A failed connection in offshore drilling can cost upwards of $250,000 per day. That means oil and gas companies could potentially lose nearly $2 million in a mere week, particularly in offshore drilling. Cold root thread rolling in oil and gas piping drastically reduces the likelihood of failure.
Rochester-based CJWinter is at the forefront of this innovative technology, which involves burnishing the root radius of a freshly cut thread. A hardened roll is then forced into contact with the thread’s root radius, adding pressure so that the hardened roll penetrates and plastically deforms the radius of the root’s surface.
Drill pipe make-up on a gas exploration rig. Drill stem breakages are very costly in the energy exploration sector. (Image courtesy ourtesy, www.offshoreenergytoday.com)
"By definition we are cold root rolling only the root of a previously or newly cut thread,” says Sandro Belpanno, a senior design engineer for CJWinter who’s responsible for crafting the company’s cold root rolling tools, alongside Paul Allart, the co-inventor.
Belpanno adds that the process involves going “back in with a roller and essentially burnishing the root diameter of that thread. And there are numerous reasons why we can increase the fatigue resistance of the thread connection component. The first is, we impart a burnished finish to the root so any of the superficial defects – for instance, scratches – are rolled over and pressed out of the material. What you are left with is a very smooth, defect-free surface.”
Benefits of Cold Root Rolling
So what are the advantages of cold root rolling versus traditional thread-forming methods?
Improved fatigue is one of the crucial ones. The cold root rolling process causes the structure of steel material to change on an atomic level, resulting in metal grain dislocations. These allow the crystal structures within the steel to interlock, which in turn makes the material stronger. This is important because it helps prevent cracks, which can lead to catastrophic failure and expensive rig downtime.
Another benefit is the increased resistance to thread root stress. Cold root rolling drastically reduces tensile stress by implementing a small zone of residual compressive stress in the thread’s root region.
“Generally speaking, you can add three to five times the fatigue life on a cold root rolled thread versus one that has not been cold root rolled,” Belpanno adds.
Cold root rolling also reduces corrosion. Imperfections on the material (particularly scratches, which often harbor corrosive chemicals utilized in drilling) increase the rate of corrosion. However, smoothing out the imperfections during the burnishing process decreases the chances of these chemicals finding their way into the material.
Thread forms that can be cold root rolled
According to Belpanno, almost all kinds of thread forms can be cold root rolled.
“Right now, the vast majority of what is out there for thread forms are standard American Petroleum Institute thread forms – probably 90 percent of the pipe in the industry is some sort of standard thread form,” he shares.
“But we’ve also rolled all kinds of proprietary forms, by all kinds of companies and all the feedback that we’ve received from someone that’s done a study is that regardless of the thread form, cold root rolling does have significant, measurable improvement on fatigue life.”
These tools are also versatile. “We try to keep our tools as modular as possible so that they’ll drop into as many machines as possible,” says Belpanno. “One of the challenges is packing as much sophistication into the tool, yet keeping it in a profile that won’t interfere with any of the other tools in the packages typically needed for these connections. A lot of work has gone into packing a lot of machinery in a very small space.”
To learn more about the advantages of cold root rolling, download CJWinter's free guide, The ROI of Cold Root Rolling in Oil and Gas Piping.
CJWinter has paid a fee for promotion of its cold root rolling technology on ENGINEERING.COM. It has no editorial input to this post. All opinions are mine – James Anderton