Trends are changing in the oil field drilling industry because most of the easily accessible oil has been tapped and well producers are forced to drill deeper to procure highly corrosive sour crude oil (H2S). Sour crude oil is a sulfurous mixture that corrodes the iron in the carbon steel pipe that extracts it. As a result, the petroleum industry is investigating new drilling technology that can overcome these corrosive effects to produce oil.
The dual-torch oscillation overlays two layers of corrosion resistant alloy onto the pipe’s inner surface.
For instance, ARC Specialties, Inc. developed a new cladding technology that controls the corrosion to safely extract and process sour crude in new deep water drilling fields. The company’s KLADARC TriPulse(tm) Hot Wire Gas Tungsten Arc Welding (GTWA) system leverages oscillation welding to deposit a metallurgically lined (or clad) two-layer corrosion-resistant alloy (CRA/Alloy 625) overlay (nominal thickness of 3.5 mm and guaranteeing the 3.0 mm minimum thickness) on clad pipe up to 20-ft in length and inside diameters up to 30-in. Ultimately, this technology reduces oxide inclusions and iron dilution in the cladding process – thus, mitigating the corrosive effects of H2S.
Paramount to this 5-axis cladding machine’s advancement is the capability to oscillate the arc inside the pipe. The crucial oscillation in the process is driven by ball screws manufactured by Nook Industries Precision Screw Group as part of its Power-Trac(tm) line of precision ball screw assemblies. The ball screw efficiently converted rotary motion to linear motion on the dual-torch oscillation axis (x & y) of the machine.
The dual-torch oscillation simultaneously overlays two layers of CRA onto the pipe’s inner surface and provides a molten “puddle” with longer residence time to bond and eliminate common problems of overlay welding such as leaving holes that penetrate through the overlay layer and thereby expose the outer steel pipe to corrosive sour crude.
The dual-torch oscillation process involves feeding CRA wire into a 20-ft. long torch that welds it circumferentially along the inner wall of the steel pipe. The circumferential weld is created by the ball screws wiggling the torch into the pipe back and forth approximately 1-in./sec, while motorized pipe rollers steadily turn the pipe. The first 20-ft of pipe is coated, then flipped 180¡. Next, the torch is put back to coat the other half of pipes’ inside diameter.
Arc Specialties’ KLADARC TriPulse™ Hot Wire Gas Tungsten Arc Welding (GTWA) system leverages oscillation welding.
Each oscillation places a heavy load on the ball screw with the 20 ft. torch decelerated, stopped, and reversed 120 times/min with loads running just under 1,000 lb during acceleration. The accelerate/decelerate rate is a harsh and rapid speed/load oscillation of 0.8-in. at approximately 1 Hz/sec. The oscillation process also moves the weld puddle side-by-side which generates approximately two times the weld yield. Additionally, this single-pass circumferential weld ensures that the CRA overlay is seamless and also allows the pipe to undergo long-radius bending after the overlay process.
A myriad of forces continue to contribute to the need to develop advanced technology to battle sour crude petroleum pipeline corrosion including; demand, environmental concerns, energy independence, and aging infrastructure. For example, many of the sour crude oil reserves located in the Gulf of Mexico reside at very deep subsea locations that present volatile conditions such as high pressures which increase the oil’s corrosivity – thus, making corrosion technology crucial to production. Corrosion technology also provides safety and protection from environmental catastrophes resulting from corroded pipelines.
Currently ARC has produced two of its TriPulse(tm) Hot Wire Gas Tungsten Arc Welding (GTWA) systems that are currently active in the Gulf Coast region _ two more are scheduled for delivery in 2010.
Nook Industries, Inc.
Filed Under: Ball screws • lead screws, Linear motion • slides, Motion control • motor controls