Radially outward orbital welding technique as a joining method used for inner tube to fitting connections in double wall tube configurations

1. A process of welding fittings to ends of a double wall pipe comprising:

placing an assembly of a second fitting and an inner pipe and an outer pipe into a fixture;

said fixture comprising:

a set of collets configured to retain said assembly of said second fitting and said inner pipe and said outer pipe;

a backing plate coupled to said set of collets, said backing plate being fluidly coupled to said second fitting; and

a conduit fluidly coupled to said backing plate; said conduit configured to fluidly couple a gas source to said backing plate;

forming a first welded joint between the inner pipe and an inner receiver of a first fitting;

forming a second welded joint between the outer pipe and an outer receiver of said first fitting;

forming a third welded joint between said outer pipe and an outer receiver of the second fitting; and

forming a fourth welded joint between said inner pipe and an inner receiver of said second fitting.

2. The process according to claim 1 , wherein said fourth welded joint comprises a welded lap fillet joint or a full penetration groove welded joint.

3. The process according to claim 1 , wherein said gas source comprises an inert shielding gas, further comprising:

flowing the inert shielding gas through the conduit to a groove formed in said backing plate;

flowing the inert shielding gas from said groove through said second fitting into a chamber formed between said inner pipe and said outer pipe to protect said fourth welded joint.

4. The process according to claim 1 , further comprising:

installing said fixture within an orbital welding device; and

aligning a welding electrode with said inner pipe and an inner receiver of said second fitting.

5. The process according to claim 1 , further comprising:

clamping said assembly of said second fitting and said inner pipe and outer pipe in a biasing member formed by said set of collets and said backing plate.

6. The process according to claim 1 , further comprising:

sealing said fourth welded joint between said inner pipe and an inner receiver of said second fitting by using an arc energy to melt either a full or a partial thickness of the fitting with the inner pipe.

7. A welding fixture comprising:

a set of collets configured to retain an assembly of a second fitting and an inner pipe and an outer pipe;

a backing plate coupled to said set of collets, said backing plate being fluidly coupled to said second fitting; and

a conduit fluidly coupled to said backing plate; said conduit configured to fluidly couple a gas source to said backing plate.

8. The welding fixture according to claim 7 , further comprising:

a groove formed in said backing plate, said groove fluidly coupled to said conduit and fluidly coupled to said second fitting.

9. The welding fixture according to claim 7 , wherein said fixture is configured to mount into an orbital welding device.

10. The welding fixture according to claim 9 , wherein said orbital welding device includes a housing supporting an orbital welding head and adaptor configured to mount a welding electrode proximate an inner diameter of a joint between said inner pipe and an inner receiver of said fitting.

11. The welding fixture according to claim 10 , wherein said welding electrode is configured to form a welded lap fillet joint between said inner pipe and said inner receiver of said fitting.

12. The welding fixture according to claim 11 , wherein said welding electrode is positioned relative to said inner pipe inner diameter and configured for making a radially outward weld in a gap between the inner pipe and the fitting, wherein said gap is sealed by melting either a full or a partial thickness of the fitting with the inner pipe.

13. A process of joining a double walled pipe with a fitting comprising:

placing an assembly of a fitting and an inner pipe and an outer pipe into a fixture, wherein said fitting and said outer pipe have a first welded joint;

mounting said fixture into an orbital welding device;

positioning a welding electrode relative to an inner diameter of said inner pipe proximate an inner receiver of said fitting; and

forming a second welded joint between said inner pipe and said inner receiver.

14. The process of claim 13 , wherein said second welded joint is formed with a radially outward weld in a gap between the inner pipe and inner receiver of the fitting.

15. The process of claim 13 , wherein said second welded joint comprises a welded lap fillet joint or a full penetration groove welded joint.

16. The process of claim 13 , wherein said fixture comprises:

a set of collets configured to retain said assembly of said fitting and said inner pipe and outer pipe;

a backing plate coupled to said set of collets, said backing plate being fluidly coupled to said fitting; and

a conduit fluidly coupled to said backing plate; said conduit configured to fluidly couple a gas source to said backing plate;

flowing the inert shielding gas through the conduit to a groove formed in said backing plate; and

flowing the inert shielding gas from said groove through said fitting into a chamber formed between said inner pipe and said outer pipe to protect said second welded joint.

17. The process of claim 13 , further comprising:

making said second weld as a radially outward weld in a gap between the inner pipe and the inner receiver of the fitting, wherein said gap is sealed by melting either a full or a partial thickness of the inner receiver of the fitting with the inner pipe.

18. The process of claim 13 , wherein said second weld comprises one of an orbital welding technique or a manual gas tungsten arc welding technique.