Noise mapping offshore using wireless sensors

Many of the latest technology developments in relation to offshore oil and gas production installations have emerged from Norwegian research studies, because that industry represents the major part of the economy in Norway.  Such research studies do not only relate to better and more efficient methods of working, but they also investigate the health and safety aspects of the industry: an area of particular concern has been hearing damage to workers offshore, which is the predominant cause of work related illness. At the Yokogawa User Group meeting held in Budapest in May 2016, Simon Carlsen of Statoil ASA in Norway explained the background to a recent project that was undertaken to improve the efficiency of the noise surveillance and monitoring systems Statoil use offshore. This was also presented to a Society of Petroleum Engineers International conference on Health and Safety in Stavanger in April (Ref 1).

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The main Health & Safety tool used for monitoring noise exposure is the ‘Noise map’, which provides noise level contours within rooms and around machinery where workers are active. These are used to establish a course of action where noise levels exceed allowed limits, whether this action is to reduce or remove the noise source (if possible), insulate the area, issue PPE to workers, and/or impose working time restrictions. Noise maps have historically been based on manual surveys that take single point readings, which are then plotted onto a site map, typically from CAD drawings. Manually taking and plotting these measurements is arduous and time consuming, and typically would be updated only on around a four year cycle. Plus the readings are (obviously) not continuous, only record the conditions when each reading was taken, and generally do not record the added effects from workers using different machinery and tools in the area.

Statoil R&D on wireless & noise instrumentation

Simon Carlsen of Statoil joined the R&D Department in 2006, bringing expertise in wireless instrumentation, and started investigating the feasibility of using wireless sensors and software techniques to create a real-time noise map. The system subsequently commenced became known as WiNoS, for “Wireless Noise Surveillance”, when formally initialised in 2013. This will consist of a network of wireless noise sensors, continuously monitoring the noise in the process area, using sound pressure level (SPL) measurements of four types: A-weighted SPL (I.eqA), C-weighted SPL (I.eqC), peak SPL (I.peak) and thirty one separate third-of-an-octave frequency band measurements from 25Hz to 16kHz. This data is much more comprehensive than the simple noise level measurements used to establish the noise maps, but will superimpose this data onto the historically available maps. These readings can then be used to update the map in real time, and create alarms available to operators.

The WiNoS sensors then use an industry standard wireless network infrastructure, which transmits the data into the control system, where special software produces the updates to the noise maps – typically on a one minute update rate (ie almost continuous). This live information can be used to create alarms to report back to workers in the area, to control their noise exposure. The objective is to reduce work-related hearing damage, by knowing the actual on-site conditions; to optimize operator time working on/near tools, to reduce daily exposure; and to provide instant feedback on the effect of noise reduction measures. In addition WiNoS allows for time synchronized measurements amongst the sensors in the network, and also allows the control room operator to trigger a download of a high resolution frequency spectrum waveform from any sensor of particular interest, to analyse the signature of the noise. This latter is a major part of the future development of the monitoring system, which will feed into plant condition and process performance monitoring studies.

noise-map-3

The WiNoS project development employed the expertise of the Norwegian companies Norsonic AS in the microphone design and the sound level measurements, and the Department of Acoustics at the research company SINTEF to develop the PC software that records the data and creates the noise maps. The software was also required to conform to the Statoil qualified communications protocol.

Choice of wireless network

A major part of the research feasibility study that preceded the WiNoS project was devoted to the choice of the wireless network to be used to efficiently and reliably transmit the data, relatively continuously from multiple sensors. The two suitable networks that were emerging at that time were WirelessHART and ISA100.

The WirelessHART system is now well-known and fairly widely used in Statoil facilities, but the early research trials showed mixed experience with the system and the relevant vendors – some of this was related to the lack of specification details written into the WirelessHART standard. But there were also challenges with achieving the power efficiency in the transfer of all the data required, and the requested large data transfer of the high-res waveform was not readily achievable.

The ISA100.11a wireless transmission standard was also in use in Statoil, and had been adopted for the wireless flammable gas detector pioneered by GasSecure in Norway – Statoil had been involved with the prototype field trials offshore. The initial trials on ISA100 equipment from Yokogawa provided high flexibility for the different application demands, allowed all the 31 one third octave values to be packed into one transmission telegram, and allowed a well-defined block transfer. The sensor could also achieve the two year life required from the installed battery pack, at the 1 minute update rate.

The decision was made that ISA100.11a was to be the preferred protocol for WiNoS, from a technical and project model perspective. Based on the earlier experience of development co-operation with Statoil, it was decided to invite Yokogawa to join the WiNoS project as a Co-Innovation partner, a role that they were keen to develop. In addition to providing the ISA100.11a wireless interface electronics for the sensor, and the interface into the third party control system, Yokogawa worked with Norsonic to develop the mechanical housing for the microphone sensor, and the electronic hardware to process the sound measurements using the Norsonic software, with the whole sensor assembly meeting ATEX requirements.

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A Yokogawa wireless temperature transmitter adapted to include the Norsonic microphone

Full system test

In March 2016, a network of 7 off Yokogawa ISA100 enabled wireless noise sensors were tested within the (land-based) industrial lab hall at Statoil Rotvoll, in Trondheim, which has dimensions 35x25x15 metres – and contains various pumps and process equipment. Further synthesized test noise sources were created using loudspeakers. The wireless sensors, the noise mapping software and the IT backhaul architecture all operated reliably and successfully.

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Dynamic noise map generated with the system test

 

A further test, offshore on an operational Statoil platform, is planned and scheduled for Spring 2017, for which Yokogawa will supply 20 production sensors and the ISA100.11a wireless system. A typical platform deck of 50×50 metres might in practice require around 12 noise sensors for effective coverage.

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Possibly future noise mapping sensors will be added in high noise plant areas

The Statoil WiNoS system is now ready for development into a commercially available product for use as an offshore platform noise mapping tool. Future research on this system will involve investigation of 3D noise mapping systems. Statoil consider that the equipment application has potential for expansion into machinery condition monitoring, to include automatic process upset or fault and leak detection.

© Nickdenbow, Processingtalk.info, 2016

References

 

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