PEX tubing for high-pressure water system
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What does it say exists in USA normative documentation about the durability of PEX tubing? First of all, SNIP 2.04.01-85 * “Domestic plumbing and plumbing of buildings” specifies only the upper allowable temperature limit of operation of hot water +75 ° C, with an estimated useful life of 25-30 years, and SNIP 2.04.05-91 * “Heating , ventilation and air conditioning »- +95 ° C with the same period of operation. As we will see the following data for specific types of tubing temperature at +95 ° C is inflated. Lack of information in SNIP 2.04.01-85 *, revealing a direct relationship between the durability of the tubing on the working temperature and pressure, often introduces inexperienced consumers of PEX tubing in error. Representations of the many vendors that their tubing are designed for temperature +95 ° C and pressure of 10 atm is absolutely nothing about their life in such settings. With these values of the working temperature and pressure, any plastic tube will serve no more than 2-3 years. Where is the fantasy life of 50 years?
Therefore, in order not to be trapped, it is necessary in addition to SniP use SP or TU, which contain much more information.
Thus, in 1996 the NGO Stroypolimer “developed and manufactured AC 40-101″ Designing and building tubinglines from the polymer “Random Copolymer”, which clearly defined parameters of operation and last but not least, the dependence of durability on the working temperature and pressure, which clearly presented in the form tablitsy.Chto concerns Metal tubing, it is truly a “pig in a poke.” Despite the fact that the recently issued a joint venture 41-102-98 “Design and installation of piping systems, heating with a metal-tubing” of any data on the dependence of pressure on temperature and longevity in this joint venture, or TU manufacturers can not be obtained. The only thing that is said in the joint venture: “Metal-tube used in the design and installation of heating, the calculated temperature not exceeding +90 ° C at a pressure in the tubing not more than 1,0 MPa. Some suppliers of metal-tubing trying to appeal to the nomograms ratio durability and a reference voltage. Maybe they do not suspect that the reference voltage is determined by the formula Kessel, a tangential stress of the tubing wall caused by internal pressure. Fatigue strength, represented in the form of a reference voltage, regardless of size tubing and shows only the behavior of the material. That is why these nomograms are not used to calculate the tubing, and for bench testing materials making up the tubing. Nevertheless it is interesting to observe how the information of some firms relative curves of metal-like tubes tend to heights beyond the clouds, like water or coolant flowing inside these tubes are not sewn on polyethylene, and on the aluminum tube.
Should be clear that the aluminum layer in PEX tubing does not bear any responsibility to provide life or improve the operating parameters. The liquid inside the tubing is flowing through the channel cross-linked polyethylene, and not aluminum. The main task of the layer of aluminum foil – to prevent the penetration of oxygen, and secondary – to partially compensate for thermal expansion. Therefore, when calculating the heating of the metal-tube must be guided by data on the durability of cross-linked polyethylene tubing.
In conclusion, it should be noted that to ensure durability of heating at 30 years of operating temperature and pressure should not exceed +80 ° C and 0.9 MPa, according to the SNIP – 0,6 MPa.
Tags: "cross-linked" polyethylene, Heating, Kessel, metal tubing, PEX, plumbing, tubing
