Apr. 29, 2013

Bug-O Systems' article "Confidence in Consistency" is featured in the April 2013 issue of World Pipelines Magazine. CLICK HERE TO DOWNLOAD PDF

Confidence in Consistency
Jeff Nelson, Bug-O Systems, USA, presents a case study of mechanized welding.

The use of mechanized pipe welding equipment can improve a fabricators weld quality and reduce the cost to manufacture some prefabricated systems. Mechanization of the welding process provides multiple enhancements such as greater productivity through an increase in actual welding time compared to clock hours, upgrades in the quality of the welds produced, reduction in fatigue for the welders and improved weld uniformity. All of these advantages make weld mechanization an intelligent choice for the pipe fabricator.

Mechanised welding for two offshore pipelines
New Industries, Inc. is located in Morgan City, Louisiana and provides large diameter, shop fabricated pressure vessels and tanks for onshore and offshore applications along with fabrication of a wide variety of production hardware used for offshore oil and gas production.  In Q4, 2012, it was presented with the opportunity to fabricate hardware in support of two Gulf of Mexico offshore pipelines.  The various projects involve fabrication of heavy wall large diameter pipe.  The horizontal fixed position welds (5G) required as part of the projects, presented an opportunity to improve production and the weld quality by exploring mechanized welding.  With help from their local Lincoln Electric representative they were put in contact with Bug-O Systems, regarding the Piper series of pipe welding systems.

Whenever possible, it is common practice for a fabricator to perform heavy wall girth welds using the automated Submerged Arc Welding (SAW) process.  In most cases, the individual sections of pipe are aligned and tacked and a root pass is performed manually.  Due to the critical nature of the offshore oil field application, it is typical for this root pass weld to be made using the Gas Tungsten Arc Welding (GTAW) process.  The weld cross section of the GTAW root pass is usually quite thin so an additional pass or even two additional passes of GTAW are performed to provide sufficient material thickness to support the heat input during SAW.  The double length section of pipe is then placed in a set of motorized turning rollers.  A Submerged Arc Welding head is positioned over the weld joint and the weld is made as the pipe rotates beneath the weld head.  The weld is made in continuous fashion with the operator adjusting the position of the weld each time a revolution of the pipe is completed.  Even using this very efficient method it can take hours to complete a weld on heavy wall pipe.  This process is the most efficient but can only be employed where the entire assembly can be rotated on the rolling device.  If the work piece cannot be rolled, a different approach must be used.

Consider the case of a girth weld in a horizontal pipe that cannot be rolled.  The pipe may be connected to a manifold or valve or some support structure.  Or it may be that there is some other structure of the assembly that limits the access to the weld joint in question.  The practice in many fabrication shops is for this weld to be made in the standard fashion used for the last 50 or 60 years, that of performing a GTAW root pass as indicated previously and then for the remainder of the weld joint to be filled using the tried and true method of Shielded Metal Arc Welding (SMAW) or Stick.  It would not be at all unusual for this method to require days of labor to complete.  During stick welding, the operator can only weld a distance which is limited by the length of the welding electrode.  The welder would then break the arc, insert a new electrode into the electrode holder, possibly reposition themselves for better access to the weld joint and proceed to weld again.  This stopping and starting could also be a source of discontinuities which often causes area for potential defects within the weld.  Throughout the performance of this weld, the manual technique of the welder is critical.  Welder fatigue can also play a large part in the consistency and quality of the weld produced.  A minor incorrect motion may cause the whole weld to be found unsatisfactory.   The necessary stopping and starting along with repositioning for each weld results in a very poor arc-on time.  It is obvious that a weld is only deposited when the arc is active.  Higher arc-on time means greater efficiency and lower cost to produce the weld.  Horizontal fixed position welds are time consuming and tedious to perform, particularly on large diameter, heavy wall pipe such as is required for these offshore projects.  This time consumption and tedium is compounded when using practices from the 1950’s.

It is possible to increase productivity by replacing the SMAW process with one of the wire fed welding processes such as Gas Metal Arc Welding (GMAW) or Flux Cored Arc Welding – Gas Shielded (FCAW-G).  The GMAW process has long received a poor reputation in the pipe industries so typically the FCAW-G process is selected.  In both of these processes, the requirement for the operator to stop and replace the welding electrode is eliminated via a constantly fed electrode wire, however the welder is still limited in the distance that can be welded without them having to reposition themselves.  Here again we have a weld stop and start which can be a location for a weld discontinuity or defect.  Switching to the FCAW-G process will certainly reduce the labor hours required to perform the weld but does not eliminate the problem of operator technique and fatigue.  The weld produced is still only as consistent as the welder.  Using either the SMAW or FCAW-G process, welds made might be perfect at the start of the shift but might suffer as the day progresses and fatigue sets in later in the day.  The work done from day to day and welder to welder is not always consistent; in time to perform, appearance or in quality.  

New Industries Inc. faced these very issues in the fabrication of In Line Valves (ILVs) and gathering manifolds using large diameter heavy wall pipe.  Many of the required welds could be performed using the SAW method with the pipe on turning rolls but there are a significant number of welds that are located in close proximity to valves or other structure that must be made with the pipe stationary resulting in 5G position welds.  It was recognized that these welds would become bottle necks during the fabrication of these projects. A single weld joint that may require a day or more to complete could cause considerable delay in the project timetable and, even though the welders that they employ usually perform outstanding welds, any human error could have drastic effect on the success of the project.

Improving arc-on time and more
Being a progressive company that is willing to explore other solutions to their fabrication challenges, New Industries began to do research to find a better way to perform these welds.  It was determined that the best options were to mechanize these 5G welds.  After considerable discussion of what the challenges were, a system was shipped to their facility in Morgan City, La and a demonstration was performed on the specific pipe for this project.  The results were very positively received and the system originally shipped in for the demonstration was then purchased.  During the demonstration it became clear that the Piper Plus solution would present the very best return if two systems were used in welding on the joint at the same time so an additional unit was ordered.

The mechanization of these 5G welds overcomes nearly all of the concerns that the manually performed weld presents.  Mechanization greatly reduces the required stops and starts since a wire fed process is used.  Arc-on time significantly improves for any given welder because the tractor that carries the welding gun does not need to stop as it travels up around the pipe.  With all motion of the welding gun controlled be motorized, digitally controlled drives, errors caused by fatigue are eliminated.  A uniform weld is created that is consistent from hour to hour, shift to shift and day to day.
 
The mechanized system uses the FCAW-G process so the starts and stop associated with stick are greatly reduced.  Due to the slag formed with the FCAW-G process the process can only be used in the vertical up progression so it is necessary to start at the bottom of the pipe, the 6 o’clock position and weld upward to the 12 o’clock position.  With this method there are only starts and stops at the top and bottom of the pipe joint.  During training the Welding Operators are taught to stagger these starts and stops in the same fashion as they would if they were performing the weld manually.  Once the welding arc is initiated at the bottom of the pipe, the arc stays on for the entire length of the joint up to the top.  Arc-on time of 60 to 80% can be attained.  

Digitally controlled and pre-programmed for precision
The consistency of the weld deposit is very uniform.  Each axis of the tractor is motorized and digitally controlled via closed loop feedback.  Forward travel is smooth and unchanging as the hardened guide wheels roll on a laser cut stainless steel band and controlled forward progression is provided by rack and pinion drive.  Cross-joint positioning of the welding gun is via a rack and pinion mounted, rigid steel weaver arm.  This axis provides perfectly controlled weaving motion with very precise and uniquely controlled side dwells.  Further, this axis provides the operator with a method to remotely “steer” the position of the weld, via a hand-held pendant, to allow adaptation for high/low and out-of-round in the fit-up or for positioning during multi-pass layers in the weld.  The vertical position of the welding gun with respect to the weld joint is similarly controlled via a rack and pinion mounted, rigid steel sliding axis.  This axis is unique in that by adjusting the vertical position of the welding gun, the welding current can be maintained at a preprogrammed value, thus improving the overall weld quality.  Wire feed is controlled via the Lincoln 4R220 Automation Wire Feeder designed specifically the demanding requirements of mechanized and automatic applications.  Welding power is provided by the Lincoln Power Wave S350 power source with capabilities for many weld modes.  Each axis is digitally controlled and preprogrammed via a single integrated control box.  The control box can retain hundreds of files each containing multiple welds passes.  These files can also be downloaded via USB drive so that they can be loaded into other systems for uniformity throughout your operation.  All of this concurrent control results in uniform welds of outstanding quality and appearance that are performed in significantly less time than needed to perform them manually.

As expected, application of these mechanized processes require updated Weld Procedure Specifications along with Procedure Qualification Records for each operator but, once developed, these procedures can be used to produce consistent results for years in multiple systems.

“We’d like to let our people be more productive and we’d like to reduce costs.  We believe automation will give us a competitive advantage.”, says Chris Pollock, Welding Engineer with New Industries, Inc.  “In busy times we can do more and take on more projects.  When things do slow down we can operate at a lower cost than our competitors and still maintain a profit margin.”

Conclusion
Bug-O Systems believes the statements made above by the client New Industries Inc. says it all.  In this ever more global and competitive market, to be able to reduce costs and remain competitive is critical.  However, when that can be achieved whilst greatly improving weld quality, consistency and with fewer cut outs and repairs is a massive quality advantage.  Mechanizing and automation has proven time and time again that with a skilled operator, it does just that and without taking the operators job away from him.  Truly New Industries and its employees could not be more pleased with the Piper System and its abilities to serve their customers’ needs whilst exceeding their expectations for timely delivery and quality.

Note  
The author wishes to express a large thank you to New Industries for allowing its story to be shared.