Hydrogen-Induced Cracking (HIC)

Hydrogen-induced cracking is a stepwise internal cracking in carbon and low-alloy steel pipelines and vessels exposed to wet H2S service, in which atomic hydrogen accumulates at inclusions and recombines, generating high internal pressure that causes blister-like cracks.

Definition

HIC is described in API 571 as a sour-service damage mechanism. HIC steel is qualified per NACE TM0284. HIC is detected by UT and identified by its characteristic step-like crack pattern oriented parallel to the rolling plane.

How this damage forms

Atomic hydrogen entering the steel — from corrosion in wet sour service, from cathodic protection, or from welding — recombines into molecular hydrogen at internal discontinuities such as elongated inclusions. Molecular hydrogen cannot diffuse back out, so pressure builds and drives planar cracks parallel to the plate surface, which may then step between planes.

How it is detected

Ultrasonic examination is the practical method: straight-beam scanning finds the mid-wall planar separations, and time-of-flight or phased array characterises the stepwise linking. It is generally not surface-breaking, so surface methods are of little use.

Why it gets missed

Visual and surface methods find nothing until the damage reaches a surface or causes blistering. Radiography is poor at it because the cracks are tight and lie across the beam in most practical geometries.

What causes it, and what prevents it

Susceptibility is governed by steel cleanliness, and HIC-resistant steels are specified for wet sour service on that basis. Where existing equipment is affected, monitoring the extent over time matters more than a single detection.

Codes that govern assessment

NACE/AMPP TM0284 for HIC resistance testing of plate; NACE MR0175 / ISO 15156 for materials in H2S service; API 571 describes the damage mechanism and where it appears.

The common reporting error

Treating it as ordinary corrosion. Wall thickness readings can be entirely acceptable while the plate is internally laminated by hydrogen damage — thickness is the wrong measurement for this mechanism.

Where Hydrogen-Induced Cracking fits in an inspection programme

A term is only useful when it connects to a decision. Hydrogen-Induced Cracking appears in written procedures, in technique sheets, and in the records an owner or accreditation body reviews afterwards — which means the way it is defined in your documentation has to match the way it is applied on site. Where the two drift apart, audits find it. Atlantis writes and reviews procedures against the governing codes, trains inspection personnel to apply them, and builds the record-keeping that makes the evidence retrievable years later. Procedure development and code consulting · NDT training and certification · Ask us about your programme.

Related terms

  • Stress Corrosion Cracking (SCC) — Stress corrosion cracking is the brittle cracking of a normally ductile material under the combined action of tensile stress and a specific corrosive environment, propagating along grain boundaries (intergranular) or through grains (transgranular).
  • Sulfide Stress Cracking (SSC) — Sulfide stress cracking is hydrogen-assisted brittle cracking of high-strength steels in wet H2S environments, principally affecting hardened steels above approximately 22 HRC such as fasteners, valve internals, and high-strength pipe.
  • Hydrogen Embrittlement — Hydrogen embrittlement is the loss of ductility and load-bearing capacity of a metal caused by the absorption of atomic hydrogen, typically affecting high-strength steels, titanium alloys, and some nickel alloys.
  • API 571 Damage Mechanisms — API 571 is the recommended practice describing damage mechanisms affecting refining and petrochemical equipment, including general/uniform corrosion, localized corrosion, environmentally assisted cracking, metallurgical degradation, mechanical damage, and high

Further reading

hydrogen assisted cracking in welds detection

More defect terms

Crack · Lack of Fusion · Lack of Penetration · Slag Inclusion · Porosity · Undercut · Overlap · Burn-Through · Weld Spatter · Lamination

Where this comes up in practice

Terms like this one appear in three places that matter commercially: the written practice that governs how your personnel are qualified, the procedures and technique sheets that define how an examination is actually performed, and the evidence an auditor or client asks for when they want to know why an inspection was accepted. Getting the terminology right is the easy part; being able to produce the qualification record, the calibration traceability and the procedure revision that applied on the day of the inspection is the part that decides audits.

Atlantis NDT provides NDT training and certification against ASNT SNT-TC-1A and ISO 9712, ASNT Level III consulting for written practices and procedure approval, inspection management software that holds qualification, calibration and procedure-revision evidence in recoverable form, and an asset integrity platform that binds inspection results to the asset they describe. Browse the full NDT glossary or ask a Level III directly.