What is the difference between internal and environmental hydrogen embrittlement?
Internal hydrogen embrittlement, also called processing embrittlement, is caused by hydrogen absorbed during manufacture, while environmental hydrogen embrittlement is caused by hydrogen generated at the surface in service and absorbed while the part is held under sustained tension. Whether the hydrogen was already in the part when it entered service or arrived afterward is the governing distinction in tracing where the hydrogen in a hydrogen embrittlement failure came from.
Internal hydrogen is absorbed during acid pickling, electroplating, electroless coating and welding. A part with internal hydrogen is charged before it is ever loaded, and can crack under nothing more than the preload applied at assembly.
The fork between internal and environmental hydrogen sets the direction of everything after it in a hydrogen embrittlement investigation. Internal hydrogen points at the manufacturing chain. Environmental hydrogen points at operations, at corrosion protection design and process fluid, and at whether the material was ever qualified for the environment it ended up in.
Why is electroplating the best-documented source of hydrogen embrittlement?
Electroplating is the best-documented source of the hydrogen behind hydrogen embrittlement for a simple reason: hydrogen is evolved at the cathode, and the part being plated is the cathode. Electroless deposition and the acid pickling ahead of plating do the same by a different route.
Hydrogen uptake during plating and pickling is not a defect in itself but an expected consequence that the finishing specification exists to manage, through bath chemistry, current density and a post-plating bake.
The evidence of a plating or pickling source of hydrogen is documentary before it is metallurgical. ASTM B850 guides post-coating treatments intended to reduce embrittlement risk, and ASTM F519 provides the notched-specimen sustained-load test used to qualify a plating process.
How does welding introduce hydrogen into steel, and which records matter?
Welding introduces hydrogen from moisture in an electrode coating or flux, on the joint surface, or in humid shop air, and the records that matter when welding is a candidate source of hydrogen are the welding procedure and its qualification, the consumable classification and storage, the preheat, and any post-weld heat treatment. The hydrogen from welding dissolves in the weld pool and diffuses into the heat-affected zone, which in a hardenable steel may be the hardest and least tolerant region of the welded assembly.
Hydrogen cracking from welding often appears hours after the weld has cooled, which is why it is traditionally called delayed or cold cracking.
Can too much cathodic protection cause hydrogen embrittlement?
Too much cathodic protection can charge high-strength steel with hydrogen: cathodic protection pushed further negative than its criterion requires sends the surplus current into evolving hydrogen at the steel surface. Cathodic protection drives a structure to a potential at which corrosion does not proceed, and the hydrogen comes from going beyond that.
On ordinary structural grades, the hydrogen evolved by overprotective cathodic protection is tolerable. On high-strength steel, such as a subsea fastener or a prestressing component, it is a charging mechanism running continuously for the life of the asset.
The record of a cathodic protection source of hydrogen is an operations record: survey potentials, rectifier settings, anode history, and whether the cathodic protection criteria applied were the ones the material selection assumed.
How does sour service with hydrogen sulfide cause cracking in steel?
Where hydrogen sulfide is present in a produced or process fluid, corrosion generates atomic hydrogen at the steel surface and the sulfide interferes with recombination, so more of that hydrogen enters the metal; in high-strength steel under load, the result is sulfide stress cracking.
Sour service is the one hydrogen source with a prescriptive materials standard behind it: NACE MR0175 and ISO 15156 set out material selection, hardness limits and qualification for equipment in H2S-bearing service. In a sulfide stress cracking failure, the question becomes whether the material sat within the NACE MR0175 and ISO 15156 limits for the conditions actually present, and whether anyone recorded those conditions.
Does hydrogen damage only affect high-strength steel?
No: not every hydrogen problem is a high-strength problem, because in lower-strength plate and linepipe, absorbed hydrogen recombines into molecular gas at elongated inclusions or laminations, where the pressure opens internal blisters and steps between them. This is hydrogen-induced cracking, and it degrades the section with no external load applied at all.
Hydrogen-induced cracking in lower-strength plate and linepipe points at steel cleanliness at the mill rather than at a finishing process.
What evidence distinguishes one source of hydrogen embrittlement from another?
A plating source of hydrogen leaves a coating to cross-section and a finishing record to audit; a welding source leaves a crack anchored to a specific thermal zone and a welding procedure to compare against what the bench actually did; cathodic protection charging leaves survey data; and sour service leaves corrosion products and a fluid analysis that either exists or does not. Because each source of hydrogen in a hydrogen embrittlement failure leaves different evidence, the sources are separable by evidence even where fracture morphology is not.
None of these kinds of evidence is conclusive alone, but together with crack geometry, strength level and the timeline they usually narrow the field of candidate hydrogen sources.
Why does the source of the hydrogen decide which parties are exposed in a hydrogen embrittlement failure?
The source of the hydrogen decides which parties are exposed in a hydrogen embrittlement failure because each hydrogen source sits with a different party. Processing hydrogen implicates a chain that may include a mill, a heat treater, a plating subcontractor and an assembler. Service hydrogen implicates the owner’s material selection, the corrosion engineer, and the envelope the equipment was actually run in.
Processing hydrogen and service hydrogen can both be true at once: a component marginal on hardness for its environment that also received an inadequate bake has two contributors, and apportionment between them rests on evidence no single party controls.
How are opinions on the source of hydrogen in an embrittlement failure challenged?
Opinions on where the hydrogen in a hydrogen embrittlement failure came from are challenged on predictable grounds: that the source was inferred from fracture appearance rather than established; that the welding procedure was never compared against what was actually done at the bench; and that cathodic protection potentials were averaged across a system rather than read at the failure location.
Hydrogen embrittlement work that treats each candidate hydrogen source as a hypothesis with its own evidence, and states plainly what excluded the others, holds up better than work that names the most convenient party first.
This article is general technical orientation, not a failure analysis, an engineering opinion, or advice on any specific matter. Determining the cause of a particular incident requires hands-on examination by a credentialed expert.