On hydrogen embrittlement of titanium materials

Does the medium contain chloride ions? Corrosion occurs easily at temperatures above 110 degrees. I’m not very familiar with hydrogen embrittlement; please advise, experts!

The description of the pitting corrosion mechanism is excerpted as follows: 5.1.3.2 Hydrogenation of titanium 5.1.3.2.1 Description of damage Hydrogenation of titanium is a metallurgical phenomenon in which hydrogen diffuses into titanium and undergoes a chemical reaction to form brittle hydride phases. This can lead to a complete loss of ductility, without any obvious signs of corrosion or thickness loss. 5.1.3.2.2 Affected materials: Titanium alloys. 5.1.3.2.3 Key factors The key factors include metal temperature, solution chemistry, and alloy composition. This is a phenomenon that occurs in specific environments with high hydrogen sulfide levels at temperatures above 165(74)°F/°C, and at pH values below 3, above 8, or at neutral pH. Electrochemical contact between titanium and more reactive materials such as carbon steel and 300-series stainless steels can lead to damage. However, hydrogenation can also occur in the absence of electrocoupling. Cracking occurs over a period of time, as hydrogen is absorbed by the components and reacts to form brittle hydride phases. The degree and extent of hydrogenation will continue to increase until the result is a complete loss of ductility. Hydrogenation also occurred in certain chemical environments due to iron accidentally being embedded in the titanium surface during manufacturing, which caused iron corrosion. Corrosion of iron and iron sulfide scales in the process stream brought in from upstream units can cause hydrogen absorption. The solubility of hydrogen in pure titanium and α-β titanium alloys is limited (50–300 ppm); once this limit is exceeded, hydrides are formed. On the other hand, β-alloys can tolerate a higher hydrogen content, up to 2000 ppm. 5.1.3.2.4 Affected units or equipment: a) Damage mainly occurs in the amine unit’s acid water stripping tower and overhead condenser, heat exchanger tubes and pipes, as well as other titanium equipment operating at temperatures above 165(74)°F. b) Hydrogenation can also occur in a hydrogen atmosphere at temperatures above 350(177)°F°C, especially in the absence of moisture or oxygen. c) Protection potential

Titanium is highly reactive and readily reacts with O2, H2, N2, and C at high temperatures. Iron acts as a conductor for hydrogen; its presence leads to the accumulation of hydrogen (when iron and titanium are in contact with a corrosive medium, an electrochemical corrosion reaction occurs). If the amount of hydrogen inhaled is too high, the microstructure of titanium changes from the α phase to the γ phase, and the γ phase is a hard and brittle phase – this is what is known as hydrogen embrittlement. It is worth noting that titanium corrosion is difficult to detect within 1–2 years. After the container is manufactured, it is essential to carry out anodization, pickling, and passivation on the titanium surface; moreover, checking for iron ion contamination prior to this process is also very important. Also, I’ve never seen a hydrogenation reactor made of titanium composite sheets; if the acetic acid content is indeed high and the temperature reaches 280 degrees, then Hastelloy could be considered as an alternative, haha. If the acetic acid content is very low, I think E308L and E309L are also good choices!

Reply to 4# happyhefei: It’s clear you’re an expert. Let’s keep communicating – for PTA hydrogenation, titanium materials aren’t necessary for acetic acid content; 304L and 316L will suffice. Oxidation reactors do require titanium material.

Let’s start with PTA: since it contains not only acetic acid but also Br ions, it is impossible in industrial production to completely eliminate the presence of Cl. As a result, there is not only corrosion caused by high-temperature acetic acid but also pitting corrosion resulting from halogens. This is quite severe – even a tiny hole the size of a pinhead can lead to corrosion through. Therefore, in some applications, austenitic stainless steel is not suitable. Secondly, regarding hydrogen embrittlement, generally speaking, titanium materials themselves are not very prone to corrosion during use. However, when they form a corrosion cell together with other materials, acting as the negative electrode, titanium is susceptible to hydrogen embrittlement, as is the case with components such as Johnson tubes. Of course, there are various theories regarding the corrosion of PTA at present; the above is merely my own understanding.

Reply to 5# realben: Thanks for the compliment! I just happen to have a basic understanding of this concept

Hydrogen embrittlement occurs during the processing and welding of equipment due to the absorption of hydrogen, or as a result of hydrogen absorption under high temperature and pressure conditions; it generally does not occur at normal temperatures