Titanium coil is also considered a type of titanium equipment. Generally, titanium coil is not prone to corrosion, but it may not occur in specific usage environments. Titanium materials can also exhibit corrosion phenomena in inappropriate environments or under operating conditions. Next, based on my own experience, I will provide you with a detailed explanation of the corrosion phenomena of titanium equipment.

1. Crevice corrosion

At the gaps or shortcomings of metal components, local corrosion occurs due to the stagnant flow of electrolytes forming electrochemical batteries. In neutral and acidic solutions, the probability of touch corrosion occurring at the gaps of titanium alloys is much higher than that in alkaline solutions. Touch corrosion does not occur throughout the entire gap surface, but ultimately leads to local perforation damage.

2. Pitting phenomenon

Titanium has no pitting corrosion phenomenon in most salt solutions, and it often occurs in non aqueous solutions and high concentration chloride solutions. Halogen ions in the solution corrode the passivation film on the surface of titanium and diffuse into the interior of titanium, causing pitting corrosion. The pitting pore size is smaller than its depth. Some organic media can also cause pitting corrosion with titanium alloys in halogen solutions. Pitting corrosion of titanium alloys in halogen solutions generally occurs in high concentration and high temperature environments. In addition, pitting corrosion in sulfides and chlorides requires specific conditions and is limited.

3. Hydrogen embrittlement

Hydrogen embrittlement (HE), also known as hydrogen induced cracking or hydrogen damage, is one of the causes of early damage and failure of titanium alloys. When it comes to the passivation film on the surface of titanium and its titanium alloys, it has high strength. The sensitivity of hydrogen embrittlement increases with the increase of strength, so the passivation film is very sensitive to hydrogen embrittlement.

4. Touch corrosion

The passivation oxide film on the surface of titanium promotes the shift of titanium potential to a positive potential, improving the acid resistance and corrosion resistance of titanium materials in aqueous media. Due to the high potential on the surface of titanium alloy, it is inevitable to form an electrochemical circuit with other metals it touches, resulting in touch corrosion. Titanium alloys are prone to touch corrosion in the following two types of media: the first type is tap water, salt solution, seawater, atmosphere, HNO3, acetic acid, etc. The stable electrode potentials of Cd, Zn, Al in this solution are more negative than those of Ti, and the rate of anodic corrosion increases by 6-60 times. The second type is H2SO4, HCl, etc. Ti may be in a passive or activated state in these solutions, and the common type of touch corrosion process is the first type of solution corrosion. Generally, anodizing treatment is used to form a modified layer on the surface of the substrate, which hinders touch corrosion.

The above four types are some analysis of corrosion phenomena in titanium equipment based on my own experience, mainly the above four parts, hoping to be helpful to everyone.