BS 6364: Specifications for Valves for cryogenic service

BS 6364: Specifications for Valves for cryogenic service

BS 6364 Standard specifies the requirements for the design, manufacture and testing of valves for cryogenic service. It is a requirement of this standard that the valves comply with the appropriate valve product British Standards, i.e.:

steel wedge gate valves: BS 1414;

Steel check valves: BS 1868
steel globe and globe stop and check valves: BS 1873;
steel ball valves: BS 5351;
steel wedge gate, globe valve and check valves DN 50 and smaller: BS 5352;
copper alloy globe, globe stop and check, check and gate valves: BS 5154;
testing of valves: BS 6755;
butterfly valves for general purposes: BS 5155.

The size range covered by this standard is DN 15 to a maximum nominal size appropriate to the above product standards, in the temperature range – 50 °C to – 196 °C, yet capable of operation at ambient conditions to allow for start-up and run-down.

NOTE 1 For marine applications where design temperatures are below – 165 °C attention is drawn to the need to check requirements with the relevant Statutory Authority.

Appendix C lists the information to be supplied by the purchaser.

NOTE 2 The titles of the publications referred to in this standard are listed on the inside back cover.

Requirements
4.1 Valves shall be supplied with extended bonnets/glands (see Figure 1). The length of the extension shall be sufficient to maintain the stem packing at a temperature high enough to permit operation within the normal temperature range of the packing material.

4.2 Valves on gas service shall be capable of operation with the valve stem at or above the horizontal position.

4.3 Valves in liquid service other than cold box applications shall be capable of operation with the
valve stem at or above 45° above the horizontal position.

4.4 For cold box applications, valves shall be suitable for use with the valve stem at or above 15° above the horizontal position and in addition the minimum gland extension length as shown in Figure 1 shall be as given in Table 1.

NOTE If any special length of gland extension is required by the purchaser he should state this (see Appendix C).

4.5 For applications other than cold box applications the minimum gland extension length shall be 250 mm (see Figure 1).

4.6 Valves shall be designed to relieve pressures above normal working pressure that may build up in trapped cavities due to thermal expansion or evaporation of liquid.

NOTE For ball valve and gate valves this requirement can be met by the provision of a pressure relief hole or passage or other means, e.g. pressure relieving seats, to relieve pressure in the bonnet and body cavities to the upstream side of the valve. The means adopted will be determined by the manufacturer unless the purchaser exercises his option in accordance with Appendix C.

4.7 Where valves, by design, are unidirectional in operation, the flow direction shall be clearly indicated either on and integral with the body of the valve or on a plate securely attached to the body of the valve.
In the design of such valves, measures shall be taken to prevent incorrect assembly.

4.8 Valve bonnets shall be bolted, welded or union type. Union type bonnets shall only be used on valves DN 50 and below, or for marine applications DN 40 and below, and the union nut shall be locked to the body. The use of screwed bonnets shall not be permitted.

NOTE Gasket materials for bolted bonnets are outside the scope of this standard (see Appendix C).
4.9 For steel valves, fabricated gland extensions shall be constructed from a single length of seamless tube butt-welded to the bonnet and gland housing.

4.10 For high pressure bronze or copper alloy valves of PN 100 rating or greater, the extension tube shall be screwed into the bonnet prior to silver soldering.

4.11 The clearance between the valve stem and gland extension bore shall be designed to minimize convection heat losses. The wall thickness of the extension shall be minimized, compatible with the rating of the valve and mechanical strength requirements in order to reduce conduction heat losses.

4.12 Valve stems shall be of one-piece construction except for end entry ball valves, in which case the valve design shall be such that the valve stem cannot be blown out of the body in the event of the gland being removed while the valve is under pressure. Rising stem valves with renewable gland packing that incorporate a back seat shall have the back seat located in the region of the gland. Gland designs incorporating lantern rings and screwed plugs in the gland body shall not be used.

4.13 Globe valves shall have tapered or conical discs. The use of flat seated discs shall not be permitted.

4.14 The maximum force required to operate the valves manually under service conditions, when applied at the rim of the handwheel or lever, shall not exceed 350 N, except for valve seating and unseating only, when it shall be permissible for this value to be increased to 500 N. Where reduction gearing is provided, it shall be suitable for operation at ambient temperature.

4.15 Valves for flammable service shall be designed to ensure electrical continuity to prevent build-up of static electricity.