Hydrogen pores may be a costly defect, as they are usually only exposed after machining and can occur in both gray and ductile iron, often appearing in a round spherical shape below the surface of the casting. Due to the fact that the inner wall of the pores is covered by graphite, the inner wall of the pores is black and shiny during inspection. The precipitation of graphite on the inner wall of this pore leads to the depletion of graphite on the outer wall of the pore.

There are several factors that can cause individual hydrogen or flake hydrogen pinholes, mainly due to the reaction of Al or titanium in molten iron with water vapor from molding sand, damp tools, or damp refractory materials. Other sources of moisture may be moist air or contaminated furnace materials, rust, and the accumulation of dead clay in the sand can also increase the moisture content of the sand. Old cores may also be used, as these cores absorb moisture from the humid atmosphere.

Hydrogen limits the Al content in molten iron to below 200ppm and greatly reduces the Ti content, prevents the occurrence of hydrogen pores, and reduces the probability of their occurrence. Careful control of scrap steel, avoiding the use of vermicular graphite cast iron as a return material (if produced with Ti), and removing glazed scrap steel can help reduce the generation of hydrogen pores. Some pig irons also contain a high amount of Ti.

Measures should be taken to dry the refractory mud and coating tools used, and sufficient new sand should be added to the sand treatment system to prevent the accumulation of dead clay in the molding sand. The moisture content in the molding sand is generally less than 3%, and before pouring, the core and coating are dried and matured.