Wet fluorescent magnetic particle testing (WFMT) is the usual first technique for finding surface-breaking cracks on the internal weld surfaces of carbon-steel vessels in wet H2S service. This guide explains why, what the industry guidance says, and what a WFMT scope has to include to produce data an owner can act on.
\nA note on the standard number: NACE SP0288 is not the wet H2S document. The guidance most refiners cite for detecting, repairing and mitigating cracking in existing equipment in wet H2S environments is NACE SP0296 (now published under AMPP). Damage mechanisms themselves are described in API RP 571.
\nWet H2S environments can produce several related forms of cracking in carbon steel: sulfide stress cracking (SSC) at hard welds and heat-affected zones, hydrogen blistering, hydrogen-induced cracking (HIC) along laminar inclusions, and stress-oriented HIC (SOHIC) near welds. SSC and the surface-breaking end of SOHIC are open to the inside surface, which is where WFMT is effective. HIC and blistering are largely sub-surface and need ultrasonic methods.
\nThe technician performing WFMT should be qualified in magnetic particle testing under the employer's written practice — commonly ASNT SNT-TC-1A — and the procedure should be approved by the employer's NDT Level III. Where the construction or in-service code references ASME Section V, Article 7 sets the magnetic particle requirements the procedure must meet.
\nWFMT results feed the owner's inspection programme under API 510 for pressure vessels: repair decisions, follow-up inspection, and, where the owner runs one, the risk-based inspection plan. Acceptance and any engineering assessment of cracks found are the owner's responsibility; Atlantis NDT does not perform RBI or fitness-for-service assessments.
\nAtlantis NDT carries out WFMT and follow-up UT on wet H2S equipment and provides ASNT NDT Level III review of the procedures behind them. For the method-level detail, see WFMT and ACFM crack detection in sour service. Affordable, accessible and fully customizable — request an inspection quote.
\nA: No. Wet H2S cracking in existing refinery equipment is addressed by NACE SP0296 (AMPP). API RP 571 describes the damage mechanisms.
\nA: 4-20 weeks depending on team size + scope. SMB: 4 weeks. Mid-size: 8-12 weeks. Enterprise multi-region: 12-20 weeks.
\nA: Only where HIC or SOHIC has broken through to the surface. Most HIC is sub-surface and is found with ultrasonic techniques.
\nAtlantis NDT — Anoop Rayavarapu (ASNT NDT Level III). Request a consultation.
","order":0,"createdAt":"2026-10-07","updatedAt":"2026-10-07","quickAnswer":{"question":"What is WFMT in wet H2S service?","answer":"Wet fluorescent magnetic particle testing (WFMT) is the usual first technique for surface-breaking wet H2S cracks on internal weld surfaces of carbon-steel vessels. The relevant industry guidance is NACE SP0296, not SP0288. Atlantis NDT carries out WFMT and follow-up UT; quote on request.","bullets":["Wet H2S cracking guidance: NACE SP0296; mechanisms: API RP 571","ASNT NDT Level III led","Free consultation + tailored quote"]}}