Eliminating the need for welded joints
When welding pipe joints, there is always the potential for weld spatter and foreign debris to enter the tubing. In most cases this debris leads to internal corrosion of the tubing assemblies and possible malfunction of the hydraulic system.
Cameron has applied shape memory alloy technology as a coupling for hydraulic control systems, thus eliminating the need to weld joints for metallic small-bore (up to 1 1/2-in) piping and tubing in these systems.
The technology and how it works
The term shape memory alloy (SMA) means that the material remembers its original shape from when it was first manufactured. While there are several types of SMA materials, the type most frequently applied by Cameron transforms from a rigid, hard metallic state to a very soft and pliable metallic state when exposed to extremely cold temperatures. 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 Cameron application of SMA technology is a higher-pressure version of SMAs currently used in the aircraft industry. Through numerous qualification tests, Cameron has adapted this alloy so it can be used in hydraulic control applications for our oil and gas services. This innovation consists of slightly less than 50% titanium, nearly 50% nickel, and a very small percentage of iron.
It is also 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 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 deg F [–100 degC].
Let's say we select an SMA coupling that was originally machined at room temperature with an ID smaller than the pipe or tube we are using. In order to ensure that 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 to make it soft and pliable. In this state, we can increase the bore of the cooled coupling to slightly larger than the pipe or tube OD by using a mandrel or shaft.
After the bore is increased, the coupling is removed from the liquid nitrogen bath and installed onto the pipe or tube, which is at ambient or higher temperature. The SMA coupling will try to transform its bore to the original dimensions, but the OD of the pipe or tube will try to prevent this from happening, enabling the coupling to clamp 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 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—including in-house leak tests, proof tests, and corrosion tests—that was approved by ABS. Parts must go through multiple test regimens before being subjected to destructive tests, such as 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.
Cameron in-house tests have proven that our SMA couplings produce a very high-quality, leakproof joint when used to connect two pipes or tubes. Specifically, they have produced very satisfactory results when tested with severe vibration and pulsation and have shown fully adequate fatigue capability without any potential failure.
Multiple benefitsIn summary, use of SMA technology provides many benefits compared with welding joints. It
- eliminates the intrusion of dirt and debris, as well as the need for nondestructive testing (NDT) and rework
- reduces training and certification costs, environmental costs, and cycle time
- maintains a very high margin of safety in terms of pipe and tube pulling and burst pressure capabilities
- provides leakproof performance
- does not depend on operator skill or expensive and complex tooling.