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Soap gives way to hydrogen

Leak testing at Degussa in Marl
Soap gives way to hydrogen

Degussa manufactures intermediate chemicals in Marl, Germany. The plant uses a H2000-C leak detector to check flanges, as well as spindle and shaft bushings, in distillation columns and reactor systems. The user-friendly, cost-effective hydrogen method has replaced a time-consuming approach that entailed isolating the connections, applying a soap solution, and checking for bubbles.

As the smallest and lightest element in the periodic table, hydrogen is the perfect tracer gas. Sensistor Technologies’ hydrogen method draws maximum benefit from hydrogen’s unique physical properties, without requiring the gas to be in its purest form. It uses an inexpensive and convenient mixture of 5 % hydrogen and 95 % nitrogen, commercially available as forming gas. This blend is non-flammable, regardless of the oxygen concentration it comes into contact with. The gas mixture is commonly employed as a shielding gas in welding. It is non-corrosive and non-toxic, and both hydrogen and nitrogen are abundant and naturally occurring.

The hydrogen method was developed specifically for industrial purposes and is currently employed in a variety of sectors and applications. These include leak detection in underground pipes and communications cables, in gas and water mains, in refrigeration and air conditioning equipment, and in the automotive and foodstuff industries – and last, but not least, in chemicals. One satisfied customer is chemicals giant Degussa, which deploys Sensistor’s hydrogen method at its site in Marl, Germany.
The bubble has burst
Leak testing is carried out regularly at the company’s intermediates plant to test flange connections in distillation columns and reactor systems. Many of these connections are insulated with thermal jackets. Before Degussa opted to use the hydrogen method, the flanges were coated in soap solution to check for leaks. “We introduced nitrogen into the system, and created a small amount of overpressure. We then watched closely for bubbles,” explains Herrmann Winkler, Plant Engineer at the site. “On each occasion, we needed to remove the insulating jackets, and reattach them once the test was complete. In many instances, we had to replace the jacket completely. Now, we fill the system with forming gas at a pressure of around 0.5 bars and use the Sensistor device to determine whether hydrogen is escaping. There is no need to remove the jacket, the hydrogen simply seeps through it.”
Hydrogen: The ideal tracer gas
Hydrogen is ideal for leak testing. It is the lightest element, with higher molecular speed and lower viscosity than any other gas. As a result, it can be easily introduced into the system to be tested, mixes more quickly with air and other gases, and is easily evacuated. More importantly, it has the highest leakage rate of any gas. Moreover, the normal background concentration of hydrogen is just 0.5 ppm, in contrast to helium, which, at 5 ppm, is ten times more common.
Background concentration in air is a limit-ing factor for any detector. The H2000 is sensitive enough to detect background concentration hydrogen. This allows it to identify even the smallest leaks of just 5×10-7 mbarl/s. The detector uses a semiconductor sensor head mounted on a convenient handle. The sensor is specifically designed for hydrogen, the presence of other gases does not effect results. The device does not contain any moving parts, making it completely maintenance-free. Degussa uses the H2000-C, the battery-driven, portable model, which has identical features to the line-powered H2000. It weighs just 6 kg, including its carrying case, and is very simple to operate. “Before using the device for the first time, it was sufficient to spend just half an hour reading the manual,” says Winkler. Winkler and his colleagues now take turns performing the tests.
Compliance with the German clean-air code
Routine checks are carried out at the Degussa plant on a monthly basis. “In addition, whenever we start up our equipment, we perform a pressure rise test. If we notice any irregularities, we employ the Sensistor device to localize the suspected source,” explains Winkler. “But when we are working with highly toxic chemicals, we also use the H2000-C to ensure that there is absolutely no leakage, testing each flange individually. Germany’s clean-air code (TA Luft) requires a very thorough approach.” TÜV, the German standards organization, has confirmed the hydrogen method’s compliance with the code, making it an officially approved alternative to helium. The helium method requires mass spectrometers in conjunction with a vacuum. The hydrogen method only very rarely requires a vacuum.
Return on Investment
It now takes a Degussa employee just two to three hours to check flange connections, spindle and shaft bushings. He simply walks around testing the equipment once it has been filled with the tracer gas. “In comparison to the old method of applying soap solution and watching for bubbles, this represents a time saving of 20 to 30 %,” says Winkler. “In addition, with the hydrogen method, the jacket does not need to be discarded. Removal and replacement of the jacket for a DN 25 flange costs around 15 euros. It doesn’t take long to run up a bill of hundreds of euros, depending on the number of flanges and their diameter.” And the forming gas required costs cents rather than euros. Despite the up-front investment, the time and cost savings have meant the switch to the hydrogen method at the Degussa plant in Marl has paid for itself within just a few months.
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Degussa at a glance
Degussa AG was established in 2001 as a result of the merger of Degussa-Hüls AG and SKW Trostberg AG. Degussa manufactures specialty chemicals, with over 300 plants employing more than 47,000 people throughout the world. In 2003, the group posted sales of 11.4 billion euros. Degussa’s operations are separated into five divisions comprising a total of 21 business units. Two of these divisions, Fine and Industrial Chemicals, and Performance Chemicals, are headquartered in Marl. The H2000-C from Sensistor Technologies is deployed at the Fine Chemicals intermediates plant – a multi-purpose plant that produces organic compounds predominantly used outside the life science industry.
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