Now showing 1 - 4 of 4
Thumbnail Image
Publication

Influence of flow accelerated corrosion on corrosion protection of mild steel in 3.5% NaCl solution

2024-03-07 , Mahalaksmi Gunasilan , Shaiful Rizam Shamsudin , Mohd Rafi Adzman , Siti Hawa Mohamed Salleh , Wan Mohd Haqqi Wan Ahmad , Mohamad K.A.A.K.

Mild steel is a primary material used to construct ships and other maritime structures. Corrosion protection systems are sometimes ineffective in aqueous mediums subjected to movement, flow, waves, and even turbulence under unpredictable conditions. This study aims to ascertain the influence of flow velocity on mild steel corrosion in the aqueous medium. The mild steel samples are immersed in a 3.5% sodium chloride (NaCl) solution for five days. They were protected against corrosion using an impressed current cathodic protection (ICCP) system. The flow velocity is increased to 200-800 rpm, while the stationary flow is also examined as a control. Data on the metal's potential and current density were collected, and the surface morphology was analyzed using a stereomicroscope. Corrosion protection occurs exclusively in stationary flow, whereas corrosion occurs in solutions flowing at a most studied velocity. Metals show corrosion severity levels ranging from 200 to 600 rpm with increasing current consumption and metal potential. At 800 rpm, the metal surface appears to begin passivating, reducing the current consumption and potential. The flow velocity accelerates corrosion, yet at the high-speed stream, the corrosion is slowed because the steel surface becomes passive and assists the corrosion protection.

Thumbnail Image
Publication

Failure investigation and analysis of locally manufactured turbine blade

2023-05-01 , Mahalaksmi Gunasilan , Shaiful Rizam Shamsudin , Rajaselan Wardan , Aleena Ramlee , Wan Mohd Haqqi Wan Ahmad , Mohd Rafi Adzman

This study aims to identify the root cause of a turbine blade failure after only 36 hours of operation and recommends measures to prevent future failures. The analysis involved four samples, including an OEM sample, three fabricated samples with cracks and parts, including a kept sample for failure analysis. Microstructural analysis using Villella's reagent as an etchant, surface morphology, and micro-elemental analysis were conducted using the benchtop SEM & EDS. The hardness of the samples was tested using the Rockwell (HRC) method. The failed blade was made of AISI 422 grade stainless steel. It failed due to chipping that initiated cracks when it was tightly fastened, facilitated by internal stress and intermetallic particles in the microstructure. Instead of turbine blades made of hardened steel, the material was found to be slightly ductile and highly prone to compression before breaking when over-tightened during assembly. Inadequate heat treatment practices caused varied microstructural patterns, including the presence of intermetallic particles and significant hardness differences between the fabricated and OEM samples, leading to internal stress. In order to prevent future failures, there is a requirement to improve quality control measures during the fabrication process, particularly in the aspect of heat treatment practices.Thorough testing and analysis of the material microstructure may also be necessary to identify and eliminate potential sources of internal stress and intermetallic particles. Proper installation and fastening of turbine blades, regular inspection, and maintenance can also help identify early signs of failure and prevent catastrophic failures from occurring.

Thumbnail Image
Publication

Root cause analysis on manufacturing defects in brass oxygen valves

2023-05-01 , Wan Mohd Haqqi Wan Ahmad , Shaiful Rizam Shamsudin , Salleh S.H.M. , Mohd Rafi Adzman , Rajaselan Wardan , Mahalaksmi Gunasilan

Brass valves are widely used in oxygen gas cylinder systems to regulate pressure and ensure safe operation. The production methods for brass valves include hot forging (700 °C), stress-relieving (300 °C), shot blasting, machining, and selective chrome plating on the external surface. Pneumatic testing at 400 bar has detected more than 10 % of the product production was found to have signs of leakage, and the most severe was when there were visible hairline cracks on the inner wall. Therefore, several tests to investigate valve failure were conducted to identify the root cause of the failure using a series of microscopic methods on the failed sample as well as the as-received brass billet. The study found that hairline cracks in brass valves were most likely caused by internal dross originating from the billet that was not properly removed during the casting process. The presence of dross in the billet manufacturing stage was identified as the primary reason for valve failure. Hot forging and other manufacturing techniques were found to be insufficient to eliminate the formation of dross, leading to a deterioration in the mechanical properties of the valves. In order to overcome this issue, flux can be added to the molten brass to help remove impurities and reduce the formation of dross. As a result, the mechanical properties of the final product deteriorated even though it had gone through the forging process.

Thumbnail Image
Publication

Corrosion behaviour of mild steel : insights from tafel extrapolation analysis in flowing 3.5% NaCl solutions and soil with diverse resistivity levels

2024-12 , Mahalaksmi Gunasilan , Shaiful Rizam Shamsudin , Nursalasawati Rusli , Mohd Rafi Adzman , Wan Mohd Haqqi Wan Ahmad

The corrosion behaviour of AISI 1006 steel in diverse environmental conditions were comprehensively investigated to offer valuable insights into corrosion mitigation strategies for critical infrastructure protection. This study employed an optical emission spectrometer, pH measurements, soil resistivity assessment, and Tafel extrapolation conducted with a potentiostat. The study encompassed stagnant and flowing 3.5% NaCl solutions, with flow velocities ranging from 0 to 12 km/h, and considered soil corrosiveness based on soil resistivity. In stagnant 3.5% NaCl solutions, minimal corrosion was observed due to limited oxygen availability, resulting in a 6.634 x 10¯3 mm/year corrosion rate. A noteworthy trend was evident in flowing 3.5% NaCl solutions, with corrosion rates peaking at 9 km/h (11.918 x 10¯3 mm/year) and subsequently decreasing at 12 km/h (10.423 x 10¯3 mm/year). This intriguing pattern may be attributed to the potential formation of a protective oxide layer at higher flow velocities, likely due to increased dissolved oxygen and mass transport. The soil's corrosiveness significantly influenced corrosion rates, with lower-resistivity soils exhibiting heightened corrosion rates. In very mildly corrosive soil, AISI 1006 steel displayed a corrosion rate of 2.818 x 10¯4 mm/year. The corrosion rate increased as soil corrosiveness intensified, reaching its peak of 6.319 x 10¯4 mm/year in severely corrosive soil. Extremely corrosive soil led to a corrosion rate of 8.033 x 10¯4 mm/year, as improved soil conductivity accelerated ion transfer and electron flow, ultimately expediting corrosionrelated electrochemical reactions. This study enhances the understanding of AISI 1006 steel corrosion in varying conditions, providing critical data for corrosion control in structures and assets, emphasising the need for tailored prevention measures.