But in 2D analysis I can't use pipe and beam elements which would represent my pipe, if I am right ? With which elements could i represent pipe ?

Which contact you suggest to use in this kind of simulation ?

This is my current 'new' set up for simulation. I wanted to use spring elements representing contact with seabed, but without success. I tried with putting bigger longitudinal stiffness of spring, but same happened, as if there is no contact detecting seabed. How to limit displacement of pipe below seabed ?