EEMUA PUB NO 225
Above ground plastic tanks: A guide to their specification, installation, commissioning, inspection, maintenance, repair and disposal
|Publication Date:||1 October 2017|
What is included
This Publication is aimed at owners and operators of above-ground plastic tanks, which are typically cylindrical in shape. The document's content is aimed mainly at tanks being operated at atmospheric pressure or at pressures above the liquid head up to 0.5 barg. It is not therefore intended for tanks which would be classed as pressure vessels under the Pressure Equipment Directive (PED), although some of its content may still be relevant and useful to users operating plastic pressure vessels in what are usually quite specific applications.
The publication covers a range of topics, from how to specify the design, through inspection, maintenance, and repair, to decisions at end-of-life and safe disposal.
Standards for thermoplastic tanks
Some standards commonly used to design thermoplastic tanks are described below:
EN 12573: Welded static non-pressurised thermoplastic tanks.
This European standard comprises the following parts:
Part 1 - General principles
Part 2 - Calculations for vertical cylindrical tanks
Part 3 - Design and calculations for single skin rectangular tanks
Part 4 - Design and calculations for flanged joints
This European standard covers tanks with a capacity of 0.45m3 and above. Because unreinforced thermoplastics are limited at increased temperatures, much of the design data in this standard is derived from EN 1778, which gives characteristic values for welded thermoplastic constructions, determination of allowable stresses, and moduli for the design of thermoplastic equipment.
Part 2 establishes rules for the design and calculations of welded static, non-pressurised, cylindrical, flat-bottomed tanks. The calculations take into account short-term and long-term active pressures as well as the hydrostatic loading. The following values are long-term pressures and represent the limiting values:
• Positive pressure - 5mbar (0.0005N/mm2)
• Vacuum - 3mbar (0.0003N/mm2)
This standard applies to tanks fabricated in polyethylene (PE), polypropylene (PP), unplasticised polyvinyl chloride (PVCU), and polyvinylidene-fluor
The standard does not take into account wind or snow loadings, nor does it combine axial loadings in the vertical shell. If these operational parameters are required, additional calculations are necessary, which are available in the German Technical code, DVS 2205-2.
DVS2205- DVS Technical Codes on Plastics Joining Technologies - "Technical section DVS 2205 - 2 "Calculation of tanks and apparatus made of thermoplastics. Vertical round, non-pressure."
Here, non-pressure means a pressure rating below the threshold where the European Pressure Equipment Directive (PED) applies, which is 0.5bar. This standard applies to tanks fabricated in PE, PP, PVCU, chlorinated polyvinyl chloride (CPVC), PVDF, and ethylene chlorotrifluoroethyl
This comprises the following parts:
DVS 2205-1: Characteristic values for strength of materials, safety concept, reduction coefficients, welding factors, and creep moduli for materials.
DVS 2205-2: Calculations for tanks and apparatus made from thermoplastics. Vertical, round, nonpressurised tanks with flat bottoms.It also includes parallel supported diagonal (sloping) bottoms and ring-supported conical bottoms.
DVS 2205-3: Design of thermoplastic tanks and apparatus - Welded joints
DVS 2205-4: Calculation of thermoplastic tanks and apparatus - Flanged joints
DVS 2205-5: Calculation of thermoplastic tanks and apparatus - Rectangular tanks
The standard is more extensive in terms of detailed tank design than EN 12573. It is generally recognised that unreinforced thermoplastic and fluoroplastic tanks are used for non-pressure duties and rarely come within the scope of the PED. The standard gives no specific parameters with regard to scope for operating conditions. Within the design process the operating temperatures, pressures, chemical resistances (reduction factors), safety concepts, creep moduli and capacities, and other factors, control the overall operating and design parameters of the finished product.
Standards for Glass Reinforced Plastic (GRP) tanks
Note: For the purposes of this guide, and in the context of plastic tanks, the term glass reinforced plastic (GRP) is assumed to mean the same as fibre reinforced plastic (FRP). While fibre reinforced plastic has a broader application as a term, in cases where the fibre used is glass, such as plastic tanks, the terms can be used interchangeably.
Some standards commonly used to design GRP tanks are described below:
British Standard 4994: Design and construction of vessels and tanks in reinforced plastics
This standard is no longer current, but many tanks in operation have been manufactured to it. The standard is a specification for the design, materials, construction, inspection, testing and erection of tanks in reinforced plastics. It covers tanks with a polyester, vinylester, epoxy or furane resin system, reinforced with glass fibres, which have been manufactured by the wet layup process. Constructions both with and without a lining of thermoplastic or fluoroplastics are included.
EN 13121 "GRP tanks and vessels for use above ground"
This standard covers tanks for above ground use that are subject to temperatures between -40°C and 120°C, and to pressures between 10bar and full vacuum. To comply with the PED, vessels designed to operate at pressures greater than 0.5bar must be subject to a third party inspection.
EN 13121: Parts 1, 2, 3 and 4: above ground GRP tanks
This European standard comprises the following parts:
Part 1 - Raw materials - Specification conditions and acceptance conditions
Part 2 - Composite materials - chemical resistance
Part 3 - Design, workmanship, inspection and testing
Part 4 - Delivery, installation, and maintenance
It specifies requirements for tank specification, the acceptance conditions for raw materials, the chemical resistance of composite materials, and the requirements for the design, fabrication, inspection, testing, and verification for pressure and non-pressure GRP tanks, with or without linings of thermoplastic or fluoroplastic for the storage and processing of fluids for above ground use. Glass lining may also be used for tanks containing aggressive liquids.
GRP composite materials include glass fibre reinforced unsaturated polyester resins, vinyl ester resins, vinyl ester urethane resins, epoxy resins, furane resins and phenolic resins. Glass fibre reinforcements include chopped strand mats, woven fabrics and woven roving fabrics, and rovings for winding and chopping applications.
ASME RTP-1: Reinforced Thermoset Plastic Corrosion-Resistant Equipment, American Society of Mechanical Engineers. This standard applies up to pressures of 1barg.
ASME BPVC: Section X - Fiber-Reinforced Plastic Pressure Vessels, American Society of Mechanical Engineers. This standard applies to pressures over 1barg; RTP-1, above, covers pressures lower than this.
DIBt 40-B1 Calculation recommendations for vertical storage containers made of glass fibre reinforced plastics, DeutschesInstitutfür
DIBt 40-B2 Calculation recommendations for glass fibre reinforced plastics vessels mounted on saddle supports, DeutschesInstitutfür
What is not included
This is a general guide, and not a design code. Relevant local and international design codes should be followed, but the reader is assumed to be an owner and operator rather than a manufacturer. For this reason, fabrication and manufacturing techniques are not covered.
Only tanks where plastic provides the primary structure are considered; lined steel tanks are not included.
Also excluded are tanks for transport containment, intermediate bulk containers (IBCs) and similar containers, spherical tanks, buried tanks, and irregular shaped tanks.
The effect of radioactivity is a specialist area which is not addressed in this document. Also omitted are the requirements for grounding on ancillaries, and extraneous metalwork, as well as issues to do with any connected pipework.
Thermoplastic tanks manufactured by rotational moulding techniques to EN 13341 intended for domestic use and the storing of heating oils, kerosene and diesel fuels, and tanks manufactured to EN 13575 are also excluded.