The use of titanium alloy in the submarine hull gave several advantages at once. Firstly, the use of a particularly strong alloy with a yield strength of 70-72 kgf / mm2 significantly increased the maximum depth of the ship — almost one and a half times compared to second-generation boats — and, secondly, the use of this material reduced the magnetic field of the vessel. Well and most important: thanks to the titanium hull, it was possible to reduce the displacement of the submarine by 30%.
Titanium is a metal having a high strength-to-weight ratio, particularly at temperatures ranging above 1000F. Its production was begun and stimulated as a result of military requirements during the Korean war. In the United States, over 80 percent of all titanium metal is used in jet engines and airframes for aircraft. The remainder is used principally in missiles, space equipment, and chemical processing equipment where its corrosion-resistant characteristics are essential.
Although the USSR has a few deposits of rutile, the only commercially important titanium mineral used for making titanium metal, it has extensive deposits of ilmenite, a very low-grade source of titanium, in the Urals area. Other large ilmenite deposits have been discovered near Kirovsk on the Kola Peninsula and near Mariupol' in the Southern Ukraine. The Ural deposits were reported to contain 400 million tons of available ore.
For several decades, titanium had been used by the Soviets in the manufacture of stainless steel, but only since 1952 had the Soviet press published articles on research in the development and use of titanium metal.
Titanium and titanium alloys have become important structural metals due to an unusual combination of properties. These alloys have strength comparable to many stainless steels at much lighter weight. Additionally, they display excellent corrosion resistance, superior to that of aluminum and sometimes greater than that of stainless steel. Further, titanium is one of the most abundant metals in the earth's crust, and as production methods become more economical, will be employed in ever growing applications.
Many titanium alloys have been developed for aerospace applications where mechanical properties are the primary consideration. In industrial applications, however, corrosion resistance is the most important property Since titanium metal first became a commercial reality in 1950, corrosion resistance has been an important consideration in its selection as an engineering structural material. Titanium has gained acceptance in many media where its corrosion resistance and engineering properties have provided the cor rosion and design engineer with a reliable and economic material. Titanium metal's corrosion resistance is due to a stable, protective, strongly adherent oxide film. This film forms instantly when a fresh surface is exposed to air or moisture.
Titanium alloys are considered to be "reactive metal," i.e., they react with atmospheric gases, such as oxygen as well as nitrogen, when at elevated temperature. Because of this, titanium processing such as melting and casting are typically performed in a vacuum or in an inert gas environment. Contamination with oxygen or nitrogen will embrittle the titanium. Similar considerations are used when welding titanium alloys.
Welding procedures for titanium that dictate complete shielding of welds until cooled using inert argon gas. One such common procedure is manual gas tungsten arc welding, which is a slow and laborious process. In addition, inspecting for weld discoloration, is another step in the process that generally results in more rework. These requirements are onerous, requiring that welding small parts be conducted inside an inert gas chamber, to building dedicated local inert gas shields for each weld joint, to adding cumbersome "trailing shields" behind the torch that continue to cover the hot weld metal with inert gas until the weld has cooled sufficiently. All these techniques restrict access and the ability of the welder to manipulate the torch to achieve good weld quality. And, the necessity to use these devices increases the difficulty and time required to produce a weld. Due to these more stringent requirements, labor hours required to weld a given weldment design are a minimum of five times more than required for a similar steel component.
Contamination of titanium with oxygen or nitrogen, and thus the quality of the weld from a strength standpoint, has traditionally been determined by the color of the weld surface. The reaction with oxygen and/or nitrogen creates a thin oxide or nitride (?) layer on the surface with the thickness of the layer being related to the color, and therefore the amount of contamination. For instance, a shiny silver colored weld indicates no contamination, straw or gold color indicates there is a minor amount of contamination and blue or purple indicates significant levels and brown or grey indicates gross contamination. Inspectors must be provided with weld color standards used for comparison purposes. Other methods of assessing contamination include portable hardness test methods and eddy current non-destructive inspection methods. This is the current state of the art in titanium welding.
Weldments produced using the conventional Gas Metal Arc Welding (GMAW) process are done without the use of additional auxiliary shielding devices, such as trailing shields, glove boxes, purge chambers, back-up shields or other shielding devices. Deposited weld metal and heat affected zones are not additionally shielded from the atmosphere by inert gas, except by gas supplied by the torch through the standard gas cup associated with conventional GMAW welding torches. The resultant weld surface color is not an indicator of the weld properties. Any weld color from shiny silver, to blue, grey or brown and scaled, is acceptable by this process.
On August 28, 1958, a party and government decree was adopted on the creation of a new high-speed submarine from new types of power plants and the development of research, development and design work for submarines. A very unusual requirement was put forward before the creators of the ship - to abandon the use of previously mastered technical solutions, materials and equipment. Everything is just new, the most promising! In the work on the project 661 took an active part of the Central Research Institute #45 (now - the Central Research Institute named after Academician A. N. Krylov). The institute investigated both the ship’s own issues related to the creation of a new nuclear-powered ship and the combat effectiveness of a high-speed submarine. Considered three alternative basic structural materials for the manufacture of durable housing - steel, aluminum or titanium. In the end, it was decided to choose a titanium. This made it possible to drastically reduce the mass of the hull (and, consequently, the displacement of the ship). Thus, one of the most important unmasking signs of the boat, its magnetic field, was significantly reduced.
The authors of the submarine project, N.N. Isanin, N.F. Shulzhenko, V.G. Tikhomirov, met a proposal for its processing in a titanium version without any enthusiasm. Titanium for them was a complete obscurity: less than steel, a modulus of elasticity, "cold" creep, other welding methods, a complete lack of experience in marine use. Specialists of the Central Research Institute named after Academician A.N. Krylov, the Central Research Institute of Shipbuilding Technology, shipyard workers were in the same position.
Titanium is stronger and weighs 33 percent less than steel; the pressure hull can be stronger without increasing displacement; its use gives a submarine a stronger hull for greater diving depth and increases resistance to explosives at lesser depths; and the submarine is essentially nonmagnetic, thus decreasing the likelihood of magnetic anomaly detection (MAD). But Titanium is three to five times more expensive than steel; it needs a totally different manufacturing process; shipyard workers must be retrained; construction halls must be reconfigured; and bending and shaping of heavy plates of titanium alloy are far more difficult compared to steel.
The Soviet Union was a world leader in metallurgy, metal working and metal thermal treatment, enabling production of very strong and unique alloys of titanium and steel. Some Soviet submarines, such as Alfa-class submarines, broke ground with construction entirely of titanium and mastered the technique of titanium welding as early as the late 1950.
In 1970 the deployment of the Alfa SSN surprised the U.S. Navy with a 45 knot speed and 2000-2500 foot operating depth. Alfa used a high power density, liquid metal reactor plant to increase the power-to-weight and volume ratios of her propulsion plant, while simultaneously reducing the hull weight needed for extreme operating depths by using a titanium pressure hull. Alfa had a sister, the Papa SSGN, which appeared to employ these same submarine design technologies for the antiship mission. These submarines, assuming they were the lead boats of new submarine classes, threatened American ASW weapons with obsolescence.
The fast, deep diving nuclear submarine threat proved in many ways to be a false alarm. Alfa did not enter serial production until later in the 1970s and only a total of six were deployed before the program was canceled. Likewise, only one PAPA was ever deployed. Instead, the Soviets focused on building more traditional boats. Recent Russian submarines have not been constructed with titanium hulls, presumably for reasons of cost.
For centuries, people attempted to descend into the oceans for scientific observation, salvage and rescue operations, animal and mineral harvesting, and attacking enemy ships in times of war. Often, such activities require vessels capable of submerging to great depths. Thus, the foremost concern in designing and fabricating the hull of a submergence vessel is that the hull be strong enough to resist the large crushing forces resulting from hydrostatic pressure. For this reason, submarines have been typically constructed of welded steel that is several inches thick.
However, there are many disadvantages of such construction. The thickness of the hull makes rolling and welding operations extremely difficult. Also, the resulting weight of the welded steel structure is immense and it impacts buoyancy and maneuverability. Furthermore, the substantially tubular, elongated structure of a typical submarine hull is impossible to shape without specialized components.
High-strength titanium is one of the most promising new hull materials. It weighs approxiraately Z76 lb/cu ft compared to a weight of 490 lb/cu ft for steel. Some alloys with yield strengths of 120,000 psi may be welded in thin sheets if extreme care is used to prevent contamination. Non-weldable alloys with yield strengths to 175,000 psi and greater are also available.
Any vessel made from magnetic materials has a Magnetic Anomaly Detectors (MAD) signature. It decreases as the cube root of distance, and does not propagate like a wave. There are significant natural and man-made noise sources. It is a good sensor for close-in detections. There has been interest in the use of non-magnetic steels (German Type 205 and 206 submarines) and building non-steel submarines (the Russian Alfa had a titanium hull). Non-magnetic steel has not been popular in more recent submarines for unknown reasons.
The high strength-to-weight ratio and outstanding seawater corrosion resistance of titanium alloys have long been recognized and have marked titanium as an important structural material in future ocean systems. A specific application in which alloy titanium has several potential advantages over high-strength steels is in the construction of pressure hulls for submarines and deep submergence vehicles.
Titanium is half as dense as steel and non-magnetic, but has major disadvantages, including inadequate resistance to brittle fracture (especially at low temperatures found in the deep ocean). Reluctance to use titanium in ship hulls was grounded in two solid facts: aircraft grade titanium was outrageously expensive and converting to titanium in a historically steel and aluminum shipyard would potentially slow welding speeds by an order of magnitude.
Prior to utilizing alloy titanium for this application, however, definite advances were needed in fabrication technology to provide more economical procedures for joining titanium into structural components. Specific factors which control the economics of joining titanium alloys include the need for extreme cleanliness and careful gas shielding to prevent harmful contamination during fusion welding, the high cost of available weld filler materials (approximately $40 per pound), and the unavailability of an electrode for shielded-metal-arc welding (SMAW). Welding titanium on a shipyard production basis is possible using lower cost, marine grades of titanium to fabricate the hull. Aerospace grade titanium used in aircraft is about nine times more expensive than steel. But “fit-for-purpose” ship hull or marine grades of titanium could be made less costly — perhaps only three times as expensive as steel — by changing the processing and finishing requirements. Although well established, the existing titanium welding processes are too slow for ship hull construction which typically requires miles of welds.
At the factory, everyone understood perfectly well that when building such a complex engineering structure as a submarine hull from a completely new material - titanium, a new approach was needed. The director of the SMP E. P. Egorov, his deputies, designers, builders, shop workers put a lot of effort into creating an unprecedented production.
Shop number 42 became a true testing ground for novelty: daily floor washing, lack of drafts, lighting, clean clothes of welders and other workers, and high production standards have become its hallmark. A great contribution to the establishment of the workshop was made by R.I. Utyushev, the deputy head of the welding workshop. Wonderful specialists invested many skills and souls in this work: the Northmen Yu. D. Kainov, M. I. Gorelik, P. M. Grom, military representative Yu. A. Belikov, A. E. Leipurt and many others - technologists, craftsmen, workers. A new concept for the design of shell structures appeared: “hard” ends were eliminated, “soft” knits appeared, smooth transitions from rigid parts to elastically flexible, etc.
This idea was fully realized then by V. G. Tikhomirov and V. V. Krylov in the design of the PC submarine project 705 "Lira" (on the codification of NATO - "Alpha"). Taking into account the experience of N. I. Antonov, their hull turned out to be ideal. But after all the trouble, the submarine hull of the project 661 was brought to perfection and all the blocks passed the tests.
As a result, the most advanced welding production with argon-helium protection was created. Argon-arc, manual, semi-automatic, automatic and other methods of welding have become commonplace for all workers in the workshop. Here, submerged-arc welding, welding in the “gap” (without cutting), argon quality requirements (dew point) were worked out, a new profession appeared - welder for protecting the reverse side of the seam (blower).
Komsomolets means "member of the Young Communist League." She was launched in May 1983 in Severodvinsk, a closed Soviet city on the Barents Sea with the world's largest shipyard. She was 400 feet long, 37 feet high and 27 feet in beam with a submerged displacement of 8,000 tons--a very large sub indeed. Komsomolets had two nuclear reactors, long thought to be of revolutionary design (liquid-metal coolant) but actually water-cooled. Her inner pressure hull was titanium, light and strong, making her the world's deepest diving submarine, and her operating depth below 3,000 feet was far below that of the best of US subs.
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