Pipeline builder employs new welding techniques and equipment to tackle America's first X80 steel pipeline.

By Steve Latvis, Miller Electric Mfg. Co
Edited by Patricia L. Smith
Mr. Latvis is regional manager, North & South America, Global Pipe Systems, for Miller Electric Mfg. Co., Appleton, Wis.

Despite the dusty environment, welders from Local 798 and Associated Pipe Line Contractors Inc. were able to lay 124.8 miles of pipe for the Cheyenne pipeline project using Miller Electric Invision 456MP power sources.

Welders used about 5,000 lb of Pipemaster 9010 stick electrodes from Hobart Brothers on the first 125-mile section of the pipeline tie-ins. The electrodes are engineered for welding high-yield strength pipe.

Building pipelines is tough work, particularly when the job is constructing the first X80 steel pipeline in the U.S. That was the challenge Cheyenne Plains Gas Pipeline Co. faced with a new $425 million natural gas pipeline stretching from just south of Cheyenne, Wyo., to Greensburg, Kans. Because the job demanded new semiautomatic and manual welding methods and equipment to construct the 380 miles of 36-in. pipe and 5 miles of 30-in. lateral pipe, Cheyenne brought in experienced partners — welding-equipment suppliers, contractors, and a team of welders — to ensure quality on the approximately 400 tie-in welds made at river and road crossings.

The advantage to using X80, which has a minimum yield strength of 80,000 lb, it that it reduces pipe wall thickness without sacrificing integrity. This, in turn, lowers total steel tonnage used and cuts down on the amount of filler metal needed to complete a joint. However, X80 is prone to hydrogen cracking during welding. This makes it more difficult to weld versus commonly used pipeline materials like X70 steel.

Cheyenne Plains worked with EWI Microalloying International of Houston (a partnership between the Edison Welding Institute and Microalloying International) to evaluate and test tie-in welding procedures to join the pipe. The contractors selected for the project also participated, including Associated Pipe Line Contractors Inc., Houston. Local 798 welders and helpers ensured the welding processes and equipment met welding procedure requirements.

Relatively similar to those used on other pipelines, the procedures for mainline welding employs a mechanized process to improve productivity to an average of 130 joints per day. On the Cheyenne Plains project, the root pass (an internal bead pass) and the hot pass (an external pass) were done with short circuit MIG (GMAW) welding, using a 0.035-in. ER70S-G solid wire and 75/25 argon/CO2 shield-gas mixture. The fill and cap passes (one each) were both done using pulsed MIG, 0.040-in. ER70S-6 solid wire, and 85/15 argon/CO2 shield-gas mixture.

The Cheyenne project utilized Miller inverters, including the Invision 456MP with built-in pulsing controls, on nearly all the mechanized welds. An automatic eight-headed internal welding system tackled root bead welding and dual-torch welding systems handled fill and cap passes. The external hot pass was completed by conventional short-arc GMAW.

Specifying the manual (stick) and semiautomatic (flux-cored) welding procedures for the tie-in welds was challenging. Because of X80's susceptibility to hydrogen cracking, procedures commonly used for welding pipe with lower yield strength properties — such as downhill welding all passes with a celluosic electrode (E6010 and E9010, for instance) — needed to be evaluated and adjusted.

"We either had to incorporate low-hydrogen stick electrodes (such as E9018) or qualified flux-cored welding procedures to address the metallurgists' hydrogen concerns," says Sonny Weems, assistant superintendent with Associated Pipe Line. "Welding uphill with a flux-cored wire was a lot quicker than welding uphill with a low-hydrogen stick electrode, so that's what we selected." Travel speeds with a ¹ /8-in. E9010M stick electrode for the fill and cap passes averaged 2 to 4 ipm. The fill and cap passes welded with a 0.045-in. E101K2 flux-cored wire averaged 4 to 6 ipm.

The final tie-in weld procedure Associated Pipe Line selected involved making a downhill root, or bead, pass with a ⁵ /32-in. E6010 electrode running at 135 to 155 amp and 22 to 25 V. The ductility of this filler metal lends flexibility to the pipe, which prevents cracked joints.

Welders made the downhill hot pass, which consumes most of the bead pass, with a ³ /16-in. E9010 electrode running at 150 to 185 amp and 25 to 34 V. This increased the weld's strength and toughness and eliminated root bead slag inclusions.

The fill and cap passes were made with 0.045-in. E101K2 flux-cored wire and 75/25 argon/CO2 shield-gas mixture, running at 165 to 175 amp (a wire feed speed of 275 to 290 ipm) and 23 to 24 V. The properties of this electrode are compatible with the properties of the base metal, addressing concerns about hydrogen cracking, yield strength, and toughness.

Consumables and equipment
Associated Pipe evaluated welding consumables and equipment for the Cheyenne project. For stick welding, the contractor selected Hobart's Pipemaster E6010 and E9010 electrodes. The electrodes met the requirements of AWS 5.5 low alloy specifications and pipeline API Code 1104, ran smoothly, and cut down on spatter, according to Weems.

For the flux-cored welding, the contractor used Hobart Brothers' Pipemaster 101K2 flux-cored wires. This all-position flux-cored wire works well for vertical up-pipe welding. The quick-freezing slag is suitable for high-deposition welding and also maintains a flat bead profile.

For the diesel engine-driven welding generator, Associated Pipe Line needed a certain level of performance and reliability for both stick and flux-cored welding. "The PRO 300 CC/CV from Miller met our needs," says Weems. "We had welders put CV boxes (constant voltage controls) on older DC generators, but they never did perform as well with flux-cored wire. Eventually, we quit using those machines and ran all the procedures with the Miller PRO 300."

When it came to the guns, Associated Pipe Line selected Bernard 150-amp Q-Guns with Centerfire consumables. The gun nozzle has a builtin spatter shield that protects the gas diffuser and removes turbulence from the gas flow. In addition, the nozzle's screw-on design maintains a fixed recess and a solid, concentric relation-ship between the tip and the nozzle. Most of the operators avoided changing out tips during the work shift, which helped lower consumable costs and increase productivity.

Operator appeal
Associated Pipe Line brought on a crew of 12 pipeline welders and their rigs for the tie-in welding. Like most U.S. pipe welders, this crew did not have experience with flux-cored welding uphill, a method vital to preventing slag inclusion. Sonny Daniell, a 30-yr Local 798 pipeline veteran, trained the crew in how to set up the machines and how to use the proper welding techniques.

Daniell says the welders quickly got up to speed on the PRO 300. "They like the smoothness of the arc, the ability to run both stick and wire feed, and the lower fuel consumption. The guys were using two to three gallons a day versus the eight to ten they used with the DC generators, and they were still running them just as hard."

The operators agree with Daniell's assessment. "It's a new experience to me," says veteran welder Lanny Dyer, "But it's a step ahead of what I've been using." Welder Junior Blair adds, "The PRO 300 has a smooth arc. I could just stick the bead pass in there without turning the heat up or down."

A quality effort Because pipelines must be built to last and operate in critical applications, the welding must be of the highest standard. Houston-based Weldsonix Inc. inspected the Cheyenne pipeline with highly accurate automated ultrasonic testing (AUT) equipment that used ultrasound waves to gather details on the quality of all four layers of welds. In turn, qualified AUT technicians interpreted this information, checking for defects such as trapped slag, lack of fusion, porosity, and weld cracking. Any weld with a defect longer than 25 mm had to be repaired. Furthermore, if a bad weld ran more than 25% of the circumference of the pipe, that section of pipe was completely cut out and replaced with a new "pup" section (for instance, two joints welded). "There is no question that there was continuous improvement throughout the project as the operators gained familiarity with the welding equipment and procedures," says Paul Manuel, a subcontractor to EWI Microalloying who provided QA assistance during the Cheyenne pipeline project. The EWI Microalloying team provided an on-board welding, QA, and NDE audit service to the project, including technical support to the contractor.