Ask the Expert – What do Industry 4.0 and Industrial IOT Mean for Predictive Corrosion Management?

Ask the Expert – What do Industry 4.0 and Industrial IOT Mean for Predictive Corrosion Management?

Dr Prafull Sharma, Chief Technology Officer, Corrosion RADAR

Dr Prafull Sharma, our ICorr Midlands Chair, currently serves as Chief Technology Officer of UK-based CorrosionRADAR Ltd., which is bringing innovative corrosion monitoring technologies using the Industrial Internet of Things (IOT). CorrosionRADAR invented a predictive CUI monitoring system, which is gaining global traction, addressing a big issue for the industry.
Dr. Prafull Sharma brings vast industrial experience, especially in the digitalisation of corrosion management, on which there are several inventions to his credit. Dr. Prafull did his PhD at Cranfield University, UK. He is also credited with over fifteen international patents and innovations.

For decades, corrosion has been one of the most significant risks to asset integrity. Across the globe, maintenance teams inspect as high a percentage as they can with the available resources. But many assets remain unchecked, leaving the potential for nasty (and costly) consequences.

Therefore, it’s no surprise that businesses have become interested in entering the era of Industry 4.0 while harnessing the potential of Industrial Internet of Things (IoT) and advancing digitalisation to control the global corrosion problem. Indeed, leading organisations are now embedding IOT methods into their processes.

Could developments in new sensing methods, device connectivity, and enhanced predictive data insights pave the way for a smarter approach
to mitigating or optimising expensive corrosion and inspection management programs?

The Global Corrosion Challenge 

The most recent AMPP (NACE) Impact Study of 2016 highlighted what the industry is up against. The annual global cost of corrosion across all sectors is 2.5 trillion US dollars (Impact Study) . Meanwhile, corrosion under insulation (CUI) is estimated to be responsible for 60%  of pipeline failures (Swift, 2019).

As assets age and portfolios widen, relying on traditional manual inspection processes can feel overwhelming. With numerous surfaces to inspect for signs of corrosion, asset deterioration can develop undetected.

What’s more, many assets are hard to reach without addressing additional safety issues and installing extensive scaffolding. And that’s before you know whether there’s something to remediate.

Asset inspection remains crucial, though. The cost of downtime due to failure or the need to make significant repairs can be eye-watering.

The industry has been stuck in this scenario for too long. However, digitalisation and industrial advances in IOT may provide an answer.

What is Industry 4.0?

Industry 4.0 represents the fourth industrial revolution, characterised by the integration of digital technologies, automation, and data-driven decision-making in manufacturing and industrial processes. It leverages advancements such as the Industrial Internet of Things (IOT), artificial intelligence (AI), big data analytics, and cloud computing to create smarter, more connected systems. In the context of predictive corrosion management, Industry 4.0 enables continuous monitoring of assets, predictive analytics for early detection of corrosion risks, and automated responses to mitigate failures, ultimately enhancing efficiency, safety, and cost savings in industries such as oil, gas, petrochemical, chemical processing, and infrastructure maintenance. In the context of predictive corrosion management, Industry 4.0 enables continuous data collection from sensors, advanced analytics to predict corrosion trends, and automated maintenance strategies—helping industries proactively manage asset integrity, reduce downtime, and extend equipment lifespan.

What is the Industrial Internet of Things (IoT)?

The Industrial Internet of Things (IoT) is a key pillar of Industry 4.0. It refers to the network of connected sensors, devices, and systems that collect, transmit, and analyse industrial data continuously. IOT enables smarter decision-making by integrating operational technology (OT) with information technology (IT), allowing industries to optimise processes, enhance efficiency, and improve asset reliability. In the context of predictive corrosion management, IOT plays a crucial role in monitoring environmental and material conditions, predicting corrosion rates, and enabling proactive maintenance. By leveraging IOT, industries can shift from reactive to predictive strategies, minimising failures and optimising asset performance.

Key Components of IOT in Predictive Corrosion Management for the Energy Industry

In energy industries such as oil, gas, and petrochemicals, IoT-driven predictive corrosion management is essential for maintaining asset integrity, minimising downtime, and ensuring operational safety. Below are the key components of IoT, along with best practices tailored to the energy sector.

Types of Sensors Used in Industries

1. Smart Sensors

Smart sensors are the foundation of IoT-driven predictive corrosion management, enabling continuous monitoring of asset integrity. These sensors measure critical parameters that influence corrosion, providing actionable insights for early detection and mitigation.

Examples of Smart Sensors in Corrosion Management


• Cathodic Protection (CP) Sensors: Monitor CP system performance
by measuring current, voltage, and potential shifts in buried or submerged structures.

• Coating Integrity Sensors: Detect coating degradation, disbondment, or permeability issues that could accelerate corrosion.

• Corrosion Rate Sensors: Measure corrosion rates using electrochemical techniques such as linear polarisation resistance (LPR) or electrical resistance (ER).

• Corrosion Under Insulation Risk Monitors: Use of wire sensors to monitor and locate high-risk locations of CUI.

• Environmental Sensors: Measure predictive parameters, such as humidity, temperature, pH, chloride, and oxygen levels, to assess corrosion risk factors.

•Wall Thickness Monitors: These devices utilise ultrasonic or electromagnetic techniques to detect metal loss in pipelines, tanks, and other structural components.

The following are some examples of best practices when
deploying sensors:

•Deploy multi-sensor arrays at high-risk locations, such as weld joints, bends, and submerged structures.

•Integrate sensor data with predictive analytics to detect early warning signs and optimise maintenance schedules.

•Use wireless and low-power sensors for remote and hard-to-access assets.

By leveraging a combination of these smart sensors, industries can gain a comprehensive understanding of corrosion dynamics and transition from reactive maintenance to predictive asset management.

2. Edge Computing

Edge devices process data locally near the sensor, reducing latency and enabling continuous decision-making.

Apply AI-based edge analytics to filter noise and detect meaningful corrosion trends.

Implement decentralised processing to reduce reliance on cloud connectivity in offshore and remote sites.

Utilise ruggedised edge computing devices that can withstand extreme environmental conditions.

3. Connectivity and Communication Protocols

Reliable data transmission is crucial for IOT performance, especially in harsh environments such as offshore platforms and refineries.

Common Communication Protocols

• 5G and Private LTE Networks: Enable high-speed, low-latency communication for continuous monitoring.

• Choose communication protocols based on environmental constraints (e.g., use satellite-based IoT for offshore rigs).

• Ensure cybersecurity protocols such as VPNs and encryption for secure data transmission.

• Implement redundant communication pathways to prevent data loss in case of network failures.

• Industrial Ethernet and Modbus TCP/IP: Used in SCADA systems for secure and stable data transmission.

• LoRaWAN and NB-IoT: Ideal for long-range, low-power transmission in remote pipeline monitoring.

4. Cloud Computing and Data Storages

Cloud platforms aggregate and analyse data from multiple assets, providing a holistic view of corrosion risks across operations.

• Ensure compliance with industry standards (e.g., ISO 27001, NIST) for data security and regulatory requirements.

• Implement AI and Machine Learning (ML) models in the cloud to refine predictive maintenance strategies.

• Use cloud-based asset management platforms to centralise corrosion monitoring across multiple facilities.

5. Artificial Intelligence and Machine Learning
(AI/ML)

AI-driven analytics enhance predictive capabilities by identifying patterns of corrosion and forecasting potential failure risks.

• Deploy AI-driven root cause analysis to identify and mitigate corrosion sources before they lead to failures.

• Train ML models using historical and continuous corrosion data to improve prediction accuracy.

• Use AI-powered digital twins to simulate corrosion scenarios and optimise maintenance planning.

6. Cybersecurity and Data Protection

With increased connectivity, securing IOT infrastructure against cyber threats is critical.

•Implement end-to-end encryption for sensor-to-cloud data transmission.

•Regularly conduct vulnerability assessments and apply firmware updates to IOT devices.

• Use multi-factor authentication and access controls for critical systems.

By integrating these IOT components effectively, oil, gas and petrochemical companies can transition from reactive corrosion management to predictive strategies, reducing unplanned downtime, improving asset longevity, and ensuring operational safety.

IOT Presents New Opportunities for Corrosion Management

Wherever you look, IOT appears to be the future. Smart cities, smart health, and digitalised education are a few examples. It’s the future for industry too. And for some sectors, it’s rapidly becoming the present:

•Advanced CUI monitoring methods using IOT also reduce the environmental impact of many assets. Catching problems early reduces the risk of deadly substances such as Methane leaking into the local environment (Environmental Defence Fund) , so digitalisation supports ESG strategies as well.

•Data-informed decision-making improves, and the risk of unexpected damage from corrosion significantly falls.

•Industry 4.0 has evolved IOT quickly, allowing remote connections to gather data for decision-making. This technological advancement is transforming how industries operate, providing benefits that many have yet to experience.

•Remote monitoring also improves personnel safety. With less need for routine inspections, maintenance teams can rely on data-based decisions to access locations where the data suggests a corrosion risk. Therefore, time in the field is smarter and safer.

•So, IOT enables wireless connectivity with devices attached to industrial assets. Devices that can continuously collect data 24/7 without the need
for physical inspection. Using a central software platform to collate every piece of insight, assets can be remotely monitored from anywhere in
the world.

•The power of this development is extensive. Organisations can utilise the technology to reach all their assets, regardless of location.

•While it’s hard to deny that new technology is an investment, it’s balanced against the typically high physical inspection and repair costs when people are restricted to a manual process. Given the unpredictability of CUI, you’re far more likely to encounter more significant damage when you lack access to remote monitoring.

IOT-Based Predictive Corrosion Management
in Action

Several technologies have developed to support remote monitoring and control of asset corrosion. Some are in their infancy, while large organisations use others daily. Many relate to internal corrosion as
well as recent advancements in external corrosion, such as corrosion
under insulation.

Internal Corrosion – Non-Intrusive Corrosion Monitoring

Ultrasonic Wall Thickness: Ultrasonic Testing (UT) thickness monitors are a key IOT-enabled tool for non-intrusive corrosion monitoring. These sensors utilise high-frequency sound waves to measure the remaining wall thickness of pipelines, vessels, and structural components, detecting metal loss caused by internal corrosion. Traditional UT inspections require manual measurements, but IOT-based UT monitors provide continuousdata without the need for shutdowns or physical access. By integrating with wireless networks and cloud platforms, these systems allow remote monitoring, automated trend analysis, and predictive maintenance planning — reducing inspection costs and minimising the risk of unexpected failures.

External Corrosion – Corrosion Under Insulation (CUI) Risk Monitoring

CUI is unpredictable and ‘hidden’, which is a huge concern for the oil, gas, and petrochemical industries.

• Damage doesn’t always develop near a damaged section of insulation. Instead, water from rain or humidity can ingress further, making it challenging to predict where corrosion might take hold.

• Many plants operate in locations that experience extreme heat or cold, making insulation necessary to maintain the temperature of liquids passing through pipes and tanks. Yet, insulation can trap moisture.

• Physical inspections require the removal of insulation and the installation of significant scaffolding to gain access, limiting what maintenance teams can see.

• The advance of IOT technology has now enabled oil, gas and petrochemical plants to install remote sensors that report early signs of asset deterioration due to CUI. Wirelessly connected, these smart sensors are embedded along the insulated structure and transmit data to an analytics dashboard. For example, they can monitor temperature gradients, humidity, and moisture ingress under insulation.

• With in-depth data insight from a wide range of assets—even those hard to reach—maintenance teams can make informed and prioritised decisions about where remedial work should be carried out. In this way, they mitigate problems before the damage spreads further and focus their physical activity on the areas at highest risk.

Cathodic Protection Remote Monitoring

Cathodic Protection (CP) remote monitoring is a crucial IOT application for managing external corrosion in buried pipelines, offshore structures, and storage tanks. CP systems utilise impressed current or sacrificial anodes to protect metal surfaces from corrosion; however, their effectiveness depends on maintaining proper voltage and current levels. IOT-enabled CP monitoring systems continuously track key parameters such as pipe-to-soil potential, current flow, and anode performance, transmitting continuous data to centralised platforms. This eliminates the need for manual site visits, ensures compliance with corrosion protection standards, and enables early detection of CP failures, thereby reducing the risk of costly asset degradation.

The Era of Predictive Monitoring

Remote corrosion monitoring, enabled by the advancement of IOT, presents a further benefit to managing asset integrity: prediction.

•Being able to monitor and predict where corrosion is likely to occur presents asset-intensive organisations with a significant opportunity to better control this primary operational risk. Thanks to IOT, embracing the capability of new industry technology will reduce maintenance costs and mitigate potential failures.

•By installing IOT remote monitoring systems with environmental sensors across your assets, you collect a huge amount of relevant and timely data. Using predictive analytics to spot patterns in the data, you can highlight risk areas before visible damage occurs.

•For example, CorrosionRADAR’s Clarity Dashboard provides data-driven insights into historical data, environmental factors, moisture, and corrosivity rate to predict corrosion progression. As data continues to populate the dashboard, the picture only becomes more apparent.

Maintenance teams can then use risk maps and actionable insights to prioritise areas for physical inspection and repair. This optimises resource allocation and ensures the effectiveness of their corrosion management process.

Why Digital Twins Help in Corrosion Management?

As technology advances further, digital twins have become helpful in detecting and managing corrosion.

•By visualising your assets virtually, even when they’re out of easy reach, you can ensure optimum safety and maximise the service life of each piece of equipment. Digital twins can also help with compliance with safety and regulatory requirements, enhancing your reputation as a responsible operator.

•Digital twins are virtual replicas of physical assets, processes, or systems that mirror their real-world counterparts. Remote sensors, simulations, and machine learning can help create an interactive ‘twin’ that enhances monitoring and enables deeper analysis. It is worth noting that there are several definitions and connotations of Digital Twins in the industry, and the above is just one of them.

•Digital twins can enable detection at the earliest opportunity, making monitoring and maintenance more proactive. Analysing data from various sources, this holistic approach provides the most data-informed decision-making currently possible.

IOT is Shaping Future Corrosion Management

•IOT is rapidly paving the way for more effective corrosion control—a challenge that many industries have struggled to overcome for decades. Being able to remotely monitor your assets, wherever they are in the world, offers levels of insight many would welcome.

•More comprehensive data insight, available without physically inspecting assets, is transforming maintenance programmes for organisations worldwide. Not only does it help spot (and predict) corrosion earlier, but such insight also reduces maintenance costs and enhances safety.

•The moment you install remote IOT monitors to help control corrosion, your risk levels reduce as you collect widespread data. And this is only the beginning. As technology advances further, there’s no end to how it can help mitigate the incredibly costly risk of corrosion.

References

[1] NACE International, 2016. IMPACT breaks new ground in the study of corrosion management. Materials Performance, [online] Association for Materials Protection and Performance. Available at: https://impact.nace.org/documents/MP0316-Impact.pdf 

[2] NACE International, 2014. Corrosion under insulation on industrial piping – a holistic approach to insulation system design. In: CORROSION 2014 Conference & Expo, 9–13 March, San Antonio, Texas. NACE International. Available at:
https://www.onepetro.org/conference-paper/NACE-2014-4084 

[3]  Environmental Defence Fund, n.d. Methane: A crucial opportunity in the climate fight. [online] EDF. Available at: https://www.edf.org/climate/methane-crucial-opportunity-climate-fight

Ask the Expert – Issue 185

Ask the Expert – Issue 185

How do we Detect and Mitigate AC Interference in Pipelines Using Software Modelling?
J N Agrawal, B Tech, MBA, ICorr CP4, FICorr, CEO of Corrsol Tech, India

Meet the Author

Jaiprakash Narain Agrawal is an expert in corrosion management and cathodic protection. He has a wide experience in pipeline integrity management and cathodic protection for 40 years. Jaiprakash has worked in projects, construction, operation and maintenance of oil and gas pipelines. Jaiprakash has presented papers in corrosion related subjects at AMPP and ASME conferences in India. He has also authored books on cathodic protection and pipeline integrity management. Jaiprakash also initiated a process for corrosion audits for gas pipelines. He has contributed to the preparation and implementation of procedures for various CP monitoring techniques. Jaiprakash received the AMPP India corrosion awareness award in 2023 for his contribution in corrosion science and technology in industry.

For the last 7 years he has been a certified ICorr Level 4 CP specialist. He is an independent consultant and CEO of Corrsol Tech and engaged in providing solutions in corrosion control, pipeline integrity management and cathodic protection. Jaiprakash has carried out pipeline integrity assessments including fitness for purpose (FFP) and remaining life assessment (RLA) of onshore and offshore pipelines. He has also been involved in conducting training and coaching in pipeline integrity management (PIM) and cathodic protection (CP).

He has published more than 30 technical papers in peer-reviewed events and journals and has provided industry training on integrity management and CO2 and H2.

Background

Electrical interference by alternating currents (AC) is a major consideration for oil and gas pipelines. Computer modelling can be used to assist with its mitigation. AC interference corrosion in pipelines typically occurs when alternating current (AC) from nearby power lines induces a voltage on the pipeline, leading to corrosion, especially at small coating defects. This phenomenon is a serious concern due to the potential for rapid and localised damage, even in pipelines with cathodic protection.

What is Software Modeling?

Computer modelling is based on the simulation of all field data and the assessment of AC interference based on computer modelling with the following outcomes:

• The results are usually more accurate than field surveys alone, as data simulation is assisted by computer modelling.

• Various mitigation strategies can be implemented based on computer modelling outcomes for the most effective and cost-‘optimised’ manner.

• The most important features required for effective mitigation are:

Configuration of grounding
Location of grounding
Selection of materials of grounding

Effectiveness can be checked after implementation of mitigation measures.

Background

Electrical interference by alternating currents (AC) is a major consideration for oil and gas pipelines. Computer modelling can be used to assist with its mitigation. AC interference corrosion in pipelines typically occurs when alternating current (AC) from nearby power lines induces a voltage on the pipeline, leading to corrosion, especially at small coating defects. This phenomenon is a serious concern due to the potential for rapid and localised damage, even in pipelines with cathodic protection.

What is Software Modeling?

Computer modelling is based on the simulation of all field data and the assessment of AC interference based on computer modelling with the following outcomes:

The results are usually more accurate than field surveys alone, as data simulation is assisted by computer modelling.

Various mitigation strategies can be implemented based on computer modelling outcomes for the most effective and cost-‘optimised’ manner.

The most important features required for effective mitigation are:
Configuration of grounding
Location of grounding
Selection of materials of grounding

Effectiveness can be checked after implementation of mitigation measures.

Impact of Contradiction Between Field Survey and Simulation Result

•Designed mitigation measures may be ‘more or less’ compared to actual or required.In case of more than required, cost will be more.

• In case of less than actual required, effectiveness will be less.

•Pipeline will be affected in case of ineffective mitigation measures. however, simulation results can be verified by the field survey results.

•Even then, errors may happen in case of inaccurate data or interpretation of the simulation results.

Possible Reasons for Contradiction in Software Simulation Results and Field Data

• Global earthing systems.

• Local earthing systems.

•Parallel underground pipelines in the vicinity of the powerline or electric traction.

• Inadequate pipeline coating parameters.

• Influence of soil resistivity in the field and simulation software.

• Actual or real-time load current instead of maximum load current
of powerline.

Computation of Induced AC Potential and AC Current Density Based on Real Time Load Current or Peak Load:

• Field survey is performed for AC induced voltage and AC current density based on real time load current while simulation is done based on peak load current.

• Hence, AC induced voltage and AC current density will vary. Simulation results are on the higher side than field surveys.

• The mitigation measures based on simulation results consider optimum conditions. 

• Powerlines generally run on load, which is less than the peak load but may reach peak’ load at peak hours.

• Powerlines are designed to withstand higher load capacity.

• Actual load current data consideration will give almost similar results as simulation software provides.

Possible Solutions to Achieve More Accurate Results

• Accurate multi-layer soil resistivity data is required for software simulation.

• Reliable and accurate software with high calculation accuracy is preferred.

• Software should allow multiple input parameters and provide precise simulation results.

• The accurate and calibrated instruments should be used with recommended technique by a certified and experienced CP technician.

• Real time load data should be used instead of peak load.

•n Simulations must consider other factors such as global earthing system (GES), local earthing system (LES), pipeline coating characteristics and parallel pipelines.

• Simulation results should invariably match with field survey.

Case Study of AC Interference and Mitigation with Computer Modelling Using the Following Input Considerations

• Material of Construction: carbon steel

• Outside Diameter (OD): 10”

• Length of pipeline: 112 Km

• Wall Thickness: 6.4 mm

• Coating: 3LPE

• Coating Leakage Resistance: 60000 Ohm-m2

• Minimum Coating Thickness: 3mm

• Pipeline Burial Depth: 1.5 meters from Finished Ground Level (FGL)

• Existing grounding locations: 32 Nos

• SV/IP stations earthing locations: 10 Nos

• Grounding material: Copper conductor/Zn anodes 10 Kg

• Number of transmission lines running parallel/crossing pipelines: 14

• KV rating of transmission lines: 132, 220, 400

• Normal load/peak load in A: 15 to 260/25 to 589

• Simulation done from peak load.

Figure 1: Interpolation of Transmission Line and Pipeline.

Interpretation of Results with Existing Pipeline Ground Points

Key Observations

•Induced AC voltage in the pipeline is proportional to the load current in the transmission line as load current varies at different lines.

•The touch voltage on pipeline exceeds the prescribed safe limit of 15V with a maximum of 16.618 V at chainage 385.63 KM.

•High values of current density between Chainage 382.8 and 386.43 km where induced AC voltages are higher and soil resistivity is low.

•The current density exceeds the prescribed value of 100 A/m2 for about 28.84 KM as shown in the figure.

•Induced AC voltage and AC current density can be interpolated to draw the conclusion that wherever AC current density is higher, AC induced voltage is also higher but higher induced AC potential may not cause higher AC current density if soil resistivity is higher.

•An interpolated graph of pipeline route with chainages and transmission line along with a graph showing chainages, soil resistivity, induced AC voltage and AC current density will establish relationship with multiple parameters.


Material Specification for Grounding Depending Upon AC Current Density and Length of Parallelism

A copper conductor wire of following specifications is required

• AWG No 6.

• Overall Diameter: 38 mm.

• Length: 25.4 m, 76.2 m and 152.4 m in horizontal configuration.

•To be placed at 1m from pipeline wall and at the same depth as of pipeline.

•Copper conductor shall be connected to pipeline through DC Decoupler.

Case Study Conclusion

The major observation is this case study was that existing grounding/earthing arrangements were not adequate to ground induced AC potential and limit AC current density because of wrong location or wrong grounding material. Further work would be required for this and other similar situations.

References

1.NACE SP 0177–2014: Mitigation of Alternating Current and Lightning Effects on Metallic Structures and Corrosion Control Systems.

2.NACE SP 21424:2018: Alternating Current Corrosion on Cathodically Protected Pipelines: Risk Assessment, Mitigation,
and Monitoring.

3.EN 50443:2012 Effects of Electromagnetic Interference on Pipelines Caused by High Voltage.

4.BS EN 15280 – 2013 – Evaluation of AC. corrosion likelihood of buried pipelines applicable to cathodically protected pipelines.

5.Criteria for Pipelines Co-Existing with Electric Power Lines, prepared for The INGAA Foundation by DNV GL.

6.CEPA – A/C Interference Guideline Final Report – June 2014 and INGAA or CEPA for mitigation measures.

7.ISO 15589 Part I – Cathodic protection of pipeline/structure transportation systems – Part I-On land pipeline/structure, issued by the International Organisation for Standardization (ISO).

Ask the Expert

Ask the Expert

Why is Effective MIC Control Still a Major Challenge for Many Oil and Gas Assets?

by Dr Ali Morshed, Consultant Corrosion Engineer, UK.

Meet the Author


Dr. Ali Morshed

Dr. Ali Morshed holds a PhD in corrosion engineering from University College London, an MSc in corrosion engineering from Imperial College London, and a DIC and CEng. He is the author of five corrosion management books and one MIC book with NACE/AMPP between 2012 and 2022. Ali is a corrosion engineer with more than 21 years of experience and started his professional career in the oil and gas industry back in 2002. Since the introduction of the Morshed Corrosion Management Model (MCMM) in 2012, he gradually expanded his work to many other industries. Ali has worked in the North Sea, North Africa, the Persian Gulf Region, and South Asia. He provides corrosion management and MIC consultancy and training services for various industries.

Background

MIC remains a major integrity threat and a common cause of failure for many upstream, midstream and downstream assets – in spite of the significant technological advances in the areas of oilfield microbiology, metallurgy and used chemicals.

Extensive field experience from both the UK’s North Sea sector and the Persian Gulf region indicates that the main root cause of the encountered MIC cases has been either the total lack of, or inadequate, knowledge and expertise in relation to bacteria and MIC fundamentals among the pertinent personnel. Simultaneously, it has also been observed that oil and gas assets which successfully managed the MIC integrity threat were the ones whose relevant personnel (particularly those managing operations and turnarounds’) possessed adequate competency, mainly through the MIC training they had received.

While MIC incompetency remains the main root cause of a number of highly expensive failures, timely, practical and adequate MIC training is regarded as the key for tackling the spiralling MIC incidents for the oil and gas and other industries assets.

What is MIC?

MIC can be defined as corrosion influenced by the presence, or activity, of micro-organisms [1]. Micro-organisms can cause corrosion problems for various oil and gas assets by their metabolic activities.  The corrosion damage inflicted by microbes can be considered “direct” when they create or further increase the environment’s corrosivity (e.g., acid production through their metabolism). The damage is considered “indirect” when they negate a corrosion control measure already in place, thus further promoting corrosion. Such affected corrosion control measures include surface coatings and some dosed chemicals, such as certain types of oxygen scavengers.

A section of failed in-service sea water piping with evidence of metal loss along the bottom of the piping, between the 5 and 7 o’clock positions, is shown in Photo 1. The morphology of pitting suggested that MIC was the cause of the failure. Later laboratory analysis of the corrosion product and biofilm taken from the failed piping section confirmed that the main cause of failure were the sulphate-reducing bacteria (SRB).

Micro-organisms are divided into different groups, of which bacteria are the most encountered in the oil and gas industry. Bacteria are further divided into various categories or families, and sulphate-reducing bacteria (SRB), remain the most predominant and insidious type.

MIC rates, provided that suitable growth conditions exist for bacteria, can be localised and up to several millimetres per year, which is quite severe compared to other corrosion mechanisms often encountered in the oil and gas industry. Corrosion rates have proven hard to predict accurately by modelling. Locations or systems most susceptible to MIC include, but are not limited to:

  • Sea water injection
  • • Fire water
  • Drains
  • Stagnant zones such as a by-pass
  • Cooling water
  • Sand wash water (where treated sea water is used to wash the sand accumulated in various pressure vessels)
  • Water displacement systems (where treated sea water is used to empty a product storage tank)
•             Wet product transfer pipelines
• Wet product storage tanks

The important caveat regarding MIC is that prevention is always less expensive than cure, because microbial control, once lost, may take years to restore, if at all!

The MIC Mitigation Process

Bacteria and associated MIC mitigation process as depicted in Figure 1 refers to a cyclic—and continuous—process composed of three stages [2]:

  • 
 
MIC bacteria monitoring stage—The necessary sampling (both liquid and biofilm [sessile]) is carried out along the pertaining inspections and corrosion rate monitoring activities (in order to produce the required input data for the assessment stage).
  • 
MIC bacteria assessment stage—The input data produced in the first stage are evaluated, trended, processed, analysed, and interpreted to determine bacteria types, density, and the concentration of various compounds consumed or produced by bacteria. The input data are also used to estimate or calculate the associated MIC risk although it should be noted that the presence of high bacterial numbers, does not alone confirm that MIC will occur. The microbial investigation is only one aspect of MIC identification and risk assessment.
  • 
MIC bacteria control stage—In this stage, various activities are carried out to reduce the existing bacteria populations and to decrease the associated MIC risk.

In other words, the MIC bacteria mitigation process consists of three stages, and each stage is composed of two components, one component pertaining to bacteria and the other to MIC. Table 1 provides the associated description and justification for each of the pertaining components.

Stage Components Justification
Stage 1: MIC and Bacteria Monitoring Bacteria 
Monitoring To produce both liquid and biofilm 
(sessile) samples for the next stage 
(assessment stage).
MIC Monitoring To produce predominantly wall thickness inspection and corrosion rate monitoring data for the next stage (assessment stage).
Stage 2: MIC and Bacteria Assessment Bacteria Assessment To determine types (i.e., metabolism) and density of the bacteria encountered in the system, along with the concentration of compounds consumed and produced by the bacteria.
MIC Assessment To determine whether or not the encountered wall losses or corrosion rates are due to bacteria activities, and also to help estimate the encountered MIC risks.
Stage 3: MIC and Bacteria Control Bacteria Control To use methods to either kill bacteria or retard their activity.
MIC 
Control To use methods to reduce or totally arrest the encountered corrosion rates due to bacteria activities.

 

Why MIC Still Remains a Predominant Cause of Failure?

Extensive field experience from the North Sea’s UK sector and the Persian Gulf region has demonstrated that the majority of the observed or studied MIC cases were caused by poor, erroneous, impractical, or late decisions and activities associated with the existing bacteria and MIC. Some of such erroneous decisions and activities included:

  • Selecting sampling locations where no water was present
  • Not capping or sealing the filled sample bottles
  • No chlorination at the sea water inlet
  • Intermittent chlorination at the sea water inlet
  • 
Increasing chlorination injection rate significantly to kill sessile bacteria and remove biofilms
  • 
Using biocide chemicals only effective against planktonic bacteria but incapable of killing sessile bacteria
  • 
Not coordinating sampling activities with biocide treatments (hence, not being able to determine biocide effectiveness)
  • Injecting biocide upstream of the oxygen scavenger injection point
  • 
Using chemicals which act as nourishment for the exiting bacteria groups

However, the “masterpiece” MIC case belongs to a seawater treatment site that stopped biocide injections for two years. Such a decision induced numerous MIC leaks with an associated repair and replacement cost of more than 100 million US Dollars, just for the first year! Their justification for doing so was that because bacteria are too tiny to be seen by the naked eye, the integrity threat they posed was accordingly  negligible; hence, there was no need for any MIC mitigation  treatment!

MIC Incompetency Under Closer Scrutiny

The above examples clearly demonstrate that the lack of or inadequate knowledge and expertise in regard to bacteria activities and MIC fundamentals has been the root cause of the majority, if not all, of the observed MIC cases across many oil and gas assets. More precisely, MIC incompetency has been the main culprit behind the encountered leaks and failures. In general, the observed MIC incompetency can be divided into the following four subject areas:

  1. Bacteria nourishment and growth conditions
  2. MIC and bacteria monitoring
  3. MIC and bacteria assessment
  4. MIC and bacteria assessment

The last three items, when are incorporated with each other comprise the overall bacteria and MIC mitigation process, as was mentioned earlier. Therefore, any shortcomings in properly carrying out any single one of them, could adversely affect the overall bacteria and MIC mitigation process, leading to more problems.

Conclusions

  • 
MIC remains to be one of the most prevalent and insidious corrosion mechanisms affecting  many oil and gas assets.
  • 
MIC management incompetency has been the main culprit behind 
the observed MIC leaks and failures.

Recommendations

  • 
Timely, proper and practical bacteria and MIC training is crucial for the pertinent personnel and managers, both in engineering and operations.

References

  1. Standard Test Method: Field Monitoring of Bacterial Growth in Oil and Gas Systems, TM0194-2014, NACE International, 2014,  ISBN 1-57590-192-7
2. A. Morshed, A Practical Guide to MIC Management in the Upstream Oil and Gas Sector, AMPP, 2023, ISBN 978-1-57590-424-5.

Photo.1: Failed Sea Water Piping Due to MIC, as Indicated by the Severe Pitting Corrosion at the Bottom Line and Later Lab Analysis.

Figure 1: Bacterial and MIC Mitigation Process and Its Three Stages [2].

Table 1- The Components Associated with Each Stage of the MIC and Bacteria Mitigation Process and Their Associated Justifications [2].

Table 1- The Components Associated with Each Stage of the MIC and Bacteria Mitigation Process and Their Associated Justifications [2].

 

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The Significance of PREN for the Corrosion Resistance of Stainless Steel by Sarah Bagnall

Sarah Bagnall, Director Consultancy Services at R-TECH Materials, CEng. MSc, BSc

Sarah is a materials engineer specialising in failure analysis, for the petrochemical, process, and power generation industries. Currently, she is Director of Consultancy Services at R-TECH Materials. With over 600 failure investigations conducted to date, Sarah has broad experience with a wide range of engineering components, metallic and non-metallic materials, and industries.  Sarah has extensive expertise in the corrosion of a wide range of materials, particularly for the chemical processing and petrochemical industries.

  1. What is the Significance of PREN for the Corrosion Resistance of Stainless Steel?

Calculating PREN and How to Apply it
Stainless steels are well known for their superior corrosion resistance, which is primarily a consequence of the significant chromium addition. When exposed to oxygen, stainless steel forms a passive film due to its 10.5% (or more) chromium content. This film protects the material from rusting and even has self-healing properties. Other elements can be added to further improve the corrosion performance, such as Nickel, Molybdenum, and Nitrogen.

Not all stainless steels are created equal. Different grades exist, and their corrosion resistance can vary significantly. The corrosion resistance between grades can be compared by using the Pitting Resistance Equivalent Number (PREN). The calculation used for PREN is as follows:

PREN = Cr% + 3.3 x (Mo% + 0.5 x W%) + 16 x N%

Examples of stainless steel grades and the calculated PREN numbers are given in Table 1 and Figure 1 below.

Performance in Service
While the PREN is useful for ranking and comparing the different grades for relative resistance to corrosion, it cannot be used to predict whether a particular grade will be suitable for a specific application, where pitting corrosion may be a hazard. All environmental and operating conditions must be taken into consideration.In some industries, notably the oil and gas sector, specifications may place tighter restrictions on the PREN for specific grades than that implied by the minimum composition of the grade defined in EN or ASTM Standards.

In practice, the vast majority of stainless steels deployed across industry are of the 300 series type with lower PREN values, where external pitting is actually quite common in service at ambient temperatures.

Corrosion resistance is not only affected by the chemical composition of the material but also by the heat treatment condition. If the material is heat treated incorrectly during manufacture or welding, microstructural changes can occur which effectively means that 
the material is no longer a stainless steel in a localised area. Exposure to temperatures in the range 370-815oC allows the precipitation of chromium rich carbides/nitrides along the grain boundaries. These precipitates are rich in chromium and deplete the area directly adjacent to the boundary of chromium, thereby increasing the likelihood of localised corrosion in the form of intergranular attack, pitting or stress corrosion cracking in a corrosive environment.

Further Guidance 
The British Stainless Steel Association (BSSA) exists to promote and develop the manufacture and use of stainless steel across the UK and Ireland. Based in Sheffield, the Association provides technical advice, information, training, and education in all aspects of stainless-steel 
usage. They may be contacted at: www.bssa.org.uk

Table 1: Comparison of Stainless-Steel Grades Based on the PREN.

Figure 1. Comparison of Stainless-Steel Grades Based on the PREN

Figure 2. Cracking of a Sensitised Stainless Steel Bolt Which Had Been Heat Treated Incorrectly During Manufacture.

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Why Do Bronze Medals Tarnish So Quickly?
By Roger Francis, RF Materials

Meet the Author
Dr. Roger Francis

Dr Francis has been a corrosion engineer for over 45 years. He has wide experience in the fields of marine corrosion, desalination, sour oil and gas corrosion, mineral processing, and the chemical and process industries. He has published over 100 technical papers in all these areas, particularly on copper alloys and duplex stainless steels. Roger has written seven books on various aspects of corrosion and has jointly edited three other books. The most recent was on corrosion in desalination plants. Dr. Francis has served on several standards committees working on corrosion testing of both copper alloys and stainless steels. In particular he was involved with the committee turning NACE MR0175 into ISO 15156.The author has served as chair of NACE Europe, two terms as the NACE (now AMPP) European Area Director and also as Chair of NACE STG 32 (Oil and Gas; metals). He was made a NACE Fellow in 2005 for his work in marine corrosion. In 2014 he received the T J Hull Award for his work in publications. In 2012 he set up his own corrosion consultancy business, RF Materials. In 2023, he received the Institute of Corrosion Paul McIntyre award presented to a senior corrosion engineer who, as well as being a leading practitioner in his field, has advanced European collaboration and international standards development.

Bronze has been used for a variety of medals for over two hundred years and given sufficient time without cleaning, they will all tarnish. Figure 1 shows an old coin with different degrees of tarnish on the two sides. Figure 2 is a bronze medal that also shows tarnishing.

There is a wide range of bronze alloys, where the chief alloying element is tin, aluminium, or silicon. The majority of bronze medals used to be made of LG2 gunmetal (Cu/5Sn/5Zn/5Pb) or something very similar. Tin bronzes are reddish, but not as strongly red as pure copper. Other elements may be added to modify the colour, for example, to make it more yellow. However, to cut costs, many modern “bronze” medals are actually brass (Cu/5Zn), which has a similar appearance to tin bronze but is not as corrosion resistant.

When a “bronze” medal is polished and shiny, the metal surface is very active and reacts readily in the air to form a very thin layer of cuprous oxide. This slightly dulls the appearance, but continued exposure to air will enable corrosion to continue, and a thicker layer of reddish brown cuprous oxide gradually forms. Although both alloys form cuprous oxide as the main corrosion product, the zinc or tin substitutes at some of the copper sites in the oxide matrix. Zinc makes the oxide layer less protective, while tin makes it more protective1. If the tin content is high enough, a separate layer of stannous oxide can form, but this is unlikely at 5% tin1. If a medal is exposed to an aggressive atmosphere for long enough, then a second corrosion product can form on top of the oxide layer, as shown in Figure 3. This is a basic copper carbonate, and it is less protective than the cuprous oxide layer.

Bronze has been used for a variety of medals for over two hundred years and given sufficient time without cleaning, they will all tarnish. Figure 1 shows an old coin with different degrees of tarnish on the two sides. Figure 2 is a bronze medal that also shows tarnishing.

There is a wide range of bronze alloys, where the chief alloying element is tin, aluminium, or silicon. The majority of bronze medals used to be made of LG2 gunmetal (Cu/5Sn/5Zn/5Pb) or something very similar. Tin bronzes are reddish, but not as strongly red as pure copper. Other elements may be added to modify the colour, for example, to make it more yellow. However, to cut costs, many modern “bronze” medals are actually brass (Cu/5Zn), which has a similar appearance to tin bronze but is not as corrosion resistant.

When a “bronze” medal is polished and shiny, the metal surface is very active and reacts readily in the air to form a very thin layer of cuprous oxide. This slightly dulls the appearance, but continued exposure to air will enable corrosion to continue, and a thicker layer of reddish brown cuprous oxide gradually forms. Although both alloys form cuprous oxide as the main corrosion product, the zinc or tin substitutes at some of the copper sites in the oxide matrix. Zinc makes the oxide layer less protective, while tin makes it more protective1. If the tin content is high enough, a separate layer of stannous oxide can form, but this is unlikely at 5% tin1. If a medal is exposed to an aggressive atmosphere for long enough, then a second corrosion product can form on top of the oxide layer, as shown in Figure 3. This is a basic copper carbonate, and it is less protective than the cuprous oxide layer.

Figure 1: 19th Century Coin Showing Different Degrees of Tarnish on the Two Sides.

Figure 2: Tarnished Medal.

Figure 3:
Old Russian Coins from The Early 19th Century Showing Green Carbonate Corrosion Product.

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Preventing Chloride Stress Corrosion Cracking (CSCC) and Degradation in Austenitic Stainless Steels

Dr Shagufta Khan, Ph.D., FICorr

  1. How can we prevent chloride stress corrosion cracking (CSCC) in austenitic stainless steels?

Chloride stress corrosion cracking (CSCC) is one of the most common reasons why austenitic stainless-steel pipework and vessels fail under service in the chemical processing and petrochemical industries however these lower stainless grades can be subject to a wide range of deterioration modes as detailed below.

Stainless steels (SS) must contain a minimum of 11 Wt % chromium, and this level of chromium allows formation of a passive surface oxide that prevents surface corrosion in an unpolluted atmosphere. Increasing Cr content to 17 to 20 %, as typical of the austenitic SS, or to 26 to 29 % as possible in newer ferritic SS, greatly increases the stability of the passive film. Examples of common grade modifications for different applications are given below in Table 1.

AISI          Euronor11z                                 DIN               British                Description                                                       Standard

304           1.4301          X5CrNil 8-10         304S31        
The general-purpose grade, widely used where good formability and corrosion resistance are required.

304L         1.4306          X2CrNi l 9-11         304Sl 1        
As 304 but with lower 
carbon content to Minimize                   carbide precipitation                  during welding.

301 and                    1.4310                    Xl 2CrNi l 8-10      301S21       
Higher strength versions of 304 that are often cold worked to give higher strength.

303      1.4305          XlOCrNiS18-9       303S31        
General purpose grades with sulphur or Selenium added 
to improve machinability.

321           1.4541          XlOCrNiS18-9       321Sl2

321S31        
As 304 with an addition of titanium to prevent carbide precipitation during welding.

347           1.4450          X6CrNiNbl8 -10    347S3l         
As 304 with addition of niobium and or tantalum to prevent carbide precipitation during welding.

316           1.4401          X5CrNiMol7-12-2  316S31        


As 304 but with molybdenum 
added to increase resistance to localised corrosion in          marine and chemical                environments.

316L         1.4404          X2CrNiMol7-13-2 316Sl 1       
As 316 but with lower           carbon content to minimise carbide precipitation during welding.

Austenitic SS can have an excellent combination of mechanical strength, corrosion resistance, ease of fabrication, and cost effectiveness.  The most widely used stainless steel grades are austenitic, with 74% production of total world SS production. Various grades of austenitic steels have excellent corrosion resistance in many environments, resisting attack by the atmosphere and by many industrial gases and chemicals.

The pitting and crevice corrosion resistance of stainless steel is primarily determined by the content of chromium, molybdenum and nitrogen. Manufacturing and fabrication practices, e.g. welding, are also of vital importance for the actual performance in service. A parameter for comparing the resistance to pitting in chloride environments is the 
PRE number (Pitting Resistance Equivalent).

The PRE is defined as, in weight-%

PRE = %Cr + 3.3 x %Mo + 16 x %N

Many of these stainless steels have good strength at high temperatures which accounts for their wide use at elevated temperatures. They are also among the primary materials selected for use at extremely low temperatures, since they do not become brittle compared to other types of steel. AISI 304 and 304L are the most popular grade of austenitic SS. Although austenitic SS are used as corrosion resistance alloys for many applications, there are many cases of failure in aggressive environments. Some of the corrosion failure types that stainless steel remains susceptible to include:

  • 
Crevice corrosion (common, often seen at piping flanges and under identification labels).
  • 
Galvanic/bimetallic corrosion (common, must have compatible fixings/fasteners).
  • 
Pitting corrosion (very common especially under labels, can occur in storage or at fabrication site prior to service).
  • 
Stress corrosion cracking (common at more elevated temperatures and where there are residual stresses).
  • 
Weld decay (less common, varies with process chemistry and applied chemical treatments).

SCC

Stress corrosion cracking is a time-dependent phenomenon that occurs in a metal when certain metallurgical, mechanical, and environmental, conditions are present at the same time. SCC is a somewhat sneaky type of degradation because it occurs at stress levels within the design stress range. The cracking can be:

  • Intergranular (IG): passing through the grain boundaries.
  • Trans granular (TG): passing through the grain matrix.
  • A mixed mode (TG and IG) of SCC,

Depending on the microstructure of the material exposed to the atmosphere and the nature of the environment. SCC is caused by weak tensile stresses, typically below the macroscopic yield stress. Figure 3 describes the necessary conditions for SCC to occur. Austenitic stainless steels may undergo SCC in hot, concentrated chloride solutions, chloride-contaminated steam, and in HTHP (high temperature and     high pressure) demineralised water in presence of oxygen.

Among all types of environmentally assisted cracking of austenitic stainless steel, CSCC is perhaps the most common. Many 
incidences of failure have been reported due to CSCC, e.g. 
condenser tubes in heat exchangers, swimming pool components, 
parts used in marine applications, under insulation of external piping 
in a refinery, and medical devices. Chloride stress corrosion 
cracking of patch repaired elbow in hydrocarbon service is shown 
in Figure 4.

API 571 defines chloride stress corrosion cracking as follows: “Surface initiated cracking of 300 series SS and some nickel-based alloys under the combined action of tensile stress, temperature, and an aqueous chloride environment. It is also referred to as chloride cracking”.  All 300 series SS are highly susceptible to pitting and CSCC where additional stresses exist. Welds in 300 series SS normally contain some ferrite, producing a duplex structure that is usually more resistant to CSCC than the base 
metal though.

Factors Affecting CSCC: Several environmental factors, like chloride concentration, temperature, pH, dissolved oxygen can have profound effect on CSCC. Nickel content of alloy and applied or residual tensile stresses can also affect CSCC.

Chloride Concentration:  CSCC is caused by inorganic chloride ions. It is known that organic chlorides do not directly cause CSCC.  In industrial processes, hydrolysis or thermal decomposition of organic chlorides may produce ionic, inorganic chlorides. Therefore, organic chlorides can also cause CSCC. The components experiencing higher tensile stresses require lower Cl- concentration for initiation of SCC. There is no lower limit of Cl- concentration for crack initiation. A few ppm Cl- in the process stream can concentrate to hundreds of ppm where evaporation takes place. Cl- can further concentrate at the base of pits when pitting corrosion starts. Increasing levels of chloride will increase the likelihood of cracking and greater than 50g/L of chloride in process fluids would certainly give cause for concern for 300 series SS.

Temperature:  Increasing temperatures increase the cracking probability if tensile stress and an aqueous chloride solution and/or external chloride build-up are present.  Although exceptional cases have been reported. Highly cold worked or sensitised materials may undergo cracking at lower temperature or even at ambient temperature. Usually cracking occurs at metal temperatures above about 50 °C and this temperature limit is considered the guideline for fixed equipment in the refining industry.

Tensile Stresses:  Tensile stress may be applied or residual. Crack initiation and propagation are guided by the aggregate of both external (i.e. applied) and internal residual stresses. Residual stress by definition is the tensile, or compressive force, that exists in the bulk of a material without application of an external load. The bending of steel plates during pipe construction, localised plastic deformation during handling, and differential cooling through the wall thickness and along the surface during rolling, are all potential sources of residual stresses in pipeline steels. Regions with different microstructures and chemical segregation at the grain boundary may also generate residual stresses in metallic components. In the absence of proper control measures, residual stresses produced during the fabrication phase can significantly contribute to SCC. Non-stress-relieved welds, highly stressed, or cold worked components, such as expansion bellows, are highly susceptible to cracking.

pH of Environment:  Cracking is more likely to occur at lower pH. However, SCC usually does not occur at pH values below 2. Uniform corrosion generally predominates at such highly acidic range. CSCC tendency decreases toward the alkaline pH region.

Dissolved Oxygen:  It is observed that oxygen dissolved in the water increases tendency to SCC. Other oxidisers in addition to oxygen (e.g., CO and CO2) can also enhance CSCC. It is unclear what oxygen concentration must be reached before CSCC starts.

Nickel Content:  Alloys tendency to SCC is affected by nickel content in a profound way. Stainless steels with a nickel content of 8 % to 12 % have greatest susceptibility toward SCC. Alloys with nickel contents above 35 % are highly resistant, and alloys above 45 % show near immunity in refining applications, but severe conditions may lead to cracking in these alloys.

Prevention of CSCC:  Prevention of CSCC by applied coatings is common in the energy sector although can be more difficult to achieve with smaller diameter piping. Reduction of tensile stress can be used to avoid CSCC.  This can be achieved by applying compressive stress by shot peening. A suitable high-temperature stress relief heat treatment of 300 series SS after fabrication will reduce residual stresses. Care should be taken that stress relief heat treatment should not result in sensitisation.

Changing process conditions is the best approach for minimizing CSCC. The acidity and corrosiveness of the process fluids can be controlled by addition of chemicals such as acid neutralizer and corrosion inhibitors. Effectiveness of corrosion inhibitors must be assured before use through laboratory test. Upgrading the metallurgy may also be opted to avoid SCC. A duplex SS might be considered for this purpose. Duplex SS has almost equal ratio of austenitic and ferritic grains in its microstructure. Duplex SS have very good corrosion resistance and they can withstand higher tensile stresses. Their resistance to pitting corrosion is also very good. Super austenitic SS have higher content of Ni so they show good resistance to cracking in chloride environments.

Low chloride-content water should be used during hydrotesting, followed quickly by thorough dry out. Designs that create stagnant regions should be avoided as chlorides can concentrate in such region. An effective external coating (e.g. epoxy phenolic coatings up to 120 oC and TSA above this temperature limit) should be applied to SS piping and equipment prior to insulating or adding piping identification. Shrink-wrapped PVC labels, coatings, or label adhesives with high levels of chlorides or other halogen ions should be avoided.

References

  1. J. F. Grubb, T. DeBold, J. D. Fritz, Corrosion of Wrought Stainless Steels, in: S. D. Cramer, B. S. Covino (Eds), Corrosion: Materials, Vol 13B, ASM Handbook (tenth edition), ASM International, Ohio, 2005, p. 54-77.
  2. A. J. Sedriks, Corrosion of stainless steels, second ed., John Wiley and Sons, New York, NY, 1996.
  3. ANSI/API Recommended Practice 571 Third Edition, March 2020, Damage mechanisms affecting fixed equipment in the refining industry.
  4. M. Hussain, T Zhang, S Khan, N Hassan, Stress corrosion cracking is a threat to pipeline integrity management, Corrosion and prevention 2020, Perth Australia organised by Australian corrosion association.
  5. S. Khan, Doctoral thesis “Corrosion of austenitic stainless steels in nitric acid at trans passive potentials: effect of material and process parameters, 2016, Homi Bhabha National Institute, India.
  6. Chidambaram Subramanian, chloride induced stress corrosion cracking of repaired pipe elbow from an oil refinery: forensic analysis.

CAPTIONS:

Table 1: Widely Used Grades of Austenitic Stainless Steel

Above: Figure 1: Commonly Observed 316L Grade Stainless Pitting Under Labels.

Left: Figure 2: Photo of Corrosion Under Labels (CUL) Seen After Label Removal.

Figure 3: The Necessary Conditions for SCC to Occur in Austenitic Stainless Steel.

 

Figure 4: Photo of Patch Repaired Piping Elbow from Hydro Cracking Plant (Corrosion Management, Issue 174).