Pipes hoop strength

Figure 2.4 Change in hoop strength of polypropylene pipes with time of accelerated ageing...

The alignment of hybrid p-form shish-kebab crystals off the axial direction was achieved via the rotation extrasion system. As a resulL the PP pipes with enhanced toughness and hoop strength were made. The hoop strength and toughness of the PP pipe were 75% and 78% higher than in the case of conventional extrusion. ... 

It should be noted that moisture-induced degradation of the fiber/matrix interface could significantly reduce the stiffness of the FRP pipes when subjected to bending, shear and compression loading conditions, while the hoop strength would not be as significantly affected. This is because a debonded fiber/matrix interface acts mainly as interlaminar cracks, and therefore would induce less impact on the strength of the pipes, especially when subject to purely internal pressure. 

The main advantage of the sandwich pipe is the increased bending resistance. It is left for an exercise to show that there is little increase in hoop strength (see Homework Problem 10.2). The beam bending stiffness depends on the second moment of area. The second moment of area of a thin pipe is... 

When constmction is complete, the pipeline must be tested for leaks and strength before being put into service industry code specifies the test procedures. Water is the test fluid of choice for natural gas pipelines, and hydrostatic testing is often carried out beyond the yield strength in order to reHeve secondary stresses added during constmction or to ensure that all defects are found. Industry code limits on the hoop stress control the test pressures, which are also limited by location classification based on population. Hoop stress is calculated from the formula, S = PD/2t, where S is the hoop stress in kPa (psig) P is the internal pressure in kPa (psig), and D and T are the outside pipe diameter and nominal wall thickness, respectively, in mm (in.). 

RTR filament-wound pipe is, however, an anisotropic material. That is, its material properties, such as its modulus of elasticity and ultimate strength, are different in each of the principal directions of hoop and longitude. It is here where the design approaches for steel and RTR pipe part company [Fig. 4-2(c)]. This behavior is a result of the construction of filament-wound RTR pipe. 

PL-3.7.6 Pipe Surface Requirements Applicable to Pipelines and Mains to Operate at a Hoop Stress of 20% or More of the Specified Minimum Yield Strength... 

WELDS IN PIPING INTENDED TO OPERATE AT HOOP STRESS LEVELS OF 20% OR MORE OF THE SPECIFIED MINIMUM YIELD STRENGTH... 

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