New statutory Tanker requirements on the installation and operation of Inert gas systems
New statutory requirements for fixed inert gas systems will enter into force on 1 January, 2016, as a result of changes to SOLAS, the Fire Safety Systems (FSS) Code and the International Bulk Chemical (IBC) Code.
Background:
In recent years, there have been several incidents involving intank explosions on small oil and chemical tankers, many of which occurred in connection with gas-freeing and tank cleaning. The main reason is believed to be the lack of an inert atmosphere in the cargo tank, as these tankers are currently exempted from using inert gas.
As a consequence, it has been decided to lower the SOLAS inert gas limit from 20,000dwt to 8,000dwt. In addition, chemical tankers’ current exemption from inerting tanks of less than 3,000m3 will be lifted for new ships. Since this is not a retroactive requirement, it will only apply to new tankers constructed on or after 1 January 2016. In-tank inspections, a practice quite common prior to loading many chemicals, might cause logistical challenges and port congestion as new chemical tankers above 8,000dwt – irrespective of their tank size – will now have to purge their tanks alongside after the tank inspection when taking on low-lash products.
As a means to avoid this, the revised SOLAS allows the application of inert gas to be postponed until after loading but before the commencement of unloading. It should be noted, however, that because of the risk of generating static electricity by using exhaust gas, only nitrogen is acceptable for this purpose. This further implies that, in order to utilize this option, an N2 inert-gas plant should be installed on board, and of course this is something to bear in mind in connection with newbuilding specifications.
Consequential amendments have also been made to the FSS and IBC Codes. In the FSS Code, it is basically the oxygen limit for inert gas supplied to the tanks which has been reduced from 8% to 5%. The amendments made to the IBC Code include operational changes in the gas freeing and handling of inhibited products where the inhibitor is oxygen dependent and the products must at the same time be carried in an inert atmosphere.
The revised gas-freeing requirements are now more aligned with what is required for oil tankers under SOLAS, ie, that the tanks requiring inert gas should, after tank cleaning, be purged down to a certain limit of flammable vapours before gas freeing with fresh air may take place. Products protected by an oxygen-dependent inhibitor are currently not to be carried in an inert atmosphere, in other words such products are today carried in tanks of less than 3,000m3 on ships above 20,000dwt when the flashpoint is less than 60°C, the only exemption being for Styrene Monomer, which may be carried under inert conditions subject to special provisions.
In order to still be able to ship these products on new ships above 8,000dwt in future, the use of inert gas has been allowed provided it is not applied until discharging commences and the O2 level is kept above that stated to be the minimum O2 level on the inhibitor certificate. And, for the reasons previously mentioned, the postponed application of inert gas requires the inert-gas medium to be N2 and an N2 inert-gas plant to be fitted.
Main changes:
- The fitting of a fixed inert gas system will be required for tankers of 8,000 tonnes deadweight (dwt) and over, constructed (keel laid) on or after 1 January, 2016. Previously, this applied only to tankers of 20,000 tonnes dwt and over.
- Tankers 8,000 dwt and over, carrying low-flashpoint cargoes, and constructed (keel laid) on or after 1 January, 2016, must be provided with a fixed inert gas system complying with Chapter 15 of the amended FSS Code (or an equivalent system – subject to acceptance by the flag administration).
- The existing clause in SOLAS Regulation II-2/4.5.5.2 for waiving the requirements for a fixed inert gas system still applies to all gas carriers, but for chemical tankers it now only applies to those constructed before 1 January, 2016. This means that chemical tankers constructed (keel laid) on or after 1 January, 2016, and carrying flammable cargoes such as those listed in the IBC Code chapters 17 and 18, will be required to have a fixed inert gas system, regardless of cargo tank size and tank washing machine capacities.
Operational requirements for chemical tankers:
New SOLAS regulation II-2/16.3.3 clarifies the operational requirements for inert gas systems, and the sequence of applying the inerting medium into the cargo tanks.
Regulation II-2/16.3.3 allows chemical tankers the option to begin inerting their cargo tanks after the cargo tank has been loaded, but before commencing unloading, but only if nitrogen is used as the inerting medium. In this instance, the nitrogen inerting should continue until the cargo tank has been purged and freed of all flammable vapours prior to gas freeing.
The changes to the IBC Code clarify the operational procedures for new and existing chemical tankers.
Chemical tankers which carry products containing oxygen-dependent inhibitors:
Operators of chemical tankers that are required to be inerted and carry products containing oxygen-dependent inhibitors should note the following requirement, specified in Chapter 15.13.5 of the amended IBC Code:
“application of inert gas shall not take place before loading or during the voyage, but shall be applied before commencement of unloading”.
IMO circulars MSC.1/Circ.1501 and MSC-MEPC.5/Circ.10 should be read in conjunction with this requirement. These circulars state that when a product containing an oxygen-dependent inhibitor is carried on a ship for which inerting is required, the inert gas system shall be operated to maintain the oxygen level in the vapour space of the tank at or above the minimum level of oxygen required under paragraph 15.13 of the IBC Code and as specified in the cargo’s Certificate of Protection.
Relevant IMO resolutions:
- Amendments to SOLAS regulations II-2/4.5.5 and 16.3.3: MSC.365(93)
- Amendments to Chapter 15 of the FSS Code: MSC.367(93)
- Amendments to the IBC Code: MSC.369(93)
Source: DNV GL
