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Shaiful Rizam Shamsudin
Root cause analysis on manufacturing defects in brass oxygen valves
Effect on Current Density on Zero Charge Corrosion Protection of Pure Mg in 3.5% NaCl Solution
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.
2021-11-12
,
Gunasilan M.
,
Shaiful Rizam Shamsudin
,
Mohd Rafi Adzman
,
Salleh S.H.M.
,
Sanusi M.S.
,
Ahmad W.M.H.W.
The cathodic protection uses two-electrode polarization, which requires large currents and substantial voltages. Efforts are being made to identify possibilities for improvements by developing zero-charge corrosion protection techniques. Studies were performed to determine the zero-charges potential effect by analyzing corrosion signs on reactive metal samples such as pure Mg. Mg samples were fed by current/voltage pulses for 120 hours, with specified pulse parameters and varied Ecorr- offsets, ranging from +2 to -218 mV. The volumetric hydrogen gas collection technique is used to determine the hydrogen evolution rate. Surface observation is carried out by stereomicroscope to determine the presence of corrosion signs on the sample surface. Overall, all current densities and hydrogen evolution rates had very low readings on the studied Ecor offset parameters. Mg samples fed with pulses at -1800 and -1900 mV vs SCE revealed zero charge potential effects since their surface was clean and showed no indications of corrosion even after being exposed to the corrosive solution for 120 hours. Thus, corrosion protection is successfully done and meets the Epzc condition.