Application and development of large-diameter titanium alloy pipes for marine use

Application and development of large-diameter titanium alloy pipes for marine

The demand for various types of high-strength and corrosion-resistant metal pipes used in large-scale equipment in the field is showing a substantial increase. Because metal pipes need to be used in complex and harsh marine environments (strong corrosion, typhoon, strong convection, high temperature, high pressure, biological adhesion), they have extremely high requirements for corrosion resistance. Titanium and titanium alloys have high toughness, non-magnetic, Unique advantages such as low density and excellent corrosion resistance have become the most ideal material for large-scale equipment in the above-mentioned fields. A lot of experience has confirmed that the service life of the low-alloy steel pipe system is 1-2 years, and the service life of the Cu/Ni piping system is only 6-8 years, which is far below the design life requirements of seawater pipelines. Titanium has the characteristics of high strength, high toughness, high specific strength, light weight, non-magnetic, seawater corrosion resistance and marine atmospheric corrosion. The corrosion life of titanium and titanium alloy pipelines is more than 120,000 hours, and the service life is more than 60 years. Under working conditions, the full life of titanium alloy material is unmatched by other metal materials, and it can be recycled 100% harmlessly after the end of the equipment life. Therefore, it is the best material for marine equipment.

　　Characteristics of marine equipment

　　① Marine equipment is a large metal building with a large tonnage, high investment cost, and large damage loss.

　　②The system has complex structure, complete functions, complex and harsh working conditions, high reliability requirements, and difficult construction techniques.

　　③Material life extension is of great significance to ensure the integrity, reliability and safety of marine equipment and structures, and to promote resource protection and sustainable development.

　　④Improving the performance of marine equipment mainly involves improving corrosion resistance, light weight, application of high-strength and high-toughness materials, reliability, and product economy throughout the life cycle.

　　The advantages of titanium alloy pipes

Titanium alloy has a series of important characteristics such as high melting point, low density, high strength, corrosion resistance, superconductivity, shape memory and hydrogen storage. It is widely used in aviation, aerospace, ships, nuclear power, medical, chemical, metallurgy, electronics, sports The fields of leisure and construction are known as the "third metal", "air metal" and "ocean metal". Pipes are used for the transmission channels of gaseous and liquid media. They are basic products in various fields of the national economy. Titanium alloy pipes are used in aviation engines, aerospace vehicles, and petroleum pipelines due to their light weight and excellent corrosion resistance. , Chemical equipment, marine environment construction and various offshore operating platforms have a wide range of applications, such as coastal power stations, offshore oil and gas exploration and transportation, sea water desalination, marine chemical production, alkali salt production, petroleum refining equipment, etc., and the prospects are very broad.

　　 The promotion and application of titanium materials is one of the most important technological development directions for shipbuilding and marine engineering equipment. Titanium alloy pipes have been widely used in ships and marine engineering equipment in developed countries. A large number of titanium materials are used to improve the safety and reliability of equipment, reduce equipment volume, reduce quality, and significantly reduce equipment damage accidents and maintenance times. Greatly extend the service life.

　　 Titanium alloy pipe processing performance characteristics

Titanium alloy has low plasticity at room temperature and large deformation resistance, but it has good plasticity and low deformation resistance in the α+β two-phase zone and β-phase zone. Therefore, the forming and manufacturing of titanium alloy materials or the preparation of various profiles (plates) , Rods, tubes, etc.) need to be heated to near the phase transition point.

Because titanium alloys are prone to chemically react with oxygen, nitrogen, carbon, etc. at high temperatures, and are easy to absorb hydrogen, the deformation performance of titanium alloys is drastically reduced and the service performance of the material is affected. In addition, the low thermal conductivity of titanium alloys often causes large blanks to be heated. This results in a large cross-sectional temperature difference, which can easily lead to cracks during the deformation process; in addition, the temperature range of the titanium alloy deformation zone is narrow, and the strain rate is more sensitive, and generally must be deformed at a lower rate; at the same time, the cooling rate after deformation directly affects its room temperature The equilibrium structure and the service performance of the components, therefore, the deformation temperature should be kept constant during the deformation process or measures should be taken to reduce the rate of temperature drop to make it have sufficient plasticity.

　　 my country's large-diameter titanium alloy pipe preparation technology analysis

　　The traditional titanium alloy seamless pipe production process is extrusion piercing, cross-rolling piercing + multi-pass cold rolling, drilling and boring. At present, the domestic use of traditional technology can prepare small-size titanium alloy pipes, and they are used in aviation, aerospace, shipbuilding and petrochemical fields, which strongly supports the development of weaponry and national economy.

(1) Traditional drilling and boring and extrusion process: Drilling and boring processing is to directly use titanium alloy bars for drilling and boring processing, without heating process and calendering, and the material utilization rate is extremely low, generally less than 50%, therefore, the overall cost Very high. At the same time, it is not suitable for processing large-diameter and thin-walled pipes.

　　Extrusion molding technology can obtain a large amount of deformation, fine grains, and it is difficult to control the uniformity of the capillary wall thickness. Extrusion molding usually uses glass powder lubrication or copper-clad lubrication. The glass powder lubricated extrusion titanium alloy pipe technology is not mature in my country. The lubrication effect in the post-extrusion stage is not ideal, which can easily cause serious surface of the die and extruded pipe. Damage, high manufacturing cost, low production efficiency and product quality; the lubrication effect of the copper-clad sleeve is better, and a better surface quality of the titanium alloy tube can be obtained, but the material of the copper-clad sleeve is large, and the package attached to the surface of the titanium alloy tube is removed. The copper sleeve consumes a lot of acid, which is easy to cause environmental pollution.

(2) Traditional piercing (Mann type) + cold rolling process: there are many cold rolling processes, the production efficiency is extremely low, multiple passes are required, the deformation of passes is small, the energy consumption of annealing between passes is high, and the pickling pollutes the environment . This process is only suitable for rolling pure titanium and alloy pipes with low deformation resistance, and cannot roll high-strength titanium alloy pipes (such as TC4). The yield of this process is about 75%.

According to the characteristics of titanium alloy materials, by controlling the process parameters such as the rolling temperature, the total diameter reduction rate, the ellipticity coefficient, the deformation rate, the front reduction rate and the cavity control, etc., the stability of the whole process is guaranteed, and the internal and external surface quality is guaranteed. , Dimensional accuracy and various performance indicators fully meet the process requirements. The preparation technology has the following advantages:

① This technology is aimed at the high deformation resistance of titanium alloys. Through the innovative improvement of cross-rolling piercing mills, multi-function rolling mills and dual-series micro-tension reducers, the rolling force of the main motor is increased, and the heating is carried out through a ring furnace. The intelligent temperature control system and fast transfer device are adopted between the piercing, hot rolling, sizing and correction processes to minimize the temperature drop rate of the blank to ensure that it has sufficient plasticity and adapt to the characteristics of the narrow deformation temperature range of the titanium alloy.

　　②This process is especially suitable for rolling and forming large-diameter titanium alloy pipes. The outside diameter can reach φ530mm, the wall thickness covers 5-36mm, and the product length can reach 12 meters or more. Compared with extrusion + cold rolling process and drilling and boring process, its processing cost is reduced by more than 50%; compared with traditional drilling and boring processing, the utilization rate of titanium alloy pipe is increased by more than 40%; compared with traditional extrusion molding process, production Efficiency is doubled. It has achieved high efficiency and low cost, and overcomes the technical bottleneck of the production of large-diameter titanium alloy pipes by two-roll skew rolling of titanium alloy. Based on the advancement of the process and the maturity of technology, the yield rate can reach up to 95%.

　　The application and development prospects of large-diameter titanium alloy pipes

At present, titanium used in domestic ship equipment mainly includes: main condenser of submarine, titanium alloy torpedo launching tank, nuclear power PWR primary circuit system emergency cooler, sonar dome, titanium alloy propeller, diesel engine smoke exhaust pipe And the sea piping system, related piping and pump valve system, deep submersible pressure shell and auxiliary system. The typical specifications of seawater pipelines: φ308x4mm, φ285x5mm; the main seawater piping system of ships: φ12.7~304.8mm.

Due to the low density, corrosion resistance and high strength of titanium and titanium alloys, the weight of the equipment can be greatly reduced. Therefore, although titanium and titanium alloys are more expensive in terms of unit price, after the overall weight of the equipment is reduced, titanium and titanium alloys On the contrary, the sexual input will not be too higher than other materials, and even lower than other materials. Titanium and titanium alloy pipes have huge application prospects. With the maturity and promotion of high-efficiency, short-flow, low-cost production technology, many copper and copper alloy pipe applications can be replaced by titanium and titanium alloy pipes.

　　①In shipbuilding, the pipes used in ships and large oil tankers are an important application field of copper alloy pipes. Copper alloy pipes for ships mainly include BFe30-1-1, BFe10-1-1 cupronickel pipes and HAl77-2 aluminum brass pipes. Since most of the contact medium at sea is seawater, the pipes are required to have excellent seawater corrosion resistance and high mechanical and technological properties. Marine engineering heat exchange devices use copper and copper alloy tubes. For example, other marine heat exchange tubes mainly include: oil coolers, water coolers and feedwater heaters for diesel engines, generators, and other auxiliary systems. The specifications of these products vary.

　　②The construction of marine engineering and large-tonnage ships requires more high-precision and larger-diameter anti-corrosion piping equipment to increase the primary transmission and displacement. At the same time, high dimensional accuracy should be used to ensure the high tightness of the pipeline assembly. It is understood that the maximum diameter of seamless copper-nickel pipes such as large-diameter marine and oil production platforms in Germany, South Korea and other countries has reached φ520mm or more.

　　 With the gradual deepening of my country's maritime power strategy, the demand for large-diameter, high-strength and high-corrosion-resistant seamless pipes continues to increase in the fields of offshore equipment, offshore oil and gas field exploration and development, and ships. The large-scale production of large-diameter titanium alloy seamless pipes and the industrial promotion and application of high-efficiency, short-process, and low-cost preparation technology will further meet the market's low-cost demand for titanium and titanium alloy products. At the same time, the current concentration of the titanium industry is not high. Manufacturers should actively cooperate with national standard formulation and design units, colleges and universities, downstream users and other related supporting equipment manufacturers to establish a national titanium technology and economic network service platform to form Work together to promote the market development of titanium alloys, and strive for policy and financial support from the state to further promote the wider application of titanium alloy pipes.

Nicole