3.2 General Requirements
3.2.1 The main physical properties of gases stored in the low temperature steel storage tanks for petrochemical services shall be in accordance with Appendix A of this code，and the design conditions for low temperature steel storage tanks for petrochemical services shall include the information indicated in Annex B of this code.
3.2.2 The low temperature steel storage tank shall be designed to satisfy the following basic requirements：
1 The liquid and the vapour can be stored under normal operating conditions.
2 It can be filled and emptied at the specified flow rates.
3 Boil-off is controlled and in exceptional cases can be relieved to flare or vent.
4 Pressure operating range specified can be maintained.
5 Ingress of air and moisture is prevented，except in exceptional cases when the vacuum relief valves have to be opened.
6 Boil-off is as specified and condensation/frost on the external surface is minimized.
7 Damage due to specified accidental actions is limited and will not result in loss of liquid.
3.2.3 Low temperature steel storage tanks for petrochemical services should not be constructed in the areas with seismic precautionary intensity higher than 9 degrees or with design basic acceleration of ground motion greater than 0.40g.
3.2.4 Seismic design shall be made for the low temperature steel storage tanks for petrochemical services that are constructed in the areas with seismic precautionary intensity equal to or higher than 6 degrees or with design basic acceleration of ground motion no less than 0.05g.Seismic design of low temperature steel storage tanks for petrochemical service shall comply with the requirements specified in Appendix C of this code.
3.2.5 Vapour barrier may be provided for the outer pre-stressed concrete tank.The liquid tightness of the pre-stressed concrete structure，without a liquid tight liner，shall be ensured by the minimum compression zone in the concrete structure.
3.2.6 All inlets and outlets should，preferably，be made at the roof of the tank.In cases where bottom inlets and outlets are used，the external pipes should be welded to the bottom connection.
3.2.7 Fixed connections should，preferably，not be located within annular spaces between the primary and secondary containers.And if fixed connections are required，they shall comply with the specifications in Article 5.7 of this code.
3.2.8 The primary container shall provide a minimum freeboard above the maximum liquid level equal to 300 mm.
3.2.9 Markers for monitoring tank settlement shall be designed for the low temperature steel storage tanks for petrochemical services.
Tank settlement should comply with the following requirements：
1 For steel storage tanks，their differential settlement（the plane inclination，in mm）at diameter direction shall not exceed 125times the ratio of tank diameter to height；the differential settlement at the perimeter shall not exceed 10mm each 10m of circumference，and the differential settlement（in mm）between the tank center and the perimeter shall not exceed 1/240 of the tank radius.
2 For concrete storage tanks，their plane inclination shall not exceed 1/500，and the differential settlement between the tank center and the perimeter shall not exceed 1/300 of the tank radius.
3.2.10 Provisions against frost heave in foundation shall be designed for the low temperature steel storage tank for petrochemical service.The foundation heating system，if required，shall be designed so that the temperature of the foundation shall not drop below 0℃at any place.
3.2.11 Thermal protection system shall be provided for the pre-stressed concrete secondary container.The thermal protection system shall cover the whole bottom and the lower part of the wall，and shall consist of steel plates（double bottom）and insulation material.
3.2.12 The height of the vertical part of the thermal protection system shall be determined based on temperature distribution and the deformation of the rigid corner.
3.2.13 Protection against the impact of lightning shall be provided for the low temperature steel storage tanks for petrochemical services，and shall be in accordance with the current national standard Code for design protection of structure against lightning GB 50057，and Code for design protection of petrochemical plant against lightning GB 50650.
3.2.14 Firefighting facilities for low temperature steel storage tanks for petrochemical services shall be in accordance with the current national standard Fire prevention code of petrochemical enterprise design GB 50160 and any other applicable current national standards.
3.2.15 The design loads of low temperature steel storage tank for petrochemical service shall include：
1 Self-weights.
2 Hydrostatic load of the medium.
3 Pre-stress.
4 Imposed loads shall include：
1）Uniformly distributed load of 1.2kN/m2 over the projected fixed roof area.If snow load exceeds 0.6kN/m2，the excess load shall be included；
2）Uniformly distributed load of 2.4kN/m2 acting on the platforms and walkways；
3）Concentrated load of 5kN over an area of 300mm×300mm placed at any location on platforms or walkways.
5 Wind loads.
6 Seismic actions.
7 Snow loads.
8 The pressure exerted by the cold insulation system（including perlite powder）.
9 Design pressure.
10 Design negative pressure.
11 Test loads.
12 Thermal effects.
3.2.16 The corrosion allowance of the components of low temperature steel storage tanks for petrochemical services shall be determined based on corrosive characteristics of the stored medium and environment.