Longitudinal strain in pipe

Several equations can be used to calculate the result of Poisson s effect on pipe in the longitudinal direction in terms of stress or strain. The following equation provides a solution for a straight run of pipe in terms of strain. Thus, the longitudinal strain in pipe due to internal pressure is... 

There is a special equation, shown in Figure 5-31, to calculate the longitudinal strain in pipe at harnessed elbows. For the sake of simplicity the effects of internal pressure, temperature gradient, and change in momentum of the fluid have been combined into one equation. 

The stresses in a pressurised pipe, free to expand in length, were analysed in Section C.3 of Appendix C. However, buried gas pipe is connected at both ends to immovable objects such as houses, and the surrounding soil prevents the pipe moving laterally. Consequently, the longitudinal strain in the pipe is zero. In this elastic plane strain situation, the hoop strain is given by Eq. (C.21) as... 

Figure 5-31. An example of longitudinal tensile strain in pipe with harnessed elbows.

Problem 3 When the pipe is placed under pressure, the hoop and longitudinal stresses in the wall are given by Eqs (C.19) and (C.21). The hoop strain for an elastic material is given using Eq. (C.18) as... 

Stretch leveling is intended to remove three-dimensional bends, roughness, and oddness at pipes and bars as well as buckles on sheets by tensile forces (see Fig. 3). In this context, internal stresses are removed by longitudinal strain. 

Therefore, before a final wall structure can be selected, it is necessary to conduct a combined strain analysis in both the longitudinal and hoop directions. This analysis will consider thermal contraction strains, the internal pressure, and the pipe s ability to bridge soft spots in the trench s bedding. In order to do this we must know more about the inherent properties of the material we are dealing with that is a structure made up of successive layers of continuous filament-wound fiberglass strands embedded within a plastic matrix. We must know the modulus of the material in the longitudinal direction and the... 

Average axial stresses (over the pipe cross section) due to longitudinal forces caused by displacement strains are not normally considered in the determination of displacement stress range, since this stress is not significant in typical piping layouts. In special cases, however, consideration of average axial displacement stress... 

Table 1. Constants in the equation for reduction in area (RA) variation with strain rate (<=) %RA = A + Blog e. Results are shown for longitudinal and transverse specimens and may be compared with results for a smaller pipe+3...

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