated as UEL and LEL, respectively. To eliminate the explosion risk the vapour concentration must be well below the lower explosive limit all the time. For safety reasons one generally says that the maximum permissible concentration of solvent or thinner in the tank atmosphere is one tenth (10%) of the LEL, i.e 0.1%. Long before the vapour concentration reaches the LEL the atmosphere in a confined space like a tank will be intolerably unpleasant, with irritating skin effects and pain to the eyes. These symptoms must be taken as a warning sign that better ventilation is needed. 8.5.2 Ventilation and air exchange For successful removal of solvent fumes, suction from the lower sections of the tank is required (solvent fumes are heavier than air). Flexible ventilation ducts should be used to allow the point of extraction to be reasonably close to the worker. The ventilation system and ducts should be so arranged that ‘dead spaces’ are avoided. In practice the solvent concentration in the tank atmosphere will rise to a high level as soon as the coating application starts, and will remain high until the coating operation is finished. Afterwards, the solvent concentration will gradually decrease, but the coating will emit solvents until it is fully dried. Solvent vapours may also accumulate in ‘pockets’ within the tank. Therefore we have little control of what will be the true solvent concentration in the tank General Tank Coating Code of Practice Issue April 2008 Page 21 of 24 atmosphere, and the solvent concentration must not be allowed to increase or remain high. Consequently, a worst case approach must be made, and this means that we calculate the total air volume to be used, and ensure that this is applied during the whole coating application period. To take care of the remaining solvents, the fans must also run during the drying period afterwards. However, since the solvent evaporation rate will gradually decrease, we can, as a rule of thumb, reduce the ventilation by about 50% when half the drying time has elapsed. 8.5.3 Finding the required ventilation rate To find the required air quantity we first calculate the total solvent content of the paints (and thinners) used. It is assumed that all this solvent will evaporate and contribute to an explosive atmosphere. These solvents must not constitute more than 0.1% of the air in the tank (10% of the LEL), and in this way the required air volume is found. The Required Air Quantity, RAQ, is the amount of air needed for each litre of paint to ventilate to the required level. Relevant RAQ values are given in the below standing table. In this table also relevant thinners are listed. To find the total RAQ the demands from the paint and the added thinner must be added. The quantity of ventilation required in cubic metres per minute during the application and drying can be calculated from the formula: RAQ = [P*A + Q*B] / t P = paint quantity applied in the tank, litres Q = extra thinner used in this paint, litres A = required air volume per litre paint (m3/l) to maintain a non-explosive atmosphere B = required air volume per litre thinner (m3/l) to maintain a non-explosive atmosphere T = application time in minutes General Tank Coating Code of Practice Issue April 2008 Page 22 of 24 Ventilation requirements for coatings and thinners. Total air volume for evaporation of solvents Coating or Thinner % Solids Required air volume, m3/l Balloxy HB Light & Lumi 82 36 Wintergrade Balloxy HB Light 71 58 Chemflake Special 96 8 Jotacote Universal 72 56 Jotamastic 87 82 36 Jotamastic 87 WG 74 52 Jotamastic 87 Aluminium 87 26 Jotamastic 87 Aluminium WG 77 46 Primastic Universal 75 50 Primastic Universal WG 70 60 Resist GTI 60 216 Tankguard HB 50 100 Tankguard Special & Storage 63 74 Thinner no 4 0 318 Thinner no 7 & 17 0 200 Thinner no 25 0 174 Thinner no 26 0 185 Coatings and thinners listed are not necessarily approved for tank use. Likewise, there may be approved tank products not listed. Example: We plan to coat a 650 m3 tank with one coat of Balloxy HB Light 200 µm dry film thickness. The tank has a calculated surface area of 1260 m2. The paint will be thinned 5% (Thinner no. 17). Application speed is 3.5 litres per minute. How much fresh air must be blown into the tank per minute to eliminate the explosion risk? And for how long time? The ambient temperature is 23 degrees C. Answer: 200 µm/0.82 * 1260m2 = 309 litres of paint. 5% to this is 15 litres thinner. Required air volume becomes 309*36 + 15*200 = 14124 m3. (309+15) litres / 3.5 l/min = 93 minutes. 14124m3 / 93 min = 152m3 / minute. Drying time (see technical data sheet) is 10 hours at 23 degrees C, i.e. the ventilation fans shall run for 11½ hour. (For the last 5 hours the fan speed may be reduced 50%, as indicated in section 8.5.2.) General Tank Coating Code of Practice Issue April 2008 Page 23 of 24 8.5.4 Monitoring the ventilation system An authorised person must check the solvent vapour content before work starts and at regular intervals (i.e. every two or three hours thereafter) until the tank coating work is finished. Particular attention must be paid to ‘dead spots’ in the tank, where high concentrations may occur locally. The maximum allowed solvent concentration is 0.1% at all times. If the solvent concentration rises above 0.1%, painting must stop until the vapour concentration is reduced to a safe level again. In order to prevent personnel losing consciousness and suffocating, the oxygen level must not fall lower than 21% by volume. Oxygen monitors must be available and used to ensure a satisfactory oxygen content in the working atmosphere. Provision must be made for 24-hour surveillance of ventilation equipment. Jotun A/S P.O. Box 2021, N-3248 Sandefjord, Norway Tel: +47 33 45 70 00 Fax: +47 33 46 46 13 www.jotun.com General Tank Coating Code of Practice Issue April 2008 Page 24 of 24