NOV Quality Tubing (QT) employs Gas-Tungsten Arc Welding (GTAW) processes to perform tube-to-tube butt welds, both in its manufacturing and service centers, and in the field. Two types of the GTAW process, manual and automated machine welding, are used to produce high quality butt welds in coiled tubing.
The GTAW process establishes an electric arc between a non-consumable tungsten electrode and the base metal. The arc generates a molten weld puddle, fusing the base metal and any added filler metal together. An inert gas flows around the electrode, shielding the molten weld pool and arc from the oxygen in the atmosphere. In the manual process both the electrode torch and filler metal are hand operated by the welder. In the automated machine process, the torch and filler metal are controlled by a computerized orbital welding machine while the process is continuously monitored by a welder.
QT utilizes established welding procedure specifications (WPS's) to join both butt welds and connections, or fittings, to coiled tubing. These procedures have been tested and qualified to ASME Boiler and Pressure Vessel Code, Section IX (Welding and Brazing Qualifications) for downhole equipment, API 1104 (Welding of Pipeline and Related Facilities) for coiled line pipe equipment, and additional testing requirements contained in QT Work Instructions. The additional requirements provide design assurance that the welds will meet the severe operating requirements of coiled tubing applications.
Both welders and welding procedures are tested and qualified to specifications exceeding industry standards, because most industry welding standards are not designed to join materials which are intended to be plastically deformed as part of their normal operating characteristics. Testing requirements assure WPS's are capable of producing welds with mechanical properties superior to those required for the base metal. Similar testing of welders assures they possess the skill to reproduce these welds consistently.
In the event a tube-to-tube weld is required in a QT-1000™, QT-900™ , QT-800™, or QT-700™, string, that string is reclassified as QT-100™ , QT-90™, QT-80™ or QT-70™, respectively.
In addition to offering welding services, QT furnishes the following welding supplies and support services to its customers.
- Coiled tubing fittings and connections
- Welding filler metals
- Welding chill blocks
- Welder training and qualification
- Consulting on welding procedures
- Weld fatigue life assessment