利用射頻濺鍍聚四氟乙烯薄膜應用於氫氣專用不鏽鋼管件銲道抗腐蝕之研究

On Enhancing Corrosion Resistance of Stainless Steel Pipe Fittings and Welds for Hydrogen Applications through Radiofrequency Sputtering of Polytetrafluoroethylene Films

氫氣搭配鋼瓶、燃料管路可提供各種形式的應用使氫氣迅速補充用途廣泛，輸送氫氣過程中會使用到的管件或閥件或是管線和組件中的銲接處，可能會因不同環境產生酸鹼環境加速輸送管件及設備腐蝕之產生，如:海中的氯化鎂、酸雨的硫、土壤中碳酸鹽等，而造成管路組件的破壞。因此，本研究利用標準鹽霧試驗與鹽霧混合硝酸分別針對氫能專用的不鏽鋼管件銲道進行不同時間（0-72小時）環境測試，其中鹽霧測試72小時等於模擬陸上放置3年海岸放置1年。管件銲道316L之NaCl與HNO3的環境中測試，在不鏽鋼銲件的表面出現的缺陷皆會加速銲件的腐蝕速度，如刻痕、凹痕、粗糙點等，由於，不鏽鋼的銲接處會在經歷熱處理的過程產生過度氧化反應，經由鹽霧試驗將加速氧化，腐蝕面積由14.74 %提升到22.9 %，大幅超過平板不鏽鋼1.9%的腐蝕狀況，HNO3實驗，腐蝕面積由7.2%提升到39.8%，原因是HNO3會先腐蝕黑色氧化層;接著開始腐不鏽鋼，約24小時產生紅鏽造成不鏽鋼永久性損傷與孔隙腐蝕，此為造成氫致開裂的原因之一研究發現，利用濺鍍聚四氟乙烯可以有效阻隔不鏽鋼與水氣接觸，抗腐蝕效果經由腐蝕電化學分析獲得證實。

Hydrogen can be conveniently replenished when hydrogen coupled cylinders and fuel piping are in use. However, during hydrogen transportation, the components such as fittings, valves, piping, and welds can be susceptible to corrosion due to different environmental factors. These factors include magnesium chloride in marine environments, sulfur in acid rain, and carbonates in soil. As a result, the corrosion damage inflicted on the piping components is accelerated. To address this issue, our study conducts environmental tests on stainless steel pipe fittings specifically designed for hydrogen energy applications. These tests involve subjecting the fittings to varying time durations, from zero to 72 hours, using the standard salt spray test and a combination of salt spray and nitric acid. It is worth noting that the 72-hour salt spray test is equivalent to three years in an onshore setting or one year in a coastal environment. Also, we conduct NaCl and HNO3 environmental tests on the welded joints of the stainless steel pipe fittings, utilizing 316L. Within these environments, the surface of the stainless steel weldments exhibits various defects such as scratches, dents, and rough spots. These defects significantly accelerate the corrosion rate of the weldments. Additionally, the welding process of stainless steel leads to the formation of an excessive oxidized layer. Through the salt spray test, we observe that the corrosion area of this oxidized layer increases from 14.74 to 22.9, surpassing the corrosion rate of flat stainless steel by 1.9%. Furthermore, when HNO3is introduced in the experiment, the corrosion area escalates from 7.2% to 39.8%. The increased corrosion shows thatHNO3iscapable of first corroding the black oxide layer and subsequently initiating corrosion on the stainless steel beneath the oxide layer. As a result, red rust forms after approximately 24 hours, causing permanent damage and porosity in the stainless steel. This phenomenon is one of the causes of hydrogen-induced cracking. Our research findings reveal that the application of sputtering polytetrafluoroethylene（PTFE）coating effectively prevents moisture contact with stainless steel, thereby providing corrosion resistance. This conclusion is fully supported by corrosion electrochemical analysis.