Cryogenic liquids and their storage tanks
Cryogenic tanks are used for the storage of cryogenic liquids. Cryogenic liquids are typically liquefied gases at -150 °C or lower. Common products include oxygen, argon, nitrogen, hydrogen, and helium. Cryogenic tanks are also used for storing gases at higher temperatures, examples of which include liquefied natural gas (LNG), carbon dioxide and nitrous oxide.
These form part of gas supply systems to be used in a wide range of applications, including metal processing, medical technology, electronics, water treatment, energy generation and the food industry. Cryogenic liquids are also used for low temperature cooling applications, such as engineering shrink fitting, food freezing and the storage of bio-samples.
Cryogenic tanks are thermally insulated, typically with a vacuum jacket, designed and manufactured to a high specification following international design codes. They can be fixed, mobile or transportable.
Static cryogenic tanks are designed for use in a fixed location, however this does include those mobile small tanks mounted on wheels for use within workshop and laboratories. Static cryogenic tanks are generally classified as pressure vessels, as such new tanks and their associated systems will be manufactured and put into service in accordance with the Pressure Equipment (Safety) Regulations. There are also a range of non-pressurised open neck vessels (Dewar flasks) available for those applications requiring direct access to the liquid. The tanks come in a range of sizes, pressures and flow rates to meet the users' varying requirements.
Tanks that are, or are intended to be, used to transport cryogenic liquids have to comply with the Carriage of Dangerous Goods and Use of Transportable Pressure Equipment Regulations.
Use, operation and maintenance of cryogenic tanks
Cryogenic tanks have to be operated and maintained in a manner that complies with all relevant legislation, for example, the Pressure Systems Safety Regulations for static tanks or the Carriage of Dangerous Goods and Use of Transportable Pressure Equipment Regulations for transportable tanks. Cryogenic tanks have to be maintained and managed by designated competent persons.
For static tanks the Regulations require cryogenic tanks to undergo regular inspection, routine maintenance and periodic formal examination. An inspection and maintenance regime should be drawn up to ensure the tank is in a safe condition to allow correct operation at all times between the formal examination periods. This will include a Written Scheme of Examination which has to be drawn up by a competent person(s) with periodic formal examinations conducted in accordance with the scheme. Refer to BCGA CP 39.
Transportable tanks require periodic inspection and testing, this can only be carried out by an Inspection Body, who in the UK is authorised by the National Competent Authority, Department for Transport (DfT). Information on Inspection Bodies who have been appointed to undertake various functions in connection with the inspection of tanks and/or pressure equipment can be found on the Vehicle Certification Agency (VCA) website.
All inspections, examinations and tests are documented and records have to be kept for the life of the tank.
Users and owners of cryogenic tanks have legal responsibilities and a duty of care to ensure their equipment is maintained and operated safely. BCGA L12 provides advice and guidance on appropriate practice.
A gas supplier will only fill a tank once they have established that it is safe to do so, refer to BCGA CP 48.
The user must carry out routine safety inspections. Daily checks are to be carried out, refer to BCGA L11.
When in use a small amount of frosting and ice may be seen. Small quantities should not be a cause for concern, but the quantity of ice should be routinely monitored. If ice continues to build-up, de-icing should take place to prevent the ice build-up becoming excessive, refer to BCGA L21.
Cryogenic tank repair and modification
Any repair or modification to a cryogenic tank shall only be carried out by a competent repairer in accordance with the design codes to which it was manufactured, taking into account current requirements in regulations and legislation. Such repairs or modifications shall not affect its integrity or the operation of any protective devices. Refer to BCGA CP 39
All repairs and modifications have to be documented and records have to be kept for the life of the tank.
Cryogenic tank revalidation
Cryogenic tanks require a formal periodic assessment to ensure they are safe for continued use. This revalidation period shall be decided by a Competent Person but shall not exceed 20 years. Due to the nature of their service a shorter period for mobile tanks is recommended. Refer to BCGA CP 39.
When revalidation takes place a report is produced which is to be kept with the tank records for the life of the tank.
Disposal of cryogenic tanks
Some cryogenic tanks contain hazardous products in their vacuum space, e.g. perlite, and therefore tanks should only be disposed off by an approved competent and specialist disposal contractor. All equipment is to be rendered non-reusable as pressure equipment.
Within BCGA cryogenic tanks are the responsibility of Technical Sub-Committee (TSC) 1. Members can access information on TSC1 via the ‘Members' area.
BCGA publish several publications providing advice and guidance on the on how to use, store, transport and handle cryogenic gases safely. All BCGA publications are accessible via the ‘Publications' page. The following are of interest:
- BCGA CP 26 - Bulk liquid carbon dioxide storage at users' premises.
- BCGA CP 27 - Transportable vacuum insulated containers of not more than 1000 litres volume.
- BCGA CP 36 - Cryogenic liquid storage at users' premises.
- BCGA CP 39 - In-service requirements of pressure equipment (gases storage and gas distribution systems).
- BCGA CP 46 - The storage of cryogenic flammable fluids.
- BCGA CP 48 - The safe filling of third-party owned and/or maintained tanks
- BCGA GN 19 - Cryogenic sample storage systems (Biostores).
- BCGA TIS 23 - BCGA policy regarding internal examination and proof pressure testing of static cryogenic liquid storage tanks.
- BCGA L 11 - Safety checks for cryogenic tanks.
- BCGA L 12 - Liquid gas storage tanks: Your responsibilities.
- BCGA L 21 - Cryogenic installations. Managing ice build-up.
Cryogenic tank providers
BCGA member companies can provide cryogenic tanks and/or a range of services and associated equipment. See full list here.