What are the factors that affect the compressive strength of steel pipes?

1. Strength anisotropy and residual stress of UOE steel pipes

As is well known, factors that affect the compressive strength of steel pipes include poor shape (roundness and uneven wall thickness of steel pipes), yield strength (YS), and residual stress. There is a significant correlation between the compressive yield strength and residual stress in the circumferential direction. The yield strength distribution of the wall thickness section measured on round bar and cylindrical specimens (both with a diameter of 6mm) indicates a particularly significant decrease in the compressive yield strength of the outer circumference of the steel pipe. The comparison of the S-S curves in the wall thickness position shows that a circular S-S curve appears from the center of the wall thickness due to the Bauschinger effect of elastic deformation on the outside. According to the comparison between UOE steel pipes and seamless steel pipes for oil wells, it can be seen that the residual stress of both types of steel pipes tends towards internal compression, but the residual stress value of UOE steel pipes is small.

2. Numerical analysis and simulation

In the numerical analysis process, a comprehensive model was used to evaluate the forming compressive strength of UOE steel pipes. In the forming model of UOE steel pipe (two-dimensional plane deformation element), the S-S curve of the plate was used, and residual stress was applied to the crushing model (three-dimensional solid element). Due to the difficulty in accurately predicting the changes in the S-S curve from sheet metal to steel pipe through numerical analysis and simulation alone, a semi experimental method (simulated deformation test) is used to predict the S-S curve. That is, apply the calculated equivalent plastic strain hysteresis to the round bar specimen sampled from the plate, and then define the compression S-S curve obtained at each wall thickness position.