38. What is acid embrittlement (or hydrogen embrittlement)? How does it occur?

The term "acid embrittlement" in steel pipes refers to the reduction in mechanical strength and increased brittleness that occurs after acid washing. This defect arises when hydrogen atoms generated during the acid washing process diffuse into the α-iron lattice spaces of the steel pipe matrix. The resulting volume expansion creates internal stress within the matrix, weakening its internal bonding strength and leading to brittleness, which ultimately reduces the mechanical strength of the steel pipe.