Abstract: It has not been all along realized to smoothly produce the Φ630 mm×30 mm Q690E seamless steel pipe for service as the main rod of the 1 600 t marine crane ship with the hot-rolling process.The rolling force and the operation difficulty are remarkably reduced by means of optimizing chemical composition of the steel to get its thermal plasticity up to 40.8%at 1 200℃;the weldability of the steel is guaranteed owing to the steel carbon equivalent that is well controlled to be under 0.62%;and prior to rolling the pipe, pipe-end quench test is conducted, and the transformation point is measured, and dip quench process employed, thus the hardenability of the pipe is ensured.The heat schedule is 940℃water-quench plus 650℃ tempering-air cooling.Thanks to implementation of all the measures as above mentioned, the yield strength of the said pipe has been finally enhanced to at least 760 MPa.