Telescopic riser tensioning apparatus

Claim 1

In an apparatus for applying tension to a string of casing extending from a vessel floating on the surface of a body of water to a subsea wellhead and having a drilling fluid therein, said apparatus including: a hollow upper coupling member fixedly connected at one end to said string of casing in a fluid-tight manner and a hollow lower coupling member having one end telescopingly receiving the other end of said upper coupling member in a fluid-tight manner and its other end fixedly connected to said wellhead in a fluid-tight manner thereby defining a bore extending through said string of pipe, said telescoping upper and lower coupling members and said wellhead, the improvement comprising the provision of: tensioning means operatively connected to both said upper and lower coupling members for telescoping said coupling members to thereby apply tension to said casing, said tensioning means including pressure transducing means for receiving pressure from the weight of said fluid in said casing and applying the force generated thereby to said tensioning means to thereby telescope said coupling members and thus tension said casing, said tensioning means including a surge chamber surrounding said coupling members and separated therefrom in a fluid-tight manner, said surge chamber being sealed off from ambient fluid surrounding said surge chamber, said pressure transducing means including at least one cylinder having a piston slidably movable therein, said piston Having a piston rod operatively connected to one of said coupling members, said cylinder being operatively connected to said surge chamber, and said tensioning means further including means associated with said lower coupling member in fluid communication with said surge chamber, and said surge chamber being in fluid communication with the interior of said cylinders above said pistons.