35. The internal and external factors affecting the pickling of steel pipes can be divided into:

1) The composition, structure, processing process, and surface condition of the steel pipe itself, as well as the composition, structure, thickness, and uniformity of the oxide scale on its surface.
2) The type, concentration, temperature, iron salt content, impurity composition, and operation methods (e.g., stirring the solution or oscillating the steel pipe) of the pickling solution used.