When welding pipe joints, there always is potential for weld spatter and foreign debris to get inside the tubing. In most cases, this debris leads to internal corrosion of the tubing assemblies and possible malfunction of the hydraulic system.
The application of new Cameron shape memory alloy technology can be used as a coupling for our hydraulic control systems, thus eliminating the need to weld joints for metallic small-bore (up to 1 1/2-in) piping and tubing in hydraulic control equipment.
The Science Behind the Technology
The term "shape memory alloy" means that the material remembers its original shape from when it was first manufactured. While there are several types of SMA materials, this particular class of SMA, manufactured by Aerofit and other companies, transforms from a rigid, hard metallic state into a very soft and pliable metallic state when exposed to extremely cold temperatures. While still in the soft state, SMA materials can be changed to any desired configuration as long as the alloy remains in the established transformation temperature condition.
The application of CAMERON SMA technology, Tinel, is a higher pressure version of SMAs currently used by Aerofit in the aircraft industry. Through numerous qualification tests, we have adapted this alloy so it can be utilized in hydraulic control applications for our oil and gas services. Tinel, also known as Nitinol, consists of slightly less than 50% titanium, nearly 50% nickel, and a very small percentage of iron.
It also is important to note that the two stable metallurgical phases are Austenitic at high temperatures and Martensitic at low temperatures. This means that at high temperatures, the Tinel alloy has high strength and is very hard, while at low temperatures, it is pliable and has very low strength. In our case, the transformation temperature for this alloy is below –148 degF [–100 degC].
Let's say we select an SMA coupling that was originally machined at room temperature with an inside diameter (ID) smaller than the pipe or tube we are using. In order to ensure the coupling can be fitted freely over the pipe or tube, it must be put into a bath of liquid nitrogen at –304 degF [–187 degC] for less than two minutes so it becomes soft and pliable. At this state, we can increase the bore of the cooled coupling to slightly larger than the outside diameter (OD) of the pipe or tube by a mandrel or shaft.
After the bore is increased, the coupling is taken out of the liquid nitrogen bath and is installed onto the pipe or tube, which is at ambient or hotter temperature. At this temperature, the SMA coupling will naturally try to transform its bore to the original dimensions. Of course, the OD of the pipe or tube will try to prevent this from happening, which allows the coupling to clamp over the pipe or tube's OD with great force. This entire transformation takes less than one minute, depending on the coupling size, and results in a weldless clamping of the coupling.
Qualification testing is key
In order to qualify this SMA coupling for hydraulic control applications, Cameron had to obtain certifications from the American Bureau of Shipping (ABS). This entity recognized the guidelines, specifications, and testing as established by various national and international standards such as ISO, API, ASTM, ASME, and others.
On the basis of these standards, we prepared a detailed qualification test plan that was approved by ABS. The regimen test system includes in-house leak tests, proof tests, corrosion tests, etc. Parts must go through multiple test regimens before being subjected to destructive tests, like determining the maximum pull pressure or maximum burst pressure by pulling the tubing out of the coupling or increasing the pressure until the tubing bursts.
Our in-house tests have proven that our SMA couplings will produce a very high-quality, leak-proof joint when used to connect two pipes or tubes. Specifically, it has produced very satisfactory results when tested in all cases with severe vibration and pulsation, and has shown fully adequate fatigue capability without any potential failure.