Application of titanium alloy in petrochemical industry

1. Application of titanium alloy in petroleum industry

1.1 Titanium alloy drill pipe

In recent years, in order to improve crude oil recovery, reduce oil and gas field production costs, and extend oil and gas field development life, more and more complex structure wells have been developed, such as extended reach wells, short-radius horizontal wells, and sidetracking horizontal wells with windows in old wells. Conventional drill pipes have encountered some difficult problems when used in these complex structure wells. For example, in ultra-short radius horizontal wells, the wellbore curvature is very small (<18 m), which causes conventional drill pipes to generate large alternating stresses. Fatigue fracture of drill pipes caused by alternating stress often occurs, causing significant losses to oil fields. In order to solve these problems, foreign countries have begun to use new materials to develop titanium alloy drill pipes, aluminum alloy drill pipes, composite drill pipes, etc. to replace conventional drill pipes.

The laboratory has confirmed that when the cyclic stress is between 30,000 psi and 40,000 psi, the fatigue life of titanium is 10 times that of ordinary steel. The elastic coefficient of titanium alloy pipes is about 16.5 msi. It has better elasticity than steel drill pipes and is more suitable for High curvature well section (Beibiao 3). At present, titanium alloy drill pipes with good economic performance have been produced. They are composed of a pipe body made of Ti-6A1-4V, which is upset at both ends and butt-welded with tool joints at both ends. The size of the titanium pipe body meets AP) standards. The length range is range 2 or 3 specified by the API standard. In order to reduce the manufacturing cost, the tool joint is made of steel, the joint thread is run-in through the upper shackle, and the outer diameter of the joint is welded with a wear-resistant band (to avoid repair welding with ordinary welding rods after the joint is worn).

A foreign oil field has used titanium alloy drill pipes hundreds of times in small curvature wells (see Table 1).

Titanium alloy drill pipe is also used in ultra-deep wells and extended-reach wells. Due to the low density of titanium alloy, the hook load can be reduced by 30%, the torque can be reduced by 30% to 40%, significantly improving the pulling force margin and safety factor of the drilling tool, and improving the ability to handle complex accidents.

1.2 Titanium alloy oil casing

Most of my country's natural gas resources are oil-containing gas fields. For example, the Xinjiang Tarim and Sichuan Basin are all high-oleophobic gas fields. The development of highly corrosive oil and gas fields has become a major problem faced by the oil and gas industry. Domestic and foreign concerns about high-containing H252 and C202 The anti-corrosion problem of pipes in oil and gas fields has been studied for many years. There are roughly three types of anti-corrosion measures: adding corrosion inhibitors, anti-corrosion coatings, and corrosion-resistant pipes. The first two can play an anti-corrosion role to a certain extent, but they cannot solve the anti-corrosion problem in long-term service under high temperature and high pressure conditions. Therefore, choosing high-quality corrosion-resistant materials for pipes has become a dominant trend.

There are two main categories of corrosion-resistant metal pipes: nickel-based alloys and titanium alloys. At present, nickel-based alloy pipes are widely used, but nickel-based alloy pipes also have shortcomings such as complex processing technology, high material cost, and easy damage to the pipe surface. At present, our country is one of the countries that lacks laterite nickel ore resources. The national laterite nickel ore reserves only account for 9.6% of all nickel ore resources. The domestic laterite nickel ore is of low grade and the mining cost is relatively high. This means that our country There is no competitiveness in laterite nickel ore. Therefore, reliance on nickel-based alloys is not conducive to the strategic development of oil and gas in the long run. my country is rich in titanium resources, with ilmenite reserves reaching 200 million tons, accounting for 28% of global reserves, ranking third in the world.

Titanium alloys have been gradually used in high-sulfur environments in recent years due to their excellent resistance to pitting corrosion. In particular, the working conditions are relatively harsh, with high CL, H, and S content. General stainless steel and even nickel-based alloys will corrode. After years of research and development, titanium alloy materials for oil casing corresponding to ordinary steel have been formed. (See Table 5). The mechanical properties of titanium alloy oil pipes are equivalent to those of nickel-based alloy oil pipes, and the joint strength meets the requirements of standard IS010400 for P110 steel grade

The titanium alloy oil pipe developed by Qinhuangdao Zhongwei Precision Mechanical Parts Co., Ltd. passed the shackle test specified in APIRP 5C5 and underwent a blast test. It exploded under a pressure of 173MPa. The blast shape was longitudinal cracking, which met the usage requirements (see Figure 1 ).

1.3 Titanium alloy conveying pipeline

Because titanium alloy pipes are easy to bend and have extremely high resistance to dynamic stress corrosion fatigue strength caused by wave impact and platform movement, the stress corrosion fatigue strength of titanium alloy pipes is more than 10 times higher than that of currently used carbon steel. At the same time, when laying fishing pipes, titanium alloy pipes Alloy pipes adapt to bending and deformation conditions during laying. The welding performance of titanium alloy conveying pipelines is good. The single-sided welding and double-sided forming technology ensures uniform and reliable welds (see Figure 2). The titanium alloy conveying pipelines also have excellent mechanical properties. They have passed the tensile mechanical properties test of the pipe body and the oscilloscope impact test. Pipe body flattening test, fracture toughness KIC test.

1.4 Offshore drilling platform parts and risers

The requirements for offshore drilling platforms are higher than those for Weidi drilling platforms. As early as the 1990s, titanium alloys have been used in all aspects of offshore drilling platforms abroad. The semi-submersible floating drilling platform of the Headway Oilfield of the Norwegian branch of the North Sea Oilfield has been used

Titanium alloy is used as a riser, which reduces the mass of the entire system by 50%, thereby reducing the lifting force of the riser by 63%, eliminating the need for huge flexible joints, reducing the system cost by 40%, and the service life is expected to be up to 25 years ( See Figure 3).

In addition, the heat exchanger in the cooling system on the offshore drilling platform uses a titanium tubular cooling device; various types of pumps (such as deep well pumps, centrifugal pumps) use cast titanium pump bodies and titanium alloy impellers; Various valves and other pipe fittings

Titanium products are also used to reduce maintenance workload (see Figure 4).

in conclusion

(1) Titanium and titanium alloys have broad application prospects in oil and gas exploration due to their low density, high specific strength, fatigue resistance, corrosion resistance and other properties. Recently, titanium alloy drill pipes, tubing, casing, etc. have been developed at home and abroad. Couplings, delivery pipes, oil refueling pipes, valves, pumps and other titanium products.

(2) In extremely harsh corrosive environments, titanium alloy products can still meet anti-corrosion requirements. The cost of titanium alloy pipes of the same length, diameter, thickness and strength is lower than that of G3 nickel-based alloys, so there is a trend to replace nickel-based alloy pipes. , (3) The addition of titanium alloy products reduces the overall mass of the system and makes the equipment more reliable, allowing the offshore drilling platform to enter deeper waters and extending the service life of the platform.