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News

Climate Center: new refrigeration tube guidance set to unify UK with EU

Institute Of Refrigeration (IOR) : 16 June, 2014  (Technical Article)
Revised guidance on the selection of copper tube and fittings for use in refrigeration and air conditioning systems has been agreed by two leading industry bodies. The Institute of Refrigeration and British Refrigeration Association have collaborated on the important update, following a proposed change in the European Standard EN14276.
Revised guidance on the selection of copper tube and fittings for use in refrigeration and air conditioning systems has been agreed by two leading industry bodies. The Institute of Refrigeration and British Refrigeration Association have collaborated on the important update, following a proposed change in the European Standard EN14276. Following some detailed development work and discussion by relevant industry committees, it has been agreed that this new approach can now be applied in the UK.
 
Gordon Adams, technical manager at Climate Center, who played a key role in the revision, says: "The result is an increase in the maximum allowable pressure (PS) for equivalent thicknesses of copper tube, which will create a level playing field for the industry across Europe. The revised guidance incorporates new design stress values for copper tube, which were not included in the original European Standard. A recent amendment, however, has proposed that stress values be included in a future review of the Standard, opening the way for a review here in the UK.”
 
The changes, which have taken two years to implement, have implications for a number of key standards and practices used in the UK refrigeration and air conditioning industry. For example, the strength pressure test required on copper tube under the Safety Standard BS EN378 has been clarified, and now allows - subject to certain conditions being met - for the test to be carried out at 1.1 times the maximum allowable pressure.
 
The main change from the existing BS1306 standard to the European Standard EN14276 is a reduction in the safety factor, allowing the use of increased pressures for tube with the same wall thickness.
 
Adams adds: "It had been recognised for some time that the British Standard was very conservative. The revised guidance gives more latitude, allowing a stress value at 150C to be used for discharge lines. Given the importance of the guidance for the safety and reliability of plant, we have gone through the data underlying the proposed changes extremely thoroughly. The key thing was to get it right, and ensure the industry could proceed to use the new approach with confidence."
 
The new guidance gives clear tables for the maximum allowable pressure of copper tube for the common diameters and wall thicknesses. It also highlights the minimum design pressures for commonly used refrigerants, bringing key information into a single reference point.
 
Institute of Refrigeration Guidance Note 25 "Selecting copper tube and fittings" is available from www.ior.org.uk. 
provides guidance on selecting copper tube and fittings for Refrigeration and Air Conditioning Systems with Air Cooled Condensers to Comply with EN378-2:2008 and updates the IOR Guidance Note 8 “Designing for new refrigerants”. 
 
The Original BRA Factfinder No.7 and IOR Guidance notes based on BS1306 covering copper pipe wall sizing calculations were updated in 2005 following the introduction of EN378:2000 and BS EN 12735:1. EN 378 has been updated and the current standard is EN378:2:2008. BS1306 has not been withdrawn, however a new standard EN14276:2007 has been introduced with a revised calculation for wall thickness. Unfortunately the design stress values for copper tube were not included in EN14276 which is the reason for previously not updating the Factfinder/Guidance notes. 
 
Recently an amendment has been proposed to include the stress values in a future revision of EN14276 and following discussions with the Institute of Refrigeration it has been agreed that this information can now be used in the UK. The effect of this will be to increase the maximum allowable pressure (PS) for equivalent thicknesses of copper tube and bring the UK into line with European Practice. 
 
Effects of changes to Safety Standard BS EN378 
 
The strength pressure test to copper pipe systems was unclear in the original version. The latest version has now been clarified and allows, subject to certain criteria being met, for the strength pressure test to be carried out at 1.1xPS. 
 
Effect of changes from BS1306 to EN14276
 
Although there is a slight difference in the formulae for calculating the wall thickness, the major change is the reduction in the safety factor allowing increased pressures for the same wall thickness. The original notes recognised that BS1306 was an extremely conservative standard and did in fact suggest that the stress values at 100C should be used for discharge lines. Now that a more realistic standard has been introduced it is recommended that the stress value at 150C is used as the discharge gas temperature can be in excess of 100C when it leaves the compressor. 
 
Effect of bending copper tube 
 
The previous note was based on the assumption that the weakest point of the tube was at the fully annealed section immediately adjacent to the brazed joint. There have been some suggestions that the pipe is weaker when it has been bent; however it should be noted that the tube is normally in the half hard as supplied condition when it is bent. The tensile strength is 250N/mm<2> in the as-supplied condition, compared to 200N/mm<2> (material condition R200) in the fully annealed condition.
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