Method for Multi-Slip Gripping of Pipe and Tubular Goods

Abstract

A slip assembly for gripping against the external surface of a section of pipe or other tubular goods and supporting axial loading has multiple sets of cooperating wedge-like slip members movably mounted within a slip bowl. A first set of slip members having a smaller taper angle (that is, having a greater vertical component) exerts a predetermined and limited radial gripping force on the pipe or other tubular good. Thereafter, a second set of slip members having a larger taper angle (that is, having a lesser vertical component) takes over and exerts additional radial gripping force on the pipe or other tubular good.

What is claimed: 
     
         1 . A method for gripping pipe and other tubulars comprising:
 a) inserting a section of pipe in a slip assembly, said slip assembly comprising:
 i) a slip bowl member having a central bore defining a tapered inner bowl surface; 
 ii) a first slip member having first tapered inner slip surface, a first tapered outer slip surface, and at least one substantially upwardly facing shoulder on said first tapered inner slip surface, wherein said first tapered outer slip surface is slidably disposed on said inner bowl surface; 
 iii) a second slip member having a second inner slip surface, a second tapered outer slip surface and at least one substantially downwardly facing shoulder on said second tapered outer slip surface, wherein said second tapered outer slip surface of said second slip member is slidably disposed on said first tapered inner slip surface of said first slip member; 
 iv) at least one die member disposed on said second inner slip surface of said second slip member; 
   b) engaging said second slip member against said pipe section and said first inner slip surface of said first slip member;   c) engaging said downwardly facing shoulder against said upwardly facing shoulder when pipe gripping force exerted by said second slip member on said pipe section exceeds a predetermined force; and   d) engaging said first slip member against said first tapered inner bowl surface of said slip bowl.   
     
     
         2 . The method of  claim 1 , wherein said outer surface of said first slip member defines a first acute angle from a longitudinal axis of said section of pipe, said inner surface of said first slip member and said outer surface of said second slip member define a second acute angle from the longitudinal axis of said pipe section, and said first acute angle is larger than said second acute angle. 
     
     
         3 . The method of  claim 1 , further comprising a gap between said upwardly and downwardly facing shoulders when said pipe gripping force exerted by said second slip member on said pipe section is less than said predetermined force. 
     
     
         4 . The method of  claim 1 , wherein the size of said gap between said upwardly and downwardly facing shoulders is adjustable. 
     
     
         5 . The method of  claim 1 , further comprising a bias spring disposed between said first and second slip members, wherein said bias spring is configured to create a gap between said upwardly and downwardly facing shoulders. 
     
     
         6 . A method for gripping pipe and other tubulars comprising:
 a) inserting a section of pipe in a slip assembly, said slip assembly comprising:
 i) a slip bowl member having a central bore defining a first tapered inner bowl surface; 
 ii) a first plurality of slip members, each having an inner surface, an outer surface, and at least one substantially upwardly facing shoulder on said inner surface, wherein said outer surfaces of said first plurality of slip members are slidably disposed on said tapered inner bowl surface and said inner surfaces of said first plurality of slip members cooperate to define a second tapered bowl surface; 
 iii) a second plurality of slip members, each having an inner surface, an outer surface and at least one substantially downwardly facing shoulder on said outer surface, wherein said outer surfaces of said second plurality of slip members are slidably disposed on said second tapered bowl surface defined by said inner surfaces of said first plurality slip members; 
 iv) a plurality of die members disposed on said inner surfaces of said second plurality of slip members; 
   b) engaging said second plurality of slip members against said pipe section and said inner surfaces of said first plurality of slip members, wherein said second plurality of slip members are axially displaced relative to said first plurality of slip members;   c) engaging said downwardly facing shoulders of said second plurality of slip members against said upwardly facing shoulders of said first plurality of slip members when axial displacement of said second plurality of slip members reaches a predetermined distance; and   d) engaging said first plurality of slip members against said first tapered inner bowl surface of said slip bowl.   
     
     
         7 . The method of  claim 6 , wherein said outer surfaces of said first plurality of slip members define a first acute angle from a longitudinal axis of said section of pipe, said inner surfaces of said first plurality of slip members and said outer surfaces of said second plurality of slip members define a second acute angle from the longitudinal axis of said pipe section, and said first acute angle is larger than said second acute angle. 
     
     
         8 . The method of  claim 6 , further comprising a gap between said upwardly and downwardly facing shoulders when said when axial displacement of said second plurality of slip members has not reached said predetermined distance. 
     
     
         9 . The method of  claim 6 , wherein the size of said gap between said upwardly and downwardly facing shoulders is adjustable. 
     
     
         10 . The method of  claim 6 , further comprising a bias spring disposed between said first plurality and second plurality of slip members, wherein said bias spring is configured to create a gap between said upwardly and downwardly facing shoulders.