Once the installation of pipelines moved offshore in the 1960s, there was a drive to increase production rates due to the high cost of lay-barges and weather window limitations. Initially this demand turned to the use of semi-automatic gas metal arc welding (GMAW), but the high incidence of lack-of-fusion defects forced equipment developers to try to mechanise the process. While many tried, it was not until 1969 that CRC-Evans developed and utilised the first commercially viable mechanised pipeline welding system.

The CRC mechanised system utilised a narrow gap bevel to reduce the weld volume. The root pass was deposited from inside the pipe using a multi-head combination internal welder/clamp, while the hot pass, fill pass, and cap pass were deposited externally using an orbital carriage or bug mounted on a guide band.

Despite many efforts to build alternative welding systems, the CRC mechanised welding system dominated the landline industry for almost 25 years. This monopoly, however, was much shorter lived in the offshore pipeline industry. Within six years of the first mechanised welded offshore line, Saipem introduced its PASSO system and started welding North Sea pipelines.

The PASSO system deposited the root pass externally using a copper backing clamp, which is slower than the internal welder. Although the remaining hot, fill, and cap pass were made using an orbital carriage/bug, it had to be re-engineered to avoid the CRC patents. This re-engineering made the equipment difficult for welders to use.

Since Brown & Root had the offshore rights to use CRC, neither that equipment nor the PASSO system were available to other offshore pipeline contractors, and further mechanised GMAW systems were developed by ETPM (Serimer-Dasa), J. Ray McDermott (H. C. Price), and Allseas Phoenix. ETPM and J Ray McDermott initially built large multi-head rack systems, and while these systems worked, they were not flexible and were too big to use on land lines. Eventually both companies also utilised band and bug systems. The last major offshore contractor to build a system was Allseas who built an automated band and bug welding system.

Until 1995, all the various welding systems were owned exclusively by offshore contractors or were rented by CRC to various land or offshore contractors. Then SERIMER started to rent its dual torch equipment and Vermaat Technic BV started to sell both single and dual head units. Both systems were state-of the-art automated equipment and are used worldwide.

Current welding technology

The old mechanised systems have given way to computer controls, and most can now be classed as automated systems. Today pipeline contractors have the choice of using internal roots, external roots with copper backing, and external roots without backing.

All of these root techniques are proven and have pros and cons. Internal roots produce the highest rates on land; they can also handle more high/low misalignment, and do not need highly skilled welders. Copper back-up clamps are cheaper than internal welders but have a small risk of copper contamination, and are about 33–50 per cent slower than internal roots.

The third root pass option, external without backing, is based upon using a special short-arc transfer power supply. The first of these, surface tension transfer (STT), was developed by Lincoln Electric. Since then a number of manufacturers such as Miller, ESAB, and Fronius have produced alternative power supplies. The advantages of this process is that it has a much lower capital/rental cost than internal welders or copper backing clamps. On large diameter pipes, however, it is much slower. For example, on a 48 inch diameter girth weld an internal root pass is almost twice as fast as external copper root, and an external copper root is four times faster than STT-type, no-backing root pass. Depending upon the diameter/length of the pipeline, schedule and terrain, each root option may be cost-effective.

Fill pass and cap pass welding can now be accomplished using single or dual head bugs, or a combination of both. After the initial development of the band and bug single head machines, many efforts were made to build a dual head bug by companies including PASSO, Evans Pipeline, CRC, B&R, and Astro-Arc, but it was Serimer-Dasa (now Serimax) that first produced a successful working dual head band and bug system. The impact of its dual head bug provided Serimer the opportunity to significantly increase production rates offshore where the number of weld stations is limited. While dual heads do not double production, they will increase deposition by 40–50 per cent. Dual head bugs require fewer weld stations, welders and side booms. On land lines the speed of the root pass controls productivity, provided enough fill and cap weld stations are used to keep pace. Alternatively, if the right-of-way or pipe logistics do not allow production rates of up to 200 welds a day on large diameter lines, it is possible to use external backup roots and dual head bugs to produce 80 to 100 welds a day with four to six weld stations.

The latest developments

Current automated pipeline welding developments tend to be centered on improved seam tracking, data logging, and stronger line-up clamps. Most equipment suppliers are taking advantage of increased computing power to improve through-the-arc tracking, contact to work distance arc voltage controls, and laser tracking. Advanced tracking technology improves weld quality, consistency, and improves production rates by allowing faster travel speeds. The industry has yet to utilise the option of tandem arc GMAW technology to increase welding speeds for major large diameter pipelines. In addition to the major automated welding equipment suppliers and users, there are now many alternative suppliers of single head orbital machines. Some are still mechanised units but work well with FCAW wires and are suitable for tie-ins.

Future welding developments

Most alternative welding process options for pipeline welding have already been examined and evaluated over the past 30 years. Some of these processes were pursued for some time, such as laser/electron beam, flash butt, homopolar, SAG, MIAB, explosion, and radial friction welding, but all ultimately failed. It is therefore the opinion of this author that the pipeline industry will not see a quantum leap in welding technology. Automated GMAW is a tried and tested process and future developments will tend to be concentrated in more computer controls and a progression from automated to robotic automation.