Riser tensioner system for use on offshore platforms using elastomeric pads or helical metal compression springs

A riser tensioner system adapted for mounting between a floating platform and a riser, and for applying a generally upward force to the riser while allowing limited vertical movement therebetween, comprising:

• a housing having a central opening extending therein, said housing being adapted for coupling to said floating platform;
• a plunger assembly adapted for telescopic movement within said central opening of said housing, and plunger assembly comprising:
• a rod having first and second end portions, said rod first end portion being adapted for being coupled to said riser;
• and
• a plate coupled to said second end portion of said rod and positioned within said housing central opening;
• and
• at least one inner spring located within said housing and having a longitudinal axis substantially aligned with the longitudinal axis of said rod, said inner spring having a first stiffness;
• at least one outer spring located within said housing and having a longitudinal axis substantially aligned with the longitudinal axis of said rod, said outer spring having a diameter greater than the diameter of said inner spring, and being adapted for receiving said inner spring longitudinally disposed therein, said outer spring having a second stiffness substantially similar to said first stiffness whereby the inner and outer springs are compressed substantially in parallel in response to receiving a load thereon;
• a spring separator positioned between and contacting said inner and outer springs, said inner and outer springs being compressed by said plunger assembly urging one of said inner and outer springs against the spring separator, and said spring separator urging the other of said inner and outer springs against said housing;
• and
• a strut having first and second end portions and an intermediate portion, said intermediate portion being rotatably coupled to said plunger assembly, said strut first end portion being rotatably coupled to said offshore drilling platform, and said strut second end portion being rotatably coupled to said riser.