Curved features on the opened crack surface indicated crack progression by fatigue.ĮDS micro-analysis in general accordance to ASTM E1508-98 was performed on the opened crack surface deposits to determine if any detrimental inorganic constituents (e.g. Red and black deposits are noted on the opened crack surfaces. Figure 3 displays a close-up view of the opened axial crack fracture surfaces. The longest, and presumably the deepest, axial crack was manually opened to examine the exposed crack surface. Multiple axial and circumferential cracks are revealed. Cracking was observed in the ID surface therefore, the stub was axially cross-sectioned to examine the internal surface.Ī close-up view of the ID surface is presented in Figure 2. The nozzle, presented in Figure 1, was from vessel xxxx in the xxxxxxxxx vaporizer system.
ANALYSIS:Ī cracked nozzle sleeve was received to determine the cause of corrosion and cracking. Increasing the wall thickness is another method of reducing the stress in the component. No material defects or deficiencies were observed.Ī more corrosion resistant and possibly higher strength steel is needed for this application. There was no evidence of sensitization in the base material, which exhibited a properly annealed microstructure. Axial corrosion fatigue was mainly driven by hoop stresses from internal operating pressures and corrosion.Įnergy dispersive x-ray spectrometer (EDS) elemental analysis detected mainly organic residue (carbon and oxygen) stainless steel oxidation corrosion products (chromium and iron oxides) and a trace of chlorine on the opened crack surface and within the corrosion deposits.Ĭhemical analysis indicated that the nozzle sleeve was fabricated from 316L, low carbon stainless steel. Circumferential corrosion fatigue cracking was mainly driven by thermal stress cycles and corrosion. Some of the shallow intergranular penetrations were driven to significant depths due to corrosion fatigue. The intergranular penetrations are attributed to general corrosive attack rather than stress corrosion cracking (SCC).
These penetrations were filled with corrosion product and were observed throughout the nozzle ID surface. Metallographic examination revealed the presence of shallow intergranular corrosion penetrations in the ID surface of the nozzle sleeve stub. Results indicate axial and circumferential cracks initiated at shallow intergranular corrosion penetrations on the inner diameter (ID) surface and propagated by corrosion assisted fatigue. Fatigue Cracking Of A 316l Stainless Steel Nozzle Sleeve From A Chemical Processing Vessel Corrosion Assisted Fatigue Cracking Of A 316l Stainless Steel Nozzle Sleeve From A Chemical Processing VesselĪ cracked nozzle sleeve stub from a chemical processing vessel of the proprietary vaporizer system was analyzed to determine the cause of cracking.