The deep sea drilling vessel "CHIKYU" is the largest science drilling vessel in the world, which is being used for the "Integrated Ocean Drilling Program (IODP)", a big international science project. From the sea bed at 2,500 meters below the surface, it will drill a further 7,000 meters deep into the mantle, in a mission to reveal the secrets in global environmental changes, the earthquake mechanism, and the birth of life. The drill pipe used for this special drilling mission is "NK DSTJTM (Double Shoulder Tool Joint)" produced by TenarisNKKTubes.

The project to build "CHIKYU" started in 1996, when the predecessor of TenarisNKKTubes was requested to produce a drill pipe to be installed in "CHIKYU”. The challenge was to make a drill pipe string which would stretch for 10,000 meters. Because conventional drill pipes did not have sufficient strength, it had to develop a pipe and thread (tool joint) with much higher performance in torque resistance (torsion strength) and tensile strength than pre-existing products.

It took two years of intense research to figure out the material composition for the new pipe to determine the best composition for sour drilling (corrosion resistance against hydrogen sulfide) and the strength in S150 (proof stress at 1034MPa). A prototype was made to start endurance testing under simulation for the actual application.

The first step to clear was "tensile strength". The weight applied to the drill pipe during the drilling was calculated to reach about 400 tons. In product development, the pipe was verified to be durable up to 500-600 tons in the machine tensile strength testing.

The second step was "torque strength". Normally, the torque strength sufficient for a drill pipe is 5-6 tons-m, but the new drill pipe was required to have more-than-double torque strength, at 14 tons-m.

The third step to clear was "fatigue strength". A drill pipe drills with a rotating movement. It was calculated that one million times of rotation would be necessary for the exploration in "CHIKYU". However, there was no testing machine in Japan that could verify one million times of rotation. Finally, one was found in Houston where the durability of the pipe was extensively and repeatedly tested.

After these efforts, a new drill pipe, NK DSTJTM was finally developed, which is about 10 meters long. For drilling in "CHIKYU", about 1,000 pipes will be connected to complete the string of 10,000 meters, which is almost three times longer than the height of Mt. Fuji. The tip of the pipe targets the mantle deep below the earth’s crust. Human beings have never had direct access to the mantle. If this project can accomplish its mission successfully, it will be a milestone in human history.