All too often, Corrosion Under Insulation (CUI) is an out of sight, out of mind problem lurking just beneath the surface. That is, until you finally spot a leak that disrupts your system, potentially causing a safety incident or near miss in the field.
The struggles of CUI are widespread and if you don’t yet have a history of CUI leaks, it’s only a matter of time until you encounter your first. So, why is CUI such a common problem and is there anything you can do to stop it? Should you be concerned about CUI at your operations?
我们在Braun Intertec的高度经验丰富的API认证技术人员团队雷竞技好Newbee赞助商无损检查(NDE) Group can shed some light on the widespread problem of CUI for system operators.
Cui是什么，是什么原因？
CUI damage, according to the definition in API 583, is characterized by either general metal wastage or pitting due to the localized breakdown of passivity. More simply, it’s a form of oxygen corrosion which occurs on carbon and low alloy steel when exposed to moisture and oxygen.
当水被绝缘层吸收或收集在它下面时，发生这种腐蚀性损坏。由于在绝缘层或管道护套中破裂并且不能从系统消散水而被吸收。水分系源从雨水，工艺操作溢出溢出甚至在潮湿环境中的金属表面凝结。
When considering your own system’s vulnerability to CUI, strictly speaking, the API 583 standard lists a temperature range of 32 F to 212 F when looking for moisture in a system. However, this range should be extended to 10 F to 350 F to account for fluctuations in the system’s operating temperature, ineffective insulation maintenance, temperature gradients within the equipment considered and various operating modes.
我们发现，由于用户倾向于报告温度，以及是否报告金属或过程温度是如何报告金属或过程温度，因此可能是测量崔损害的风险和严重程度的棘手因素。但是，一般来说，在170 f和230 f之间的较高温度范围内更严重的损坏。
Other factors to consider when it comes to CUI risk are contaminants in the insulation. Chemicals like chlorides and sulfides are sometimes present and can contribute to a corrosive environment.
Why do CUI inspections and maintenance programs matter and who should be concerned?
Effective CUI programs matter for all systems. However, these programs are especially important for older systems with aging piping or where insulation has not been well maintained. Where corrosion is present, it’s common to see anywhere from 5-15 millimeters of corrosion every year—but in the most extreme situations this rate of corrosion can be much more severe. The issue of unaddressed corrosion within your system isn’t merely a question of reliability. This yearly rate of corrosion represents a major safety risk for your personnel that should not go ignored.
相当简单地，每个系统运营商都应该关注CUI。预计，高湿度，高降水区的系统易于具有最糟糕的CUI问题。然而，由于附近的冷却塔羽毛和蒸汽跟踪泄漏，即使在绝缘下的干燥气候水分下也可能仍然可以。
Similarly, all operating conditions, whether it’s in active operation or not should still have a CUI program. In fact, systems that cycle in and out of the CUI temperature range during regeneration cycles or are frequently out of service at ambient conditions, can experience the most destructive corrosion damage even when normal operation of the system is outside the CUI temperature range.
What standards inform CUI programs?
API standards 570, 571, 574 and 583 all cover aspects of CUI from damage mechanisms, areas susceptible to corrosion as well as the design, maintenance and inspection practices for piping. API 570 is most useful when looking for the areas most commonly vulnerable to CUI. API 583 is the primary resource to reference for inspection and prevention techniques.
全国腐蚀工程师协会（NACE）也发表了一个有用的resourceon the topic of CUI guidelines.
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