BS EN 13648-3:2002 – Cryogenic vessels — Safety devices for protection against excessive pressure — Part 3: Determination of required discharge — Capacity and sizing

1 Scope
This standard provides a separate calculation method for determining the contributing mass flow to be relieved resulting from each of the following specified conditions: vacuum insulated vessels with insulation system (outer jacket + insulating material) intact under normal vacuum. Outer jacket at ambient temperature. Inner vessel at temperature of the contents at the relieving pressure;
vacuum insulated vessels with insulation system remaining in place but with loss of vacuum, or non vacuum insulated vessels with insulation system intact. Outer jacket at ambient temperature. Inner vessel at temperature of the contents at the relieving pressure;
vacuum or non vacuum insulated vessels with insulation system remaining fully or partially in place, but with loss of vacuum in the case of vacuum insulated vessels, and fire engulfment. Inner vessel at temperature of the contents at the relieving pressure; vessels with insulation system totally lost and fire engulfment.
Good engineering practice based on well established theoretical physical science shall be adopted to determine the contributing mass flow where an appropriate calculation method is not provided for an applicable condition.
2 Normative references
This European Standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text, and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies (including amendments).
prEN ISO 4126-1, Safety devices for protection against excessive pressure – Part 1: Safety valves (identical to ISO 4126-1).
prEN ISO 4126-6:2000, Safety devices for protection against excessive pressure – Part 6: Application, selection and installation of bursting disc safety devices (ISO/DIS 4126-6:2000).
3 Calculation of the total quantity of heat transferred per unit time from the hot wall (outer jacket) to the cold wall (inner vessel)
3.1 General
p (bar abs) is the actual relieving pressure which is used for the sizing of a safety valve. This shall not be greater than 1,1 PS, where PS is the maximum allowable pressure for which the vessel is designed.
T a (K) is the maximum ambient temperature for conditions other than fire (as specified e.g.by regulation/standard)
T f (K) is the external environment temperature under fire conditions (in any case T f = 922 K, i.e. 649°C or 1200 F)
BS EN 13648-3:2002 – Cryogenic vessels — Safety devices for protection against excessive pressure — Part 3: Determination of required discharge — Capacity and sizing