[ad_1]
Regular non-destructive testing (NDT) inspections of air coolers, also known as air cooled heat exchangers (ACHEs), are crucial for maintaining operational efficiency and ensuring safety of compressor stations within the LNG industry. However, the complexity of inspecting tubing within these units, compounded by technological challenges of these carbon steel tubes with large aluminium fins, hinders inspection companies from relying on the commonly used remote-field testing (RFT). Furthermore, logistical constraints, such as the elevated location of ACHEs, make access for certain inspection methods challenging. For example, the use of internal rotary inspection system (IRIS), which requires extensive cleaning and access to water, can be cumbersome and time-consuming in such environments. Near-field array (NFA) technology emerges as a solution by leveraging C-scan imaging to overcome these challenges and provide accurate assessments of ACHE tubing integrity. By delving into the specific challenges associated with current inspection practices and exploring the capabilities of NFA technology, this article aims to highlight the potential benefits of adopting NFA as a high-resolution detection solution for ensuring the reliability and safety of compressor stations.
Compressor station – air cooler inspection
Compressor stations play a key role in natural gas transmission and distribution networks by compressing gas to maintain pressure levels and facilitate its movement through pipelines. Within these stations, air coolers (Figure 1) help regulate the temperature of the gas to ensure efficient compression and prevent overheating. These systems are commonly constructed using carbon steel tubes with aluminium fins. This design is favoured for its efficiency in dissipating heat from the compressed gas flowing through the tubes. A notable characteristic of air coolers is their frequent installation at elevated locations to optimise their performance. This design necessitates the inclusion of ladders and catwalks for accessing various parts of the air cooler structure such as the header box, which connects the tubes to the inlet and outlet headers.
The tubing in air cooling systems is subject to various environmental and operational factors that can lead to wear, corrosion, or other forms of defects over time. Regular inspection of this tubing is essential to identify any defects or vulnerabilities that could compromise the integrity and performance of the system.
RFT technology is a standard NDT method for inspecting carbon steel heat exchanger tubing; however, when it comes to inspecting tubing with large aluminium fins, like those found in ACHEs, RFT is not a suitable technique. The aluminium fins block or interfere with the electromagnetic fields used by RFT probe, which makes it incapable of detecting defects in the underlying tubing. As a result, alternative inspection techniques such as magnetic-flux leakage (MFL), IRIS, near-field testing (NFT), and NFA are used for inspecting air cooler tubing with aluminium fins to offer sensitivity and reliability in defect detection.
Magnetic-flux leakage
MFL stands out among inspection methods for its capability to identify flaws like corrosion, cracks, or material loss in ferromagnetic materials such as carbon steel tubes. This technique relies on a powerful magnet to magnetise the ferromagnetic material under test. Material loss due to defects results in the magnetic field experiencing flux leakage, which is then detected by receiver coils. MFL exhibits sensitivity to both inner diameter (ID) and outer diameter (OD) defects in ferrous materials. Its effectiveness extends to aluminium-finned carbon steel tubes, as the presence of these fins minimally affects the magnetic field. However, MFL sensitivity can be influenced by the pulling speed of the probe which, if not controlled properly, could cause the sizing of defects to become challenging.
Internal rotary inspection system
Introducing IRIS for tubing inspection in air cooled heat exchangers presents both benefits and challenges. IRIS is a widely used NDT technique that utilises a rotating ultrasound probe to enable cross-sectional imaging of the tubing wall for precise flaw detection and wall thickness measurement. While IRIS offers high-resolution imaging and accurate defect detection capabilities, its application in ACHE tubing inspection is not without limitations, especially when considering the challenges posed by access platforms and ground-level access points. Key factors that complicate the application of IRIS for ACHE tubing inspection include:
- Carrying the necessary inspection gear up to the elevated catwalks poses a logistical challenge in itself. The equipment required for IRIS inspections, including the probe, cables, and other accessories, can be heavy and cumbersome to transport, especially when navigating narrow spaces on the catwalks. This challenge not only increases the physical strain on inspectors but also adds to the time and effort required to set up the inspection.
- Moreover, deposits and certain corrosion patterns on the tube surfaces can diffuse the ultrasound signals emitted by the IRIS probe. As a result, signal loss in certain regions of the tubes may occur, potentially causing significant flaws to be overlooked.
Enjoyed what you’ve read so far? Read the full article and the rest of the June issue of LNG Industry by registering today for free!
Read the article online at: https://www.lngindustry.com/special-reports/21062024/tube-insights/
[ad_2]
Source link
