The company’s headquarters in Newcastle, UK is home to the world’s largest steel tube umbilical assembly plant. To date TechnipFMC Umbilicals has designed and manufactured more than 5,500 km of umbilicals worldwide, including the deepest ever installation in the Gulf of Mexico and the largest diameter and heaviest weight per metre umbilical in Norway.
Umbilicals form the critical link between a subsea production arrangement and a remote facility providing control, power, communications and chemical services. Umbilicals comprise multiple controls including fluid conduits to provide hydraulic control and chemical injection service, electrical power and communications via signal cables, fibre optic cables. In 2014, TechnipFMC Umbilicals opened the world’s largest and most capable steel tube umbilical assembly plant in Newcastle upon Tyne, complementing their Thermoplastic Umbilical plant. The facility enables the production of longer and more complex umbilicals with tube diameters of up to 3” (7.5cm).
Despite the enormous amount of research and technological development that has gone into developing umbilical tubing, the corrosion resistant alloys used are relatively standard, Dr. An explains. “Super duplex (25%Cr) seamless tubing is largely the material of choice for umbilical systems. Other grades used in the umbilical system include lean duplex (19D), duplex (22%Cr), stainless steel 316L, Inconel 625 and Titanium grades 2 and 5.” This application mainly uses seamless tubes although, depending on the project, welded tubes are now starting to find favour.
“The tubes used are fairly small diameter, usually ½” to 1” and are supplied in coils of welded seamless straight tube (10 – 25m in length) together.”While small in size, the quantity that TechnipFMC Umbilicals uses is impressive. “Almost 100% of our steel tube umbilical projects for our European clients specify super duplex,” explains Dr. An.
While super duplex is the material of choice there are some exceptions. Super duplex can be used for the majority of vent applications, however alloy 625 is preferred by some clients for venting applications when high H2S content is present in the vent line.
Pushing ahead material development
Umbilicals require a good combination of mechanical strength and corrosion resistance, making super duplex the ideal material. “The operation fluid is not usually a corrosion concern,” explains Dr. An, “seawater is a far greater concern.” As umbilical systems operate under extremely challenging conditions this application is helping to drive ahead material development.
“We have started to receive enquiries for much more extreme conditions such as ultra-deep 4000 m wells at high pressures of up to 20,000 psi and temperatures as high as 110°C,” explains Dr. An. “Currently the maximum operating pressure for the tubes is 15,000 psi, so a move towards 20,000 psi will require developments in hyper duplex or even the development of a new material. While the hyper duplexes currently available can meet the requirements for this higher pressure for certain tube size, they do not yet meet other requirements in the specification.”
Super duplexes also face design limitations with relation to operating temperatures in seawater which need to be overcome, Dr. An explains. “In seawater applications duplexes are limited to an operating temperature depending on the service condition and design life. We are actively looking for new materials which will allow us to increase temperatures to 80-85°C, which is the maximum temperature for a gas lift umbilical in the current market. Any material that could be used at 85°C with excellent seawater resistance while maintaining good mechanical properties similar to super duplex stainless steel would be a great option for future use.”
“The combination of increased temperature, depth and pressure will require umbilical tubes that have higher strength, greater corrosion resistance and increased toughness and yet be even lighter in weight. These combined mechanical and corrosion criteria are a real challenge.”
Despite the need for advances in material development, welding can hold back the development of umbilical technology, Dr. An explains. “The design of an umbilical is limited to the achievable quality of the welds used. You can design an umbilical that is perfect for the operating conditions but if the welds are not of the same standard it will fail. TechnipFMC Umbilicals works closely with academic bodies on issues such as improving inspection technology, weld porosity and geometry. TechnipFMC Umbilicals has developed a 3D computed tomography technology to optimise radiography inspection on the butt weld and is developing an integrated inspection station for the girth weld.
“Whenever we consider using a new material, the welding performance is the most important factor we consider.”
This situation is similar for pipelines where welds need to be the strongest part of the whole. “The main difference is that you can use anode protection in pipelines but with umbilical tubing you must rely on the corrosion resistance of the tubes. Other than a completed FBE coating system, it is difficult to add any additional corrosion protection in the bundle.”
Tough environment for high tech lines
“The main strength of the line is provided by its internal pressure; highly dynamic environments, such as shallow water, require improved fatigue performance of the umbilical to prevent damage. However the internal tubes are robust with a very high level of design and manufacturing standard, making them able to withstand environmental and operating conditions.”
In 2016, and for the 2nd year in a row, Technip was certified as a Global Top Employer by the Top Employers Institute. Dr. An revealed that one of her favourite aspects of the job is the annual Materials Forum hosted within the TechnipFMC group.
“The group has an excellent network of materials specialists and every year colleagues from all disciplines around the globe – offshore and onshore, pipeline and umbilical – come together to exchange lessons learned, expand their knowledge and discuss material challenges. The Forum is great for people to communicate, learn, and set targets for upcoming R&D projects. It means we can communicate and work easily together because we all know each other. I don’t think any other company in the world has such an extensive and knowledgeable materials network.”