It pays to invest refrigerant leak detection

Published:  25 February, 2014

It pays to invest in refrigerant leak detection as part of your overall maintenance strategy. PWE reports.

With plant and process managers under pressure to contain leaks and minimise the environmental impact as well as the cost of lost refrigerant, leak detection has now become more of a priority than ever. All sealed systems leak and every pressure system has leaks because every joint seam or weld may contain flaws that are too small to detect.

A leak can be present as a result of a weakness in the weld or a small groove between pipe fittings. Even the tightest of systems which may have operated for years without a top up charge will still have leaks, but so small they do not show up on a gauge and performance will be largely unaffected.

If regular testing and detection is not carried out these leaks can soon become larger detectable leaks and could have a detrimental effect on your plant’s performance. Repairing leaks is not the problem, but with many techniques and technologies available, using the most appropriate method for your system to find them, can be confusing, as there are many common leak detection methods available.

With a greater focus on implementing EU directives, F-Gas Regulations and pressure from trade bodies, leak detection is now a mainstream issue.

It is estimated that as much as 30% of refrigerant is lost annually through leaks in refrigeration and HVAC equipment. The environmental impact, refrigerant replacement costs and tightening legislation means that end users now give leak detection a very high priority.

Leak detection methods

There are various methods of leak detection available; one of the oldest methods is the bubble spray. A soapy solution is applied at the suspected area and in theory the escaping refrigerant will produce bubbles indicating where a repair is required. It is simple enough but the disadvantage is that with small leaks or if conducted in a draughty or exposed environment it is not accurate.

Fluorescent leak detectors rely on a fluorescent dye being added to the air conditioning or refrigeration plant. The dye then mixes with any lubricant and circulates throughout the system. When the refrigerant leaks so does the dye and it can be detected by scanning the system with an ultraviolet or blue lamp.

Pressure decay testing relies on the principle that when a leaky part is pressurised with nitrogen, then isolated using valves, a loss of pressure over time will be apparent and the pressure decay rate will be converted to a leak rate according to the equation

Q = (P1-P2) V/t

Q = leak rate

P1-P2 = the change in pressure over the test period

V= test volume

T = test period

(The temperature is assumed to be held at a constant)

This is a relatively simple and low cost technique, but the test results can be influenced by environmental factors, or where parts are hotter or colder than ambient temperatures as a result of a welding operation. Small pressure decays can also be impossible to see on a pressure gauge.

As the industry focuses on compliance with the F-Gas regulations and customers demand leak reduction, refrigerant users are constantly searching for more effective solutions.

One of the latest solutions is a ‘next generation’ precision leak detection gas that not only addresses environmental concerns and provides customers with an effective solution for detecting leaks right down to less than five grams per year.

Jim Bishop from A-Gas says its Trace-A-Gas is a 5% Hydrogen and 95% Nitrogen mixture which is non-flammable and non-toxic. Hydrogen is a light element and is the smallest molecule, so it moves quickly through a system and will pass through even the smallest leak. Its low viscosity makes it easy to flush out and vent away.

Leak detection devices with high levels of sensitivity are able to detect even ‘pinhole-sized’ leaks, which are far more problematic to locate. Developed to focus on the difficult- to-find leaks, this method has been proven to be far more effective at detecting smaller leaks than traditional methods such as the bubble soap spray or pressure decay.

Following extensive testing, Bishop explains Trace-A-Gas was subsequently trialled on a pilot site using a supermarket refrigeration pack. Using Trace-A-Gas a pinhole leak which had gone undetected by a bubble soap spray and a further four tiny leaks were highlighted including one on a joint covered by Armaflex. None of these had shown up during an overnight pressure decay test at 27.5 bar.

The trials also confirmed that this method was up to 100 times more sensitive than soapy bubble spray and that combined with a suitable electronic hydrogen detector, offers a very valuable tool in the battle to eradicate leaks.

All leak detectors require a level of skill in using them and their effectiveness and ease of use are important considerations by service engineers when selecting a leak detection system. Consideration says Bishop should be given to the size of plant and accessibility is of equal importance.

A good leak detection kit will offer the following:

• The ability to test all areas of the system, including insulated or difficult to access pipework where a spray device cannot easily be used

• Real time results, which ensures less time is spent on site

If unchecked, leaks can have a detrimental effect on plant whilst compromising company’s legal obligations. They can impact health and safety requirements, increase running costs as well as servicing costs and have a detrimental impact on the environment.

Considering the high cost of refrigerant, repair of equipment and the time it takes to locate leaks, it makes good business sense to have in place a preventative maintenance programme.

Taking a proactive approach and ensuring that leak detection is a part of your overall maintenance strategy will help pinpoint leaks quickly, accurately and minimise refrigerant losses.

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