What types of corrosion of titanium pipe include?

The corrosion form of titanium includes two categories: general corrosion and local corrosion: general corrosion is a form that is completely and uniformly corroded; local corrosion is a form of local corrosion relative to general corrosion. It can be divided into: crevice corrosion, spot Corrosion, stress corrosion cracking, galvanic corrosion, abrasion, hydrogen absorption and hydrogen embrittlement.

1. Crevice corrosion: Corrosion that occurs between the flanges or flanges and the gaps near the deposits generally occurs in the narrow gaps.

2. Pitting corrosion: Corrosion that occurs in the process of opening holes, such as the corrosion phenomenon caused by the presence of halogen ions such as C1-, B-wide, and I-.

3. Stress corrosion cracking: In a specific environment, due to the effect of tensile stress, a kind of brittle failure.

4. Abrasion: The fluid promotes electrochemical corrosion due to mechanical action.

5. Galvanic corrosion: also known as dissimilar metal contact corrosion, it is a phenomenon that promotes the corrosion of the metal with the lower potential in the state of electrical short-circuit.

6. Hydrogen absorption and hydrogen embrittlement: Take hydrogen out of the material. When the amount of hydrogen taken out exceeds the solid solution limit of the material, brittle hydrides will be formed and hydrogen embrittlement will occur.
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Titanium plate manufacturing process and characteristics

TC4 titanium alloy has good mechanical properties at room temperature and high temperature, and is widely used in the manufacture of aviation structural parts and aero-engine fans, drums, etc., and has accounted for more than 50% of the total aviation titanium alloys. Many load-bearing structural parts of aircraft, especially variable cross-section structural parts, require the raw material bars to have good notched stress fracture performance. The purpose is to ensure that the parts have a strong ability to inhibit the initiation and propagation of cracks in a state of high-stress concentration. Without breaking and failing. The upper limit of the specifications of this type of TC4 titanium alloy bar in the relevant domestic technical standards is Ф220mm. At present, there are no public reports on the preparation process of TC4 titanium alloy bars requiring notched stress fracture performance at home and abroad. It is generally believed that the high hydrogen content or poor uniformity of the TC4 titanium alloy will reduce its room temperature notch stress fracture performance.

In industrialized mass production, it is also common that the notch stress fracture performance of such bars is unqualified due to improper process. The raw material procurement contract of a special forging requires the provision of ~b350mmTC4 titanium alloy bars in the range of beyond specifications in accordance with current technical standards. Under the premise of ensuring the same mechanical properties, the ultrasonic flaw detection level is required to be changed from GB/T5193 of the original smaller specifications of bars. The grade B in the medium is raised to grade A, so the relevant process research on the preparation of large-size TC4 titanium alloy bars with special needs has been carried out.

Titanium rod manufacturers use sponge titanium and master alloys to prepare 5t consumable electrodes. The 6720mm TC4 titanium alloy ingots are obtained through 3 times vacuum waste smelting through the ALD vacuum waste electric arc furnace imported from Germany. Because the microscopic concentration of hydrogen under high stress reduces the notch stress fracture performance J, certain measures have been taken to control the hydrogen content of the ingot in the experiment on the raw material selection and smelting process of the ingot. Samples are taken from the surface of the head, middle and tail of the ingot to test its chemical composition.

(1) By adopting the forging process of phase zone blanking and two-phase zone upsetting + straight drawing, it is possible to prepare Φ350mm large-size TC4 titanium alloy bars whose structure, performance and flaw detection level meet the technical requirements of the supply.

(2) The structure with good primary equiaxialization is beneficial to improve the notch stress fracture performance at room temperature, and the short rod-like α-phase structure with strong direction consistency will reduce the notch stress fracture performance.
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Analysis of Causes of Fracture of Titanium Alloy Screw Bolt

Titanium alloy has a high specific strength, a wide working temperature range and excellent corrosion resistance. It is widely used in the aerospace field to make compressor blades, discs, casings and fastening parts; however, it is different from structural steel and stainless steel. Compared with superalloys, it has greater sensitivity to surface damage and defects.

Any negligence in the processing, assembling and use of titanium alloy parts will cause unexpected adverse consequences for the use performance of titanium alloy parts, and even serious fracture accidents may occur.

There have been many fracture accidents in the use of titanium alloy screws, most of which are related to fatigue; therefore, fatigue resistance is one of the most important indicators to measure the reliability of titanium alloy parts. The fatigue resistance of titanium alloys is particularly sensitive to the surface integrity of parts. Many surface factors, such as pollution, scratches, inclusions, corrosion, etc., can induce the initiation and propagation of fatigue cracks, leading to parts fracture.

1. The cracking property of right-angle joints is fatigue cracking, and the reason for cracking is related to the large stress that the joint bears and the thick oxygen-rich α layer in the source area;

2. In view of the large force on the joint, it is recommended to appropriately increase the design margin under the premise of completely removing the oxygen-rich α layer.

3. In order to avoid fatigue fractures caused by wear and tear and destroy the surface integrity of the titanium alloy, the titanium screw manufacturer recommends that the single lug is in vertical contact with the bolt during the assembly process; at the same time, in order to better ensure the surface integrity of the titanium alloy bolt, it is recommended Increase the chamfer at the edge of the single ear hole, and increase the bushing structure at the bolt connection position.
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How do different titanium fittings work?

Titanium pipelines mainly transport severely corrosive and dangerous media. When the media with corrosive media passes through the titanium pipe fittings, the media carries a certain pressure, and each part of the various pipe fittings bears different pressures. The three most commonly used pipe fittings ( Elbow, tee, reducer) to analyze.

1. Elbow

The elbow is one of the important pipe fittings of various piping systems. In addition to changing the flow direction of the medium, it also improves the flexibility of the pipeline. When the medium passes through the elbow, the pressurized medium rushes directly to the back of the elbow, and the medium flows along the back to the outlet. It can be seen that the back of the elbow bears greater pressure and severe erosion and corrosion, indicating the backload Greater than any part.

2. Three links

The working condition of the tee is similar to that of an elbow. When the medium passes through the tee, it directly rushes to the intersection of the branch and straight road of the tee, where the bearing pressure and erosion-corrosion are greater than other parts. The branch is the pressure relief and diversion state of the main pipeline.

3. Reducer

The working condition of the reducer, when the medium passes through the reducer, the medium often flows from the large end to the small end. The gradual decrease of the cross-sectional area causes the pressure of the cone of the reducer to be increased, and the inner surface of the cone has a larger bearing capacity. The pressure is subject to severe erosion and corrosion.

The above analysis shows that titanium pipe fittings are extremely important parts of titanium pipelines, which directly affect the life of titanium pipelines.
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What factors have affected the development direction of titanium alloy plates?

It has always been loved by people for its good physical properties, lightweight, beautiful appearance, durability, easy recycling of materials, high reuse rate, and no pollution. However, the high price of titanium alloy plates, poor wear resistance and other factors, directly Affected the extensive use of titanium alloy plates. Therefore, how to reduce the price of titanium alloy materials and improve the wear resistance of titanium alloys has become the development direction of titanium alloy materials in the future.

Titanium alloy has high strength, low density, corrosion resistance, long service life, and high waste recycling price. After being scrapped, the value of titanium scrap is still equivalent to more than 60% of the purchase value of raw materials. It can be said that titanium material is the least wasted material. The green environmental protection of titanium will not cause any adverse effects on the environment; titanium alloy resources are rich and are the earth The upper storage volume ranks third, which can be said to be inexhaustible and inexhaustible. Therefore, the high cost of titanium alloy plate is only the first time the investment is relatively large.

However, if used for many years, titanium alloy plate is an ideal material for economical and practical use. In addition to the use of titanium alloy plates in the chemical, aerospace, and medical industries in China, even some household products have begun to try to use titanium alloy plates, such as titanium alloy doors and windows.

In order to improve the performance and grades of existing doors and windows in some domestic home furnishing industries, they have changed the low-level structure that only pursued labor-saving, material-saving, and low-price in the past, and realized the goal of shifting from sliding windows to better-performing casement windows. A transition from the main to realize diversified system designs such as single-layer, double-layer, three-layer and small opening and large fixing. At the same time, attention should be paid to the selection of frame materials, glass, spacers, and sealants for titanium alloy doors.

Titanium alloy doors can use TC4 and titanium plates to make door edges, handles, spoke reinforcement rings and ribs. Nowadays, some high-end villas have begun to use titanium alloy panel doors. After a long period of time, it has been proved that the use effect is very good, fully achieving the expected design goals, and adding beautiful scenery to people's lives and environment.
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What problems should be paid attention to during the cutting process of titanium plate?

Many people don't know how to cut more trouble-free in the process of using a titanium plate. Actual titanium plate cutting has a certain scientific basis. Here are 7 kinds of titanium plate cutting techniques.

(1) When cutting semi-automatically, first put the guide rail on the surface of the titanium plate, and then put the cutter on the guide rail, the order should not be reversed.

(2) Reasonably determine the cutting parameters according to the thickness of the titanium plate to obtain a good cutting effect.

(3) Check whether the cutting nozzle gas is unblocked. If there is a blockage, it should be cleared in time.

(4) In addition, before blowing out the slag, the slag should be cleaned up.

(5) The distance between the cutting nozzle and the surface of the titanium plate should be appropriate, too close or too far is not good.

(6) The preheating of the titanium plate should be sufficient to avoid affecting the cutting process.

(7) If you want to cut out workpieces of different sizes first, then you should cut out workpieces of different sizes first.
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Characteristics and special functions of titanium materials

The characteristics and special functions of titanium materials such as titanium alloy processed parts, titanium alloy forgings, titanium alloy pipes, etc.

The passivation of titanium depends on the presence of an oxide film. The corrosion resistance of titanium alloy workpieces in oxidizing media is obviously better than that of reducing media. High-speed corrosion will occur in the reducing medium. Titanium is not corroded in corrosive media such as seawater, wet chlorine, chlorite and hypochlorite solutions, nitric acid, chromic acid, metal chlorides, sulfides and organic acids. However, in the medium that reacts with titanium to generate hydrogen (such as hydrochloric acid and sulfuric acid), titanium generally has a high corrosion rate. However, if a small amount of oxidant is added to the acid, titanium will form a passivation film. Therefore, in a mixture of sulfuric acid-nitric acid or hydrochloric acid-nitric acid, titanium has corrosion resistance even in hydrochloric acid containing free chlorine. The protective oxide film of titanium is usually formed when the metal contacts water, even in the presence of a small amount of water or water vapor. If titanium is exposed to a strong oxidizing environment without water, it will quickly oxidize and produce a violent spontaneous combustion reaction. This behavior occurs in the reaction of titanium with fuming nitric acid containing excess nitrogen oxides and titanium with dry chlorine. However, in order to prevent this reaction, a certain amount of water is necessary.

Titanium is non-magnetic. It is used for submarine shell and will not cause explosion.

The thermal conductivity of titanium is only 1/5 of steel, 1/13 of aluminum, and 1/25 of copper. Poor thermal conductivity is a disadvantage of titanium, but it can be used in some cases.

The elastic modulus of titanium is about 55% of iron. As a structural material, low elastic modulus is a disadvantage.

The tensile strength of Ti-6Al-4V titanium alloy is 960mpa, the yield strength is 892mpa, the difference between the two is only 58mpa.

Titanium has a strong binding force with hydrogen and oxygen. Care should be taken to prevent oxidation and hydrogen absorption. Titanium welding should be carried out under argon protection to prevent contamination. Titanium tubes and thin plates should be heat treated in vacuum, and the micro-oxidizing atmosphere should be controlled during the heat treatment.

The clock of the same shape and size is made of titanium and other metal materials (copper and steel). When each clock is struck with the same force once, you will find that the vibrating sound of the titanium clock lasts for a long time, that is, the energy that is struck to the clock is not easy to disappear.

Special functions of titanium and titanium alloy machining parts:

Ti-50%Ni (atomic fraction) alloy has the ability to restore the original shape under certain temperature conditions, so it is called titanium shape memory alloy.

NbTi alloy, when the temperature drops to close to zero, the conductor made of NbTi alloy will lose resistance, so that any large current will pass through, the conductor will not generate heat or consume energy, so NbTi alloy is called a superconducting material .

Ti-50%Fe (atomic fraction) alloy has the ability to absorb a large amount of hydrogen. Using this feature of ferro-titanium alloy, hydrogen can be stored safely, that is, without using steel high-pressure cylinders to store hydrogen. Under certain conditions, titanium-iron alloy can also release hydrogen, so it is called hydrogen storage material.
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