Why API 510 Included Sweating Service for CUI Management and How Remote Monitoring Helps

Corrosion under insulation (CUI) continues to threaten oil, gas, and petrochemical plants. In fact, CUI failures now account for 20% of major oil and gas accidents according to the UK’s Net Zero Technology Centre.

Given the costly consequences of failure, organisations allocate significant resources to manually inspect vessels for signs of deterioration. Providing guidance on where to prioritise inspection, API 510 has recently introduced a new phrase: sweating service. This addition highlights additional higher CUI risk scenarios.

Meanwhile, technological advances mean you can now continuously monitor vessels remotely, 24/7, with advanced wired sensors. This innovative move means organisations on the front foot are detecting CUI earlier, enabling maintenance instead of costly repair work.

This article looks at the addition of sweating service to the 11^th edition of API 510 before considering its impact on CUI maintenance and the potential benefits of using remote monitoring.

Recent API 510 Modifications

Respected as an inspection code for pressure vessels, API 510 was first published in 1958. It provides essential best practice for inspection, repair, alterations, and rerating of vessels in the oil, gas, and petrochemical industries.

Not surprisingly, API 510 has evolved as technology and methodologies develop. Updates are common and the 11^th edition of API 510 included some minor revisions that may impact your approach to CUI monitoring.

Introducing “Sweating Service”

One such modification was the addition of a new term: sweating service. You’ll find it in 5.5.6.2 and 5.5.6.3. And yet, the API 510 document provides no definition.

So, to make sense of these two sections, we must first consider what sweating service means in this context.

Vessels are generally insulated to protect them from hot or cold weather. Should the temperature fall to the point where water starts to condense, “sweating” under the insulation can occur. Similar to dew forming on a lawn in the cold morning, this is what API 510 means by sweating service.

Let’s look at how API 510 has used sweating service in sections 5.5.6.2 and 5.5.6.3.

API 510 Section 5.5.6.2

This relates to using carbon and low-alloy steels. In these instances, it’s common for CUI to cause localised corrosion. But vessels in sweating service may suffer from general corrosion, with localised corrosion occurring at coating failure locations (API 580 defining “failure” as loss of containment).

In short, vessels in sweating service may require more thorough CUI monitoring to mitigate risk.

API 510 Section 5.5.6.3

This considers when it may be necessary to remove insulation and specifically look for corrosion damage. Until the 11^th edition of API 510, the list covered eight scenarios. Now, there’s a ninth relating to vessels in sweating service:

1. Consequences of CUI leakage
2. History of CUI for the vessel or comparable equipment
3. Visual condition of the external covering and insulation
4. Evidence of fluid leakage (e.g. stains)
5. Equipment in intermittent service
6. Condition/age of the vessel coating under insulation, if applicable
7. Potential for the type of insulation to absorb/hold more water (e.g. calcium silicate vs cellular glass)
8. Ability to apply specialised NDE that can effectively locate CUI without insulation removal
9. Potential for damage due to vessels in sweating service

While the first scenario (consequences of CUI leakage) focuses on an actual failure (loss of containment), the remaining points focus on the increased probability of failure. Vessels in sweating service present higher risk, so it’s easy to see why CUI monitoring in these situations should be prioritised.

A Simple Phrase, Higher Risk

Once you understand what sweating service means in the context of pressure vessels, you can understand why it’s now included in API 510. Many organisations have vast areas of metal under insulation to visually inspect, so it can be challenging to identify corrosion before it becomes a costly remedial job. By appreciating what the highest-risk scenarios are you can allocate resources more effectively and better manage the risk of failure due to CUI.

Putting the Spotlight on CUI Monitoring

With energy conservation a primary goal, more oil, gas, and petrochemical plants include extensive insulation in their designs. This comes with corrosion risks, so knowing how best to detect any onset early is a priority.

Understanding the Risk

When water and corrosive elements – such as chlorides – become trapped under insulation materials, the risk of external corrosion increases. As discussed earlier, vessels in sweating service present a particularly high risk.

When CUI occurs, metals such as carbon and low alloy steels can deteriorate and thin. Also, stainless steel and aluminium may suffer external stress corrosion cracking (ESCC).

The corrosion can develop quickly, and if not detected, lead to loss of containment. The outcome then becomes one of outage and costly repair work to put the vessel in operation again.

Why Failures Occur

There are many reasons why CUI can lead to vessel failures. While some relate to equipment design and specification, many concern having the right processes in place and adequate skills to manage the risk. Common reasons include:

• Aged or excessive insulation
• Poor equipment design
• Low investment in CUI mitigation programs and technologies
• Lack of knowledge about CUI risk
• Inadequate corrosion management strategies
• Limited incident investigation procedures
• Lack of learning from previous mistakes

Equipment coming towards the end of its service life can present a common risk for CUI failure as protective coatings and insulation deteriorate, becoming less effective over time.

Asset integrity management must therefore focus on early detection and management ahead of repairing damage when it occurs. This requires documented procedures and clearly communicated accountabilities. It may also need appropriate investment to achieve an effective process.

It’s worth noting that CUI risk can be significantly lessened at the design stage of equipment. Far better to involve experienced engineers from the outset to help eliminate unnecessary insulation and water traps.

CUI Monitoring Best Practice

CUI management should always start with a good strategy. It may be helpful to structure this into a Plan-Do-Check-Act (PDCA) model to ensure effective prioritisation and ongoing momentum.

An effective CUI management strategy also needs management commitment, effective risk assessment, and successful program execution.

Senior leadership teams must buy in to the importance of a CUI management plan. They must ensure resources, such as software and technology, are available in addition to the skills needed to drive it forward.

Those who understand the assets and likely complications must carry out risk assessments. Inspections should be thorough, fully documented, and unbiased. When undertaken correctly, this phase of CUI monitoring will highlight the priorities to act on first.

No amount of inspection is effective without work execution. This requires a documented plan, appropriate budget, and an experienced team including maintenance planners and plant managers.

How Remote Monitoring Helps

Corrosion monitoring is an established method for managing asset integrity. While not new, innovative technology can now provide new levels of insight, transforming CUI monitoring into a predictive and proactive process.

With the advent of digitalisation and Industry 4.0, wired sensors now exist to identify moisture and corrosion under insulation. By installing them on critical industrial assets, monitoring teams have access to in-depth data 24/7. They can then make data-driven decisions to pinpoint where physical inspection will be most effective, reducing the overall costs of CUI management and improving safety.

By embracing remote CUI monitoring, organisations change their approach from a calendar-based inspection plan to a more predictive (and effective) maintenance plan. They can identify risk faster and respond quickly before it develops into a failure situation.

A Data-Driven Future for CUI Monitoring

API 510 continues to be a helpful guidance document when it comes to inspecting vessels for signs of deterioration. Constantly evolving as knowledge and technology develops, the 11^th edition has expanded the list of likely risks and highlighted the need for an optimum CUI monitoring process.

As many organisations have industrial assets at least part-way through their working life, effective CUI monitoring will help maximise their time in service.

Physical inspection will always be part of the monitoring process. But going forward, remote CUI monitoring will provide a more dynamic approach that positively shifts the emphasis from deterioration reaction to maintenance prediction.