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Save to Reading List By Nicholas Woodroof, Oilfield Technical Editor, Mon, Aug 12, 2019 3:00 PM
Hydraulic and instrumentation (H&I) systems are vital and often very large installations on both land-based plants and marine offshore applications. Hydraulic and instrumentation (H&I) systems are vital and often very large installations on both land-based plants and marine offshore applications. Гидравлические и контрольно-измерительные системы (H&I) являются жизненно важными и часто очень крупными установками как на наземных предприятиях, так и на морских морских установках. Hydraulic and instrumentation (H&I) systems are vital and often very large installations in both onshore and offshore installations.液压和仪表(H&I) 系统在陆基工厂和海上海上应用中都非常重要，而且通常非常大。液压和仪表(H&I) Гидравлические и контрольно-измерительные системы (H&I) важны и часто очень велики как на наземных предприятиях, так и на морских морских установках. Hydraulic and instrumentation (H&I) systems are important and often very large in both onshore and offshore installations. Typically, they consist of kilometers of high-quality stainless steel, nickel-based alloys or copper pipes with close dimensional tolerances. The tubes are connected to fittings, each of which is made with high precision and is expensive. Therefore, it is not surprising that engineering firms and facility owners will strive to find the most economical material solutions while avoiding compromising the quality and durability of the installation.
When choosing material for H&I installations in inland regions, the most commonly used alloy is stainless steel of type 316L (UNS S31603) with matching fittings. When choosing material for H&I installations in inland regions, the most commonly used alloy is stainless steel of type 316L (UNS S31603) with matching fittings. При выборе материала для установок H&I во внутренних регионах наиболее часто используемым сплавом является нержавеющая сталь типа 316L (UNS S31603) с соответствующими фитингами. When selecting material for H&I installations in the interior, the most commonly used alloy is Type 316L Stainless Steel (UNS S31603) with matching fittings.在内陆地区为H&I 装置选择材料时，最常用的合金是带有匹配配件的316L 型不锈钢(UNS S31603)。 316L При выборе материалов для установок H&I во внутренних районах чаще всего используется сплав из нержавеющей стали типа 316L (UNS S31603) с соответствующими фитингами. When choosing materials for H&I installations in the hinterland, 316L stainless steel alloy (UNS S31603) with matching fittings is most commonly used. Unless there are any specific plant-related conditions that require special attention, this will provide the system with enough corrosion resistance to adapt to the environment it is in, providing a cost-effective long-term solution. However, in the case of onshore or offshore installations, the conditions are significantly different, as the system will be subjected to waves that cause salt deposits to form on the pipes and connecting surfaces.
Corrosion occurs naturally whenever metals are exposed to corrosive substances. Once corrosion begins, the rate of corrosion is controlled by several factors, including the temperature of the metal alloy and the concentration of corrosives. In the marine environment, high concentrations of chlorides can initiate corrosion processes in stainless steels and nickel-based alloys. Consequently, the stainless steel grades most commonly used in inland waters are not suitable for these coastal and offshore conditions.
In the marine environment, stainless steel is subject to two main forms of local damage: pitting and crevice corrosion. Pitting forms localized corrosion that can cause pipe leakage when the pipe wall is breached. Crevice corrosion occurs when oxygen access to a localized narrow space is limited, resulting in corrosion within the crevice. With respect to H&I equipment, pitting corrosion is commonly seen on the tubes and fittings, while crevice corrosion occurs most frequently beneath clamps or inside fittings. With respect to H&I equipment, pitting corrosion is commonly seen on the tubes and fittings, while crevice corrosion occurs most frequently beneath clamps or inside fittings. Что касается оборудования H&I, точечная коррозия обычно наблюдается на трубах и фитингах, в то время как щелевая коррозия чаще всего возникает под хомутами или внутри фитингов. With regard to H&I equipment, pitting is commonly seen on pipes and fittings, while crevice corrosion occurs most commonly under clamps or inside fittings.对于H&I 设备，点蚀常见于管材和管件上，而缝隙腐蚀最常发生在夹具下方或内部管件上。 H&I Для оборудования H&I питтинговая коррозия характерна для труб и фитингов, в то время как щелевая коррозия чаще всего возникает под арматурой или на внутренних фитингах. For H&I equipment, pitting corrosion is common on pipes and fittings, while crevice corrosion occurs most often under rebar or on internal fittings. In case of severe crevice corrosion inside the joint while the system is under pressure, the joint can loosen and become a dangerous projectile. In loaded 316L stainless steel parts, chloride stress corrosion cracking can occur if the ambient temperature is high or the process fluid inside the pipe is hot. Stresses in the material can be caused by external loads or cold working of the material, and a rupture of the pipe will lead to the complete failure of this part of the system.
Corrosion processes can have a significant impact on industrial plants, leading to costly downtime, high maintenance bills and, if not detected, potentially dangerous and devastating damage. Despite these risks, standard stainless steel grades such as 316L are still frequently used for these harsh environments, perhaps due to lack of alternatives, lack of awareness, or cost cuts. However, when specifying for an industrial H&I installation in a marine environment, the choice of stainless steel grade is a crucial consideration. However, when specifying for an industrial H&I installation in a marine environment, the choice of stainless steel grade is a crucial consideration. Однако при выборе промышленной установки H&I в морской среде решающее значение имеет выбор марки нержавеющей стали. However, when selecting an H&I industrial installation in a marine environment, the choice of stainless steel grade is critical.然而，当指定用于海洋环境中的工业H&I 装置时，不锈钢等级的选择是一个至关重要的考虑因素。 H&I 装置时，不锈钢等级的选择是一个至关重要的考虑因素〠 Тем не менее, выбор марки нержавеющей стали является важным фактором при выборе промышленных установок H&I в морской среде. However, the choice of stainless steel grade is an important consideration when selecting industrial H&I installations in marine environments.
A choice of 316L stainless steel tubing with a plastic coating is one alternative when selecting H&I material for marine environments. A choice of 316L stainless steel tubing with a plastic coating is one alternative when selecting H&I material for marine environments. Выбор трубы из нержавеющей стали 316L с пластиковым покрытием является одной из альтернатив при выборе материала H&I для морской среды. The choice of plastic coated 316L stainless steel pipe is one of the alternatives when choosing H&I material for a marine environment.在为海洋环境选择H&I 材料时，可选择带塑料涂层的316L 不锈钢管。 H&I 材料时，可选择带塑料涂层的316L 不锈钢管。 При выборе материала H&I для морской среды выбирайте трубы из нержавеющей стали 316L с пластиковым покрытием. When selecting H&I material for marine environments, choose plastic coated 316L stainless steel tubing. This solution exhibits some degree of corrosion resistance and a lower initial cost compared to choosing high alloy stainless steels. However, this solution is often unsatisfactory in the long run for a number of reasons. First, the plastic coating must be removed from the metal at all fitting locations. The fitting will then need to be protected with some kind of casing to limit corrosion, but even then this area will always be the weak link in the system. Great care is also required during installation and throughout the service period of the H&I system to protect the coating from mechanical damage. Great care is also required during installation and throughout the service period of the H&I system to protect the coating from mechanical damage. Great care is also required during installation and during the entire service life of the maintenance and repair system to protect the coating from mechanical damage.在安装过程中和H&I 系统的整个服务期间也需要非常小心，以保护涂层免受机械损坏。 H&I Great care is also required to protect the coating from mechanical damage during installation and throughout the life of the maintenance and repair system. Leaks inside the plastic coating can expose the underlying metal with a high risk of crevice corrosion. Many plastic coatings also degrade when exposed to ultraviolet (UV) radiation from sunlight, high temperatures, or other atmospheric conditions, which can cause them to become brittle and eventually crack.
As an alternative, offshore installation operators can switch to more alloyed grades of stainless steel, whose chemical properties make them more resistant to aggressive environments. The most widely used options are austenitic grades such as 904L, super austenitic 6Mo, or nickel based 625, but super duplex (SD) 2507 can also be used. In terms of pitting, 904L has the lowest tool life, 6Mo and 2507 have similar levels tool life, and alloy 625 has the highest tool life. In terms of seawater crevice corrosion, 6Mo and Super Duplex have the same resistance and are far superior to 904L. However, alloy 625 has been reported in many cases to have surprisingly poor seawater crevice corrosion resistance, which can be a problem, for example, under rebar. It is also important that the fittings used for the H&I installation should match the tube material as using lower alloyed fittings will lower the overall performance of the H&I system. It is also important that the fittings used for the H&I installation should match the tube material as using lower alloyed fittings will lower the overall performance of the H&I system. Также важно, чтобы фитинги, используемые для установки H&I, соответствовали материалу трубы, поскольку использование фитингов из более низкого сплава снизит общую производительность системы H&I. It is also important that the fittings used for the H&I installation match the pipe material, as using lower alloy fittings will reduce the overall performance of the H&I system.同样重要的是，用于H&I 安装的配件应与管材相匹配，因为使用低合金配件会降低H&I 系统的整体性能。同样重要的是，用于H&I Также важно, чтобы фитинги, используемые для установки H&I, соответствовали трубкам, поскольку использование фитингов из низколегированного сплава может ухудшить общую производительность системы H&I. It is also important that the fittings used to install the H&I match the tubing, as the use of low alloy fittings can degrade the overall performance of the H&I system. Using the correct fitting is especially important for compression fittings where the sleeve and fitting body must be rigid and strong enough to deform the tubing.
To understand the characteristics of different grades exposed to the marine environment, we conducted a field study using pipes made from 316L, Alloy 825, 904L and SD 2507. Testing was carried out in two separate coastal areas: on the west coast of Sweden (temperate climate) and in Florida (tropical climate). The tests were carried out for 12 or 13 months, and the samples were exposed to waves at both sites. The test matrix included pipe with fittings (not 825) and 316L elbows to see if it would promote stress corrosion cracking in cold formed materials. Fittings used in all tests were made from 316L steel.
The results from the field testing show that 316L and Alloy 825 are not suitable material choices for marine H&I installations in any of the test environments, as both alloys suffered from extensive pitting corrosion after testing. The results from the field testing show that 316L and Alloy 825 are not suitable material choices for marine H&I installations in any of the test environments, as both alloys suffered from extensive pitting corrosion after testing. Результаты полевых испытаний показывают, что 316L и сплав 825 не являются подходящим материалом для морских установок H&I ни в одной из испытательных сред, так как оба сплава подверглись обширной точечной коррозии после испытаний. Field test results show that 316L and alloy 825 are not suitable materials for marine H&I installations in either test environment, as both alloys have experienced extensive pitting after testing.现场测试结果表明，在任何测试环境中，316L 和合金825 都不适合船舶H&I 装置的材料选择，因为这两种合金在测试后都遭受了广泛的点蚀。 Field test results show that in any test environment, 316L and alloy 825 are not suitable material selection for marine H&I equipment, because these two alloys suffered extensive pitting after testing. Результаты полевых испытаний показали, что как 316L, так и сплав 825 не являются подходящим материалом для морских узлов H&I в любых условиях испытаний, поскольку оба сплава подверглись обширной точечной коррозии после испытаний. Field test results showed that both 316L and alloy 825 were not suitable materials for H&I marine assemblies under any test conditions, as both alloys suffered extensive pitting after testing. Although the 316L was not cracked in the outlet, crevice corrosion was found in the tube below the coupling. Note that the threaded coupling model 316L has been corroded at both control points. In moderate marine conditions off the coast of Sweden, 904L showed minor pitting corrosion on the pipe but no crevice corrosion within the joint. Super Duplex (SD) 2507 was the only brand that did not show pitting or crevice corrosion after testing under tropical Florida conditions.
From field testing, it can be concluded that for temperate coastal regions, the minimum level of corrosion resistance provided by 904L may be sufficient for some applications. However, for more severe conditions, the characteristics of this alloy will be unsatisfactory. In this case, Super Duplex is the only alloy tested that does not corrode. Alloy 825 actually performs slightly worse than 316L and is therefore not recommended for H&I systems in marine environments. Alloy 825 actually performs slightly worse than 316L and is therefore not recommended for H&I systems in marine environments. Сплав 825 фактически работает немного хуже, чем 316L, и поэтому не рекомендуется для систем H&I в морской среде. Alloy 825 actually performs slightly worse than 316L and is therefore not recommended for H&I systems in marine environments.合金825 的性能实际上比316L 稍差，因此不推荐用于海洋环境中的H&I 系统。 H&I 系统。 Сплав 825 фактически работает немного хуже, чем 316L, и поэтому не рекомендуется для систем H&I в морской среде. Alloy 825 actually performs slightly worse than 316L and is therefore not recommended for H&I systems in marine environments.
Alloy 904L is a good material for coastal installations in temperate climates. However, for installations in tropical regions, higher quality alloys should be considered. Typical choices for these conditions are SD 2507, Super Austenitic 6Mo, or Alloy 625 as above. From a cost standpoint, super duplex stainless steel will be cheaper than the other two options, in addition to the advantage of higher yield strength, allowing thinner pipe walls to be selected. The main disadvantages associated with super duplex tubing are that, due to their high yield strength, they are more difficult to bend in the field and the number of fitting manufacturers is limited.
Ultimately, the specific grade of material that should be selected will depend on the climate and specific environmental conditions at the site and location of installation. There may also be restrictions on acceptable grades, such as if an operator adheres to a specific set of industry standards that define or exclude certain material options.
In tropical and offshore H&I installations, SD (super duplex) 2507 is the most attractive solution, displaying no pitting or crevice corrosion during the field investigations carried out. In tropical and offshore H&I installations, SD (super duplex) 2507 is the most attractive solution, displaying no pitting or crevice corrosion during the field investigations carried out. В тропических и морских установках H&I SD (супердуплекс) 2507 является наиболее привлекательным решением, поскольку во время проведенных полевых исследований не было выявлено точечной или щелевой коррозии. In tropical and offshore installations, H&I SD (Super Duplex) 2507 is the most attractive solution as no pitting or crevice corrosion has been identified during field studies.在热带和海上H&I 装置中，SD（超级双相）2507 是最具吸引力的解决方案，在进行的现场调查期间没有显示点蚀或缝隙腐蚀。在 热带 和 海上 & i 装置 ， ， （超级 双））） 2507 是 具 吸引力 的 解决 ， 在 进行 的 现场 调查 没有 显示 点蚀 缝隙。。。。。 腐蚀 腐蚀 腐蚀 腐蚀SD (Super Duplex) 2507 является наиболее привлекательным решением для установок H&I в тропиках и на море, поскольку во время проведенных полевых исследований не было выявлено точечной или щелевой коррозии. SD (Super Duplex) 2507 is the most attractive solution for H&I installations in the tropics and offshore as no pitting or crevice corrosion has been identified during field studies. As mentioned earlier, it also has a high yield strength, which allows thinner pipe walls to be selected. The result is a lighter system that has real advantages in a variety of applications such as cargo ships or weight-sensitive offshore vessels.
The use of super austenitic 6Mo grades is still common. Their corrosion resistance is quite high compared to SD 2507 and the pipes are easier to handle in the field due to their lower yield strength. Having multiple accessory suppliers may also have been a reason for this class. Due to the higher cost of Alloy 625, this material is usually only considered in very special cases, such as when H2S cracking resistance is critical.
The results show that SD 2507 exhibits excellent corrosion resistance properties as well as high material strength and mechanical properties in marine and coastal environments and in various climatic conditions. The higher initial investment that may be called for is rewarded with a robust damage resistance that prolongs service lifetime and limits the costs of maintaining the H&I system. The higher initial investment that may be called for is rewarded with a robust damage resistance that prolongs service lifetime and limits the costs of maintaining the H&I system. Более высокие первоначальные инвестиции, которые могут потребоваться, вознаграждаются надежной устойчивостью к повреждениям, которая продлевает срок службы и ограничивает затраты на обслуживание системы H&I. The higher initial investment that may be required is rewarded with robust damage resistance that extends the life and limits the maintenance costs of the H&I system.可能需要更高的初始投资，从而获得强大的抗损坏能力，从而延长使用寿命并限制维护H&I 系统的成本。 h Для обеспечения надежной устойчивости к повреждениям, продления срока службы и ограничения затрат на обслуживание систем H&I могут потребоваться более высокие первоначальные инвестиции. Higher initial investment may be required to provide reliable damage tolerance, extended service life, and to limit maintenance costs for H&I systems.
Read the article online: https://www.oilfieldtechnology.com/offshore-and-subsea/12082019/marine-capable-materials/
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