Trelleborg’s Andrew Stafford considers how the maritime LNG sector can utilise process technologies seen in similar onshore applications
The internet has fundamentally changed the way in which users look at data communications. No longer are they limited to discrete point-to-point master and slave arrangements; now such systems are more fluid, with open interfaces where it is simple to add functionality.
Radio and distributed cloud networking are now accepted as valid solutions in a large-scale industry with various discrete I/O sensors, such as pressure, flow and temperature transmitters being integrated in conventional distributed control systems (DCS), with feedback control on various actuators and utilising wireless networks.
Ship-to-shore links (SSL) have a legacy dating back to the 1970s and involve connecting a cable or hose umbilical between the terminal and LNG carrier (LNGC). The typical and common arrangements are described within The Society of International Gas Tanker and Terminal Operators (SIGTTO) Emergency Shut Down (ESD) arrangement guidelines, as well as ISO28460. These links can be either fibre optic, electrical, or pneumatic.
One of the most challenging issues around SSL links is to maintain compatibility. The fleet of LNGCs has expanded rapidly over the last 15 years and the operating philosophy has changed from a liner trade based on project vessels to a spot market with global coverage.
Originally, LNGCs were equipped with adequate link connections to meet their trading patterns, whether the routes were southeast Asia to east Asia, or North Africa to Europe. As long as the loading and discharge ports had similar or known link types, a vessel would only need the simplest implementations.
The move to spot cargo trading has changed how links are evaluated. There is now a commercial driver to have the most flexible trading asset with compatibility on a global scale, which would translate to having all possible combinations of link types installed on LNGCs to suit any possible trading route. Although a limited number of connectors are used, the configuration of each terminal can contain subtle differences that require the vessel to change pin-outs to match the terminal facility.
ISO28460:2010 was published in an effort to simplify the link options. It detailed the options it considered appropriate and gave information on the types of links expected to be installed, as well as their standard configurations. This standard however is not enforceable, and has not been retrospectively applied, so the carriers are still in a situation of having to install all connector types with enhanced technologies to enable configuration switching to ensure compatibility.
There have long been discussions that wireless solutions should be considered for the SSL. They are used extensively in many other sectors, and for some specific applications could simplify the connection process, especially in fast turnaround bunkering type arrangements or inclement climates where temperature could be detrimental to hardwire solutions.
Radio SSL requirements
SSL-ESD systems are required to transmit an ESD signal without delay. This is easily achievable using hardwired fibre optic or electrical links. However, for pneumatics and radio-based systems this can be problematic. Radio-based systems would have to be configured with minimal latency, yet enhanced availability.
Wireless sensors and communication are well accepted in standard industrial process control. These applications are subject to site-specific radio surveys and have all the required antennae located in appropriate locations.
However, installing these radio systems on floating applications poses several challenges, including: vessel movement during operations; potential for other port activities taking place nearby; changeable weather conditions; and differing designs/size/topside construction of vessels using the facility.
All these considerations can have a detrimental effect on the radio link quality.
The challenge is to find a solution that can be implemented worldwide. Unlicensed frequencies are options. However, as with industrial, scientific and medical (ISM) radio band frequencies, there is no regulatory protection offered against interference from other sources operating in the spectrum. Interference could cause a healthy ESD signal to either be received as a trip, or to affect the link integrity monitoring and cause spurious ESD events or alarms.
Redundancy could be implemented using frequency diversity, whereby two totally separate bands are used to form a redundant link. While offering protection against short-term localised loss of signal from an event affecting a single frequency, frequency diversity is not immune to spark gap transmissions; therefore, the atmospheric effects of lightning can cause dropout of all radio communications for a period. Cost is also a consideration of implementing redundant frequency diverse solutions.
The bandwidth considerations of link requirements need careful consideration, as the chosen frequency band must be able to transmit the minimum features as previously defined. There are however considerable benefits to wireless ESD link solutions, such as a potential for the links to become connected and active at a distance before the vessel is actually alongside. For bunkering, this offers advantages in being able to have the supplier and receiver tanks in similar conditions, so there are no excessive pressures to be handled during the minimal bunkering period.
The same benefit is offered in large scale. However, as the cargo transfer time is extended compared to bunkering, the time saving at the beginning may not be considered as much of an advantage. Pre-berth testing however does make a radio system seem beneficial.
Probably the single most common failure of a hardwired SSL will be with the physical connectors or umbilical cables, as they can be mistreated and suffer from dirt and water ingress, which can degrade the quality of the link. It has even been known for a vessel to move along the berth and damage the cable through stress. Radio has none of these failure modes, so long as the installations are permanent and there is no chance of a vessel sailing while retaining some key terminal components on board.
In more complex vessel arrangements, such as a floating storage and regasification unit (FSRU), there could be mechanisms offered by radio connectivity to provide a more integrated solution between terminal, FSRU and LNGC. This is because current solutions are based on discrete links between single-party connections and so there is no overview of all connected systems.
The process of transferring LNG will always involve a physical connection between two parties, either via loading arms or hoses. Hardwired ESD links form a small part of this connection process and so long as the links remain common and are well tested, they will be a negligible component of the overall connection. There are ways of speeding this connection up, and there are currently bunkering projects underway to integrate the ESD link cabling with other equipment being transferred between the two parties. It may only save a couple of minutes, but it is an example of how these systems can still be enhanced after 40 years of field operation.
The primary concern when considering the efficiency of radio ESD links is that a proliferation of various solutions will be implemented before it is understood that global compatibility is required. LNG and LPG vessels trade worldwide and so any radio solutions will be based around a frequency and bandwidth for the operation to establish a reliable safety communication link. Any practical solution would have to ensure that these parameters are accepted globally at all ports and be compatible with radio frequency licence allocations for all countries.
Andrew Stafford is technical director at Trelleborg Marine Systems.