Hydrogen embrittlement is one of the few mechanisms where recognising the damage is straightforward and locating its origin is the entire dispute. The fracture looks much the same whether the hydrogen entered on a plating line, from a welding consumable, from an overprotected cathodic protection system, or from an H2S-bearing production fluid. Each origin sits with a different party, under a different specification, and leaves a different documentary trail. Separating them is answered as much by records as by microscopy.
The first fork: internal or environmental
The governing distinction is whether the hydrogen was already in the part when it entered service or arrived afterwards. Internal, or processing, embrittlement describes hydrogen absorbed during manufacture: acid pickling, electroplating, electroless coating, welding. The part is charged before it is ever loaded, and can crack under nothing more than the preload applied at assembly. Environmental embrittlement describes hydrogen generated at the surface in service and absorbed while the part is held under sustained tension.
That fork sets the direction of everything after it. 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.
Plating and pickling
Electroplating is the best documented source 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. That is not a defect in itself but an expected consequence the finishing specification exists to manage, through bath chemistry, current density and a post-plating bake.
The evidence 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.
Welding
Welding introduces hydrogen from moisture: in an electrode coating or flux, on the joint surface, in humid shop air. It 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 assembly. Cracking often appears hours after the weld has cooled, which is why it is traditionally called delayed or cold cracking. The records that matter are the procedure and its qualification, consumable classification and storage, preheat, and any post-weld heat treatment.
Cathodic protection pushed too far
Cathodic protection drives a structure to a potential at which corrosion does not proceed. Push it further negative than the criterion requires and the surplus current goes into evolving hydrogen at the steel surface. On ordinary structural grades that 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 is an operations record: survey potentials, rectifier settings, anode history, and whether the criteria applied were the ones the material selection assumed.
Sour service and a prescriptive standard
Where hydrogen sulphide is present in a produced or process fluid, corrosion generates atomic hydrogen at the surface and the sulphide interferes with recombination, so more of it enters the metal. In high-strength steel under load the result is sulphide stress cracking. This is the one 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. The question becomes whether the material sat within those limits for the conditions actually present, and whether anyone recorded those conditions.
Hydrogen damage in lower-strength steel
Not every hydrogen problem is a high-strength problem. 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. It points at steel cleanliness at the mill rather than at a finishing process.
What each source leaves behind
Sources are separable by evidence even where morphology is not. A plating origin leaves a coating to cross-section and a finishing record to audit. A welding origin leaves a crack anchored to a specific thermal zone and a procedure to compare against what the bench actually did. Cathodic charging leaves survey data. Sour service leaves corrosion products and a fluid analysis that either exists or does not. None is conclusive alone, but together with crack geometry, strength level and the timeline they usually narrow the field.
Why the source decides the parties
The practical consequence is that the source determines exposure. 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.
Both can be true at once: a component marginal on hardness for its environment that also received an inadequate bake has two contributors, and apportionment rests on evidence no single party controls.
Where these opinions are challenged
Predictably: 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; that protection potentials were averaged across a system rather than read at the failure location.
Work that treats each candidate 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.