State of the art and current trends on the metal corrosion and protection strategies in deep sea 深海金属腐蚀和保护策略的最新进展和当前趋势
Yangmin Wu, Wenjie Zhao*, Liping Wang* 吴阳敏， 赵文杰*， 王丽萍*Key Laboratory of Advanced Marine Materials, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, 315201, China 中国科学院宁波市材料技术与工程研究所， 中国 宁波， 先进海洋材料重点实验室， 315201
A R T IC L E I N F O
Article history: 文章历史：
Received 14 March 2024 收稿日期 2024 年 3 月 14 日
Revised 19 June 2024 修订于 2024 年 6 月 19 日
Accepted 12 July 2024 录用日期 2024 年 7 月 12 日
Available online 27 July 2024 2024 年 7 月 27 日在线提供
Deep sea, with rich oil, gas, and mineral resources, plays an increasingly crucial role in scientific and industrial realms. However, the highly corrosive feature of deep sea hinders further exploration and development, which requires metal materials with robust corrosion resistance. This review covers an in-depth and all-around overview of the up-to-date advances in corrosion and protection of metals in deep-sea environment. Firstly, the unique characteristics of deep-sea environment are summarized in detail. Subsequently, the corrosion performances of metals in both in situ and simulated deep-sea environments are illustrated systematically. Furthermore, corrosion prevent strategies of metals, including sacrificial anode protection, organic coatings, as well as coatings achieved by physical vapor deposition (PVD coatings), are highlighted. Finally, we outline current challenges and development trends of corrosion and protection of metals in deep-sea environment in the future. The purpose of this review is not only to summarize the recent progress on metal corrosion and protection in deep sea, but also to aid us in understanding them more comprehensively and deeply in a short time, so as to boost their fast development. 深海拥有丰富的石油、天然气和矿产资源，在科学和工业领域发挥着越来越重要的作用。然而，深海的高腐蚀性阻碍了进一步的勘探和开发，这需要具有强大耐腐蚀性的金属材料。这篇综述深入、全面地概述了深海环境中金属腐蚀和保护的最新进展。首先，详细总结了深海环境的独特特征;随后，系统地说明了金属在原位和模拟深海环境中的腐蚀性能。此外，还强调了金属的防腐蚀策略，包括牺牲阳极保护、有机涂层以及通过物理气相沉积 （PVD 涂层） 实现的涂层。最后，我们概述了未来深海环境中金属腐蚀与保护的挑战和发展趋势。本文的目的不仅是总结了近年来深海金属腐蚀与防护的研究进展，也是为了帮助我们在短时间内更全面、更深入地了解它们，从而促进其快速发展。
Deep sea, a treasure trove of resource needed by humans, is a potential strategic resource base that has not been fully recognized and utilized by both the scientific and industrial communities [1-3]. Compared with shallow sea areas, deep sea is rich in mineral, energy, and other resources. According to public data, the amount of natural gas hydrate resources on the seabed is several times than that of known coal, oil, and natural gas in the world. Furthermore, it is also endowed with abundant copper, nickel, cobalt, manganese, and other metals [4,5], which can greatly alleviate the urgent matter of resource shortage faced by humans. The exploration and utilization of deep sea have great potential and broad prospects for the sustainable development of mankind. 深海是人类所需的资源宝库，是一个潜在的战略资源基地，尚未得到科学界和工业界的充分认识和利用[1-3]。与浅海地区相比，深海拥有丰富的矿产、能源和其他资源。根据公开数据，海底天然气水合物资源量是世界上已知的煤炭、石油和天然气的数倍。此外，它还拥有丰富的铜、镍、钴、锰和其他金属 [4,5]，可以大大缓解人类面临的紧迫资源短缺问题。深海的勘探利用对人类的可持续发展具有巨大的潜力和广阔的前景。
Various countries have launched a series of investigations in the deep sea, and the depth of exploration continues to reach new heights [6-8]. Actually, as early as 1960s, numerous countries have performed corrosion and failure experiments on metal materials in the deep sea environment and obtained a lot of valuable data [8-10]. Among them, the US, Norway, as well as Italy have made 各国纷纷展开了一系列深海调查，勘探深度不断攀升至新高度 [6-8]。实际上，早在 1960 年代，许多国家就已经对深海环境中的金属材料进行了腐蚀和失效实验，并获得了大量有价值的数据 [8-10]。其中，美国、挪威和意大利都取得了
great progress in deep-sea exploration [11-13]. Although the research of China in deep sea realm started late, it has made rapid progress. Luoyang Ship Material Research Institute not only conducted deep sea experiments on metal materials, but also integrated environmental factors and in situ electrochemical testing apparatus in the device [14-16]. China’s new deep-sea manned submersible Fendouzhe (Striver) successfully achieved a 10,000meter sea trial in the Mariana Trench, with a maximum diving depth of 10,909m10,909 \mathrm{~m}. 深海勘探取得重大进展 [11-13].中国在深海领域的研究虽然起步较晚，但进展迅速。洛阳船舶材料研究所不仅对金属材料进行了深海实验，还将环境因素和原位电化学测试装置集成到装置中 [14-16]。中国新型深海载人潜水器奋斗者（奋斗者）在马里亚纳海沟成功实现 10000 米海试，最大下潜深度 . 10,909m10,909 \mathrm{~m}
However, the exploration of deep sea is still in its infancy. Although the capabilities of deep sea exploration have been boosted significantly in recent years, most projects are still focused on preliminary scientific research [17-19]. The insufficient performance of related marine engineering equipment is the major root limiting the development of deep-sea exploration. The deep sea is an extremely harsh service environment for marine equipment equipped with various kinds of metals. Metal materials are prone to corrosion, which would ultimately result in equipment failure [16,20]. 然而，对深海的探索仍处于起步阶段。尽管近年来深海勘探能力得到了显著提高，但大多数项目仍侧重于初步科学研究 [17-19]。相关海洋工程装备性能不足是制约深海勘探发展的主要根源。深海是配备各种金属的船用设备的极其恶劣的使用环境。金属材料容易腐蚀，最终会导致设备故障 [16\u201220]。
In deep-sea environment, metal equipment will suffer from serious corrosion due to the coupling effects of high hydrostatic pressure, low temperature, dissolved oxygen, as well as microorganisms, threatening the stability of metal-based structures [21-24]. The submarine oil pipeline rupture, resulting in oil and gas leakage, is a typical example of metal failure [25]. As expected, the equip- 在深海环境中，由于高静水压、低温、溶解氧以及微生物的耦合作用，金属设备将遭受严重腐蚀，威胁金属基结构的稳定性 [21-24]。海底输油管道破裂导致油气泄漏，是金属失效的典型例子 [25]。正如预期的那样，设备-
Fig. 1. Trends in the number of publications on corrosion and protection in deepsea environment from 2011 to 2023. The data were collected from Web of Science database by using the keywords of “deep sea” & “corrosion”. 图 1.2011 年至 2023 年深海环境中腐蚀和保护的出版物数量趋势。数据是从Web of Science数据库中收集的，使用了“深海”和“腐蚀”的关键词。
ment is susceptible to corrosion failure, which plagued the further explore in deep sea. Therefore, it becomes imperative to understand the metal corrosion mechanism and design suitable protection strategies to extend the service cycle of equipment in deepsea environment. Ment 容易受到腐蚀破坏的影响，这困扰着深海的进一步勘探。因此，了解金属腐蚀机理并设计合适的保护策略以延长设备在深海环境中的服务周期变得势在必行。
More and more efforts have been devoted to combating the corrosion of metals in deep sea, including sacrificial anode protection, organic coatings, and PVD coatings [26-28]. Sacrificial anode protection is an effective strategy that involves connecting the protected metal to a sacrificial anode with a more negative potential [29,30][29,30]. The sacrificial anode metal will occur the oxidationreduction reaction, releasing electrons, and generating a corrosion current. By consuming the sacrificial anode metal, the corrosion reaction of the protected metal is prevented, with the advantages of easy installation and low cost. 人们越来越多地致力于对抗深海金属的腐蚀，包括牺牲阳极保护、有机涂层和 PVD 涂层 [26-28]。牺牲阳极保护是一种有效的策略，涉及将受保护的金属连接到具有更大负电位 [29,30][29,30] 的牺牲阳极。牺牲的阳极金属会发生氧化还原反应，释放电子，产生腐蚀电流。通过消耗牺牲阳极金属，可以防止被保护金属的腐蚀反应，具有易于安装、成本低等优点。
Benefiting from high chemical stability, mechanical property, and great adhesion, organic coatings can greatly be utilized for corrosion protection of metal substrates in deep-sea environment [31,32]. Furthermore, their ability to isolate corrosion-related species from metal substrates enables organic coatings to act as the physical barrier to block corrosion molecules. Moreover, the simple integration of functional additives (such as glass flake, mica, and graphene) in the organic coatings equips them with robust barrier properties to further provide corrosion protection for metal equipment [33-35]. Therefore, applying organic coatings has emerged as a promising protection strategy employed in deep sea in recent years. Besides, the tribocorrosion failure of key friction pair materials in deep-sea equipment seriously threatens the operation reliability and long-life service safety, much attention has been paid to PVD coatings, such as graphite-like carbon (GLC) coating used for metal protection in the harsh environment [36-38]. Recently, some reports have manifested remarkable improvement in the mechanical and anti-corrosion performances of GLC coatings by designing multi-layered structures to decrease the defects [39,40], which is another effective strategy for the corrosion resistance of metal substrates in deep sea. 有机涂层具有高化学稳定性、机械性能和出色的附着力，可以极大地用于深海环境中金属基材的腐蚀保护[31,32]。此外，它们能够从金属基材中分离出与腐蚀相关的物质，使有机涂层能够作为物理屏障来阻止腐蚀分子。此外，功能性添加剂（如玻璃鳞片、云母和石墨烯）可以简单地掺入有机涂料中，使其具有强大的阻隔性能，可以进一步为金属设备提供防腐蚀保护[33-35]。因此，应用有机涂层已成为近年来深海采用的一种很有前途的保护策略。此外，深海设备中关键摩擦副材料的摩擦腐蚀失效严重威胁着运行可靠性和长寿命服役安全性，人们非常重视PVD涂层，例如在恶劣环境中用于金属保护的类石墨碳（GLC）涂层 [36-38]。近年来，一些报道表明，通过设计多层结构来减少缺陷，GLC涂层的机械性能和防腐性能得到了显著改善[39,40]，这是深海金属基材耐腐蚀性的另一种有效策略。
Nowadays, the study of the corrosion and protection of metals and related protection strategies in deep-sea environment is gradually becoming a hot topic, attracting more and more attention from scientific researchers. As summarized in Fig. 1, the number of publications and studies on the corrosion behaviors in deep sea has been increasing progressively. 如今，深海环境中金属的腐蚀与防护及其防护策略的研究逐渐成为热门话题，越来越受到科研人员的关注。如图 1 所示，关于深海腐蚀行为的出版物和研究数量一直在逐步增加。
At present, metal corrosion and protection technologies are evolving at an amazing rate but still remain in the early stage. Although incredible advances have been achieved, there is still a lack of a review to systematically summarize the latest progress in metal corrosion and protection technology in deep-sea environment. Thus, this well-timed review involves a comprehensive overview of metal corrosion and protection in deep-sea environment. In this review, we start by introducing the crucial factors 目前，金属腐蚀和保护技术正在以惊人的速度发展，但仍处于早期阶段。尽管已经取得了令人难以置信的进步，但仍然缺乏系统总结深海环境中金属腐蚀和保护技术最新进展的综述。因此，这篇适时的综述涉及深海环境中金属腐蚀和保护的全面概述。在这篇评论中，我们首先介绍关键因素
of deep sea, followed by summarizing the corrosion behaviors of metal and alloys in situ and simulated deep-sea environment. Then, we present the typical corrosion prevention strategies for metals in deep sea in detail, involving sacrificial anode protection, organic coatings, as well as PVD coatings. Finally, we propose the prospects and challenges on how to construct efficient corrosion prevention for metals in deep-sea environment through the elaborate control of anti-corrosion strategies, which will contribute to guiding the future study. ，然后总结了金属和合金在原位和模拟深海环境中的腐蚀行为。然后，我们详细介绍了深海金属的典型防腐蚀策略，包括牺牲阳极保护、有机涂层以及 PVD 涂层。最后，我们提出了如何通过精心设计的防腐策略来构建深海环境中金属高效防腐蚀的前景和挑战，以期为未来的研究提供指导。
2. The characteristics of deep-sea environment 2. 深海环境特点
Compared with shallow sea environment, deep sea presents significantly different environmental characteristics in many aspects such as hydrostatic pressure, dissolved oxygen, temperature, pH value, salinity, seawater velocity, as well as microorganism (Fig. 2). These factors vary with the area and depth of seawater, and have unique characteristics. The protection and failure performances of materials are closely related to these factors, and their corrosion mechanisms in the deep sea environment can be significantly different from those in shallow water. 与浅海环境相比，深海在静水压力、溶氧、温度、pH 值、盐度、海水流速以及微生物等许多方面表现出显著不同的环境特征（图 2）。这些因素随海水的面积和深度而变化，并具有独特的特征。材料的保护和失效性能与这些因素密切相关，它们在深海环境中的腐蚀机理可能与浅水环境中的腐蚀机制有显著差异。
2.1. Hydrostatic pressure 2.1. 静水压力
Hydrostatic pressure is one of the most important environmental factors that distinguish the deep sea from the shallow one. In general, when other factors remain unchanged, hydrostatic pressure changes in direct proportion to the seawater depth, that is, when seawater depth increases by 100 m , hydrostatic pressure increases by 1 MPa . Although the specific conditions of different sea areas are various, the general law between hydrostatic pressure and sea water depth is roughly determined. Hydrostatic pressure has a significant impact on the corrosion of metal materials and is currently the most widely studied factor. 静水压力是区分深海和浅海的最重要环境因素之一。一般来说，当其他因素不变时，静水压力的变化与海水深度成正比，即当海水深度增加 100 m 时，静水压力增加 1 MPa。虽然不同海域的具体情况各不相同，但静水压力与海水深度之间的一般规律是大致确定的。静水压力对金属材料的腐蚀有重大影响，是目前研究最广泛的因素。
For passive alloys, such as various stainless steel and aluminum alloys, hydrostatic pressure alters the composition and stability of the passivation film generated on the surfaces, reducing the mechanical properties of the film and ultimately resulting in decreased corrosion resistance of the systems. Besides, hydrostatic 对于钝化合金，例如各种不锈钢和铝合金，静水压力会改变表面产生的钝化膜的成分和稳定性，从而降低膜的机械性能，并最终导致系统的耐腐蚀性降低。此外，静液压
Fig. 2. The relationship between crucial factors and corrosion prevention performances of metals in deep sea. 图 2.关键因素与深海金属防腐性能的关系.
pressure promotes the adsorption of Cl^(-)\mathrm{Cl}^{-}on metal surfaces by increasing their activity, which reduces the corrosion resistance of the formed oxide layer by generating soluble chloride oxides. Furthermore, hydrostatic pressure accelerates the rapid dissolution of pitting corrosion in low-alloy high-strength steel, extending towards the surrounding area. This increases the corrosion rate and leads to the transition of the metal from localized pitting corrosion to comprehensive corrosion. 压力通过增加金属表面的活性来促进其吸附 Cl^(-)\mathrm{Cl}^{-} ，从而通过生成可溶性氯化物氧化物来降低形成的氧化层的耐腐蚀性。此外，静水压力加速了低合金高强度钢中点蚀的快速溶解，并延伸到周围区域。这增加了腐蚀速率，并导致金属从局部点蚀转变为全面腐蚀。
For organic coatings, in the atmosphere environment, the failure process of the system includes three stages, which are water transport, transport and interfacial reaction, and interface electrochemical reaction. Whilst with hydrostatic pressure, the failure process is changed to four stages: more complex water transport, interface electrochemical reaction, coating cracking, and diffusion of corrosion products. Besides, alternating hydrostatic pressure (AHP) can accelerate the transport of corrosion-related molecules (such as H_(2)O,Cl^(-)\mathrm{H}_{2} \mathrm{O}, \mathrm{Cl}^{-}, and O_(2)\mathrm{O}_{2} ), leading to the early occurrence of electrochemical reactions. What’s more, the diffusion mechanism of corrosion species inside the coating matrix changes from ideal Fick to non-Fick diffusion in the AHP environment. Furthermore, the “push-pull” effect on the coating/metal interface leads to the rapid decline of adhesion strength between the coating and substrate during the initial immersion, which is the root cause of the coating failure in harsh environment. Finally, the intrinsic structure of the coating will be seriously damaged in AHP, accompanied by a large number of defects and accelerate the rapid failure of the coating. 对于有机涂料，在大气环境中，系统的失效过程包括三个阶段，即水输送、输送和界面反应以及界面电化学反应。而在静水压力下，失效过程变为四个阶段：更复杂的水传输、界面电化学反应、涂层开裂和腐蚀产物的扩散。此外，交变静水压 （AHP） 可以加速腐蚀相关分子（如 H_(2)O,Cl^(-)\mathrm{H}_{2} \mathrm{O}, \mathrm{Cl}^{-} 和 O_(2)\mathrm{O}_{2} ）的传输，导致电化学反应的早期发生。更重要的是，在 AHP 环境中，涂层基体内腐蚀物质的扩散机制从理想的 Fick 扩散变为非 Fick 扩散。此外，涂层/金属界面上的“推拉”效应导致涂层与基材之间的粘合强度在初始浸泡过程中迅速下降，这是涂层在恶劣环境中失效的根本原因。最后，涂层的本征结构在 AHP 中会受到严重破坏，并伴有大量缺陷，加速涂层的快速失效。
2.2. Dissolved oxygen 2.2. 溶解氧
Dissolved oxygen is a complex and variable factor, varying in content with different seasons and regions. In shallow areas, the oxygen content of water is close to or reaches the saturated state due to its full contact with air and photosynthesis of plants. As the depth gradually increases, the sunlight fades gradually, and oxygen is partly consumed by microorganisms on the seabed. The oxygen minimum zone occurs where heterotrophic oxygen consumption exceeds oxygen produced depending on the local conditions between 200 and 1500 m depth [41,42]. As the depth further increases, some areas will be supplemented by oxygen-containing ocean currents and resources, and the oxygen content rises to a higher value. 溶氧是一个复杂且可变的因素，其含量随季节和地区而变化。在浅水区，由于水与空气和植物的光合作用完全接触，水的氧含量接近或达到饱和状态。随着深度逐渐增加，阳光逐渐变暗，氧气部分被海底的微生物消耗。根据当地条件，在200-1500 m深度之间，异养耗氧消耗量超过产生的氧气时，会出现最低氧区[41,42]。随着深度的进一步增加，一些区域将得到含氧洋流和资源的补充，氧含量上升到更高的值。
Dissolved oxygen mainly participates in corrosion reactions by absorbing electrons, as shown in the following equation: 溶解氧主要通过吸收电子参与腐蚀反应，如下式所示： O_(2)+2H_(2)O+4e^(-)=4OH^(-)\mathrm{O}_{2}+2 \mathrm{H}_{2} \mathrm{O}+4 \mathrm{e}^{-}=4 \mathrm{OH}^{-}
Therefore, the content of dissolved oxygen is crucial for the corrosion rate. 因此，溶解氧的含量对腐蚀速率至关重要。
Dissolved oxygen is a crucial factor in deep sea. Sawant et al. [10] studied the corrosion behaviors of mild steel, stainless steel, copper, brass, and cupro-nickel in coastal and oceanic waters of the Arabian Sea and Bay of Bengal. They observed that the order of corrosion rate was mild steel > copper > cupro-nickel > brass > stainless steel in shallow sea, and mild steel > cupro-nickel > brass > copper > stainless steel in deep sea (from 2300 to 3000 m ). Fu et al. [43] pointed out that dissolved oxygen is a crucial factor that affects the corrosion rate of ship hulls in the deep sea. They found that as the dissolved oxygen content increased, the corrosion potential of the substrate also increased, resulting in a higher corrosion rate. These results obviously suggest that dissolved oxygen is a crucial factor influencing corrosion reaction in deep sea. 溶解氧是深海中的关键因素。Sawant等[10]研究了低碳钢、不锈钢、铜、黄铜和铜镍合金在阿拉伯海和孟加拉湾沿海和海洋水域的腐蚀行为。他们观察到，腐蚀速率的顺序是浅海中的低碳钢 > 铜 > 铜 > 黄铜 > 不锈钢，以及深海（从 2300 到 3000 米）的低碳钢 > 铜 > 黄铜 > 不锈钢。Fu等[43]指出，溶解氧是影响深海船体腐蚀速率的关键因素。他们发现，随着溶解氧含量的增加，基材的腐蚀电位也增加，导致腐蚀速率更高。这些结果显然表明，溶解氧是影响深海腐蚀反应的关键因素。
2.3. Temperature 2.3. 温度
Temperature not only directly affects the corrosion behavior, but also couples with other factors to accelerate the failure of ma- 温度不仅直接影响腐蚀行为，还会与其他因素耦合加速马的失效
terials. The temperature of the surface region varies with the seasons. Besides, the temperature drops rapidly at the first 300 m and then decreases slightly until it reaches 1000 m below the sea level. Below this depth ( 1000 m ), the temperature fluctuates around 2^(@)C2^{\circ} \mathrm{C}, with weak variations in various regions. In addition, the temperature in the hydrothermal vent fields, as it emerges from the chimneys, maybe as high as 400^(@)C400{ }^{\circ} \mathrm{C} [9]. In evaporative oceans such as the Sulu Sea and the Mediterranean Sea, the temperature exhibits regional uniqueness, typically exceeding 10^(@)C10{ }^{\circ} \mathrm{C} below 3000 m , which can have a significant impact on microbial physiology and corrosion in these regions [44,45]. 特里亚斯。表面区域的温度随季节变化。此外，温度在前 300 m 迅速下降，然后略有下降，直到达到海平面以下 1000 m。低于此深度 （ 1000 m ），温度在 2^(@)C2^{\circ} \mathrm{C} 周围波动，各个区域的变化较弱。此外，热液喷口场中的温度，当它从烟囱中出来时，可能高达 400^(@)C400{ }^{\circ} \mathrm{C} [9]。在苏禄海和地中海等蒸发海洋中，温度表现出区域独特性，通常超过 10^(@)C10{ }^{\circ} \mathrm{C} 3000 m 以下，这可能对这些地区的微生物生理学和腐蚀产生重大影响 [44,45]。
In general, an increase in temperature will promote the diffusion rate of dissolved oxygen and enhance the conductivity of seawater, which greatly accelerates the reaction between the cathode and the anode, that is, corrosion acceleration. However, in deepsea environment, temperature does not change significantly, so the influence of this factor on corrosion is generally rarely considered. 一般来说，温度的升高会促进溶解氧的扩散速率，增强海水的电导率，从而大大加速阴极与阳极的反应，即腐蚀加速。然而，在深海环境中，温度不会发生显著变化，因此通常很少考虑该因素对腐蚀的影响。
2.4. pH 2.4. pH 值
Generally speaking, pH value is associated with oxygen content. The higher the oxygen content, the higher the pH value. At the surface of the ocean, the oxygen content of seawater is saturated, and the pH value achieves 8.0-8.28.0-8.2, which has little direct effect on corrosion behavior. As the depth increases, the pH value also gradually decreases to 7.4. Overall, pH value remains relatively stable in deep-sea environment across different sea areas, and its impact on corrosion is not readily apparent. 一般来说，pH 值与氧含量有关。氧含量越高，pH 值越高。在海洋表面，海水的氧含量达到饱和，pH 值达到 8.0-8.28.0-8.2 ，这对腐蚀行为几乎没有直接影响。随着深度的增加，pH 值也逐渐降低到 7.4。总体而言，不同海域的深海环境 pH 值保持相对稳定，其对腐蚀的影响并不明显。
2.5. Salinity 2.5. 盐度
Seawater contains various kinds of salt and is a strong electrolyte solution. The composition of seawater is mainly sodium chloride ( NaCl ), with the content from about 33%33 \% to 37%37 \%. The variation of NaCl content in the deep sea is negligible, and the quantity is mostly regarded as 3.5wt.%3.5 \mathrm{wt} . \%. Therefore, the corrosion of metals is not appreciably affected. 海水中含有各种盐分，是一种强电解质溶液。海水的成分主要是氯化钠（NaCl），含量大约 33%33 \% 到 37%37 \% 。深海中 NaCl 含量的变化可以忽略不计，数量多以 3.5wt.%3.5 \mathrm{wt} . \% 。因此，金属的腐蚀不会受到明显影响。
2.6. Seawater velocity 2.6. 海水速度
In general, seawater velocity in deep ocean is lower than that at the surface. The direction and magnitude of velocity in different areas vary greatly, which are affected by global thermohaline circulation. When the velocity rate increases to a certain extent, the protection film of the metal is destroyed by erosion, and the corrosion rate will increase as a result. Passive metals, such as titanium and stainless steels, tend to be more resistant in high-velocity seawater environment. 一般来说，深海中的海水速度低于表面的海水速度。不同区域的速度方向和大小差异很大，这受全球温盐环流的影响。当速度加快到一定程度时，金属的保护膜被侵蚀破坏，腐蚀速度会随之增加。钝化金属，如钛和不锈钢，在高速海水环境中往往更耐用。
2.7. Microorganism 2.7. 微生物
Microorganisms in deep sea live in high hydrostatic pressure, low temperature, dark, and low nutrient environments, mainly including actinomycetes, fungi, non-extremophilic bacteria, and various extremophilic bacteria such as alkaliphiles, thermophiles, psychrophiles, as well as piezophilic bacteria [46]. Microbiologically influenced corrosion (MIC) seriously destroys the reliability of metal marine equipment. In the case of MIC, microorganisms act to initiate, facilitate, or accelerate electrochemical corrosion reactions. The corrosion mechanism of metals influenced by microorganisms mainly includes as follows. Firstly, the formation of biofilms can promote corrosion when an inhomogeneous biofilm is formed, while slowing down the corrosion rate of the metal when the uniform and dense film is generated. Secondly, a diffusion barrier is formed, which can prevent the diffusion of oxygen to the cathode and corrosive anions to the anode, as well as 深海微生物生活在高静水压、低温、黑暗和低营养的环境中，主要包括放线菌、真菌、非极端微生物，以及嗜碱性、嗜热性、嗜冷性细菌等各种极端微生物，以及嗜压性细菌[46]。微生物影响腐蚀 （MIC） 严重破坏了金属船用设备的可靠性。在 MIC 的情况下，微生物的作用是引发、促进或加速电化学腐蚀反应。受微生物影响的金属腐蚀机理主要有以下几种。首先，当形成不均匀的生物膜时，生物膜的形成可以促进腐蚀，而当产生均匀致密的膜时，可以减缓金属的腐蚀速度。其次，形成扩散屏障，可以防止氧向阴极扩散，防止腐蚀性阴离子向阳极扩散，以及
