Detection and characterization of chloride induced stress corrosion cracking on SS304 under thermal insulation using acoustic emission technique

• Published in: Engineering failure analysis 2025-02, Vol.168, p.109094, Article 109094
• Main Authors: Nuthalapati, Suresh, Kee, K.E., Che Ismail, Mokhtar B., Karuppanan, Saravanan, Hossain, T.M.
• Format: Article
• Language: English
• Subjects: Acoustic emission technique; Drip test; SS304; Stress corrosion cracking; Thermal insulation; U-bend
• ISSN: 1350-6307
• DOI: 10.1016/j.engfailanal.2024.109094

•ASTM C692 directed testing on U-bend samples under mineral wool insulation with a 3.5% chloride solution.•SCC induced on SS304 AR and SE samples as detected by AET.•AE signals were characterized significantly and correlated with SCC.•SCC locations were determined, and its stages were firmly established.•Microstructures visuals revealed single crack in AR and multiple cracks in SE. This study investigates the detection of chloride-induced stress corrosion cracking (CI-SCC) in SS304 stainless steel using the acoustic emission technique (AET). Test samples in as-received (AR) and sensitized (SE) conditions were bent into a U-shape according to ASTM G30. These samples were placed on a hot pipe-spool at 90 °C and insulated with mineral wool. Over 28 days, the insulated samples were intermittently wetted with a 3.5 wt% sodium chloride (NaCl) solution using a drip test apparatus in line with ASTM C692. CI-SCC detection was performed by connecting AET to the U-bend samples. Post-test analysis revealed that acoustic emission (AE) signals, such as energy, RA (rise time/amplitude), counts, and average frequency, varied significantly during different SCC stages. Microscopic examination confirmed SCC in both sample types. In SE sample, cracks initiated from corrosion pits and propagated toward neighbouring pits due to compromised integrity from heat sensitization, producing low-energy AE signals. In contrast, AR sample exhibited high-energy emissions, indicating structural differences. Additionally, mineral wool insulation showed a higher water absorption rate as per EN13472, contributing to a corrosive environment. This study can help to estimate AET’s potential in assessing damage severity and preventing failures in thermally insulated systems.