Pipeline Welding Technology

Pipeline welding plays an important part in both the onshore and offshore pipeline industry. Throughout the years there have been significant advancements to help ensure a pipelines durability and reliability. Here, Bob Teale takes us through the history and what’s to come.

Pipeline welding, as we know it today, started in 1927 with the introduction of Lincoln’s Fleetweld 5 cellulosic electrode. While there is no doubt that cellulosic electrodes have proven to be very effective and will remain so for years to come, they are technically limited in terms of strength, toughness, and production rates.

Once offshore pipeline construction started, there was a drive to increase production rates due to the cost of lay-barges and narrow weather windows. Initially this demand turned to using a semi-automatic CO2 gas metal arc welding (GMAW) process, but the high incidence of lack-of-fusion defects forced equipment developers to mechanise the process. While many tried, it was not until 1969 that CRC-Evans produced the first viable mechanised pipeline welding system.

The CRC mechanised system used a narrow 5° bevel, with the root deposited from the inside using a combination internal multi-head welder/clamp. The hot, fill, and cap passes were deposited externally using an orbital bug and guide band.

Despite efforts to build alternative systems, CRC dominated the landline industry for almost 25 years. This monopoly, however, was much shorter lived offshore. Within six years of the first mechanised welded offshore pipeline, Saipem introduced its PASSO system. which used a copper backing-clamp; with the root pass made, the remaining passes were deposited externally using an orbital bug.

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

Until 1995, all the various welding systems were owned exclusively by offshore contractors or were rented by CRC to contractors; at that time, Serimer started to rent equipment, and Vermaat Technic BV started to sell both single and dual-

head units. These were state-of-the-art automated systems and are now widely used worldwide.

Current welding technology

Most mechanised systems have now given way to computer controls and can 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 alignment high/low, and do not need welders. Copper back-up clamps are cheaper than internal welders but have some risk of copper contamination and are 33–50 per cent slower.

The third-root pass option, external without backing, is based upon using a special short-arc transfer power supply. The first of these was developed by Lincoln Electric—STT (Surface Tension Transfer). The advantages of this process is that it is a much lower capital/rental cost, although on large diameter pipes, it is much slower. For example, on a 48 inch internal diameter girth weld, an internal root pass is almost twice as fast as an external copper root pass, and an external copper root pass is four times faster than no-backing root passes. Depending upon the diameter and length of the pipeline, as well as the schedule and the terrain, each root option may be cost-effective for the appropriate circumstances.

Fill-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 (PASSO, Evans Pipeline, CRC, B&R, and Astro-Arc), but it was Serimer-Dasa (now Serimax) who 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, fewer welders, and fewer side booms.

The latest developments

Current automated pipeline welding developments tend to be centred 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 and arc voltage controls, and laser tracking is also available. Advanced tracking technology improves weld quality, and consistency, and improves production rates by allowing faster travel speeds. In addition to the major automated welding equipment suppliers/users, there are now many alternative suppliers of single head orbital machines. Some are still mechanised units but work well with flux-cored arc welding wires.

Future welding developments

Most alternative welding process options for pipeline welding have been examined and evaluated over the past 30 years. Some of these welding processes were pursued, such as laser/electron beam, flash butt, homopolar, SAG, MIAB, explosion, and radial friction, but all ultimately failed. While some are working on hybrid laser/GMAW bugs, it is the opinion of this author that the industry will not see a quantum leap in welding technology.

The industry also has the option to use tandem arc GMAW technology to increase welding speeds for major large diameter pipelines. Automated GMAW is tried and tested, and future developments will tend to be in more computer control and a progression to robotic automation.

The following is a timeline for major offshore GMAW welding system developments:

1969 CRC Band & Bug P-100 used on first land line

1970 CRC Band & Bug P-100 first used offshore

1978 Saipem—PASSO Band & Bug used offshore

1981 ETPM—Serimer T-2 Rack used offshore

1981 Saipem—PASSO Band & Bug used on land

1982 J. Ray McDermott—HC Price Rack S used offshore

1988 ETPM—Serimer Dual head bug: Saturnax 8 used offshore

1989 ETPM—Serimer T-4 Rack used offshore

1991 CRC Computer control Band & Bug P-200 first used

1993 Allseas Develop Automated Phoenix Band & Bug

1994 Serimer Dual head band & bug: Saturnax 8 first used on land

1995 J. Ray McDermott—Add laser tracking & computer controls to Rack

1995 Vermaat Band & Bug System single & dual head units

1995 Lincoln Electric STT power supply, no-backing root passes

1998 J. Ray McDermott—Utilise Dual head JBBS/Vermaat bugs offshore

2001 CRC P-450 Tandem Head Bug first used on X100

2002 Saipem Develop PRESTO Dual head bug for J-Lay

Source: http://pipelinesinternational.com/news/the_long_and_welding_road_to_pipelines/63321