What is acid embrittlement (or hydrogen embrittlement), and how does it occur?

The so-called acid embrittlement of steel pipes refers to the phenomenon where the mechanical strength of steel pipes decreases and the steel becomes brittle after pickling. The defect of acid embrittlement in steel pipes arises due to the generation of hydrogen atoms during the pickling process. Some of these hydrogen atoms diffuse into the α-iron lattice spaces within the steel pipe matrix. Due to their volume expansion, stress is generated inside the steel pipe matrix, which weakens the internal bonding force of the matrix, causing the steel pipe matrix to become brittle and subsequently reducing its mechanical strength.