Section 1 Special Requirements
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Offshore Units, July 2022 - Part 11 Production, Storage and Offloading of Liquefied Gases in Bulk - Chapter 17 Special Requirements - Section 1 Special Requirements

Section 1 Special Requirements

Parent topic: Chapter 17 Special Requirements

1.1 General

The provisions of this Chapter are applicable where reference is made in column ‘i' in the Table 19.1.2 Explanatory notes to the summary of minimum requirements.

1.2 Flame screens on vent outlets

When carrying a cargo referenced to this Section, cargo tank vent outlets shall be provided with readily renewable and effective flame screens or safety heads of an approved type. Due attention shall be paid to the design of flame screens and vent heads, to the possibility of the blockage of these devices by the freezing of cargo vapour or by icing up in adverse weather conditions. Flame screens shall be removed and replaced by protection screens in accordance with Pt 11, Ch 8, 1.2 Pressure relief systems 1.2.16 when carrying cargoes not referenced to this Section.

1.3 Cargo pumps and discharge arrangements

1.3.1 The vapour space of cargo tanks equipped with submerged electric motor pumps shall be inerted to a positive pressure prior to loading, during carriage and during unloading of flammable liquids.

1.3.2 The cargo shall be discharged only by deepwell pumps or by hydraulically operated submerged pumps. These pumps shall be of a type designed to avoid liquid pressure against the shaft gland.

1.3.3 Inert gas displacement may be used for discharging cargo from Type C independent tanks provided the cargo system is designed for the expected pressure.

1.4 Carbon dioxide – High purity

1.4.1 Uncontrolled pressure loss from the cargo can cause ‘sublimation’ and the cargo will change from the liquid to the solid state. The precise ‘triple point’ temperature of a particular carbon dioxide cargo shall be supplied before loading the cargo, and will depend on the purity of that cargo, and this shall be taken into account when cargo instrumentation is adjusted. The set pressure for the alarms and automatic actions described in this Section shall be set to at least 0,05 MPa above the triple point for the specific cargo being carried. The ‘triple point’ for pure carbon dioxide occurs at 0,05 MPa and –54,4°C.

1.4.2 There is a potential for the cargo to solidify in the event that a cargo tank relief valve, fitted in accordance with Pt 11, Ch 8, 1.2 Pressure relief systems, fails in the open position. To avoid this, a means of isolating the cargo tank safety valves shall be provided and the requirements of Pt 11, Ch 8, 1.2 Pressure relief systems 1.2.10.(b) of this Part do not apply when carrying this carbon dioxide. Discharge piping from safety relief valves shall be designed so they remain free from obstructions that could cause clogging. Protective screens shall not be fitted to the outlets of relief valve discharge piping so the requirements of Pt 11, Ch 8, 1.2 Pressure relief systems 1.2.16 of this Part do not apply.

1.4.3 Discharge piping from safety relief valves are not required to comply with Pt 11, Ch 8, 1.2 Pressure relief systems 1.2.11, but shall be designed so they remain free from obstructions that could cause clogging. Protective screens shall not be fitted to the outlets of relief valve discharge piping so the requirements of Pt 11, Ch 8, 1.2 Pressure relief systems 1.2.16 of this Part do not apply.

1.4.4 Cargo tanks shall be continuously monitoring for low pressure when a carbon dioxide cargo is carried. An audible and visual alarm shall be given at the cargo control position and on the bridge. If the cargo tank pressure continues to fall to within 0,05 MPa of the ‘triple point’ for the particular cargo, the monitoring system shall automatically close all cargo manifold liquid and vapour valves and stop all cargo compressors and cargo pumps. The emergency shutdown system required by Pt 11, Ch 18, 4 Linked emergency shutdown (ESD) system of this Part may be used for this purpose.

1.4.5 All materials used in cargo tanks and cargo piping system shall be suitable for the lowest temperature that may occur in service, which is defined as the saturation temperature of the carbon dioxide cargo at the set pressure of the automatic safety system described in Pt 11, Ch 17, 1.4 Carbon dioxide – High purity 1.4.1.

1.4.6 Cargo hold spaces, cargo compressor rooms and other enclosed spaces where carbon dioxide could accumulate shall be fitted with continuous monitoring for carbon dioxide build-up. This fixed gas detection system replaces the requirements of Pt 11, Ch 13, 1.6 Gas detection of this Part, and hold spaces shall be monitored permanently even if the ship unit has Type C cargo containment.

1.5 Carbon dioxide – Reclaimed quality

1.5.1 The requirements of Pt 11, Ch 17, 1.4 Carbon dioxide – High purity also apply to this cargo. In addition, the materials of construction used in the cargo system shall also take account of the possibility of corrosion in case the reclaimed quality carbon dioxide cargo contains impurities such as water, sulphur dioxide, etc. which can cause acidic corrosion or other problems.

1.6 Nitrogen

1.6.1 Materials of construction and ancillary equipment such as insulation shall be resistant to the effects of high oxygen concentrations caused by condensation and enrichment at the low temperatures attained in parts of the cargo system. Due consideration shall be given to venitilation in such areas, where condensation might occur, to avoid the stratification of oxygen-enriched atmosphere.

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