Pneumatic Friction Welding System

Case Study

Project Details

Client:

RasGas Company Ltd

Location:

Qatar

Equipment:

R1004 pneumatic friction welding system and vacuum clamp.

Pipeline Details:

Train 1 & 2 return lines 66"OD with a 17mm wall thickness.

Inner Coating:

1000micron DFT Interline 955 Glass Flake Vinyl Ester.

Outer Coating:

1000micron DFT Coal Tar Epoxy.

Project Description

The client required M10 carbon steel studs to be welded to the inside of the pipeline so that sacrificial anodes (Cathodic Protection) could be retro fitted. Throughout this process it was critical not to damage the outer coal tar epoxy coating as the pipeline was buried and therefore very difficult to repair. The studs were required to be welded in a square pattern, 100mm between centres.

The Solution

Proserv Offshore's R1004 system is a pneumatically powered welding unit requiring 150 CFM @ 120psi. The system works by spinning a stud at around 6,000 rpm and forcing it onto the parent material. The heat created by the friction then forges the two materials together producing a strong plastic weld. On this particular project, the stud welds were created without removing the paint on the pipe interior.

A vacuum clamp was used to support the welding unit's axial load. Once the first weld position was confirmed using a centre mark, the remaining three studs were constrained via an inbuilt template ensuring the correct spacing of the remaining studs.

It was also found that the vacuum clamp could still hold the welding head in position even when it was positioned over the spiral welds on the pipeline.

The Benefits

The benefits of friction stud welding include:

Minimal surface preparation - can weld through most paints, coatings and oxidised surfaces.
No requirement for pre or post weld heat treatment.
No external damage to the pipe coating helping to maintain pipeline integrity.
Superior weld properties over conventional arc welding. A fine grained forged weld that is stronger than the parent material.
Shut-down time is reduced significantly due to quicker assembly and set-up.
Welding system is easily operated by two Proserv Offshore Technicians.
In air or underwater application - suitable for remote operation by ROV.

Conclusion

Friction welding was successfully used to weld 176 M10 studs through the glass flake coating without damaging the outer coal tar epoxy coating. The welding studs were approved and certified by Lloyds Register.

Proserv Offshore has an extensive track record of friction welding projects for welding retro fit anodes, earthing points, grating attachment, structural bosses and corrosion sensors. Proserv Offshore are also qualified for carrying out this process in hazardous zoned areas.