Experimental and numerical investigation of the gripping force in lined pipe

Corrosion Resistant Alloys (CRAs) have many applications in oil, gas and petrochemicalindustries, especially in service fluids contains H2S and/or CO2 compounds. The mainproblem associated with CRAs is that they have not enough strength to withstand therequired working pressure, economically. Hence, in high pressure applications, theyare used as a thin internal coat inside the cheaper non- CRA pipes. In double wallpipes, if the internal surface are coated by welding process; the manufactured pipe isknown as clad pipe which has size and diameter restrictions in production stage; but ifa thin corrosion resistant pipe is mechanically bounded to the internal surface of thecarbon steel pipe; the produced double wall pipe is known as a lined pipe. Lined pipesin addition to corrosion superiority, have the improved mechanical strength due to theresidual pressure between inner and outer pipes. This contact pressure also determinesthe amount of gripping force at the interface of two pipes. This issue investigated bymany researchers; however, there is lack of experimental data to validate thenumerical and analytical studies. Therefore, this study focused on experimentalmeasurement of the gripping force in mechanically bounded double wall pipesproduced by Thermo Hydraulic Shrink Fit (THSF) process. The measurementsshowed that the gripping force between outer 4-inch carbon steel and inner 3-inchstainless steel pipes when processing in 350°C and 40 MPa is about 90MPa. Thisamount of gripping force can be enough for most of applications. In addition togripping force measurements, cross sections of produced pipe from different sectionsof the pipe length are cut and visually inspected for the existing of possible defects.The results showed that lamination type defects are likely for this type of productionmethod. Besides, the Finite Element Method (FEM) analysis of the residual contactpressure is conducted. The results are interpreted and discussed.

Keywords:

Corrosion Resistant Alloys (CRAs) , Piping , Oil and gas industry , Thermo Hydraulic Shrink Fit (THSF) process , gripping force