Failure and Fracture Analysis of Austenitic Stainless Steel Marine Propeller Shaft

Abstract

A fractured in-service ship-propeller shaft (50.8 mm, i.e., 2-inches nominal diameter) was examined to determine the causes of failure and to recommend preventive measures to minimize the risk of recurrence. The findings of the failure analysis investigation suggest strongly that the shaft failed due to rotating bending fatigue initiated from the surface and close to the keyway area. The origin is located on a surface flaw (recess or dent) of approximately 100 lm depth, which could have probably being caused either during installation, operation, or maintenance. In addition, scoring lines formed due to friction-related processes and found on the journal surface were considered as stress raisers acting as potential sites for fatigue crack initiation. Careful review of the shaft service conditions and the implementation of suitable inspection procedures adapted to the vessel planned maintenance are recommended as necessary corrective actions for failure prevention.Keywords Fatigue Á Fractography Á Stainless steel shaft Á Fracture mechanics Brief Background HistoryA single part of the broken shaft (50.8 mm; i.e., 2-inches nominal diameter), along with one being still in operation, is shown in Fig. 1. The matched piece (2nd half) of the fractured shaft was not available (probably sank after fracture). Both shafts were driven by a dual heavy duty ship engine (2 9 720 HP), transmitting rotational motion to the propellers, and they have been in service for almost 14 years. Shaft fracture, during navigation, led to significant loss of engine power and temporary loss of vessel stability, without any additional safety-related consequence. A simplified drawing that shows a general layout of the shaft and the related components along with the fracture location is shown in Fig. 2. The above incident led to the activation of a failure analysis procedure in order to evaluate the cause of failure and recommend preventive measures to minimize the risk of recurrence. Analytical TechniquesMacrofractographic evaluation was performed using a stereomicroscope. Chemical analysis for steel grade identification was conducted using optical emission spectrometry. Hardness testing was performed using a universal hardness tester employing standard Rockwell C technique according to ASTM E-18 and Vickers hardness technique under 5 kg-force applied load according BS EN ISO 6507-1 standard. In addition, high-magnification fractographic observations were conducted on ultrasonically cleaned specimens, using a scanning electron microscope with a secondary electron detector for topographic evaluation and an energy dispersive x-ray spectrometer for elemental analysis.

A Short Review on Fracture Mechanisms of Mechanical Components Operated under Industrial Process Conditions: Fractographic Analysis and Selected Prevention Strategies

“…Metals 2019, 9, 148 12 of 20 where, σ r,th is the threshold stress range (MPa), HV is the Vickers indentation hardness, A is the defect projection area normal to the maximum stress (µm 2 ), and R is the stress ratio (equals to σ min /σ max , for a pure tensile stress regime, σ min = 0, R = 0). In a recent work, the above analysis was used to analyze the level of stress required for the propagation of fatigue crack in an austenitic stainless steel propeller shaft, due to the presence of a mechanical surface defect [40]. The fatigue crack origin located on a surface defect appeared as a "dent or pit" coming most probably from localized mechanical damage (Figure 7b), see also [40].…”

“…In a recent work, the above analysis was used to analyze the level of stress required for the propagation of fatigue crack in an austenitic stainless steel propeller shaft, due to the presence of a mechanical surface defect [40]. The fatigue crack origin located on a surface defect appeared as a "dent or pit" coming most probably from localized mechanical damage (Figure 7b), see also [40]. The investigation findings suggested strongly that the propeller shaft failed due to combined rotating bending/torsional fatigue initiated from the shaft periphery and close to the keyway.…”

Analisis Fatigue Failure Pada Shaft Propeller Sebagai Instrumen Utama Penggerak Kapal

“…Bahan yang digunakan dalam analisa adalah baja tahan karat austenitik atau baja kromium-nikel dengan kandungan nikel diatas 8% [3,8]. Baja pada paduan baja kromium-nikel memiliki kandungan karbon yang tergolong tinggi (0,99%) sehingga memiliki ketahanan yang tinggi terhadap gesekan.…”

Influence of a static torque on plasticity and asperity-induced closure effects during fatigue crack growth in bainitic steel cylinders loaded in push-pull

“…The crack growth rate was computed as: (3) with K threshold = 6 MPam. This value was estimated based on the crack growth rate during the marker blocks.…”