Fast and Accurate Corrosion Monitoring with Bruker 3D Optical Microscopes for Cost Saving in the Refining Industry

The annual cost of degradation of materials and infrastructure in the oil transport and refining industry caused by corrosion is roughly $8 billion. Fast and accurate imaging and quantifying techniques for structural damages are required for research scientists and engineers exploring oil production materials and additives and their influence in the rates and extent of corrosion. Changes in infrastructure over time can be clearly monitored and documented when accurate metrology and high-quality images are available.

Moreover, the impact of prevention techniques, such as additives can be effectively characterized. The 3D optical microscopes offered by Bruker offer large field-of-view images with high resolution and highly accurate vertical scale data to characterize damaging corrosion. These metrology and imaging capabilities are crucial for corrosion monitoring to mitigate detrimental effects of this unavoidable material and environmental process.

Corrosion Is Inevitable, but Controllable

In the oil refining industry, managing the local area failures due to fracturing or pitting in the surfaces is a key challenge presented by corrosion.  In the US alone, there are over 2.5 million miles of pipelines.  Pipelines transporting crude oils are not actually corroded by them. The corrosion found in these pipelines is caused by the presence of sediments or water in trace amounts, leading to leakages or failures over time. The higher proportion of acid or sulfur present in the heavy crude oil does not cause any problem in the cool environment while being transported through the pipelines, but they become corrosive in nature at elevated temperatures (for instance, 200°C) of the refining environment.

Finding and Fixing Is Not Ideal - How About an Ounce of Prevention?

Mechanical inspection devices called "intelligent pigs," or ultrasonic pulse technologies are used for routine analysis of the pipeline environment, allowing the detection of areas of heavier corrosion (Figure 1). Although corrosion can be handled by a "find it and fix it" approach, scientists are continually striving to create better materials, additives, and preventive techniques to lower and eventually control corrosion and its damaging effects.

Figure 1. Internal pipeline corrosion shown. Pits, up to 10 mm deep in some cases, can develop.

The application of organic coatings to prevent corrosion represents a major portion of preventive expenditure (Figure 2). Highly precise measurement instrumentation is required to test the effectiveness and adherence of these coatings to surfaces on a very small scale. Although corrosion takes place on a very small scale in controlled experimentation, the data is useful to predict the functional performance of large infrastructures over time.

Figure 2. Costs of corrosion preventive measures

Scanning Electron Microscopy—Accurate but Slow and Limited

Scanning electron microscopy (SEM) is a highly precise and accurate imaging method employed for the measurement of coatings. This robust imaging and measurement technique is applied to measure and test tiny, localized corrosion pits that are under the influence of material coatings and additives applied for reduction or prevention of corrosive effects.

The longer sample preparation process is a major drawback of SEM, involving sampling sectioning and orienting to enable the measurement of vertical dimensions along with lateral dimensions. This data is crucial for the identification and quantification of the extent and depths of corrosion pitting. Also, SEM is a two-dimensional measurement method, providing profile information or data about a cross-section of an area of interest. True three-dimensional data is critical to gain insight into the nature of 3D corrosion pitting and defects.

Bruker 3D Optical Microscopes Provide Accurate, Fast Corrosion Metrology

Quantifying corrosion is a challenging process. The extent of corrosion on a surface cannot be described by a single measurement. However 3D measurement of surface degradation, such as pitting, offers a sophisticated approach for corrosion to be fully measured, visualized and quantified. Optical profiling measures surface roughness and shape using the interference of light, resolving surface anomalies from millimeter-scale step heights through nanometer-scale roughness. This method operates at scales characterized by corrosion. The 3D analysis allows the estimation of hundreds of parameters to completely describe surface corrosion, such as the amount of material loss over time, directionality of corrosion, ratios of peaks to valleys, and much more.

Bruker’s 3D optical microscopes have targeted automation and analysis capabilities that can save the time and cost related to corrosion research and product development in the oil and gas industries. The ability of Bruker microscopes to achieve a very high speed allows scientists and engineers to monitor and corroborate their research ideas regarding materials and coatings, which represent the two major components of corrosion prevention costs. Bruker's Vision64^® software incorporates a powerful Gaussian filter to flatten images, and its multi-regional analysis pinpoints corrosion pits and measures their volume and size.

Corrosion Coupon Measurements

Many pipeline operators monitor corrosion using corrosion "coupons," which are usually the representative samples of the material used to make the pipelines (Figure 3). The coupons are typically a strip, ring, rod, or disc shaped to fit between pipe joints or into a testing cell. They are positioned in strategic locations in the pipelines and then periodically removed and analyzed for corrosion. They are a cost-effective tool to determine corrosion rates quantitatively in a system under operation. The weight of corrosion coupons is measured before and after exposure to estimate weight loss, and they are also usually analyzed for cracks and pits (Figure 3). The life expectancy of a material can be determined by monitoring an exposed coupon’s mils-per-year corrosion rate. The coupons also visually indicate the type of corrosion that may be taking place in the system of interest.

Figure 3. 3D display image of corrosion coupon with representative pits circled in green.

Evaluating corrosion coupons is a simple and commonly used corrosion monitoring method, as they provide the most reliable physical evidence for corrosion possible. The coupons provide data on average material loss, the nature of the corrosion, extent and rate of corrosion, and distribution of localized corrosion. Corrosion coupon results can show trends indicating acceptable or unacceptable corrosion protection, the need for enhancements in inspection or protection processes or programs, or the gains made by modifications to a treatment program (Figure 4).

Figure 4. Corrosion coupon samples.

The Bruker NPFLEX™ 3D optical microscope platform (Figure 5) provides a cost-effective and suitable 3D metrology solution for corrosion coupon monitoring. The NPFLEX has a large XY stage and working area, allowing it to handle large jigs that are capable of holding multiple corrosion coupons for analysis (Figure 6c).

As a result, a number of materials and coatings can be tested simultaneously under similar conditions. Imaging internal diameters or positioning larger samples is a challenge for smaller optical microscopes from an end-on perspective. This issue is resolved by the NPFLEX as it has a large gantry that can hold larger components, such as corrosion coupon trays (shown in Figure 6e), or custom multi-coupon jigs (Figure 6c and 6d), for measurement of multiple coupons with one simple configuration.

Figure 5. Bruker’s NPFLEX 3D optical microscope. Its large nominal working volume handles small or large sample coupons and multi-sample trays.

It is possible to configure the NPFLEX with a small roller stage option to accelerate measurements on tiny cylindrical coupons as this option facilitates multiple small cylindrical components to be mounted simultaneously (Figure 6d). With a number of multi-coupon holders and a roller stage, the NPFLEX can acquire information from several coupons in one measurement run. This increases measurement efficiency and shortens operator time.

Figure 6a. Measurement of small cylindrical corrosion coupon on an NPFLEX.

The ability to be utilized near-line in production is an advantage of the NPFLEX, thanks to its bridge gantry design that is immune to vibration levels typically present in near-line industrial environments. Also, further stability is provided by the integrated air table to achieve repeatable results in a compact design. The system can be fully accessed from both the front and back due to the open-gantry bridge design, facilitating service and support. Furthermore, data can be collected from areas that are difficult to access, thanks to the ultra-long working distance objectives.

Figure 6b. NPFLEX 3D Analysis Plot showing corrosion pits: Linear stitched measurement data from small cylinder coupon captured with NPFLEX.

Figure 6c. Metal corrosion coupons mounted on a cylindrical jig on the NPFLEX rotational stage chuck.

With these features, the NPFLEX can perform reproducible measurements on a number of samples even at challenging angles. The conversion of metric surface dimensional data into standard reports is easy, providing an objective and comparable measurement capability over time. The automatic corrosion pit identification and analysis feature of the system is really helpful even during coatings and materials development processes. The research lab may measure newly developed materials against the existing materials in use.

Figure 6d. Multiple small cylindrical corrosion coupons in a multicoupon jig, ready for measurement on an NPFLEX.

Figure 6e. Automated coupon tray on NPFLEX stage

Multi- Region Analysis (MRA) - Automatic Identification and Computation for Analysis

MRA is a robust analysis capability of the Bruker Vision64 software that facilitates detection and investigation of a number of areas of interest in the acquired image automatically (Figure 7). This rapid and automated method of determining and monitoring the sizes and depths of corrosion is a key, time-saving feature for materials and coatings development and corrosion monitoring. The ease and speed of data collection to understand experiment results saves costs significantly for materials science research and the development of better coatings. The Bruker 3D microscopy is a valuable tool for the development of preventive materials and coatings, which represents the highest portion of the cost involved in the corrosion prevention process.

Figure 7. MRA analysis results table showing computations on corrosion pits and representative sizes and depths.

Conclusion

In the oil and gas industry, corrosion is an expensive and challenging issue. However, a number of techniques are available to handle the challenges with a special focus on lowering costs and improving reliability. With large sample area, analysis cap, and automatic data acquisition capabilities, Bruker's NPFLEX is a turnkey solution for people working in the development of new corrosion preventive coatings and materials solutions. These features enable Bruker's 3D optical microscopes to reduce metrology and analysis costs, both in terms of dollars and time spent on this crucial step of the corrosion prevention process.

This information has been sourced, reviewed and adapted from materials provided by Bruker Nano Surfaces.

For more information on this source, please visit Bruker Nano Surfaces.