Hydrogen Induced Cracking Test Hydrogen-induced cracking is a hidden failure mode. It builds silently inside carbon steel pipelines, pressure vessels, and fittings operating in sour (H2S) service, often with no external warning before a rupture. Corrosion-related damage remains a leading contributor to pipeline incidents, and the oil and gas production industry absorbs an estimated $1.372 billion in annual corrosion-related costs, according to an AMPP corrosion cost reference.

HIC testing under NACE TM0284 is how mills and end users verify a steel's resistance before it enters critical service. Get the applicability wrong, and you either risk a field failure or waste money testing material that never needed it.

This article breaks down what the test actually measures, how the procedure works, and where specifications commonly overreach.

TL;DR

  • HIC testing measures steel’s resistance to stepwise cracking in wet H2S service
  • Governed by NACE TM0284: 96-hour exposure, then metallographic sectioning
  • Applies mainly to carbon steel plate and rolled/welded pipe
  • Not used for castings, stainless, nickel alloys, or duplex steels
  • Prevention starts upstream with clean steel, inclusion control, and proper heat treatment
  • A traceable supplier helps you meet HIC specs without failed lots or over-ordering

What Is a Hydrogen Induced Cracking Test?

Hydrogen induced cracking (HIC) is stepwise internal cracking in steel. Atomic hydrogen enters the steel from wet H2S exposure, combines into molecular hydrogen at inclusions or discontinuities, and builds pressure until blisters link into cracks running parallel to the rolling direction.

HIC differs from sulfide stress cracking (SSC) and stress corrosion cracking, though all three sit under the wet H2S damage family. TM0284 evaluates HIC only—not SSC, SOHIC, pitting, or general mass-loss corrosion.

The test quantifies three ratios after controlled exposure:

  • CSR (crack sensitivity ratio) — total crack area relative to specimen cross-section
  • CLR (crack length ratio) — cumulative crack length relative to section width
  • CTR (crack thickness ratio) — cumulative crack depth relative to section thickness

HIC crack sensitivity ratio CLR CTR CSR measurement diagram

Why Material Form Matters

HIC testing is almost exclusively relevant to plate and rolled/welded pipe made from plate. Their planar grain structure and elongated inclusions create the pathways cracks need to link up.

Here's where a lot of specifications go wrong: HIC does not occur in castings, and it's rarely applicable to forgings. ISO 15156-2 notes that conventional forgings with sulfur content below 0.025% are not normally considered sensitive to HIC or SOHIC. Austenitic and duplex stainless steels, nickel alloys, and copper alloys are essentially immune to the mechanism, according to ISO 15156-2:2020.

Why HIC Testing Matters in Materials Selection and QC

Extending HIC requirements from a piping spec to valves or forgings drives up cost and schedule without adding value. If the material isn't susceptible, testing it just burns lab time and money.

Applied to susceptible materials, HIC testing:

  • Prevents catastrophic in-service ruptures in sour oil and gas, refining, and pipeline applications
  • Provides objective, standardized CSR/CLR/CTR data for procurement and engineering sign-off
  • Supports compliance with NACE/ISO 15156 and project QA requirements
  • Reduces risk of field failures and unplanned shutdowns
  • Helps buyers avoid over-specifying tests on materials (castings, stainless, forgings) where HIC doesn't apply

That last point is where budgets quietly disappear. Know the cracking mechanism before you write the RFQ, and you spare the lab—and the project—unnecessary work.

How the HIC Test Works – Step by Step (NACE TM0284)

The published procedure follows a consistent sequence. Common mistakes include improper specimen orientation during sectioning and skipping proper metallographic preparation before examination.

Work through the six steps below in order to keep orientation, exposure, and crack measurement aligned with NACE TM0284.

Step 1 – Specimen Preparation and Sectioning Specimens are cut to defined size and orientation from plate or pipe per the standard. Get the sectioning orientation wrong, and the crack measurements won't reflect real susceptibility.

Step 2 – Immersion in Test Solution Specimens go into either Solution A (sodium chloride and acetic acid, saturated with H2S) or Solution B (synthetic seawater saturated with H2S), typically at ambient temperature and pressure.

Step 3 – 96-Hour Exposure Period This duration is fixed. According to laboratory descriptions from Element's HIC testing service, the standard exposure runs 96 hours at roughly 1 bar — simulating sustained sour service conditions. Extended fitness-for-purpose testing can run longer, but that's a separate application test, not the standard qualification.

Step 4 – Post-Exposure Sectioning and Polishing Specimens are re-sectioned, metallographically polished, and etched to reveal cracks under magnification.

Step 5 – Microscopic Examination Technicians measure every visible crack for length and thickness at magnification and record the values used to calculate CSR, CLR, and CTR.

Step 6 – Calculate and Report CSR, CLR, CTR Here's a detail that trips up a lot of procurement teams: TM0284 sets the test method, not the pass/fail limits. Acceptance criteria come from the purchaser's specification or a referenced standard like ISO 15156-2, which lists Table B.3 benchmarks (CLR ≤15%, CTR ≤5%, CSR ≤2%) for unstressed flat-rolled steel under stated conditions.

6-step NACE TM0284 hydrogen induced cracking test procedure flow

HIC Testing in Practice – A Simplified Example

Picture a fabricator receiving an order for carbon steel pipe fittings destined for sour gas service. The customer's spec invokes HIC testing across the entire piping package.

Before running anything, the fabricator should check:

  1. Is the fitting plate-based? If it's forged from low-sulfur material, HIC testing may not apply at all.
  2. Did the spec extend a piping requirement too broadly? Many "piping-grouped" component lists lump in valves and forgings that are exempt from TM0284 by mechanism, not just by convention.
  3. What does the purchaser actually need? Sometimes a spec writer copies HIC language from a plate/pipe section without checking whether it fits a forged fitting.

A fabricator who catches this early flags the applicability question to the purchaser before ordering lab work, avoiding unnecessary cost and schedule delay.

Once testing is confirmed and completed, the documented CSR/CLR/CTR results fold into the material certification package for full traceability.

Carbon steel pipe fittings inspection for sour gas service applications

Sourcing HIC-Compliant Alloy Steel — How Aero-Vac Alloys & Forge Can Help

Navigating whether HIC testing applies to your material form isn't always straightforward, and getting it wrong costs real money either way. Aero-Vac Alloys & Forge, an ISO 9001:2008 and AS9100-certified manufacturing distributor, helps you confirm testing scope before you place an order.

What that looks like in practice:

  • Fast procurement of exact specifications, whether you need plate, bar, tube, or forgings
  • Live technical support to talk through testing scope before you commit to an order
  • Full material traceability and documentation for your certification package
  • Just-in-time delivery for custom cuts and sizes, so applicability questions don't stall your schedule

Aero-Vac has served oil and gas, power generation, and industrial customers who need documented, certified alloy steel for demanding service environments. Those buyers can't afford ambiguity about whether a spec requirement applies to their material form.

If HIC testing scope is unclear on your order, raise it with a technical contact before lab work starts, not after.

Conclusion

HIC testing gives engineers and procurement teams objective, standardized evidence of a steel's resistance to hydrogen-driven cracking in sour environments. But that value only holds up when the test gets applied to the right material forms — plate and rolled pipe, not castings, forgings, or stainless alloys where the mechanism doesn't apply.

Review specifications carefully with a knowledgeable supplier before ordering HIC testing. Getting material selection right upstream reduces both cost and risk downstream.

Frequently Asked Questions

What is hydrogen-induced cracking?

Hydrogen-induced cracking is internal stepwise cracking that forms when atomic hydrogen diffuses into steel and recombines at traps such as inclusions. Pressure builds at those sites and cracks the metal, especially in wet H₂S (sour) service.

What is the procedure for hydrogen-induced cracking testing?

NACE TM0284 calls for specimen sectioning, 96-hour immersion in Solution A or B, then post-test sectioning and metallographic examination. Results are reported as CSR, CLR, and CTR.

Which metals are most resistant to hydrogen embrittlement?

Austenitic and duplex stainless steels, nickel alloys, and copper alloys are essentially immune to HIC. High-strength carbon and low-alloy steels are the most susceptible.

Does HIC testing apply to castings or forgings?

HIC does not occur in castings and is rarely applicable to forgings. Current standards focus mainly on plate, pipe, and certain flanges.

How long does an HIC test take to complete?

The fixed exposure period is 96 hours, plus additional time for specimen preparation, post-test sectioning, and metallographic evaluation.

Does NACE TM0284 include pass/fail acceptance criteria?

No. TM0284 defines the test methodology only. Acceptance criteria, such as maximum CSR/CLR/CTR values, come from the purchaser's specification or a referenced standard like ISO 15156-2.