Sensory perception

In offshore application, the workers’ lives and the asset’s integrity can all come down to the tiny sensors within a gas detector.

City Technology’s John Warburton discusses why gas sensors are so essential to high-performance gas detection while examining how the right sensor solution can deliver tangible savings and value in offshore applications.

Twenty years ago, computers were purchased with little understanding of inner component workings or the clever technology that actually made the device perform so well and effectively. Today, thanks to a an effective global marketing campaign from a leading processing chip manufacturer, we now all appreciate that our computers are only ever as good as their processing capacity, regardless of any other impressive functionality they might offer.

This is a good analogy for the gas detection industry; there is much focus on the gas detection solution itself and all the value such a device can bring, but the sensor component itself is equally important.

No room for failure

Fixed and portable gas detection forms an intrinsic part of offshore safety. The sensors used within such devices have a very hard job to undertake. Not only must they detect gas risks accurately and reliably, but they must do so consistently and in all environmental conditions. Factors like sea spray or salt particulates, cross-sensitive compounds, poisons and temperature, pressure and humidity fluctuations must all be considered and compensated for effectively. A high-quality sensor must be designed in such a way that it can overcome any challenges.

Failure is not an option in such applications: Lives and assets depend on the highest grade of safety provision.

Gas risks are numerous and ever-present offshore, including hydrocarbons like methane, alcohols like methanol, and toxic gases like hydrogen sulphide, sulphur dioxide, nitrogen oxide and carbon monoxide.Standards and minimum provisions vary considerably across the globe. ATEX and EN/UL/FM/CSA regulations are constantly evolving, and they represent a high provision of safety in terms of global standards. As an interesting example, the poisoning of flammable sensors is a recent hot topic in the Asia Pacific region, following the Chinese government’s recent announcement of the new flammable gas detection GB153221.1 Standard which becomes effective 2015, designed to enhance safety through more stringent controls over flammable detector performance.

Globally, society is becoming increasingly safety conscious, which has resulted in more stringent insurance criteria. This criteria is a catalyst for greater accountability and protection. As a result, today’s sensors need to work harder than ever.

Meeting offshore needs

Maintenance is also a key consideration for offshore applications because of the vessels’ distance from land-based resources. The right sensor choice can assist dramatically with this aspect; extended calibration and easy sensor switch-out functions deliver considerable value. Reliability is also essential - a sensor with an inherently stable design can facilitate such ongoing maintenance value, by its ability to compensate effectively for any factors that could be a potential challenge. One of the most important jobs of a portable gas detector in offshore applications is protection in confined spaces like tanks, pipelines, drains, culverts and hollow platform legs. Fixed gas detection is featured prolifically offshore; flammable, hydrogen sulphide and oxygen detection is required at driller stands, shale shakers and drill floors; compressors, pipelines and seals require flammable detection; drains and run-off gullies must also be monitored for hydrogen sulphide, carbon dioxide, and nitrogen oxide. These are just a few examples.

With increased safety regulations, a lot is demanded from gas sensors.

Geological and environmental impacts

Aside from the obvious associated industry risks, it is worth noting that regional factors can have a big impact on sensor use. For example, in the Caspian Sea, oil and gas demands have led to exploiting sourer wells rich in hydrogen sulphide.

Depending on the geology, varying well constituents will be extracted presenting a huge variety of flammable risks that must be negated. A flammable sensor must be able to cover all these gases, their differences, and compensate accordingly to deliver leading-edge performance. Any sensor manufacturer will tell you this takes considerable effort, scientific talent and expertise. Extracted, raw crude can contain a diverse mix of hydro- carbons in varying quantities, from small chains like methane hydrate; to aromatics, like benzene; and alkynes, like butadiene. Flammable sensors must be able to adapt to the different flammability of these hydrocarbons.

Cash is king

Second only to safety, cost is the next biggest factor in selection. A manufacturer should deliver the following essential combination: highest performance/accuracy (in all-weather/temperatures/potential cross-interference conditions); intelligent affordability (real-world value fully aligned with the offshore industry itself); and reliability.

I am often asked what to consider when selecting the right sensor solution. The offshore oil and gas industry provides the ideal context to highlight the core attributes needed, because it represents some of the most challenging locations for gas sensors to work in. There is the potential for ingress by compounds and water vapour/sea spray that must be prevented using filters, sinters and small capillaries. Ambient conditions can change and temperature can fluctuate due to weather systems and the effects of being out on deck and then inside.

Sensors from leading manufacturers should be designed and tested to respond to such conditions and meet the maximum range a device could ever encounter, working between -40°C and 55°C. They should include technologies and components that allow the sensor to adapt quickly to fluctuations.

Other sensor challenges

Humidity is a particular concern for electrochemical cell (ECC) sensors. Shifts can be large depending on climatic conditions. Leading-edge ECC sensors must work effectively across various RH conditions, meeting the demands of even the most challenging locations through their intelligent component design, which must prevent drying out or saturation. A sensor with inherently stable design will also overcome any potential issue created by pressure fluctuations.

Accidents happen and portable devices can easily be dropped. Fixed gas detectors are also subject to vibration from sea storms and on-structure processes, so sensors need to be highly robust and capable of withstanding impacts and mechanical vibrations.

Sensors must also be able to minimize the effects of cross- interference, which could cause inaccurate readings and nuisance alarms. There are various compounds that can impact sensor performance including alcohol-based deicers and a high performance sensor must be able to perform accurately in the presence of cross-interference compounds.

A sensor specifically designed and tested to meet the needs of an offshore application is a must and it is recommended to work with a manufacturer well-versed in your application. Benchmark recommendation is to request proven data on performance – if a manufacturer cannot prove the suitability of your sensor to your application, this is a red light indicator the sensor is not optimized for such a use.

Reduce maintenance – save money

Various factors combine to make a sensor capable of extending maintenance intervals. The impact of sensor swap-out ease and sensor testing should also be considerations. All aspects will impact any potential saving/value you may be able to leverage.

Something that is often overlooked is the importance of repeat ability; you need to be able to rely on your manufacturer’s processes and controls so that each sensor you use works exactly as it should, every time. A gas 

detector cannot afford to lose even a moment’s effective detection performance and it uses its sensing capability to fulfill this remit. Just one faulty sensor can really be the difference between life 

and death, so take a holistic approach to selecting a manufacturer and be sure that their production practices can deliver consistent high quality results. One sure fire way to assess this yourself is to ask to see manufacturing facilities and processes and also failure ppm data (the calculation of how many sensors out of every million are probable to fail).

John Warburton is the Strategic Marketing Manager of City Technology, and , part of Honeywell Inc.,works to deliver sensing solutions entirely optimized and tested to meet the demands of offshore applications.