Socketing of Pipe

Abstract

A method of modifying compressive strains in formation of a pipe ring groove ( 16 ), in which a differential temperature profile is established across the pipe wall in a narrow bending locus (l 3 ) corresponding to the ring groove position, and the material is bent to form the ring groove. The temperature differential creates a differential in elastic modulus between the inner and outer surfaces of the pipe material, modifying the strain induced in inner concave and outer convex surfaces of the ring groove during the bending step.

1 . A method of modifying localised compression of surfaces of a bend formed in post-forming a jointing formation in plastics material pipe, including the steps of:
 controlling a temperature profile across the material of the pipe wall to create a differential in elastic modulus of the pipe material between opposite surfaces of the pipe material at a bending locus; and   bending of the pipe wall at said bending locus to create concave and convex surfaces of the bend.   
     
     
         2 . A method according to  claim 1  wherein said step of controlling the temperature profile comprises differential heating of the pipe wall at said bending locus such that the temperatures of the concave surface is less than the temperature of the convex surface. 
     
     
         3 . A method according to  claim 1  wherein said step of controlling the temperature profile comprises differential cooling of the pipe wall at said bending locus such that the temperatures of the concave surface is less than the temperature of the convex surface. 
     
     
         4 . A method according to  claim 1  wherein said step of controlling the temperature profile comprises cooling of the concave surface and heating of the convex surface. 
     
     
         5 . A method according to  claim 1  wherein said step of controlling the temperature increases the elastic modulus of the pipe material at the concave surface of the bend relative to the elastic modulus of the pipe material at the convex surface of the bend. 
     
     
         6 . A method according to  claim 5 , wherein said step of controlling the temperature reduces compression of the concave surface due to said bending. 
     
     
         7 . A method according to  claim 1  wherein said pipe is a molecularly oriented plastics pipe. 
     
     
         8 . A method of forming a circumferential ring groove in plastics material pipe, said ring groove having an enlarged diameter portion with a concave inner surface, including the steps of:
 establishing a localised differential in temperature between inner and outer surfaces of the pipe at a locus substantially corresponding to the enlarged diameter portion of the ring groove such that the modulus of elasticity of the pipe material of said inner surface is higher than the modulus of elasticity of the pipe material of said outer surface at said locus, and   maintaining said temperature differential while bending said pipe material to create said ring groove, such that said higher elastic modulus inner surface is bent to a concave shape and the lower elastic modulus outer surface is bent to a convex shape.   
     
     
         9 . A method according to  claim 8  further comprising the step of establishing an opposite temperature differential across the pipe wall at locii substantially corresponding to the position of a base of the ring groove. 
     
     
         10 . A method according to  claim 8 , wherein the circumferential ring groove is part of a pipe socket of enlarged diameter and wherein said enlarged diameter portion of the ring groove has a greater diameter than said pipe socket diameter. 
     
     
         11 . A method according to  claim 10 , including creating a plurality of temperature zones of different temperature characteristics in the end portion of the pipe in which the socket is to be formed, one of said temperature zones corresponding to said ring groove position and establishing said temperature differential. 
     
     
         12 . A method according to  claim 11 , wherein said temperature zones comprise a first temperature zone extending between the ring groove position and the end of the pipe, a second temperature zone extending between the ring groove and the position of the rear of the socket and a third temperature zone being said temperature zone corresponding to the ring groove position. 
     
     
         13 . A pipe having a ring groove made by the method of  claim 8 , having reduced compressive strain on the concave inner surface of the ring groove. 
     
     
         14 . Apparatus for forming a circumferential ring groove on a pipe, said ring groove having a concave inner surface and a convex outer surface, comprising:
 temperature control means establishing a temperature differential between said inner and outer surfaces of the pipe at a locus corresponding to said ring groove such that the pipe material at said inner surface has a higher elastic modulus than that of the pipe material of the outer surface; and   bending means bending said pipe material at said locus to form said ring groove.