WRC 573-2018 PDF

Full title and description

WRC 573-2018 — Effects of Heat Treatment and Chemical Composition on High Temperature Hydrogen Attack Resistance of C-1/2 Mo Steels. This Welding Research Council bulletin reports an experimental autoclave study that evaluated how heat treatment condition and elemental composition (notably Mo/C ratio) influence susceptibility to high temperature hydrogen attack (HTHA) in carbon‑½ molybdenum steels.

Abstract

High temperature hydrogen attack (HTHA) is a metallurgical degradation mechanism that affects carbon and low‑alloy steels in hot hydrogen environments. WRC 573 documents autoclave "HTHA box" experiments on two heats of C‑½Mo steel (in normalized & tempered and annealed & tempered conditions) exposed at severe temperature and hydrogen pressure to compare HTHA resistance, and presents metallography, methane profiling, and cryo‑fractography to characterize damage and mechanisms. The bulletin identifies superior HTHA resistance for normalized & tempered microstructures and for materials with higher Mo/C ratios.

General information

• Status: Current / Active.
• Publication date: 2018 (published Jan 1, 2018 in publisher listings).
• Publisher: Welding Research Council, Inc. (WRC).
• ICS / categories: Metallurgy / Corrosion / Steels (materials engineering; high‑temperature hydrogen damage).
• Edition / version: 2018 edition (WRC Bulletin 573).
• Number of pages: 62 pages.

Scope

This bulletin describes laboratory HTHA exposure experiments using purpose‑built autoclave "HTHA boxes" that create a through‑wall hydrogen pressure differential representative of piping and vessel service. It compares the effect of two heat‑treatment conditions (normalized & tempered vs. annealed & tempered), examines two heats differing in Mo/C ratio, and documents damage assessment methods (methane content profiling, optical and electron metallography, and cryo‑fractography). The work is intended to inform material selection, heat‑treatment practice, and inspection planning for equipment operating in high‑temperature hydrogen service.

Key topics and requirements

• High Temperature Hydrogen Attack (HTHA): mechanisms, conditions that promote attack, and inspection relevance.
• Experimental method: autoclave "HTHA box" exposures (900°F / 900 psi in the study) to accelerate damage and evaluate through‑wall methane formation and fissuring.
• Heat treatment effects: normalized & tempered microstructures showed greater resistance to HTHA than annealed & tempered in the tested heats.
• Chemical composition influence: higher Mo/C ratio reduced carbon activity and improved HTHA resistance (thermodynamic stability of carbides).
• Damage characterization techniques: methane profiling vs. distance from exposed surface, optical/SEM metallography, and cryo‑cracking fractography to reveal intergranular HTHA morphology.
• Implications for practice: material specification, heat‑treatment selection, weld/post‑weld heat treatment, and targeted NDT/inspection methods for HTHA‑susceptible equipment.

Typical use and users

Primary users are materials and corrosion engineers, welding and metallurgical specialists, fitness‑for‑service (FFS) engineers, plant inspection and integrity teams, and technical staff in refinery, petrochemical, and hydrogen‑service plants who must assess or mitigate HTHA risk in pressure vessels, reactors, and piping. The bulletin is used to guide material selection, heat‑treatment decisions, inspection planning, and root‑cause analysis of HTHA incidents.

Related standards

Relevant related documents and guidance include other WRC bulletins on HTHA and hydrogen‑assisted damage (for example WRC 574:2019 compendium on HTHA damage), API RP 941 (steels for hydrogen service), ASME inspection and pressure‑equipment rules, and industry fitness‑for‑service and NDT standards addressing hydrogen damage detection and mitigation.

Keywords

HTHA, high temperature hydrogen attack, C‑1/2 Mo, Cr‑Mo steels, heat treatment, normalized and tempered, annealed and tempered, Mo/C ratio, autoclave HTHA box, methane profiling, metallography, cryo‑fractography, material selection, petrochemical, refinery, inspection, Welding Research Council.

FAQ

Q: What is this standard?

A: WRC 573‑2018 is a Welding Research Council technical bulletin reporting experimental research into how heat treatment and chemical composition affect resistance of C‑½Mo steels to high temperature hydrogen attack.

Q: What does it cover?

A: It covers autoclave exposure experiments designed to accelerate HTHA, measurement of methane penetration and damage, detailed metallography and fracture examination, and comparisons of microstructural and compositional factors (notably heat‑treatment condition and Mo/C ratio) that influence HTHA susceptibility.

Q: Who typically uses it?

A: Materials, corrosion and welding engineers, inspection and integrity teams in refineries and petrochemical plants, and researchers studying hydrogen damage mechanisms. It supports material selection, inspection planning, and FFS assessments.

Q: Is it current or superseded?

A: The 2018 WRC bulletin is listed as current by standards resellers and remains an active WRC publication; users should check with the Welding Research Council or authorized distributors for any later updates or related bulletins.

Q: Is it part of a series?

A: Yes — it is one of a sequence of WRC bulletins addressing hydrogen‑related damage and metallurgy; related WRC documents (for example WRC 574:2019) compile HTHA damage observations and complementary data.

Q: What are the key keywords?

A: High temperature hydrogen attack (HTHA), C‑½Mo, Mo/C ratio, heat treatment, normalized & tempered, annealed & tempered, methane profiling, metallography, cryo‑fractography, petrochemical/refinery integrity.