Pipes under external pressure

To determine wall thickness and stiffening requirements for straight pipe under external pressure, the procedure outlined in ASME BPV Code Section VIII, Division 1, UG-28 through UG-30 shall be followed, using as the design length, L, the running centerline... 

IP-3.3.4 Curved and Mitered Segments of Pipe Under External Pressure... 

Equation 4-6 is the classical theoretical relationship for long thin cylinders under external pressures. These theoretical values for collapsing pressure are based on considerations of perfect geometry and perfect uniformity in the shell material. In any actual vessel, the idealized condition cannot be obtained and it was found that the collapse of commercial tubing and pipe occured at a critical pressure, approximately 27% less than the theoretical critical pressure. Using a safety factor of 4 for equation 4-5 we obtain... 

DESIGN OF PIPES AND TUBES UNDER EXTERNAL PRESSURE... 

Another rapid loading condition in underwater applications is the application of external hydrostatic stress to plastic structures (also steel, etc.). Internal pressure applications such as those encountered in pipe and tubing or in pressure vessels such as aerosol containers are easily treated using tensile stress and creep properties of the plastic with the appropriate relationships for hoop and membrane stresses. The application of external pressure, especially high static pressure, has a rather unique effect on plastics. The stress analysis for thick walled spherical and tubular structures under external pressure is available. 

Pipe-Wall Thickness. Once the design pressure and temperature have been established and the pipe material and size selected, the wall thickness is calculated using the appropriate section of the code. In rare cases, a thin pipe must be made thicker to withstand handling. Occasionally the thickness is affected by external loads or vibrations. All codes prescribe essentially the same design formula for metallic hoUow circular cylinders under internal pressure ... 

The hoop stress at the outer surface of a pipe of internal diameter 2/ j and external diameter 2R2 under internal pressure P is given... 

EN 911 Elastomeric sealing ring type joints and mechanical joints for thermoplastics pressure piping - test method for leaktightness under external hydrostatic pressure. 

Fig. 24.16 Buckling resistance of pipes of Hostalen under external water pressure at 20 C. The curves show the beginning and end of buckling...

Arjomandi K, Taheri F (2011b) Stability and post-buckling response of sandwich pipes under hydrostatic external pressure . International Journal of Pressure Vessels and Piping, 88(4), 138-148. 

Shouman and Taheri (2009, 2011) did an experimental and numerical study to investigate the behaviour of repair in externally defected pipes under combined loading. They considered internal pressure, axial force and moment and proved that increasing the thickness of the wrap would not improve the strength of the pipe in the axial direction. FurthermOTc they found that the length of composite repair affects the bending response of the repaired pipe. 

Thin-wallcd and thick-walled cylinders arc forms of pipeline primarily used in the offshore industry to transport gas and hquid under pressure. Cylindrical pipes are also used as a stmctural load bearing member to restrain the motion of a platform, for example, in response to wind, waves and currents (to within a specified limit). When a pipe is exposed to a combination of internal and external pressure, the pipe material will be subjected to pressure loading and, as a result, will develop stresses in all directions. The resulting normal stresses induced by the pressure loading are functions of the pipe diameter, wall thickness and cylindrical shell boundary conditions (open-ended cylinder or closed-ended cylinder) (Kashani and Young, 2008). 

Cascade coolers are a series of standard pipes, usually manifolded in parallel, and connected in series by vertically or horizontally oriented U-bends. Process fluid flows inside the pipe entering at the bottom and water trickles from the top downward over the external pipe surface. The water is collected from a trough under the pipe sections, cooled, and recirculated over the pipe sections. The pipe material can be any of the metallic and also glass, impeiMous graphite, and ceramics. The tubeside coefficient and pressure drop is as in any circular duct. The water coefficient (with Re number less than 2100) is calculated from the following equation by W.H. McAdams, TB. Drew, and G.S. Bays Jr., from the ASME trans. 62, 627-631 (1940). 

---