DXe® – Next-generation subsea wellhead connector delivers reliability and safety in high-fatigue conditions

By Judy Murray / Michael Rogers

Dril-Quip technicians use proprietary test equipment to carry out physical validation testing on the DXe® Wellhead Connector at the Houston facility
Dril-Quip technicians use proprietary test equipment to carry out physical validation testing on the DXe® Wellhead Connector at the Houston facility (photo: Dril-Quip)

Minimising expenses is a business imperative in the offshore industry. For many OEMs, that means cutting manufacturing costs to remain competitive. However, not all companies tackle this challenge in the same way. Dril-Quip has a unique approach. By investing in R&D and advanced technologies, the company has developed products that are differentiated by their ability to enable operators to work smarter, faster, safer, cleaner, and more cost-effectively.

The company’s e-Series products are helping to improve efficiencies and reduce carbon footprint. And, according to company experts, they are ideally suited for the Norwegian continental shelf. One product, in particular, the DXe® Wellhead Connector, overcomes the challenges of the high-pressure, high-temperature (HP/HT) environment and severe bending, high-fatigue conditions of offshore Norway.

Energy Northern Perspective spoke with Dril-Quip’s Torstein Lunder, Business Development Manager in Norway, and Scott Ellisor, Product Manager for Subsea Wellheads and Connectors in Houston, to find out more.

Meeting changing industry needs
“The evolution to bigger rigs, bigger BOPs, and stiffer flex joints and risers, and the use of these rigs in shallower water depths has increased the loading and stress on subsea wells, particularly on the connection between the BOP and the wellhead,” Lunder explains. “Dril-Quip developed the DXe connector as a solution to these greater demands and the more stringent industry standards and requirements that were created as a result.”

Loads applied to the DXe® Connector travel only through segments made from ductile alloy steel and do not pass through the connector bolts, which are not subject to cyclic stresses at operating loads
Loads applied to the DXe® Connector travel only through segments made from ductile alloy steel and do not pass through the connector bolts, which are not subject to cyclic stresses at operating loads (illustration: Dril-Quip)

The DXe connector leads the industry in fatigue resistance whether it is used as a BOP stack connector, subsea tree connector, or riser tieback connector, Lunder says, noting that it is also designed for flexibility. “It can be configured to latch onto wellheads manufactured by other companies simply by swapping the latch segments. That means the DXeconnector delivers the same level of performance whether it is used with Dril-Quip equipment or on other profiles like the commonly used H4.”

According to Lunder, the demands of the industry are the primary drivers for product development at Dril-Quip.

“Our original DX connector is a good example,” he says. “It was introduced in the 1990s to provide a robust BOP connection, which is one of the reasons it became popular in the Norwegian market. The first one was used on the Heidrun concrete TLP (tension-leg platform) development in 1992. And since then, they have been installed on various projects and rigs globally, including installation on several of the latest generation rigs.”

Recent testing has proven just how durable the first-generation DX connector is. According to Lunder, a connector that was installed in the Norwegian North Sea in 1992 was recently removed from service. “After nearly 20 years in operation, the connector showed no signs of degradation,” he says. “When Dril-Quip engineers disassembled it to the component level and performed NDE inspection, they found no cracks, defects, or blemishes. Even more impressive is that once they finished testing, the connector was re-assembled and returned to service.”

Now, the next-generation DXe wellhead connector is outperforming the durable DX. “It is increasing the number of BOP days in high-fatigue conditions and setting the new standard for the industry,” Lunder says. “That’s why we have given it our ‘e’ designation, which identifies our products that enhance performance, increase efficiency, eliminate risks, provide better well economics, and align with environmental sustainability,” he says.

Testing proves performance
Rigorous testing has validated the connector’s exceptional performance. “We have tested the DXe connector far beyond the latest industry requirements to demonstrate that we can offer a connector design that exceeds today’s standards,” Lunder says.

Load testing with no bolts proves the reliability of the DXe® Connector
Load testing with no bolts proves the reliability of the DXe® Connector (photo: Dril-Quip)

Scott Ellisor, who was involved in the testing program, reports that during a period approaching six months, the DXeconnector underwent 90 million cycles without failing.

“The results we achieved by testing the DXe to 90 million cycles prove that this connector exceeds the fatigue life of all other connector products in the industry to date,” he says. “It demonstrates that operators no longer have to settle for products designed more than 50 years ago because there is a product on the market that can meet increasingly severe and critical service requirements.”

That means it’s possible to drill in harsh environmental conditions without worrying about running out of BOP days or experiencing a connector failure and leaking wellbore fluid to the ocean, Ellisor explains. “With this level of performance, our connector alleviates fatigue concerns and eliminates the additional equipment required to put a bandage over underlying design and performance issues.”

Lunder adds, “Although our DX connectors have always performed exceptionally well, the new DXe connector is in a totally different league when it comes to superior stress capabilities, risk reduction, and cost savings.”

He points out that, from an environmental standpoint, that level of performance is essential. “The wellhead connector is the only kit in the chain of products from the rig down to the subsea well that has no redundancy backup to prevent fluid leakage from the wellbore to the environment during drilling. A connector failure can have dire consequences, and this is a responsibility we take very seriously,” he says.

No bolts, no bolt failures
Operators can be confident in the DXe’s ability to mitigate environmental risk because Dril-Quip’s unique design has removed bolts from the load path, eliminating bolt failures and stress cracking caused by drilling riser and tension loads.

Lunder describes how the stress adds up: “All the loads down onto the wellhead are coming from the rig, through the riser system, through the BOP, through the BOP connector, and onto the wellhead. And, of course, a wellhead is designed to distribute that load to the conductor housing and take most of the load down the conductor. The DXe is so effective at handling loads that it eliminates the need for a BOP tethering system, which translates to tangible opex savings.”

“From the beginning, when we developed the DX connector for subsea fields like those in Norway, we’ve understood that with the loading through these connectors, the stress life depends on how much load you put into them during the lifetime of the well,” Lunder explains.

Metocean data, drilling vessel motions, soil conditions, and a riser fatigue spectrum were used to develop and conduct a full-scale fatigue test program on a complete system to evaluate the fatigue characteristics of Dril-Quip’s DXe® Connector properly
Metocean data, drilling vessel motions, soil conditions, and a riser fatigue spectrum were used to develop and conduct a full-scale fatigue test program on a complete system to evaluate the fatigue characteristics of Dril-Quip’s DXe® Connector properly (photo: Dril-Quip)

“If you have bolts in the load path and those bolts fail, you lose hydraulic pressure, and you lose contact stress and loading through the gasket,” Ellisor says. “If you get separation in your gasket, hydrocarbon fluids can leak into the ocean. That’s why Dril-Quip has taken technology in a different direction. We consider this a critical interface and believe our connector is the most robust component and the highest integrity barrier to well fluid breaches in the industry.”

Removing bolts from the load path has removed the failure points that can lead to hydraulic pressure leaking to the ocean floor or reservoir flow leaks, Ellisor says. “That speaks to the safety built into the connectors, as well as the environmental considerations, that make our e-Series products Green By Design™.”

Self-aligning gasket simplifies installation
The innovative DXe gasket represents a paradigm shift for subsea gaskets. The most robust gasket currently available in the market, it is rated for up to 200° C and 20 ksi and has been hydrostatically tested to 4,600-metre water depths. Another feature that sets the DXe gasket apart is that it is self-aligning.

“Historically, if you put a gasket in the wellhead, and it’s not perfectly installed, you’d damage or crush the gasket, which could lead to leakage or damage to the wellhead. We developed the DXe gasket to eliminate these risks,” Ellisor explains. “The self-alignment of the system allows you to land the gasket without worrying about it being perfect because the gasket has features to prevent it from being set incorrectly. You can set the gasket in place, and if it’s not perfectly flat, it will self-correct.”

Operator collaboration
Asked how input from operators has contributed to the development of the DXe connector, Lunder says, “Much of our design process is based on how operators change their specifications and requirements, especially majors like ExxonMobil, Equinor, and TotalEnergies that have specifications that exceed industry standards.”

“And it’s not only the operator who’s using the connector,” he continues. “Since these connectors are also used on drilling rigs, some operators are now asking drilling contractors to ensure their rigs have compliant connectors for wells with high-fatigue applications.”

Delivering what end users need is ultimately the goal.

“We understand that fatigue performance is particularly important in the Norwegian sector, and there is growing interest in using more reliable BOP connectors. It’s one of the regions that has experience with shallow-water fatigue issues and that really understands the need for absolute reliability in BOP connectors,” Ellisor says.