Titanium Beta C Springs

Titanium Beta-C Springs

Titanium Beta-C AMS 4957 alloy has a high level of corrosion resistance due to the existence of a consistent and continuous oxide layer which is formed spontaneously upon exposure to oxygen. Because of the high corrosion resistance, Titanium Beta-C springs can be used for subsea oil & gas applications.

Titanium Beta-C alloy has 4 % of molybdenum which makes it excellent resistance to corrosion in reducing environments such as Hydrogen Sulfide (H2S).

Titanium Beta-C Springs FAQs

What is Titanium Beta-C and why is it used for springs?

Titanium Beta-C is a beta titanium alloy, AMS 4957, with a nominal composition of chromium 5.50 to 6.50, molybdenum 3.50 to 4.50, aluminum 3.00 to 4.00, vanadium 7.50 to 8.50, and titanium as the balance. Its corrosion resistance comes from a consistent and continuous oxide layer that forms spontaneously on exposure to oxygen and reforms if it is damaged. The beta structure is what makes the alloy useful for spring work, since it is formable in the solution treated condition and then heat treats to very high strength, which alpha titanium grades cannot match to the same degree.

What applications do Titanium Beta-C springs go into?

Subsea oil and gas is the main one. The oxide layer gives excellent corrosion resistance in seawater, and the 4 percent molybdenum adds resistance in reducing environments including hydrogen sulfide, which is what puts the alloy into sour subsea and downhole service where stainless springs fail. Coiling Technologies builds springs for deep sea, oil and gas, and petrochemical work, and has produced specialty deep sea hardware including Inconel springs for the research submersible ALVIN, which operates to 21,000 feet (6,500 m). Beta-C also appears in weight sensitive marine and defense hardware needing a non-magnetic spring.

How does titanium's lower modulus change my spring rate calculation?

This is the number that catches designers out. The table lists a modulus of rigidity of 5.60x10^3 ksi and a modulus of elasticity of 13.2x10^3 ksi. Compression spring rate scales directly with the shear modulus, so a Beta-C spring built to the same wire diameter, coil diameter, and active coil count as a stainless spring at 10.8 x 10^3 ksi produces only about 52 percent of the rate. Matching the steel spring's rate means larger wire, a smaller mean diameter, or fewer active coils. The upside is more available deflection at the same stress.

How much weight does Beta-C save against a stainless spring?

Density on the table is 0.174 lb./in3, against 0.285 lb./in3 for the nitrogen strengthened stainless in the same material line and 0.27 lb./in3 for Alloy 20. That is roughly 39 percent lighter than the stainless option for an identical part, and because the aged alloy reaches high tensile strength the strength to weight ratio improves further. On subsea and downhole tools the saving compounds, since every pound of tool weight has to be handled, deployed, and supported. Titanium 6Al-4V is lighter again at 0.16 lb./in3 so the two titanium grades trade weight against strength and temperature.

How hot can a Beta-C spring run, and how fine can the wire go?

Max Temp is 400°C (750°F) and Min Size is 0.005 in (0.130 mm). The 400°C figure is the higher of the two titanium grades Coiling Technologies coils, since Titanium 6Al-4V is listed at 350°C (660°F), so Beta-C is the choice when the well or the process runs hot. As with any spring alloy, the temperature ceiling is about load retention under sustained stress rather than the point at which the metal degrades. Downhole tools in particular should be specified against bottom hole temperature, not surface temperature.

Why does the molybdenum content matter for sour service?

Molybdenum at 3.50 to 4.50 percent improves resistance in reducing environments such as hydrogen sulfide, which is the condition that defines sour service. Titanium alloys as a class are not subject to the sulfide stress cracking mechanism that limits high strength steels, which is why titanium appears in the NACE MR0175 and ISO 15156 materials selection for sour service. A customer can name that standard, or an AMS or API requirement, as a build and heat treat requirement on the drawing. Coiling Technologies holds ISO 9001:2015 for its quality management system and can build to a customer specified standard.

What does solution treated and aged mean for a Beta-C spring?

Beta-C is used in the solution treated and aged condition. The alloy is coiled in the solution treated state, where the beta structure is soft and formable, then aged to precipitate fine alpha within the beta matrix, and that precipitation is what drives tensile strength up to spring levels. The aging cycle sets the spring's final properties, so time and temperature control matter as much as the coiling. Aging also produces a small dimensional change, so free length, solid height, and rate should be verified after heat treatment rather than before. Heat treating is performed in house at Coiling Technologies.

What service data should I include in an RFQ for a subsea titanium spring?

Beyond load, rate, and envelope, the service environment decides whether Beta-C is the right alloy. Give the operating and maximum temperature, the fluid and its chloride content, whether the service is sour and at what hydrogen sulfide partial pressure, the external pressure or working depth, expected cycle count, and any material or heat treatment standard your purchase order names. If a non-magnetic requirement or a weight target drives the design, state it, because both change the material short list. The engineering team can develop a design from performance requirements when a finished drawing does not exist yet.