Plastic Constructions Ltd
PO Box 95198
Swanson
Auckland 0653
Code of Practice: HSNOCOP 56
Version: 1.0
Date of Approval: May 2012

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The purpose of this approved code of practice is to provide a standard for the design and construction of above ground tanks constructed from Polyethylene or Polypropylene.
This code provides a means of compliance with the requirements of clause 8(2) for the design construction and installation of tanks of hazardous liquids, 77(b)(i) for the marking of stationary containers and clause 93(1)(a) for the duration of a test certificate in Schedule 8 of the Hazardous Substances (Dangerous Goods and Scheduled Toxic Substances) Transfer
Notice 2004 (as amended).
This code of practice applies to the design and construction of vertical, cylindrical, aboveground tanks for the storage of hazardous liquids that:
1.
are constructed from polyethylene or polypropylene, and
2.
are used for storing toxic, corrosive and ecotoxic substances (classes 6, 8 and 9 hazard classifications), but
3.
Are NOT used for the storage of liquids that also have a flammable classification
(Class 3.1).
Tanks design and constructed to this code are intended for use at locations where hazardous substances are manufactured, stored, or used. The tanks are not suitable for use in transport.
This approval by Environmental Protection Authority is limited to providing a means of compliance with the requirements of clauses 8 (2), 77(b)(i) and 93(1)(a) in Schedule 8 of the
Hazardous Substances (Dangerous Goods and Scheduled Toxic Substances) Transfer Notice
2004 (as amended).
Compliance with this code does not remove the requirement to comply with other sections of the HSNO legislation or other legislation such as the Health and Safety in Employment
Regulations.
The HSNO regulations are largely performance based, that is, they specify a desired outcome without prescribing how to achieve it. They do not require a single means be used to comply with any regulation and this allows for variations in method.
The HSNO Act provides for Codes of Practice approved by ERMA New Zealand to identify acceptable solutions to comply with the specified regulatory requirements.

An Approved Code of Practice provides users with a method of meeting the control requirements with a degree of prescription and assistance.
In addition, specific provisions of the HSNO regulations and transfer notices permit Codes of
Practice to be approved by the Environmental Protection Authority as alternatives to the legislated requirements.
In the Hazardous Substances (Dangerous Goods and Scheduled Toxic Substance) Transfer
Notice 2004 Schedule 8, clause 8(2) specifies standards for the design and construction of above ground stationary tanks. Sub-clause (h) enables the Authority to approve a code as an alternative to the nominated standards.
Clause 77(b)(i) of Schedule 8 specifies requirements for marking of stationary container systems. Clause 77(b)(ii) enables the Authority to approve a code as an alternative to the specified marks.
Clause 93(1) of Schedule 8 provides for the test certificate of the stationary container system to have a duration given by specified standards. Sub-clause (i)(D) and (ii)(C) enable the Authority to approve a code as an alternate to the nominated standards.
4.1 Standards
Every above-ground tank constructed under this code of practice must be designed and constructed in accordance with the following standards.
4.1.1. BS EN 1778:2000 Characteristic values for welded thermoplastics constructions – Determination of allowable stresses and moduli for design of thermoplastics equipment.
This standard provides the characteristic values for welded thermoplastic constructions. It allows for the determination of long –term allowable stresses, long-term elastic modulus values, and for the de-rating factors to be applied when the materials are exposed to different chemicals.
The standard also allows engineers competent in plastic design to make ‘fit for purpose’ judgements in relation to unusual plastic constructions.
4.1.2. BS EN 12573-1 General Principles
This standard provides requirements for the determination of allowable stresses including the calculation of cyclical loadings and combination loadings for tank designs detailed in EN
12573-2.

4.1.3. BS EN 12573-2 Calculation of vertical cylindrical tanks
This standard establishes the rules for the design and calculation of welded static, vertical, non-pressurised, cylindrical, flat bottom thermoplastic tanks.
4.1.4. BS EN 12573-3 Annex A3.7 design and calculation for single skin rectangular tanks
This standard provides detailed design information for rectangular tanks. Annex A3.7 provides general details for the correct construction of nozzles welded into thermoplastic vessels.
4.1.5. BS EN 12573-4 Design and calculation of flanged joints
This standard provides additional direction for engineers designing vertical thermoplastic vessels, especially when transportation requirements necessitate construction in sections and assembly on site.
4.2.1 Polymer
The permissible polymers are High Density Polyethylene and Polypropylene.
4.2.2 Stabilisation against Ultra-Violet Degradation.
The material used for construction must be stabilised against ultraviolet degradation, with a minimum carbon black content of 2%, unless the tank is to be installed so that it is not directly exposed to ultraviolet light.
4.2.3 Maximum tank size
The maximum storage capacity is 20,000 litres.
4.2.4 Testing parent material and welds including butt fused
As materials may vary from different manufacturers, all materials must be tested for compliance with BS EN 10002-1.
During manufacture electronic spark testing to be carried out on all welds to check for leaks.
On completion of each vessel, a Hydrostatic test of 48 hours duration minimum must be performed.

4.2.5 Minimum design life
High Density Polyethylene (HDPE) tanks must be designed for a minimum service life of 25 years. Polypropylene tanks must be designed for a minimum service life of 15 years.
4.2.6 Limitation on substances stored
The substances stored are limited to toxic (Class 6) corrosive (class 8) and ecotoxic (Class 9) liquids that do not have a flammable classification (Class 3.1). The substance must be compatible with the material used for construction.
As provided for in clause 93(1)(a) of Schedule 8, the maximum validity period for the stationary container system test certificate for above-ground tanks constructed under this code of practice is 5 years.
In addition to the requirements of clause 77(b)(i) of Schedule 8, the tank is required to be marked with: a.
The calculated design life. b.
The contents the tank is designed and the relevant substance chemical reduction factor. c.
The location the tank is designed to be used in, that is, either external (resists ultraviolet light) or internal (inside a building only – not resistant to direct exposure to ultra-violet light).
The factor of safety in clause 7 of EN1778:2000 is to be not less than 2.0