Field Joint couplings are vacuum insulated field welded connections between two sections of Vacuum Jacketed Pipe. They have a long heat leak transition between the outer jacket and the inner pipeline to reduce the heat input into the system. After the inner weld is made, the joint is insulated and a coupling is moved into place over the section. The coupling is then field welded to the collars on the ends of the two piping spools. This coupling is then evacuated to a low vacuum to insure a low heat leak. This type of system is usually installed by Quality Cryogenics' field crew.

Equipment Required:

GTAW welding equipment and ASME qualified welder (with qualified procedure) to make a fillet weld on SA-312 Type 304 Stainless Steel pipe

• Field Joint insulation kit (supplied with VJP section by Quality Cryogenics)
• Multilayered insulation (paper and foil pre-wrap)
• Molecular sieve packages
• PDO
• Field Joint assembly kit (supplied with VJP section by Quality Cryogenics)
• Field joint coupling with pump-out port and plug
• Socket weld coupling
• Vacuum Pump
• Evacuation fixture

Assembly Procedure:

A. Before welding the VJ Pipe sections together, slide the outer coupling over the end of one section.

B. Move the two sections together engaging the inner line weld socket.

C. Weld at the weld socket with an approved ASME procedure.

D. Appropriately inspect weld to insure a leak proof seal.

E. Slide the next VJ Pipe section into place and repeat the steps A to D.

F. If pressure testing is specified, do so now.

G. Clean and dry the joint area. All parts exposed to vacuum must be clean, free of any oils or solvents, and dry.

H. Insulate the field joints in the following manner.

• Attach the sieve packages to the inner pipe using copper wire or aluminum tape. The proper amount of sieve is provided with each Field Joint kit depending on pipe size.

• Puncture each package with a number of small holes (20).

• Wrap the insulation pre-wrap over the inner line. The insulation should be wrapped around the inner line, overlapping itself half way.

• Secure the insulation loosely with copper wire or aluminum tape.

• Secure the Hydrogen getter packet to the outside of insulation with copper wire.

I. Attach field joint coupling.

• Slide the coupling over the insulation so that it is centered over the non-insulated area.

• Weld the coupling to the collars attached to the outer jacket on each side of the joint using an approved ASME procedure.

J. Attach the vacuum pump operator to the pump-out port, and then evacuate the field joint coupling below 15 microns.