I thought it might be the Scale Factor in the second buckling calculation. I set the Scale Factor to 0.2. I made a finer grid on the pipe and made a calculation. I got negative parameters for the first two modes:

If you read the documentation, then this means that there will be a crush. I checked with a non-linear calculation, and multiplied my load by nga, the resulting multiplier F * k. It turned out 100000N * 0.16222 \u003d 16222N. This means that the pipe will lose stability at 1.6 tons. I made such a load. But the pipe survived, and the stress was only 30 MPa.