Home News & Events Bug-O Pipe Welding Article featured in November World Pipelines Magazine

Bug-O Pipe Welding Article featured in November World Pipelines Magazine

Nov. 05, 2012

Bug-O Systems is proud to share our recent "On Budget Pipe Welding" article featured in World Pipelines magazine. Click here to view the pdf.

 

ON BUDGET PIPE WELDING
JEFF NELSON, APPLICATION MANAGER, BUG-O SYSTEMS, USA, LOOKS AT SELECTING THE CORRECT PIPE WELDING EQUIPMENT TO MEET A PROJECT’S NEEDS AND, CRUCIALLY, ITS BUDGET.

The welding of any pipeline is a complicated affair, be it a short feeder line or a major cross country project. The planning is expected to take years and the execution is often expected to be accomplished with little impact to the environment, project cost being on or under budget, and with tremendous pressure placed on a very short timeframe for completion. Pipelines are typically made of steel and welding is the preferred and proven method used to join the pipe sections into a complete pipeline. Selecting the correct welding process and equipment can affect all three of these issues; – time, environmental impact and cost – and can have a significant impact upon success.

Welding in itself presents a broad array of options. Performing a weld can be relatively simple and straightforward or it can be a very complicated and sometimes a frustrating operation. Recent advances in testing and more stringent requirements on material and production quality can have a huge impact on the final success of a pipeline project. Determining the correct welding process to use and then determining the method by which that process will be applied can have considerable influence upon the overall outcome of the project.
 
In general, how pipeline welding processes are applied can be broken down into three categories: manual, mechanised, and automatic. Each of these categories presents advantages and disadvantages for any given application. This article will consider some of the advantages and limitations to various welding processes and how they can be applied in the welding of pipelines, thus determining how they can affect a project and its bottom line.

Most of the processes typically utilised for pipeline welding can be performed manually. What follows is a short explanation on welding processes for pipeline welding.

Shielded metal arc welding (SMAW) process
This process goes by various names in various areas such as SMAW, stick or MMA. SMAW requires a very low initial investment in equipment. The SMAW process is well understood and accepted in the industry globally. Most welding procedures for this process are pre qualified, which means that there are pre established welding parameters that have been found to produce acceptable quality welds if these procedures are followed. The welding consumables used for this process, the electrodes or ‘rods’, are relatively inexpensive and easily available as are the welding power sources.

Flux cored arc welding (FCAW) process
FCAW is also globally familiar to the pipeline industry. Instead of the welding consumable being supplied in short individual lengths as in SMAW, in FCAW the consumable is supplied in a small diameter wire that is continuously fed into the weld by an external wire feeder. Flux cored wire is manufactured in two forms, self shielded and gas shielded. Both of these can be used via manual control to produce high quality welds on pipe. Due to the greater amount of shielding gas created by the self shielded wire along with often times built in denigrates and descavenger designed into the fill, the nature of the gas itself, along with the additives in the fill, tends to lend itself for use in more inaccessible locations and without wind screens. Gas shielded FCAW requires additional protection from the surrounding environment. As the weld being produced is protected by an externally supplied gas rather than from the burning of the flux itself, it is necessary to protect the welding area from wind. This is typically ensured via a small shed or enclosure that is placed over the pipe and provides an area of still air that does not affect the shielding gas.

The wire used in FCAW is somewhat more expensive than that used in the SMAW process but, due to the continuous nature of the wire, the arc on time is increased and is thus more efficient. The equipment necessary to utilise the FCAW process is more expensive than SMAW, as a wire feeder and a welding gun must be added. The gas shielded FCAW requires the additional costs involved with the added shielding gas such as the gas itself, the regulators and hoses, along with the necessary shed to protect the operation. However in both cases, the additional costs involved can be justified when considering the increased efficiency in performing the welds. In comparison, it is not uncommon to see as much as a 60% increase in weld deposition rate when going from SMAW (vertical down) to self shielded FCAW (vertical down) and an increase of almost 80% is possible, if the gas shielded FCAW process is utilised.

The SMAW and the self shielded FCAW processes, although commonly used for large diameter, long run pipelines, are perfectly suited to making short run, smaller diameter pipelines – particularly in hard to access areas. The equipment is easy to set up and is quite portable. The gas shielded FCAW process lends itself to longer runs that are more easily accessible due primarily to the requirements of the welding sheds.

Limitations
The primary limitation to these two processes is how they are utilised. The person making the weld itself must be a very skilled individual with outstanding eye hand co ordination, along with a thorough understanding of what needs to be completed and how to do it. The quality of the weld produced is completely controlled by the person producing the weld. While it is advantageous to have the welder intimately involved with all aspects of the weld, there can be a very large variation in quality between individual welders. This lack of uniformity and the requirement for such highly capable individuals presents issues when considering the overall cost of the project.
 
Mechanised welding
In order to further increase the productivity of the FCAW process, it is possible to apply the process in a mechanised fashion. In mechanised welding, the welding process is controlled in the same way as when manually applied, however, the welding gun itself is held by a motorised tractor that is mounted to a track that encircles the pipe. Systems of this sort are typically small and light in weight and can be easily installed around the pipe. The track is referred to as a rail, ring or band. This track upon which the tractor travels is usually made to fit the specific pipe diameter being welded. The tractor is mounted to this track and the welding gun is attached to the tractor via some sort of adjustable clamping mechanism. The welder will physically position the tractor in the proper location and via controls provided as part of the system, initiate the weld and make adjustments to the weld as the tractor travels around the pipe. The tractor is often equipped with an oscillation assembly that provides a weaving motion during travel. This weaving motion provides an improved bead appearance and allows the initial weld passes to create an even layer within the weld joint. Additionally, many of the oscillation assemblies are equipped with a remote steering function that allows the welder to electronically adjust the position of the weld while it is being made. Depending on the pipe wall thickness, it is often necessary to perform multiple passes and layers of welds to fully fill the prepared joint. With the track in place, the tractor can perform repeated passes in order to fill the joint without the track being repositioned. With FCAW, it is a common practice to weld in the vertical up progression. With mechanised welding, two tractors can be placed on the same track, each welding up one side of the pipe. In this manner the total time to weld is reduced, as there are two welds being performed simultaneously.

When mechanised, the gas shielded FCAW process is most often used. As such, the same shack type shielding environment from wind that is needed for manual gas shielded FCAW must be provided. The costs of the tractor and ring assemblies are not high considering the increase in productivity that is obtained. Compared to manual self shielded FCAW, a mechanised gas shielded FCAW weld can provide an improvement of 60% in deposition. If compared to manual SMAW performed vertical down, there is a possible increase in deposition of 160%. The cost of a typical entry level pipe welding mechanisation system will be roughly the same as a fully outfitted welding system with power source, wire feeder and all the necessary accessories. However, with the expected improvement in efficiency, these costs are quickly offset by the high quality of the welds and much higher productivity.

High quality welds means high quality welders
There is a common misconception when mechanised pipe welding is being discussed which implies that it is not necessary to hire high quality welders or that using mechanised welding will eliminate jobs for welders. This could not be any farther from the truth. Performing a weld with a mechanised system requires a trained welder who can observe the welds and make the proper corrections as events arise. A person unfamiliar with the nuances of the weld puddle will not become a successful welder by using a mechanised system. The person operating the machine can be no less qualified than the person performing the weld by hand. The difference is that the machine makes the welder much more efficient and without any signs of fatigue. With the tractor system, once the arc is initiated at the bottom of the pipe, there is no need to stop the weld until the top centre of the pipe is reached. The welder can reposition for a better view of the weld without extinguishing the arc. There is no need to stop and reposition so the welder can better access the weld or stop because the welder’s position is uncomfortable. Fatigue and loss of concentration are virtually eliminated. The only difference is that with the mechanised system the welder becomes much more efficient and their manual dexterity is not as critical. As a result, the quality and appearance of each weld is consistent and easily quantifiable.

If a longer length feeder line is being produced or if there is a short length but large diameter or thicker wall pipe, the use of a simple mechanised system can show significant improvements in productivity. Reduction of welder fatigue along with the improvement in arc on time provides a perfect fit for applications of this sort.

Summary
Automatic welding is the highest level of welding mechanisation. This is typically applied on projects that require high production rates such as very long cross country or offshore projects. With this level of mechanisation, the tractor can be a sophisticated system with multiple welding arcs welding at the same time from the same tractor along with a control system that integrates an intelligent vision system that ‘sees’ the weld position and automatically adjusts the position of the weld to adapt to changes in the bevelled joint. In the automatic application, the welding process is often the gas metal arc (GMAW) or GMAW pulsed process. This process can provide high deposition rates and high welding travel speeds. A project manager can expect to see a 200% improvement on weld deposition when comparing the most basic automatic welding system to basic SMAW.

Today, when project managers are faced with determining the best way to make the welds for a pipeline, they have a range of possible solutions. Considering line length, pipe diameter, time constraints, pipe wall thickness and the availability of labour, weld process and the way it is applied can have a very real effect on the project’s overall success.