This document is a specification for vertical, cylindrical tank systems, built on site, above ground and of which either the primary liquid container or the liquid tight barrier is made of steel. The secondary liquid container, if applicable, can be of steel or of concrete or a combination of both. A primary liquid container made of pre-stressed concrete is excluded from the scope of this document.
This document provides general requirements and specifies principles and application rules for the structural design of the tank system during construction, testing, commissioning, operation (accidental included), and decommissioning. This document applies to all tank system components attached to and located within the liquid, vapour, purge gas, membrane or membrane tank outer containers of the tank system. It does not address the requirements for ancillary equipment such as pumps, pumpwells, valves, instrumentation, external staircases and walkways, roof mounted platforms, external pipe supports, etc. The requirements for those components are covered by the relevant European Standards, structurally designed in accordance with Eurocodes where appropriate, and meeting applicable safety regulations.
This document also does not address tank system operating procedures unless specified for determination of the relevant resistance and protection criteria for the tank systems. It specifies minimum performance requirements for the tank system, tank system foundation and protection systems. From a process piping standpoint, the scope of this document is limited to the following boundaries:
a) the face of the first flange outside of the tank in bolted flanged connection;
b) the first threaded joint outside of the tank in threaded connection;
c) the first circumferential pipe welded joint outside of the tank in welding-end pipe connection, which does not have a flange.
This document is applicable to storage tank systems designed to store products, having an atmospheric boiling point below ambient temperature, in a dual phase, i.e. liquid and vapour. The equilibrium between liquid and vapour phases being maintained by cooling down the product to a temperature equal to, or just below, its atmospheric boiling point in combination with a slight overpressure in the storage tank system.
The maximum design pressure of the tank systems covered by this document is limited to 500 mbar. For higher pressures, reference can be made to EN 13445, Parts 1 to 5.
The operating range of the gases to be stored is between 0 °C and −196°C.
The tank systems covered by this document are used to store large volumes of hydrocarbon products, ammonia and other non-hydrocarbon gases with low temperature boiling points, generally called “Refrigerated Liquefied Gases” (RLGs). Typical products stored in the tank systems are: methane, ethane, propane, butane, ethylene, propylene, butadiene (this range includes the Liquefied Natural Gas (LNG’s) and Liquefied Petroleum Gas (LPG’s)), ammonia, nitrogen, oxygen and argon.
NOTE 1 Properties of the gases are given in Annex A.
The requirements of this document cannot cover all details of design and construction because of the variety of sizes and configurations that may be employed. Where complete requirements for a specific design are not provided, the intention is for the designer, subject to approval of the purchaser's authorized representative and of the regulatory body, to provide design and details that are as safe as those laid out in this document.
EN 14620 consists of multiple parts. This document specifies general requirements for the tank system concept, selection and general design considerations.
In case of a conflict between general requirements of this document and the requirements in other parts of EN 14620 related to a specific liquefied gas, the product-specific requirements set forth in the other parts prevail.