Flat bottom storage tanks form an integral part of the production process of industrial gases. They are typically large volume tanks that contain mainly either liquid nitrogen or oxygen, though some are in argon service. Cryogenic flat bottom tanks consist of an inner tank and an outer jacket that are field constructed on an insulated foundation. The space between the inner and outer tanks is insulated, usually with expanded perlite.
The industrial gases industry does not carry out periodic internal inspection of bulk cryogenic storage tanks.
This policy has been established over many years, based on operating experience, the inherently stable and benign conditions within an operating cryogenic storage tank and an absence of the traditional failure mechanisms for such equipment including corrosion, erosion, fatigue.
An annual inspection should be carried out to guard against any degradation mechanisms developing and to confirm that the environment within the tank outer jacket is dry and inert and that there are no obvious indications of cryogenic and/or pressure leaks.
EIGA has carried out a survey of its members who operate across Europe as well as those who operate in the United States, South Africa, Australia and Asia to understand if there are any regulatory requirements to carry out a periodic internal inspection of bulk liquid oxygen, nitrogen and argon storage tanks. In no case was there a regulatory requirement to carry out a periodic internal inspection of these tanks.
This Technical Bulletin is intended to support and requests to carry out an internal inspection of flat bottom tanks.