HTHA per API RP 941, Nelson curve, hydrogen + temperature exposure, advanced wave UT detection. Catalogued by API 571 as a major damage mechanism affecting fixed equipment in refining and petrochem. This guide walks through mechanism, susceptibility, detection, and prevention.
\nHigh-temperature hydrogen attack (HTHA) occurs when carbon and low-alloy steels are exposed to hydrogen at high temperature and partial pressure. Hydrogen diffuses into the steel and reacts with carbides to form methane, causing decarburization and internal fissuring that can lead to cracking. API RP 941 provides the Nelson curves used to select materials and assess susceptibility; carbon steel is now assessed with particular caution after industry failures below the former curves. Reference: API RP 571 (3rd ed.) paragraph 3.36 and API RP 941.
\nTechnique selection should follow the damage mechanism, with procedures approved under the employer's written practice.
\nOwners that run risk-based inspection (API RP 580/581) use damage-mechanism susceptibility and measured inspection results to set inspection priorities and intervals, and damage beyond code acceptance may be referred for an engineering fitness-for-service assessment (API 579-1/ASME FFS-1). Both are owner and engineering responsibilities; Atlantis NDT does not provide RBI or FFS services. The Atlantis Digital Twin platform can display the underlying inspection data on a 3D model.
\nA: Advanced ultrasonic techniques performed by specially qualified teams: TFM/FMC, PAUT, TOFD and backscatter-based methods, applied as industry practice (API is developing guidance on HTHA inspection; check publication status); in-situ replication metallography where accessible.
\nA: API RP 571 (3rd ed.) paragraph 3.36 and API RP 941. API RP 571 describes the mechanism, critical factors, affected equipment and inspection and monitoring options.
\nA: The owner's authorized inspector under API 510, 570 or 653, or the owner's RBI assessment where one is used. Atlantis NDT does not provide RBI services.
\nA: With ASNT Level III consulting on NDE procedures and technique selection, ASNT SNT-TC-1A training for the technicians who perform the examinations, and inspection software (Atlantis ERP and the Digital Twin platform) that holds the inspection records.
\nRecommended practices and guides inform an inspection programme; binding requirements come from the in-service codes (API 510, API 570, API 653), the construction codes and the regulations that apply to the asset. NDE personnel are qualified under the employer's written practice (commonly ASNT SNT-TC-1A, ANSI/ASNT CP-189 or ISO 9712), and NDE procedures are approved by the employer's NDT Level III. Acceptance of indications follows the governing code; damage beyond its rules may be referred for an engineering fitness-for-service assessment (API 579-1/ASME FFS-1), which Atlantis NDT does not perform. Keep procedure revisions, calibration records and personnel certifications traceable; Atlantis ERP can hold these records.
\n\nAPI RP 571 (3rd edition, 2020) catalogues the damage mechanisms affecting fixed equipment in refining; its numbering changed from earlier editions, so cite the edition you use. Related mechanisms to screen alongside this one include sulfidation, naphthenic acid corrosion, high-temperature hydrogen attack, wet H2S damage, amine and chloride SCC, CUI and MIC.
\nUse the edition required by the contract, governing requirements and applicable jurisdiction. Record that edition in the procedure and evaluate changes before adopting a later publication.
\nPAUT, TOFD and conventional UT have different capabilities and coverage limits. Select the arrangement for the expected flaw, material, geometry and access, and demonstrate the required performance under the approved procedure.
\nA: 4-20 weeks depending on team size + scope. SMB: 4 weeks. Mid-size: 8-12 weeks. Enterprise multi-region: 12-20 weeks. Atlantis NDT delivers phased rollout with clear milestone gates.
\nA: No — pricing varies by region, scope, delivery model, and team size. Atlantis NDT is positioned as affordable, accessible, and fully customizable. Free 30-min consultation + tailored quote.
\nA: Atlantis ERP has an open REST API, so it connects to SAP, Maximo, NetSuite or any other system that accepts API connections; each integration is scoped with you during implementation. Free integration scoping consultation.
\nA: Request a free 30-min consultation at /contact. We reply within one business day. We scope your asset class + damage mechanisms + code requirements + delivery model preference + integration needs in a single call.
\nAtlantis NDT — led by Anoop Rayavarapu (ASNT NDT Level III in UT, RT, MT, PT and VT). Free consultation. request a free consultation. Pricing varies by region and scope.
","order":0,"createdAt":"2026-06-24","updatedAt":"2026-10-18","quickAnswer":{"question":"What is High-Temperature Hydrogen Attack (HTHA) 2026 and how do I detect it?","answer":"High-temperature hydrogen attack (HTHA) occurs when carbon and low-alloy steels are exposed to hydrogen at high temperature and partial pressure. Hydrogen diffuses into the steel and reacts with carbides to form methane, causing decarburization and internal fissuring that can lead to cracking. Informational guide by an ASNT NDT Level III; RBI and FFS decisions stay with the owner.","bullets":["Hydrogen partial pressure and temperature relative to the API RP 941 curves","Detection: Advanced ultrasonic techniques performed by specially qualified teams: TFM/FMC, PAUT, TOFD and backscatter-based methods, applied as industry practice (API is developing guidance on HTHA inspection; check publication status)","Mitigation: Material selection per API RP 941 with appropriate margin"]}}