Tips on Tanks and Vessels Selection
Why you should consider saving money with tanks from Jones Industrial Mixers?
1. Processes, mixers, platforms and tanks should be designed as one system from the very start!
Too often people purchase a tank and then try to fit a suitable mixer. This can be a very expensive problem – especially if the related and important mixer dimensions don’t tie up and can’t work with the tank. Worst example of many – deep cone and resulting problem to lift the product!
2. Types of materials to use with different chemicals are an important tank design consideration.
We assess all the process parameters and our in-house chemical and mechanical engineers can make the right material selection for your tank and products, and can save you costly errors – leading to fast tank deterioration or even fast failure. Quite likely we will surprise you with unique ideas and total cost savings.
3. Jones works with professional tank designers and manufacturers to optimize designs of the mixer, the tank, the fittings and the piping and the platform into one complete integrated system.
Let us save you money with the correct and smart design approach from the start. Let’s discuss various options to balance your needs and ensure the right package from the start. Mixer designs are much more complex than often assumed and a careful appraisal of the process and all liquids properties or indeed dry products properties is essential to get the right mixing results.
4. Hazardous products like solvents require compliance with SANS 310 & frequently other standards.
We design for hazardous products and important safe operational details and can manage to avoid over-design, but we will still comply with SANS 310 and other important design standards.
5. Tank lids, tank vents, loading and unloading systems and automation with load cells are all designed by Jones to match your key processing needs.
Allow Jones to work with you on your total requirements of all fittings and accessories – to ensure that your requirements are fully met and achieved. Avoid later costly adjustments when these important design considerations are not included from the start.
FROM THE SMALLEST CONTAINERS AND VESSELS TO THE LARGEST TANKS WE PROVIDE AN UN-BEATABLE COMBINATON OF FAIR PRICES AND SAFE AND EFFICIENT DESIGN PACKAGES
Where should you start the tank selection process?
1. The process conditions and details of products to be reacted, or just mixed, are the starting point of any tank design. Typically, two or more raw materials, are involved in any mixing process. Each process has unique or somewhat unique requirements and characteristics.
2. Once the chemicals (i.e. raw materials) are identified and listed, the key properties should be listed, preferably in a spreadsheet. Chemicals in the rows and properties in the columns. The quantities of each chemical will vary, and the second column can usefully list the kilograms of each used in the recipe.
The columns must show specific gravity or bulk density, viscosity, temperature at start of process, and any other appropriate properties of importance. For example, the powder raw materials should show the prime particle sizes, if available.
If there is a temperature rise during the processing, or if the tank will be heated to better process more viscous products, these details should be shown in a column of the final maximum temperature expected.
3. With the chemicals identified and the properties defined, we can proceed to assess what tank materials can be considered. Chemical compatibility tables show the chemical concentrations (such as 10% or 50% in water or other carrier solvent and typically 2 to 4 different concentrations), temperature conditions and the various wall materials of tanks under consideration. While these corrosion charts enable a quick review of options, a second opinion is recommended, preferably from an experienced person, who is aware of special hazards and unique factors. This is an area of caution in design.
Often plastic tanks will be suitable for a particular chemical but will be rejected as a tank material option on the grounds of temperature conditions being too high for that plastic material. But be cautious even with various steel, or stainless-steel choices, as there may be some special conditions. Some are recorded on the internet and some not. Practise caution.
4. Review of the chemicals as possible hazardous products should be considered at this point, if not immediately obvious. Products such as solvents or solvent laden products such as paints are classified as hazardous products under SA National Standards and will thereby require special design considerations.
5. Review of pressure or vacuum conditions, or even likely but not expected such conditions, is also essential as these conditions make for very unique design parameters in such pressure vessels or tanks.
6. Hazardous products and pressure vessels require special design standards to be applied. Pressure and temperature charts will highlight various standards to be followed. We show the master chart in the ‘Standards by Pressure-Temperature’ charts, also on this site.
7. Armed with the chemicals details, the process conditions such as temperatures, SG and viscosity, the reviews of likely pressure or vacuum conditions and whether there are other hazardous conditions or products, it is now possible to consider the material choice for the tank. Plastics (fibreglass or roto moulded tanks) and metals can be considered.
8. At this stage we recommend a design review session with Jones Industrial Mixers, to also ensure that the proper style of mixer and mounting thereof, if a mixer is planned or in use. Equally we can advise on a tank only design and assist to optimise the final design parameters and indeed the detailed tank costs.
What you should consider for tanks handling Hazardous Chemicals in Coatings and Other Process Industries!
Assessment Step 1
Common solvents used in solvent-based paints or lacquers, other coatings, pastes and similar chemical products are unequivocally classified as hazardous chemicals, by definition, in SANS 10228 (The Identification and Classification of Dangerous Chemicals for Transport); and in SANS 310 (Storage Tanks for Hazardous Chemicals) and SANS 347 (Categorization for all Pressure Equipment) by referral in these additional standards to SANS 10228. The use of the term ‘Transport’ does not negate all non-transport applications, as it is used as a reference categorization by definition – in the standards referred to above. It is important to be aware that SANS 10228 is based on the International Standards for hazardous chemicals and is thus thoroughly globally researched. Solvent tanks and vessels designs in coatings plants thus undoubtedly fall under these standards and by reference these standards also fall under the Occupational Health and Safety Act.
Note: Reference to paints and lacquers in SANS 10228 is also specifically made in classifying paint solvents as flammable and thus hazardous and the content of solids in paints and lacquers is dealt with as: “Flammable liquids are liquids, or mixtures of liquids, that might contain solids in solution or in suspension (for example paints, varnishes and lacquers)”.
Assessment Step 2
Tank or vessel designers must establish if pressure or vacuum conditions exist, or may reasonably arise, when assessing design criteria. Jones Industrial Mixers stresses the importance of a systems analysis to address all risks that may arise upstream and downstream from given installations.
Note: Although the South African Pressure Equipment Regulations (PER) do not deal with vacuum service, ASME VIII deals with vacuum service under the consideration of external pressures and thus does not exclude vacuum conditions from professional pressure vessel design. A vessel working in vacuum service is simply another form of pressure vessel when designed under ASME VIII. Simply to exclude vacuum service from a pressure vessel design by reference to the SA Pressure Regulations (PER) is to confuse the purpose of pressure vessel grading, as applied in SANS 347, with total vessel design considerations and can lead in some cases to unnecessary high risk exposure. SANS 347 refers to ASME VIII, which as referred to above, deals with vacuum service.
Assessment Step 3
Designs of tanks and vessels for hazardous chemicals must thus be grouped in one of the following categories:
3a. Hazardous and under pressure or vacuum = SANS 10228, SANS 310, SANS 347, ASME VIII
3b. Hazardous and not under any pressure or vacuum = SANS 10228, SANS 310
For convenience the full standards names are listed:
SANS 10228 – SANS 10228:2010 The identification and classification of dangerous chemicals for
transport
SANS 310 – SANS 310:2011 Storage tanks for hazardous chemicals – Above-ground storage tank
facilities for flammable, combustible and non-flammable chemicals
SANS 347 – SANS 347:2007 Categorization and conformity assessment criteria for all pressure
equipment
ASME VIII – ASME VIII Division 1: 2010 Rules for construction of pressure vessels
Assessment Step 4
In this article the design of equipment for solvents in the coatings industry is always under the requirements of SANS 310 and it is thus important to take note that proper compliance with this standard requires the appointment of a formally registered professional engineer, technologist or technician for design and other compliance requirements. Non-compliance with standards for such hazardous products is not wise and may be grounds for significant legal claims or other damages claims against the owner party in the event of a future tank or vessel failure. Care in this regard is strongly recommended.
When could you have unforeseen pressure or vacuum conditions in tanks in your factory?
Companies in the process industries should fully consider the possibility of unlikely but foresee-able and possible unforeseen pressure or vacuum conditions arising during operations and not make a conclusion that the tank is a pressure tank only if the tank is specifically designed for pressure or vacuum service. The notes which follow below are a summary of such conditions that can arise from process changes or other events during tank operation, as observed by Jones Engineers and that should be carefully considered in all future tank designs.
1. Inadequate or ‘no vent’ designs.
Comments: We noted the reported catastrophic failure at Rossing from inadequate vent outlets and rapid tank loading. We have also observed vacuum collapse in smaller tank sizes.
These failures result when tanks are emptied with such low or no vent in-feed facilities that air cannot enter fast enough to break the vacuum formed by rapid product discharge.
2. Vent blockages during tank or vessel service.
Comments: Vents can be easily blocked by well-intended people. They often put plastic bags over tank vents or other openings during maintenance or shutdowns to keep rain out of the tank or to prevent debris from entering the tank. There have also been bird nests built in vent pipes. Left in place at start-up time, this can lead to a tank collapse when product is discharged, as a vacuum can easily follow. Special vent designs can be discussed with Jones Engineers on your request.
3. Tight closure lids
Comments: Our observations include ‘dairy grade’ wall thicknesses in paint manufacturing services where SG regularly reaches 1.5 and higher; tank legs with thin material ‘box legs’ but used on high SG services.
4. Hot solvent cooling overnight under closed cover.
Comments: We noted the reported catastrophic failure at Rossing from inadequate vent outlets and rapid tank loading. We have also observed vacuum collapse in smaller tank sizes.
5. Press on thicker paste using standard floor pot or tank.
Comments: When thicker pastes are to be discharged from a process tank by a press and press plate, the tank in which the plate is pressed downwards must be designed for the full pressure.
6. High air pressure used to discharge residual product from closed vessel such as gear box.
Comments: Where vessels are not designed to be emptied with high pressure, very dangerous conditions can arise with thin wall designs or brittle materials used.
What you should consider to avoid major risks of tank failure in your factory?
Many companies in the process industries are inclined to consider or use poor design practices in the case of tanks and vessels selection – and some run on the ‘edge of disaster’ in tank applications – with often inadequate tanks or vessels. The notes which follow below are a summary of poor designs and practices observed by Jones Engineers that should be carefully assessed in future tank installations.
1. Inadequate design.
Comments: Our observations include tanks not built to SANS or other international standards; ‘own’ designs; low cost and high-risk designs. In recent years, we have seen designs in solvent coatings environments where the mandatory SANS 310 for hazardous chemicals is not complied with. This can lead to a high-risk exposure, such as a fire or an explosion.
2. Wrong metallurgy or wrong materials selection.
Comments: Our observations include tanks clearly made with inadequate or ‘optimistic’ assumptions of corrosive conditions, galvanic corrosion from mixed steel and galvanized fittings, and ignoring temperature effects on material corrosion (especially with plastic tanks).
3. Too thin walls, base or wrong SG assumptions or no SG assessment. SG = Specific Gravity.
Comments: Our observations include ‘dairy grade’ wall thicknesses in paint manufacturing services where SG regularly reaches 1.5 and higher; tank legs with thin material ‘box legs’ but used on high SG services.
4. Inadequate or ‘no vent’ designs.
Comments: We noted the reported catastrophic failure at Rossing from inadequate vent outlets and rapid tank loading. We have also observed vacuum collapse in smaller tank sizes.
5. Inadequate support structures.
Comments: Our observations include tanks clearly made with ‘optimistic’ assumptions of design that do not comply with the required standards such as API 650 referred to in SANS 310 (standard for solvent based paints); recent observations include very thin gussets on tank supports and no re-enforcing rings or inadequate spreader plates and leg gussets.
6. Poor welding quality.
Comments: Poor welding procedures are the main cause of weld failure – pitting and crevices lead to local stress concentrations; lack of inspection has been revealed where some welds are of very poor quality.
Jones Industrial Mixers provides several tank design services for our valued clients. This list is not exhaustive and must be treated as guidelines only. There may be other important design and operational considerations that clients should consider. We thus do not accept any liabilities for designs not completely reviewed and signed-off by Jones. Kindly discuss all your design details or changes with Jones.
