Offshore platforms for oil and gas production are complicated technological systems, the successful operation of which largely depends on the provision of their fire safety. A fire hazard with serious consequences determines high requirements to the fire protection equipment, which can be fulfilled using robotic fire suppression systems.
Oil and gas production platforms are objects of increased risk, which is due to the presence of flammable and explosive materials, large number of densely located technological equipment and social and household utilities, remoteness from the main forces and means of fire and rescue services. The analysis of fire- and explosion-induced accidents at oil and gas production platforms that took place in the world indicates the severe consequences associated with the death of people, destruction of technological equipment and pollution of the surrounding water area leading to irreparable losses, significant material damages and environmental disasters.
Statistics of accidents that occurred at oil and gas production platforms for a certain period showed [1] that losses from equipment damage due to fires make 52% of the total number of accidents (Table 1).
Table 1
The table clearly shows that fires have the most severe consequences. That is why the reliability of the fire protection systems and equipment of offshore platforms in general is critically important.
Prevention of fire spreading and explosion as a result of an accident on the platform, with entail catastrophic consequences, can be achieved as a result of prompt and timely fire and emergency operations undertaken in order to localize and extinguish the source of combustion, cool the technological equipment with the purpose of prevention of its further destruction. Carrying out of these measures by efforts of the platform personnel seems to be rather difficult task due to their small number and the need of evacuation from the emergency facility. Involvement of external forces and means using vessels equipped with equipment for water/foam fire-extinguishing agents supply may not have the desired effect due to their untimely arrival to the emergency platform at the initial stage of the fire, when it is still possible to localize and eliminate the source of combustion, impossibility of water-foam agents supply directly to the combustion zone as a result of dense location of technological equipment, as well as possible severe meteorological conditions (Fig. 1). All this necessitates the maximum automation of the process of detection and extinguishing the combustion sources on oil and gas production platforms using unmanned technologies.
Fig. 1. Fire extinguishing on the platform using specialized vessels
The solution of this problem can be achieved through the use of robotic fire suppression systems (RFSS) representing a set of automatic fire alarms and remotely controlled fire monitors, which make it possible to detect a fire source in its initial stage automatically, activate the targeting system of fire monitors and supply fire extinguishing agents directly into the source of fire and on the protected equipment. The distinctive feature of robotic monitor systems is the possibility to adapt them to the conditions of non-deterministic development of an emergency, thereby optimizing the fire extinction mode, providing the necessary intensity of water-foam agents supply to the most dangerous technological zones without the direct presence of people. A RFSS is capable of protecting large areas from one location, which range from 5 to 15 thousand sq. m at a flow rate of 20 to 60 L/s, respectively. Water supply is carried out only through the main water line, without a web of distribution networks typical for sprinkler and deluge systems.
If necessary, the system can be controlled remotely from a safe place via a radio channel. The software control and developed algorithms make it possible to optimize the modes of supply of fire extinguishing agents, taking into account the dynamics of situation development and external natural factors, particularly, the wind load. The RFSS are made on the basis of remotely controlled fire monitors, IR fire detectors, and TV cameras for video control. The sensitivity of a fire source detection is 0.1 sq. m, and the response time is within few seconds. The coordinates and dimensions of the fire source are determined in a 3D coordinate system. Fire extinguishing data are recorded by video cameras supported by logging the sequence of actions. During standby time, the system performs self-testing and reports about the need for correction to a specified address, maintaining it in constant operational readiness.
In its basic version, a RFSS includes two or more firefighting robots, consisting of the following components: a fire monitor with elevation and train power drives, a nozzle with a spray angle variation drive, and a control panel (Fig. 2). These components are connected to the switch unit (BK-16) at the input, and the control unit (CU) at the output. Taking into account the specifics of RFSS operation under conditions of possible formation of explosive gas concentrations, the elements and assemblies can be made in an explosion-proof design.
Fig. 2. Schematic diagram of a robotic fire suppression system
The monitor has 3D position control mechanisms and includes moving elements. To provide movement pf the elements, an electric, hydraulic or pneumatic drive can be used. A mechatronic system is a combination of electromechanical components with power electronics controlled by built-in microcontrollers. This reduces the weight and size of the system and increases its reliability. The positions of the working body in space and the environmental data are determined by the sensor part of the system: position sensors, pressure sensors, IR sensors. The signals transmitted by the sensors are analyzed, and a decision on further actions is made based on the results of this analysis. The control system is based on the principles of feedback, subordinate control and hierarchy of the robot control system. The position-based drive control system (by monitor’s angle of rotation) is closed by positional feedback. Within the position control system, there is a speed control system with its own feedback, in which, in turn, there is a current control loop with appropriate feedback. The hierarchy of the robot control system implies the division of the control system into horizontal layers that control the general behavior of the robot, calculation of the required path of the monitor’s movement, behavior of its individual drives, and the layers that directly control the driving motors.
The control unit generates control commands for targeting the monitor and fire extinguishing. The fire detecting and TV-monitoring device is installed on the monitor so that its optical axis is located in the direction of fire-extinguishing agent supply. This device is connected to an IR and UV signal processing device, in which the algorithms of the fire source coordinates determination are implemented by software, with a video monitoring device and a control device. As a result, each point of the protected area is covered with at least two streams and monitored by two fire detection and TV monitoring devices. On the monitors, a driven butterfly valve and a pressure sensor connected to the switching unit at the input and to the control device and addressable fire detectors at the output are installed additionally.
Flame detection is performed through complex frame-by-frame analysis of the image from the IR matrix and video camera, with confirmation by a UV sensor, allowing to cut off false signals. Regions of increased temperature are determined on the image from the IR matrix, and data on the temperature parameters fluctuation, boundaries and structure dynamics are accumulated and evaluated for these regions. For the same areas, the analysis of the flame characteristic features on the video image (fluctuations, color, dynamics of boundary changes) is performed. The analysis algorithms are implemented in such a way as to exclude false response to the radiation of heated bodies, welding, flashing beacons, sunlight and artificial light sources. To reduce the signal-to-noise level on a video image, a HD-SDI video camera without compression is used as a source, thus making it possible to improve the resolution for video analysis and achieve high-quality Full HD video to the video recorder. Video image analysis is performed at a frequency of 25 Hz, and infrared image analysis at 15 Hz. In case of flame detection, the detector transmits the fire source coordinates to the firefighting robot. Firefighting robots transmit data on the fires detected to the object interface, which determines the location of the fire in the protected area in a 3D coordinate system by the triangulation method, taking into account the measurement errors.
The leader in the creation of optical detectors of ignition operating both in visible and infrared ranges, is Tyco, USA, a part of Johnson Controls. The Flame Vision FV-312SC flame detector developed by these companies is equipped with a built-in TV-camera. The product is expensive and subject to sanctions. Within the frameworks of import substitution works, FR LLC managed to develop a domestic flame detector IP 328/330-1-1 in an explosion-proof design, which has a much lower cost and higher performance and accuracy in determining the ignition coordinates (Fig. 3). Explosion-proof firefighting robots have been created on their basis.
Fig. 3. IP 328/330-1-Ех Flame Detector
The purpose of a robotic fire suppression system and firefighting robots included in its composition is to direct the stream to the fire source according to specified coordinates, and extinguish the fire source over a given area with a given coverage intensity. The angular coordinates of the fire source in the horizontal plane coincide with the angular coordinates of the monitor targeting coordinates. Due to the curved stream trajectory in the vertical plane, the angle of inclination of the monitor must be higher than the angular coordinate of the target (source of ignition) in order to hit the target. The difference between them forms the elevation angle, which depends on the distance to the source, target angle, network pressure, flow rate, spray angle, and nozzle design. The problem of targeting the stream to the fire source with given coordinates is reduced to determining the elevation angle. In this case, it is important that the calculated trajectory coincides with the real stream trajectory with sufficient accuracy. The theory of ballistics proposed equations for the body’s path of travel in the air. For an approximate calculation of the stream, these equations may be used only on the initial path of travel, and require to determine the empirical coefficients. This is due to the need to take into account the change in the stream area, the shape and mass of water droplets fragmented during their flight, the transition from a compact stream to a two-phase turbulent liquid/air flow with variable density. Taking into account a large number of factors influencing the stream trajectory, and the absence of an accurate mathematical model of the stream trajectory, a special method was developed using experimental data for a family of trajectories in this work. For data acquisition, we performed engineering photo survey of the trajectories of several hundred streams with different flow rates, pressures, and targeting angles. A technique was developed for predicting trajectories based on the available experimental data (Fig. 3-4). As a result, a good degree of coincidence of real and calculated stream trajectories was achieved. The calculated trajectories can be used both to determine the covering zones and the targeting angle according to the given coordinates. The Ballistics software presented on the firerobots.ru website is widely used by designers from various companies.
Fig. 4. Stream trajectories as a function of targeting angle for flow rate and pressure data
Fig. 4-1. Application for stream trajectories calculation and stream targeting angle determination
The research work on the stream ballistics based on experimental data and confirmed by numerous experiments, made it possible to solve the problem of stream targeting to the fire source at given coordinates and extinguishing the source within a given area with a given coverage intensity.
The accuracy of the stream supply to the fire source according to the specified coordinates along the ballistic trajectory depends on the flow line pressure change, and on the stream deflecting wind speed for outdoor systems. By technical solutions according to European patent 2599525 “Automated FFC integrating a TV-system" the function of stream determination relative to the fire source was introduced into the IP 328/330-1-1 flame detector. This makes it possible to correct the stream targeting according to the calculated data of its ballistic trajectory.
In Fig. 5, areas with significant differences from the background are highlighted with green color. Blue color shows the result of approximation of the upper part of the contour (second order polynomial), taking into account the influence of perspective. It can be seen that the blue curve coincides with the ballistic trajectory of the stream.
Fig. 5. Digitized video frame with identification of fluid flow
Under operating conditions of oil and gas production platforms, in the presence of wind action, it is necessary to take into account the corrective component when targeting the water-foam stream supply to the fire source. In order to correct the fire monitors targeting for water-foam stream supply to the combustion source under conditions of an external wind load, studies were carried out [1], as a result of which an integrated vision system was designed, which made it possible to assess the real deviation of the stream from a given direction and enter the correction factors in the above ballistic stream calculations of the monitor targeting algorithm. Fig. 6 shows the results of operation of the developed application software that solves the problem of determining the parameters of the stream trajectory to control the monitor by azimuth using the horizontal projection of the solid model (Fig. 6 a) and elevation using the vertical section of the solid model (Fig. 6 b).
Fig. 6. The result of the application software for adjustment of fire monitor targeting
These techniques are used in new automatic fire suppression systems operating in extreme conditions dangerous to human life, and in unmanned technologies, especially important for objects located in sparsely populated areas of Siberia and the North, and can also be used for fire protection of offshore oil production platforms.
Technical requirements applicable to the RFSST are defined in GOST R 53326-2009. It should be noted that Russia is the first country in the world where a new type of automatic fire suppression systems, namely the robotic fire suppression systems, have been legislatively and normatively introduced. They are included in the country's Federal Law No. 123-FZ “On fire safety”, the Code of Regulations SP5.13130.2009 for fire suppression systems designing, the state standard GOST R 53326-2009, and the departmental fire safety norms VNPB 39-16 for robotic fire suppression systems [3]. Fixed firefighting robots based on fire monitors have found wide practical application [4-5]. For example, RFSST developed by FR LLC were used in the objects of the oil and gas sector: the Syzran, Moskow, Tuapse, Achinsk and some other oil refineries, oil platforms of the Lukoil company, offshore oil terminals in Burgas and under the Sakhalin-1 and Sakhalin-2 Projects, oil berths in the Black Sea (Novorossiysk), the Baltics (Vysotsk, Ust-Luga), the Arctic zone on the White Sea (Vitino). As applied to offshore platforms, RFSSs are currently used to protect the runway of the ice-resistant platform LSP-2 in conjunction with the technological platform LSP-1 at Yu. Korchagin oilfield in the northern part of the Caspian Sea. LSP-2 includes a support block, living module for 105 cabins with a runway located at the top (Fig. 7). To eliminate the need for people to be on duty at the monitors, two electrically-driven robotic monitors are installed there instead of two manually controlled monitors. The monitors can operate in remote control mode using wired remote controllers, as well as using a remote radio controller from any room or area of the open deck, accessible via a radio channel. The possibility of local manual control of the fire monitors also retained.
Fig. 7. General view of the offshore platform at Yu. Korchagin oilfield in the northern part of the Caspian Sea with a landing ground equipped with RFSS
