A background to leak detection techniques

Leak detection technology can reduce the risks of contamination in the manufacturing process and exposure of staff to hazardous chemicals, as Kenji A Kingsford explains

Leak detection technology can reduce the risks of contamination in the manufacturing process and exposure of staff to hazardous chemicals.

In this article Kenji A Kingsford examines leak detection techniques with the emphasis on fibre-optic systems.

Effective leak detection can make a considerable difference to a company's productivity and, in highly competitive industries, even a 1% difference in yield can have the same considerable impact on profit and give one company a competitive edge over another.

One factor that can affect productivity is contamination of the process through leakage.

Without effective leak detection technology, contamination may not be discovered until the end of the manufacturing process, when it is almost certainly too late.

By the time contamination is detected, the end product may already have been ruined.

This can translate into thousands of pounds in loss of product and productivity, scheduling efficiency and other negatives.

Other obvious risks from for example, chemical leaks include environmental and human safety issues.

Contact with strong chemical solutions such as acids will cause extensive injury and inhalation or contact with caustic fumes can irritate workers' lungs, eyes and skin.

Yet with all these risks many manufacturing plants are still slow to incorporate leak detection technology, largely due to cost considerations.

Leak detection isn't cheap, but compared to the savings achievable by early detection, it is more than justified.

There are many different leak detection technologies available and the best of these combine secondary containment systems with some form of leak detection technology, to identify component failure before critical contamination happens.

Secondary containment systems allow time to respond to component failure before it becomes critical, while reducing hazards by safely containing chemicals.

Combined with leak detection, this allows timely identification and replacement of failed system components.

Rapid identification of the failed component significantly reduces hazard to humans and reduces the risk of system contamination because the failed part can be replaced before it becomes a source of contamination.

Visual inspection will reveal leaks dripping directly from failed components.

Viewing ports linked to secondary containment systems also allow visual detection of fluid leakage.

Unfortunately manual inspection may expose workers to hazardous chemicals.

The increasing trend towards process automation also means fewer humans are available to observe leaks in time.

Capacitive sensing uses an electric field to detect changes in mass caused by fluid build-up.

Its drawbacks include collateral damage to other components caused by external chemical contact as leakage drips, and it introduces the risk of explosion.

Capacitive sensing typically generates the sensing field using metal wires interconnected within the containment, where a single spark could ignite flammable chemicals and fumes.

Also, even if there is no leak, metal wires can be attacked by chemical fumes, which may cause unreliable operation.

Conductive sensors also detect the presence of fluids, but are restricted to use with conductive chemistries such as acids.

Non-conductive fluids such as de-ionised water and various solvents will not be detected.

There is also a risk of explosion through ionic contamination due to metallic contacts interacting with process chemicals, and the signal may be interrupted if wiring is attacked by chemicals or fumes.

Ultrasonic detection uses ultrasonic sound waves to detect disruption of the field.

It poses problems similar to capacitive sensing, such as risk of explosion and failure due to chemical attack.

Fibre-optic leak detection systems feature a non-contaminating plastic or glass probe that detects the difference in refractive index at the surface of the probe when liquid is present.

They will detect any type of fluid and are not sensitive to turbidity or conductivity of the fluid being detected.

Fibre-optics are intrinsically safe, requiring no electricity or metal wire, and pose no risk of explosion due to sparks or electric current.

Systems use two cables: one signals down to the tip, the other signals back up the cable.

This is a fail-safe system, since any change in the returning signal will activate an alarm.

Finally, there is no undesirable electronic 'noise' to affect surrounding equipment, making this a very safe, low-impact technology that identifies problems quickly, with minimal loss of productivity.

Fibre-optic leak detection, combined with secondary containment with leak ports, allows efficient, effective monitoring of critical chemical systems in real-time.

Timely warning allows components to be changed quickly, reducing the risk of contamination of the process due to component failure, and ensuring human safety.

There are several approaches to setting up a fibre-optic leak detection system.

Selection is largely influenced by cost and the level of detection accuracy required.

A dedicated fibre-optic leak detector for each component in the system allows rapid identification of the specific component that has failed.

Failure detection occurs at the earliest possible stage while fluid is still within the secondary containment component, and there is no damage to other components from the chemical leakage.

This is a very accurate and timely method.

A 'neural network' set-up - where a number of components are connected together -also allows rapid identification of failed components with the benefit of reduced cabling compared to dedicated detectors.

This is a sophisticated and more costly solution, which requires proprietary software and processor capabilities.

Using a leak detection module in conjunction with a fibre-optic module allows up to 16 components to be monitored with a single fibre-optic sensor.

This technique will not identify the specific failed component, but will pinpoint failure within the group.

Visual inspection can then determine which component has failed.

This method is one of the most affordable, but may not be appropriate where accurate identification of a specific component is required.

The risks associated with contamination in wet-process applications are considerable and fibre-optic leak detection, in conjunction with secondary containment, is the best available technology to detect component failures before exposure to the external environment.

It also eliminates risk to humans and damage to other system components.

While the initial investment may appear high, a cost comparison between the installation of a fibre-optic system and the potential loss of productivity will demonstrate the savings achievable by proactive prevention of contamination.

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