Materials like API 5L Grade X80 steel are a common choice.
In addition to providing increased strength and pressure tolerances, which allow more materials to pass through, high-strength pipe also offers the ability to work with thinner wall thickness (as little as 18 millimeters). This wall thickness decreases the weight of the pipe and offers considerable savings in terms of transportation cost and labor. Specifically, it minimizes fuel usage and cost for hauls to the jobsite, and also reduces the amount of welding to complete a weld joint.
Such benefits were behind the decision to use API 5L Grade X80 steel for the Petro China (CNPC) WEST-EAST III pipeline project. Upon its completion, this 7,378-kilometer pipeline will cross 17 provinces — from Xinjing to Fujian, China — to deliver 30 billion cubic feet of gas each year. Contractors, like Daqing Oil Field Company began construction on this project in May of 2012 and anticipate its completion by 2015.
According to Zhongbin Shan, secretary general of the China Petroleum Engineering Construction Association, welding specifications for the project prohibited the use of E6010 stick electrodes. As on other high-strength pipelines, these types of filler metals are unable to meet the low hydrogen requirements for welding API 5L Grade X80 steel. The welds are also less able to withstand the impact of thermal expansion and contraction, frost and other environmental loadings commonly caused by temperature extremes in remote pipeline areas.
As a result, for the 2,545-kilometer section of the pipeline project for which the Daqing Oil Field Company is responsible, the company embraced new welding technologies to uphold the integrity of welds on the high-strength steel and also meet their demanding productivity requirements. Those technologies included welding equipment with advanced processes from Miller Electric Mfg. Co., as well as welding wires from Hobart Brothers Company. The new technologies offered quality and speed, as well as lower repair rates and cost savings.
A new root pass
The Petro China (CNPC) WEST-EAST III pipeline project consists of API 5L Grade X80 pipe that is 1,219 millimeters in diameter, with wall thicknesses ranging from 18.4 to 33 millimeters.
To weld the root pass on its portion of the pipeline, Daqing Oil Field Company used the Miller PipePro® pipe welding system featuring Regulated Metal Deposition (RMD®) technology. The PipePro welding system is a multiprocess power source optimized for welding pipe.
The contractor paired the PipePro welding system with Metalloy® 80N1 metal-cored wire from Hobart Brothers Company on the root pass. The two technologies combined to increase productivity, as well as provide a high level of quality.
According to Shan, the company saw “excellent fusion on the back of the welds, lower repair rates and faster welding compared to cellulosic [E6010] products.”
RMD is a modified short circuit transfer MIG welding process that precisely controls the welding current during all phases of metal transfer, resulting in a highly stable arc and minimal weld puddle agitation. When combined with the Metalloy 80N1 metal-cored wire, RMD (as Shan noted) provided the contractor with consistent and reliable root reinforcement on the inside of the pipe. This process ensured they were able to gain proper sidewall fusion, even in instances of high-low misalignment commonly found in pipeline applications. The technologies offered the additional advantage of a fast freezing puddle capable of bridging gaps up to 5 millimeters wide.
Because the wire is a continuously fed, RMD also eliminated the downtime to address stub loss and to change over stick electrodes as previously required with the Stick welding process.
Shan adds, “The two technologies gave the contractors good arc performance and stability. It also offered high deposition efficiency and rates, as well as increased travel speeds.”
Specifications for the project included operating in the amperage range of 120 to 180 amps and 14 to 18 volts, with a wire feed speed of 120 to 180 inches per minute (ipm). It also required a filler metal with a minimum of 550 MPa (megapascal) tensile strength, good impacts at low temperatures and low hydrogen levels. The Metalloy 80N1 provided all three; the filler metal offers 565 MPa tensile strength when used with a shielding gas mixture of 75 percent argon and 25 percent carbon dioxide.
Shan goes on to explain that the contractors were able to minimize grinding and other cleaning, which also contributed to their increased productivity on the project, because the RMD and metal-cored wire combination generates little to no spatter. They also experienced less weld defects, which minimized the cost and downtime for rework.
According to Shan, training did not pose a problem. RMD provides a consistent arc length even with varying wire stick-out, so it accommodates for the techniques of differently skilled welders.
“This newer technology provided good arc performance,” says Shan. “It’s easier to operate and requires less training time.”
Fill and cap passes
For the fill and cap passes on the welds with root passes, Daqing Oil Field Company also relied on the PipePro Pipe welding system combined with Fabshield® X80 self-shielded flux-cored wire in 2.0-millimeter diameter.
As with RMD, the Flux-Cored welding process with self-shielded wire allowed the contractor to complete fill and cap passes faster than Stick welding, as well as gain better impact properties and create lower-hydrogen welds than possible with stick electrodes.
In particular, the Fabshield X80 wire provides 7.3 ml of diffusible hydrogen per 100 g of weldment compared to cellulosic stick electrodes that average higher than 16 ml of diffusible hydrogen per 100 g of weldment. These lower hydrogen levels reduced the opportunity for cracking in welds on the Petro China (CNPC) WEST-EAST III pipeline project, along with reducing downtime for addressing rework.
As with Stick welding, the self-shielded Flux-Cored welding process offered by the PipePro welding system is suitable for welding in windy and dirty environments encountered in pipeline welding applications; the wire generates its own shielding gas to protect the weld pool. The process also offers increases in travel speeds and greater deposition efficiency — 78 to 87 percent compared to 50 to 65 percent with Stick welding. The greater deposition efficiency ultimately allowed the contractor to use less filler metal to get the same job done faster, effectively saving money and ensuring the welding operators were able to create more welds in a shorter amount of time.
Settings for the fill and cap pass using the Flux-Cored welding process included 17 to 20 volts, 80 to 120 ipm and 160 to 280 amps.
“Compared to Stick welding, the Flux-Cored process gave the contractor higher productivity — up to three to five times the deposition rate,” says Shan.
Shan also noted that it minimized cleanup time because the wires produce a slag that is much easier to remove, and the Flux-Cored process required less preparation (e.g. grinding) — again, all factors contributing to greater productivity.
Other benefits offered through the Flux-Cored welding process for fill and cap passes included greater control over the welding arc and relatively easy operator training. And as with the RMD process, the Flux-Cored welding process substantially reduced the amount of starts and stops needed to complete the joint (compared to Stick welding).
Together with the RMD process and metal-cored wire for the root passes, these advantages ensured that Daqing Oil Field Company gained the best productivity and quality for their portion of the Petro China (CNPC) WEST-EAST III pipeline project, all while simplifying training and minimizing costs.
Multiprocess, multi-operator welder generator
In addition to the PipePro pipe welding systems, welding on the Petro China (CNPC) WEST-EAST III pipeline project benefited from the contractor’s use of the Big Blue® Duo Pro multiprocess and multi-operator welder/generator for some of its Flux-Cored welding, as well.
According to Shan, Daqing Oil Field Company especially enjoyed the “good fuel economy and low noise, as well as the higher output,” from the machine.
In addition, the Big Blue Duo Pro allows two welding operators to weld at the
same time, without sacrificing output or requiring additional investment in equipment, effectively doubling productivity on those joints. In essence, it is one dependable engine with two premium pipe-quality arcs; the welding operators can work independently of one another without concern of arc interaction.
Further, the machine offers efficient, stable generator power that makes it durable enough to withstand the rigors of welding in the extreme temperatures and terrain of China.