The AD 2000 guidelines HP 100 R (2004-02) “Construction regulations – Metal piping” are particularly important in this context. These technical guidelines can be applied to meet the basic safety requirements of the EC Pressure equipment directive (PED). Another technical regulation that may also be applied to fulfil the main requirements of the PED is DIN EN 14276-2 (2007-08) “Pressure equipment for refrigerating systems and heat pumps; Part 2: Piping – General requirements”. All of these standards are available from Beuth publishing house.
The mentioned regulations apply to Germany. Please consult the corresponding ones effective in your country.
Details on the percentage of weld inspections of pipes are given in the AD 2000 guidelines HP 512 R (2003-01) “Construction regulations – Design examination, final testing and pressure testing of piping” and in DIN EN 14276-2 (2007-08) “Pressure equipment for refrigerating systems and heat pumps; Part 2: Piping – General requirements”. HP 512 R calls for an external check and non-destructive testing (NDT) of the welded joints before initial pressure testing of a piping system using either air or nitrogen. Specifically, the system must meet the following requirements:
However, for circumferential seams and pipe dimensions of DN £ 600 mm they must be tested 100% and for pipes where DN > 600 mm random samples of 10% of the seam length must be tested. DIN EN 14276-2 specifies the percentage of welds to test as part of the specifications of the welding seam factor and the test category.
The mentioned regulations apply to Germany. Please consult the corresponding ones effective in your country.
Ammonia systems are primarily used in the food and beverage industry where a large amount of refrigeration is required. As far as is currently known, there is no restriction on their use by food law regulations. The legal requirements concerning installation, configuration requirements and safety equipment are primarily intended to protect humans and the environment and are partly covered by DIN EN 378 (2000-09) “Refrigerating systems and heat pumps – Safety and environmental requirements”. Further information on NH3 systems is available in the German VDMA guidelines 24020-1 (2007-03) “Operating requirements for refrigerating systems; Part 1: Ammonia refrigerating systems”.
The mentioned regulations apply to Germany. Please consult the corresponding ones effective in your country.
According to Art. 10 of the German labour protection law or Art. 22 of the accident prevention regulations BGV A1 (2004-01) “Principles of prevention” employers are generally obligated to:
DIN EN 378-3 (2000-09) “Refrigerating systems and heat pumps – Safety and environmental requirements; Part 3: Installation site and personal protection” contains specifications for NH3 refrigerating systems in section 9.3.4 “Emergency showers”. According to this, NH3 systems with a capacity exceeding 50 kg must be equipped with an emergency shower and an eye bath. The water for these facilities must be thermostatically controlled (mixed hot and cold water), in order to avoid thermal shock. The EC safety data sheets for gas suppliers also call for immediate treatment with copious amounts of water in the event of skin or eye contact with NH3. Information on the requirements that apply for emergency showers may also be found in the German BGR 120 (1993-10; updated 1998) “Guidelines for Laboratories”.
The mentioned regulations apply to Germany. Please consult the corresponding ones effective in your country.
Article 3 of the German chemicals prohibition ordinance (2003-06) applies. This ordinance stipulates that substances and preparations that carry the hazard symbol T (Toxic) or T+ (Highly Toxic) according to the ordinance on hazardous substances may only be sold if
NH3 carries the hazard symbol T (Toxic) and is covered by this ordinance. If NH3 is used by a specialist company for the construction or repair of a refrigerating system, for example, confirmation is required that this company shall use the substances provided as an end user in the permitted manner.
The mentioned regulations apply to Germany. Please consult the corresponding ones effective in your country.
There are at present no regulations containing specifications of this type concerning sealing requirements. Junctions must, however, be tested using detectors or a suitable method with a sensitivity comparable to the bubble test in accordance with DIN EN 1779 (1999-10) “Non-destructive testing – Leak testing – Criteria for the method and technique selection”. The manufacturer must demonstrate that the testing method used meets these requirements. The detection limit is also the permitted leakage limit for each individual junction. The maximum leakage is thus dependent on the molecular weight of the refrigerant. The qualification requirements for staff performing leak testing are given in DIN EN 473 (2006-01) “Non destructive testing – Qualification and certification of NDT personnel – General principles”.
n the event of a leak from an NH3 system adequate alarm indication is deemed sufficient, since the human nose, depending on an individual’s sensory ability, is able to detect ammonia concentrations of as low as 5–50 vppm (volumetric parts per million; 5 vppm = 3.5 mg/m3). It should, however, be borne in mind that a leak of 500 g NH3/a, for example, cannot be detected by scent, since the concentration generated does not reach the odour threshold.
NH3 refrigerating systems should therefore be tested for leaks in accordance with the state of the art. The German VDMA guidelines 24243 (2005-08) “Refrigerating machines and systems – Leak tightness of refrigerating systems and heat pumps – Leak detection/leak testing” for instance may be used as a guide. This distinguishes between rough gas-tightness or rough leak detection methods and fine leak detection methods. The rough methods include the pressure drop test, the bubble test and chemical methods with short exposure times. For ammonia the bubble test may have a sensitivity of as low as approx. 3,000 g/a in unfavourable conditions.
Finally, a fine leak test should always be conducted for NH3 refrigerating systems using leak detectors. Using installation leak detectors a sensitivity of around 15 g NH3/a may be attained. The rate of leakage from detected leaks can however only be estimated with most installation leak detectors, since they only provide a semi-quantitative signal. If it is necessary to measure the rate of leakage, leak detectors which provide a quantitative signal are required, for example a photo-acoustic detector, which uses infrared absorption.
The mentioned regulations apply to Germany. Please consult the corresponding ones effective in your country.
In principle, leak detection/testing of a refrigerating system which uses CO2 as the refrigerant should be performed in the same way as on any other refrigerating system. General information on leak testing of refrigerating systems can be found in DIN EN 378-2 (2000-09) “Refrigerating systems and heat pumps – Safety and environmental requirements; Part 2: Design, construction, testing, marking and documentation”. The entire system must be subjected to leak testing, either as a whole or in part – either at the factory or at the installation site. There are a number of methods which may be used to perform leak testing, depending on the manufacturing method used. According to DIN EN 378 the method of leak testing chosen must be approved by a suitably qualified specialist (e.g. a refrigeration engineer). The results of the leak test must be recorded. For further details on leak detection/testing please refer to the German VDMA guidelines 24243 (2005-08) “Refrigerating machines and systems – Leak tightness of refrigerating systems and heat pumps – Leak detection/leak testing”, which may be used as a guide.
The mentioned regulations apply to Germany. Please consult the corresponding ones effective in your country.
Leak detection requires the use of specialised installation leak detectors for CO2. Leaks are most often found at threaded joints and soldered joints as a result of poor workmanship. These positions need to be checked thoroughly using the leak detector. Ensure the necessary distance between the probe and the leak is maintained, and make sure the probe does not become contaminated. It is very important to ensure that the correct speed is maintained during leak detection – do not proceed too fast! Avoid exhaling in the direction of the measuring probe of the installation leak detector, since exhaled breath contains a high proportion (4%) of CO2 and this may cause misleading readings. It is therefore advisable to wear a mask while performing leak detection on the refrigerating system.
By courtesy of the Bundesfachschule Kälte-Klima-Technik