November 2021

Maintenance and Reliability

Continuous corrosion monitoring improves process optimization

Corrosion is one of the most insidious challenges in the oil refining industry.

Corrosion is one of the most insidious challenges in the oil refining industry. When it is uncovered too late or a slow leak has begun, it can lead to catastrophic outcomes. However, monitoring corrosion requires resources and vigilance, as well as the right analytical tools to determine when and where a problem might arise.

The issue of corrosion has become more critical in recent years as refineries opt for less expensive opportunity crudes to meet forecast production and financial margins. Many of these cheaper feedstocks tend to be more corrosive, which further solidifies the demand for a comprehensive monitoring program.

Finding the right solution to meet safety standards for assets and personnel, while maintaining budgets, requires an in-depth look at both existing tools and new options on the market. In addition, finding that midpoint between corrosion risk, process data and impact on the plant can provide a root cause analysis from which to build a suitable preventative maintenance process.

In many legacy systems, traditional methods of corrosion monitoring are used that do not necessarily provide the data to best plan production and asset maintenance. However, more and more facilities are reexamining those methods as they consider and implement more efficient and digitally accessible solutions (FIG. 1).

FIG. 1. Modern plant operators face a variety of challenges, requiring a tightrope balance to meeting set operational standards.

Traditional corrosion monitoring

Although several types of instrumentation have traditionally been used in corrosion monitoring in oil refineries, two are most commonly found: intrusive corrosion [or electrical resistance (ER)] probes and manual ultrasonic inspection.

Intrusive corrosion probes consist of an intrusive element with a sacrificial tip that sits in the process fluid and is (normally) made from the same material as the surrounding equipment. As the sacrificial tip corrodes, its electrical resistivity changes, which is recorded externally; these are also increasingly available for wireless connection. The corrosion of the sacrificial tip is used to infer the level of corrosion being experienced by the surrounding equipment.

Alternatively, manual ultrasonic inspection is an equally well-established technique for measuring metal wall thickness. This technique involves placing a transducer directly onto the metal surface and generating ultrasound, which is transmitted through the metal until it is reflected off the inside metal surface (back wall). The reflected ultrasound signal is recorded, and the time difference between the sent and reflected signals provides the measurement of the wall thickness. While the technique can be reliable, the completion of a full set of measurements for a medium-sized refinery with 80,000-plus corrosion measurement points is time consuming and labor intensive, such that the wall thickness at an individual location may be measured only every 3 yr–5 yr. This is far from ideal when monitoring critical pipelines.

In addition, manual ultrasound has poor repeatability because it is unlikely that the same technician will measure at the exact same location that was measured before. The fluid flowing through the pipes also cannot be too hot, or it may damage the transducer or injure the technician taking the measurement.

A better way to measure

Ultrasound might be an effective way to measure corrosion, but it requires a more reliable way of deployment to be of real use to a facility. To ensure better corrosion measurement coverage, a different ultrasound tool is becoming the device of choice in refineries. This permanently attached, continuous-monitoring ultrasonic measurement device transmits data wirelessly to a central location, thereby providing real-time measurement data-to-desk. The device attaches magnetically for easy use, can withstand temperatures up to 600°C (1,100°F), and can be deployed at scale.

There are several benefits to deploying this device:

  • Instantly access real-time data to drive informed decision-making
  • Eliminate risk to personnel when inspecting dangerous locations manually
  • Shift from reactive to proactive maintenance.

The main benefit is that with instant data available, combined with process data, it becomes possible to gain a more complete overview of operations. It can show where potential trouble spots are growing and what type of hydrocarbon blend is moving through the pipes at what time, thereby pinpointing when trouble first emerges (FIG. 2).

FIG. 2. A comprehensive solution of hardware and software delivers secure and reliable corrosion data data-to-desk continuously.

With the increased use of more corrosive opportunity crudes, it becomes essential to know where those feedstocks might be causing problems and how to stay ahead of such issues by scheduling preventative maintenance instead of reactive maintenance.

Software completes the picture

Online corrosion monitoring is only as good as the software that is used to analyze the data. Independent market research shows that corrosion monitoring software and software services are growing faster than any corrosion hardware has over the past 5 yr. Operators can now have access to an abundance of data, but if they cannot see the patterns in it or the software does not show them what is actually happening inside the facility in an easy-to-read format, then it is not useful.

Real-time asset monitoring means providing end users with continuous, consistent analytics, instead of having to download and export data, and then perform manual calculations. Pre-packaged analytics that focus on the health monitoring of plant assets, along with the corrosion application, allow end users to monitor the risk and impact of corrosion in the plant. Having this data available makes it possible to correlate wall thickness against process variables to better manage risk and drive more efficient operations (FIG. 3).

FIG. 3. Analytics inside software allow end users to perform root cause analysis, plan maintenance strategies and improve informed decision-making.

Better outcomes

With better quality and more current information, a refinery can mitigate risk and manage its crude strategy, choosing less favorable and cheaper feedstocks, while ensuring that the plant is operating safely. Online, non-intrusive corrosion monitoring is fast becoming a refining industry best practice with the availability of data-to-desk monitoring systems that provide previously unachievable quality and frequency of wall thickness measurements.

Maximizing operations, both in terms of productivity and profitability, while balancing the impact of corrosion on fixed assets, removes a great amount of worry and potential for unplanned maintenance shutdowns. HP

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