腐蝕鋼板機械性質衰減模型研究：以實船及加速腐蝕鋼板分析

Declining Model of Mechanical Properties for Corroded Steel Plate: An Empirical Study of Real Ships and Accelerated Corrosion Test

徐一仁(I-Jen Hsu)

指導教授 ： 李岳聯

國立臺灣大學/工學院/工程科學及海洋工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202104193

摘要

財團法人中國驗船中心(CR Classification Society, CR)現有的腐蝕程度檢測方式，大多是以目視檢查油漆外觀防鏽塗層狀況及使用超音波測厚儀測量鋼板厚度，並以剩餘厚度來決定是否換板。此種方法雖較簡便，但盲點不少，故期望能針對海洋環境下腐蝕後之鋼材的材料性質進行實驗分析，並整理出腐蝕後之鋼板特性，供設計及檢驗人員參考。而對實船鋼板的實驗結果顯示，腐蝕初期機械性能仍不會有明顯變動，唯有伸長率會快速下降。而在使用定電流極化下進行的加速腐蝕結果顯示，在平均厚度下降5%到 35%間的均勻腐蝕對於鋼板的拉伸強度、降伏強度以及伸長率都影響不大，但面臨局部腐蝕時，鋼板的伸長量會隨著蝕孔腐蝕深度上升而大幅下降，當深度達到厚度的20%時，伸長量最多會下降至原先的60%。此結果結合微結構分析能得出腐蝕並不影響材料性質以及微結構，但局部腐蝕造成的表面形貌不平整使得該處應力及應變集中，進而造成撕裂提前發生，伸長量也隨之減少。最後，求出伸長量衰減率與孔蝕深度的經驗公式，並與舊板相互比較。

關鍵字

腐蝕 ； 船舶結構 ； 剩餘強度 ； 局部腐蝕 ； 機械性質

並列摘要

Intermediate and special surveys may be required in association with visual inspections and ultrasonic thickness every five years. The reduced material strength was determined by measuring the thickness. However, this way has many blind spots. The study aims to analyze the material properties of the corroded steel in the marine environment. Base on the test results of steel plate of real ships, the mechanical property remains constant in the mild corrosion; however, the extension rate decreases rapidly. The results of acceleration corrosion test show that, when general corrosion which thickness decreased between 5% and 35% of original thickness occurs, the Young’s modulus, yielding strength, and ultimate tensile strength still remains constant, and the extension rate slightly decreased, but when faced to local corrosion, the reducing extension rate of steel plate increases as the pitting depth increased. The extension rate would decrease to 60% when the pitting depth up to 20% of original thickness. Combining the results of microstructural analysis can show that the corrosion cannot affect the material property and microstructure, but the uneven surface induce by local corrosion will cause stress concentration and further decrease the extension rate. Finally, the empirical formula between extension rate and pitting depth was established and compare to the result from the steel plate of real ships.

並列關鍵字

corrosion ； ship structure ； residual strength ； local corrosion ； mechanical properties

參考文獻

[1] C. C. SOCIETY, Rules for the Construction and Classification of Steel Ships. 2018.

[2] E. McCafferty, Introduction to corrosion science. Springer Science Business Media, 2010.

[3] X. Zhang, G.-y. Xiao, B. Liu, C.-c. Jiang, and Y.-p. Lu, "Influence of processing time on the phase, microstructure and electrochemical properties of hopeite coating on stainless steel by chemical conversion method," NEW J CHEM, vol. 39, no. 7, pp. 5813-5822, 2015.

[4] A. Fattah-Alhosseini, M. Mosavi, and A. Allahdadi, "An electrochemical impedance study of AISI 321 stainless steel in 0.5 M H2SO4," INT J ELECTROCHEM, 2011.

[5] J. Paik, J. Lee, and M. Ko, "Ultimate compressive strength of plate elements with pit corrosion wastage," P I MECH ENG M-J ENG, vol. 217, no. 4, pp. 185-200, 2003.