Case Study: 100 % X-Ray on Subsea Inconel-Clad Pipe (CNOOC)
How TIP TIG met a zero-rework, 100 % X-ray requirement on ID Inconel-clad subsea pipe joints for CNOOC — after conventional TIG and pulsed MIG could not.
When the weld requirement is 100 % X-ray with zero rework on ID Inconel-clad subsea pipe, most processes run out of room. This is how TIP TIG met that requirement for CNOOC after the conventional options could not.
At a glance
| Project | CNOOC subsea Inconel-clad pipeline |
|---|---|
| Operator | China National Offshore Oil Corporation |
| Application | ID Inconel-clad subsea pipe joints, 5G position |
| Pipeline | ~32 km, platform to shore |
| Requirement | 100 % X-ray, zero rework |
| Processes that fell short | Conventional TIG, pulsed MIG |
| Result with TIP TIG | 100 % X-ray, zero rework — manual and automated |
The challenge
CNOOC, China’s largest offshore oil and gas producer, was laying a subsea pipeline roughly 32 km long, feeding pipe from an offshore platform to shore. The joints were welded on the barge as pipe was fed out — 5G fixed-position welds, with the welder working all the way around a pipe that cannot be rotated.
What made it hard was the joint itself: ID Inconel-clad pipe. A corrosion-resistant Inconel layer on the inner diameter protects the pipe from the aggressive subsea service, and that clad layer has to survive the weld. On top of that, the project carried a hard rule: zero weld rework. Every joint had to pass 100 % X-ray the first time.
Why the usual processes fell short
CNOOC’s engineers had access to the most costly, sophisticated weld equipment available, and they tried the obvious routes first:
- Conventional TIG could hold the quality, but the heat input was a problem for the clad layer, and 5G TIG welds were simply too slow for a pipeline of this length.
- Pulsed MIG had the speed, but it could not consistently meet the 100 % X-ray requirement on the ID Inconel-clad welds.
Neither process could deliver clad-weld quality and the productivity the project needed, at the same time. With zero rework as a non-negotiable, that gap is where the project stalls.
Why TIP TIG fits this joint
This is exactly the corner TIP TIG is built for. The hot-wire process holds TIG-grade weld quality while running 100–300 % faster than regular TIG, and it does so at the lowest heat input of any wire-fed process. On an ID clad joint, low heat input is not a nicety — it is what keeps the corrosion-resistant Inconel layer intact and preserves its properties. TIP TIG runs both manual and automated, so the same process qualification covers hand welding and mechanised welding on the barge.
The result
CNOOC turned to TIP TIG. In two weeks of testing at the TIP TIG facility, the process demonstrated the required 100 % X-ray, zero-rework quality — manual and automated — while meeting the production rate for the 5G welds. CNOOC placed an order for the manual and automated TIP TIG equipment, and TIP TIG delivered the training, the weld procedures and the equipment for the multi-million-dollar project.
The short version: where conventional TIG was too slow and pulsed MIG could not hold X-ray quality on the clad, TIP TIG met both requirements at once — and did it on one of the most demanding joints in offshore construction.