Conta bağlantılı PVC boruların deformasyon davranışının laboratuvar deneyleri ile belirlenmesi

Modelling of joints in pipelines is a critical issue influencing both the short and long term performance of these systems. Defects at pipe joints can contribute significantly to reduction of the overall performance of the pipe system. The most common problems attributed to joint defects are infiltration, exfiltration, and erosion of the soil surrounding the pipe that can ultimately produce pipe failure. Joints are known to be the source of a number of pipe failures or installation problems due to the fact that in many cases they are the weakest points along a pipeline. Many design variables affect joint performance and it is difficult to predict the behavior of joints in service. The interaction between the pipe and the gasket is a complex phenomenon and represents a challenging modeling problem. Although joints can have a major influence on the pipe performance, little research has been conducted in regard to their design.This research reports on preliminary comparisons of the FEA (finite element analysis) with pipe assembly experiments. In the FEA, the three dimensional response of a rubber-gasketed bell-and-spigot jointed PVC (polyvinyl chloride) pressure pipe was examined to develop an understanding of the effect of gasket modulus, friction coefficient, insertion length and joint rotation on the pipe-joint behavior. The numerical analyses were performed using ABAQUS version 6.7. The finite element analysis procedure was conducted in two steps representing the insertion of the spigot into the bell, and the bending of the pipe across the assembled joint. In the analyses, a pipe of SDR (standard dimension ratio) 28 and nominal size 135 mm has average internal diameter 133 mm, average wall thickness 5 mm, average external diameter 143mm, average bell depth of 100mm was modeled.In this research, the jointed pipe specimens which were modeled using ABAQUS in the former study were tested in the laboratory to investigate the behavior of the pipe-joint assembly during insertion and bending. Two types of insertion tests were performed representing the joint behavior in conditions with and without gasket lubrication. The results of the insertion tests showed that lubrication decreases the amount of force needed for the insertion of the spigot into the bell end of the pipe. The peak forces needed for the insertion of the lubricated and non-lubricated specimens correspond to an insertion distance where the outer surface of the cylindrical part of the spigot comes in contact with the gasket, and the gasket is fully compressed between the spigot and the bell. A similar trend was observed in the finite element analyses. The results of the laboratory tests confirm the general pattern of force versus displacement behavior calculated in the finite element analyses, though further work is needed to establish the exact constitutive characteristics of the gasket so that better direct comparisons can be made. In order to check the accuracy of the experimental work, testings were carried out on two different test machines (Zwick Z020, and Instron 8802 test machines). The comparison of the results of the Zwick and Instron tests showed that almost the same results were obtained by the Zwick and Instron tests for the non-lubricated samples. However, although the general shapes of the curves were the same for the lubricated samples, the magnitude of the forces needed for 6.0 cm insertion were seen to be very different. The difference in the magnitudes of the forces might be caused by uneven spreading of the lubricant or the pipe?s out of roundness, which are known to be very important parameters that may affect the insertion process for these pipes. The comparison of the results of the insertion tests for lubricated samples with the FEA results show that the best fit between the FEA and the experimental results was achieved for the lubricated sample tested in the Instron machine. The higher differences in the results of the other tests and the FEA are thought to be caused by some factors such as the pipe out of roundness, the change in the gasket stiffness along the spigot taper, and the experimental variability along spigot cylinder.The results of the bending tests showed that the joint behavior is highly variable. Therefore, it is difficult to determine if lubrication influences bending in jointed pipes. However, these experiments were undertaken 6 weeks after insertion and it is not clear how much of the lubricant remained. This behavior results because time after insertion in the field could also influence the effectiveness of the lubrication, so that short term bending response under construction loads, for example, could be different to those after extensive time periods. Keywords: PVC pipe, pipe joint, vertical deformation, bending deformation.Gömülü boru hatlarının bağlantı yerlerinde karşılaşılan hasarlar, tüm boru sisteminin davranışını olumsuz yönde etkileyebilecek önemli sorunlara yol açabilir. Hasarlı boru bağlantılarında meydana gelen su sızıntısı ve buna bağlı olarak boru etrafındaki zeminde meydana gelen erozyon, zamanla borularda göçmeye neden olan en yaygın problemlerden biridir. Bu nedenle, boru bağlantılarının tasarımı, boruların uzun ve kısa dönemli davranışını büyük ölçüde etkileyen önemli bir konudur. Ancak, boru bağlantılarının boru hattı boyunca en kritik noktalardan biri olmasına ve boru performansı üzerinde büyük bir etkiye sahip olmalarına rağmen, boru ve conta arasındaki etkileşimin modellenmesindeki zorluk nedeniyle bu konu üzerinde çok sınırlı sayıda çalışma yapılmıştır. Bu çalışmada, boru ve conta arasındaki sürtünme, boruların birbiri içine itilme boyu ve ek yerinde meydana gelen dönmenin boru davranışı üzerindeki etkilerini incelemek amacıyla conta bağlantılı bir PVC boru üzerinde laboratuar deneyleri ve sonlu elemanlar analizleri yapılmıştır. Deneyler, boruların birbiri içine itilmesi için gerekli itme kuvvetini ve boruların eğilme davranışını belirlemek amacıyla iki aşamada gerçekleştirilmiştir. Elde edilen sonuçlar, aynı geometri ve malzeme özelliklerine sahip PVC boruların ABAQUS sonlu elemanlar programı kullanılarak modellendiği üç boyutlu sonlu elemanlar analiz sonuçları ile karşılaştırılmıştır. Deney sonuçlarıyla sonlu elemanlar analiz sonuçlarının karşılaştırılması, analizlerin boruların çeşitli şartlar altındaki temel fiziksel davranışını modellemekte başarılı olduğunu, ancak borularda üretim hataları ya da saklama koşullarındaki dikkatsizlikler nedeniyle ortaya çıkabilen boru en kesitlerinin tam dairesel olmaması durumunun boru davranışı üzerindeki önemli etkisini incelemenin gerekliliğini ortaya koymaktadır. Anahtar Kelimeler: PVC boru, boru bağlantısı, düşey yer değiştirme, eğilme