The Insulation Effect of pipe-In-Pipe as Shown in Zhong-Lo Pipeline

The pipeline from Zhong Yuan to Lo Yong (hereafter refered to as Zhong-Lo pipeline) was insulated with polyurethane hard foam plastic (hereafter refered to as foam plastic) coated by yellow jacket constiuting such structure as pipe sheathed by another one. In the commisioning of Zhong-Lo pipeline, it is clearly shown that this way of insulation is superious over the convetionnal asphalt coating in effect. It is through calculation of the general heat transfere coeffcient K and thermo conductivity K′ (including the trial calculation of thermal conductivity before it being put into production and the estimation of it during operation) that the K′ dluctuation curve has been obtained, veryfying the supposition that K′ values vary in different gedlo- gical areas. Meanwhile the bottle-neck' section along Zhong-Lo pipeline is determined by the greatest K′ value, which is lowest in temperature and greatest in friction. Through determination of the minimum and maximun throuthut, numbers of heating stations, analysis of shutdown time and necessary calculation concerned, the advantages revealed are: the minimum throughput has been raised by 30% in comparison with the former design; cutting down a number of heating stations so as to save a great deal of fuel; three times that of the previous shutdown time allowable Besides, the article points out the defects in structure as well as construction of sucha way of insulation.