Method for thermally insulating welded joints of pre-insulated pipes

Abstract

The invention relates to pipe heat insulation and in particular to methods of heat insulation installation on welded joints of subterranean pipes for transporting oil and oil products. The method includes applying an anticorrosive layer on the welded joint using heat-shrinkable polymeric tape, mounting heat insulating polyurethane foam pipe coverings on the tape, using tie straps with locks to secure the pipe coverings, gluing hot-melt adhesive tape at the edges of a pipe protective envelope to overlap the envelope and the pipe coverings, installing a metal casing symmetrically relative to the center of the weld joint, and sealing the metal casing and the envelope with a heat-shrinkable polymeric fabric. The technical result provides anticorrosive protection and heat insulation of the welded joint of steel pipelines, provides improved heat insulation installation on the pipeline, and reduces the cost of installation and labor intensity.

1 . A method of providing heat insulation of a welded joint of pipes to be laid below ground and having factory heat insulation, a protective metal envelope, and factory-fitted anticorrosive free end portions, comprising:
 positioning a gasket having heat-shrinkable polymer tape about the welded joint; positioning a heat-insulating coating having polyurethane pipe coverings about the gasket, the polyurethane pipe coverings including at least two segments of a shape that defines an opening for receiving the welded joint, the polyurethane pipe coverings having geometrical dimensions that are similar to a space between the factory heat insulation of the pipes, the heat insulation coating being aligned with the protective metal envelope of the pipes;   covering transverse joints of the polyurethane foam pipe coverings with a sealant;   fastening the polyurethane pipe coverings with tie bands having locks;   installing a metal casing such that it overlaps the protective metal envelope of the pipes and is positioned around the heat-insulating coating, the metal casing having loose ends that overlap near a top of the welded joint; and   sealing a joint between the metal casing and the protective metal envelope using a heat-shrinkable polymer tape.   
     
     
         2 . The method of  claim 1 , further comprising sealing a joint between the protective metal envelope and the polyurethane pipe coverings using a hot-melt adhesive tape. 
     
     
         3 . The method of  claim 1 , further comprising forming a tool joint between the ends of the factory-fitted heat insulation and adjacent polyurethane pipe coverings by forming a stepped shape in a longitudinal direction in the factory-fitted heat insulation and the adjacent polyurethane pipe coverings. 
     
     
         4 . The method of  claim 1 , further comprising tying the polyurethane pipe coverings together using temporary belts until they are adjacent to each other and to adjacent edges of the factory-fitted heat insulation prior to fastening the polyurethane pipe coverings with the tie bands, and removing the temporary belts after fastening the glass foam pipe coverings with the tie bands. 
     
     
         5 . The method of  claim 1  wherein sealing the joint between the metal casing and the protective metal envelope using a heat-shrinkable polymer tape further includes sealing a first joint between the metal casing and a first protective metal envelope using a first polymer tape, sealing a second joint between the metal casing and a second protective metal envelope using a second polymer tape, and placing a third polymer tape to overlap the first polymer tape and the second polymer tape. 
     
     
         6 . The method of  claim 1 , further comprising:
 abrasive blast cleaning the welded joint and the end portions of the pipes prior to positioning the gasket about the welded joint;   placing four contact thermometers equidistant about a perimeter of the welded joint;   drying the welded joint to a predetermined temperature based on measurements from the four contact thermometers; and   applying a uniform layer of primer to the cleaned and heated welded joint and end portions of the pipes prior to positioning the gasket about the welded joint. Method of  claim 1 , characterized in that before installing the gasket, the surface of the weld joint and adjoining area is prepared by cleaning the metal surface by abrasive blast method, and drying to a predetermined temperature with the control on the four equidistant points around the perimeter of the weld joint with the help of a contact thermometer.   
     
     
         7 . The method of  claim 1 , further comprising:
 heating a loose end of the heat-shrinkable polymeric tape;   fastening the loose end of the heat-shrinkable polymeric tape to an upper generatrix of the end portions of the pipes;   wrapping the heat-shrinkable polymeric tape around the end portions of the pipes such that the heat-shrinkable polymeric tape has a sag;   positioning a second loose end of the heat-shrinkable polymeric tape over the first loose end such that the second loose end overlaps the first loose end by at least 100 millimeters (100 mm);   heating the second loose end and fastening the second loose end on the first loose end;   securing the overlap of the first loose end and the second loose end using a locking plate having a higher adhesive layer melting temperature than that of the gasket; and   shrinking the heat-shrinkable polymeric tape by heating the sag such that the heat-shrinkable polymeric tape has a thickness of at least 2 mm when a diameter of the pipes is less than or equal to 820 mm and has a thickness of at least 2.4 mm when the diameter of the pipes is greater than 820 mm.   
     
     
         8 . The method of  claim 1 , further comprising determining a quality of the gasket by inspecting an appearance of the gasket, measuring an amount of overlap of the gasket on a factory-fitted anticorrosive coating of the pipes, measuring a thickness of the gasket, measuring a dielectric continuity of the gasket to ensure it is at least 5 kilovolts per mm, and measuring an adhesion of the gasket to the welded joint and to pipe sections that include the factory-fitted anticorrosive coating to ensure it is at least 70 Newtons per centimeter. 
     
     
         9 . The method of  claim 1 , further comprising cutting the polyurethane pipe coverings to have a width that is within 7 mm of a distance between factory-fitted heat insulation of the pipes. 
     
     
         10 . The method of  claim 1 , wherein the heat insulation coating has a thickness that is less than a sum of a thickness of the factory-fitted heat insulation and a thickness of the protective metal envelope. 
     
     
         11 . The method of  claim 1 , further comprising validating an installation by visually inspecting an appearance of the heat insulation coating, measuring a size of overlap of the metal housing on the factory-fitted protective metal envelope, and measuring a distance between each of the fasteners and between an edge of the metal housing and the fasteners. 
     
     
         12 - 19 . (canceled)