Hydrogen blisters are the result of HIC, and, per API 579 paragraph 2.5.3.2, the following is stated:

The Remaining Life Cannot be Established With Reasonable Certainty - Examples may be a stress corrosion cracking mechanism where there is no reliable crack growth rate available or hydrogen blistering where a future damage rate cannot be estimated. In this case remediation methods should be employed, such as application of a lining or coating to isolate the environment, drilling of blisters, or monitoring. Inspection would then be limited to assuring remediation method acceptability, such as lining or coating integrity.

Note that coatings are not an acceptable mitigation method for avoidance of stress corrosion cracking, but it may be an acceptable method to minimize HIC damage.

Thus hydrogen blisters, or HIC damage, cannot be analyzed. Blisters are formed when the hydrogen proton, H ⁺, diffuses into the steel. The temperature (between 32 F to 130 F) allows the hydrogen proton to diffuse through the steel at a higher rate. The diffusion of the proton stops when two hydrogen protons, H ⁺, recombine into the hydrogen molecule. The H ₂ molecule is too large to diffuse through the lattice and becomes trapped in the steel. As the temperature increases, the metal lattice opens up more, and the H ⁺ proton diffuses through the metal wall into the atmosphere. Hydrogen panels on the outside surface of the pipe are used to detect hydrogen diffusion.

HIC damage occurs between 32 F and 130 F.