The Mapping Dilemma: A Flexible & Hybrid Approach to Tank Floor Inspections

Table of Contents

• The Persistent Challenge of Tank Floor Inspections
• Conventional Tank Inspection Techniques and Their Limits
• Merging Flexibility and Precision- A Hybrid Solution
• Technical Advantages of a Hybrid Approach
• Key Takeaways
• FAQs

The Persistent Challenge of Tank Floor Inspections

Storage is vital to every industry, and storage tanks embody that utility for many global industries, like the Oil and Gas, and Petrochemical industries. They help contain materials like crude oil and chemicals, which expose them to harsh conditions created by the presence of corrosive elements, water accumulation, and cyclic loading.

These operating conditions make the storage tanks vulnerable to effects like pitting under depositions of sludge, stress corrosion cracking (SCC), and erosion caused by the interaction with abrasive particles in the material contained by the tanks.

To counter or foresee such damage, industries employ Non-destructive testing (NDT) in the condition monitoring of storage tanks. This helps solidify the working processes of the respective industries that can conduct their operations with the assurance that their tanks will not undergo failure during use. These techniques are limited when specific challenges arise in certain situations, requiring the use of more refined and advanced techniques providing hybrid solutions to these persistent hindrances.

Conventional Tank Inspection Techniques and Their Limits

Non-destructive testing has helped reinforce the integrity of tanks and their operability. Conventional NDT methods have helped industries around the globe monitor and assess tanks that help contain important material. 

While aiding in determining the structural integrity, these conventional NDT methods often hit snags during inspection processes. These may occur due to varying reasons that may or may not affect the possibility of the inspection being a success. The following come under conventional NDT inspection techniques used to inspect tanks:

1. Manual Tank Visual Inspection

Manually inspecting tanks requires the operator to physically enter the claustrophobic interiors of the tank to perform inspections. This method requires the use of torches, mirrors, and cameras along with a considerable amount of physical effort that can increase the likelihood of untoward incidents.

Apart from these hurdles, the presence of obstructions like internal sumps and heating coils can further block the operators’ visibility during visual inspections, leaving a small percentage of the tank floor unexamined. The results can also be subjective due to the human involvement in the interpretation of corrosion patterns and the severity of flaws. Permits, gas testing, and isolation of inspection areas also add to the downtime during this entire process.

2. Ultrasonic Testing (UT)

Portable tank testing equipment is used to measure wall thickness using high-frequency sound waves to impinge the test surface. Ultrasonic testing, however, requires surface preparation that uses abrasive cleaning methods to remove rust or coatings before inspection.

The scanning grids in UT may also miss localised pitting that may cause catastrophic accidents due to leaks. UT probes must also be well aligned, as misalignment may cause measurement errors.

Image Credit: Evident Scientific

3. Magnetic Flux Leakage (MFL)

The MFL equipment induces magnetic fields to detect distortions caused by corrosion while performing tank testing. This tank inspection method is inapplicable to nonferrous tanks made of aluminium or FRP. 

MFL also results in false negatives in tanks lined with epoxy as the lining tends to dampen MFL signals. It provides complete coverage during an inspection. Industries also sacrifice the resolution when selecting high-speed MFL scans for NDT inspections, which is unfavourable in many scenarios.

Image Credit: IndiaMART

4. Radiographic Testing (RT)

Radiographic inspection of tanks relies on X-ray or gamma-ray tank testing equipment for a visual representation of weld integrity and subsurface flaws. The radioactive nature of materials used in this NDT technique requires cordoning off inspection zones which affects any operations in its vicinity.

This method cannot quantify the depth of corrosion in its test subject, which can affect tank inspection wherein the remaining thickness is a vital factor. Film-based RT can also be costly when a high number of weld inspections are required. This method is not preferred as the second side is inaccessible at the bottom of the tank.

5. Hammer Testing

Also referred to as Acoustic Tap Testing, this method involves an audio-based assessment of the tank floor’s integrity with repetitive strikes of hammers. This practice is extremely experienced-based and relies on the technicians' abilities, which may result in false negatives for thin tank floors. 

The high costs, downtime and inconsistencies in results due to high human involvement make these methods difficult to implement in complex scenarios. Remote visual inspection tools do help overcome many of these hurdles, but their limited depth perception and obscurity caused by glare from oily surfaces (crude tanks) make them less than ideal in high-stakes applications.

Merging Flexibility and Precision- A Hybrid Solution

The barriers posed by conventional methods have been addressed by Industry 4.0 methodology when the traditional methods failed to accommodate data gaps, labour shortages, and unsustainable operating practices. 

Industry 4.0 measures led to the introduction of hybrid systems that took a three-pronged approach, that converged the merits of robotic NDT systems, predictive maintenance, and the expertise of seasoned NDT professionals to refine tank floor inspections. The three prongs of hybrid tank floor inspections comprise the following:

I] Robotic Non-Destructive Testing

Robotic NDT is a vast spectrum of technology, with many elements, providing online inspection abilities that are used to take random bottom plate readings. The data is processed using statistical analysis. Some of the elements of this technology include:

Autonomous Platforms

Inuktun Versatrax

Image Credit: Research Gate

1. Crawlers

Crawlers are mobile robots that carry omnidirectional MFL arrays and phased array ultrasonic testing probes. The MFL array sensors are capable of detecting minute corrosion losses in tank floors made of ferrous material. PAUT probes, on the other hand, can carry out volumetric analyses of the tanks with successful inspections of weld seams with minuscule cracks.

Image Credit: Nortek Group

2. Drones

Quadcopters with the clearance to perform in hazardous environments of an explosive nature can perform the remote visual inspection of confined spaces, providing streaming footage to the organisation. It can be equipped with sensors to perform different types of inspection on a subject.

Image Credit: Flyability

3. Multi-Sensor Fusion

The combination of multiple sensor technology for the NDT inspection of assets has picked up momentum in the recent past. Electromagnetic Acoustic Transducers (EMAT) and MFL technology are used together, where EMAT conducts a non-contact UT inspection, while MFL is used for corrosion mapping in oily testing environments. 3D LiDAR technology is also integrated with drones, wherein tank floors’ topography maps can be obtained with an accuracy of mere millimetres, providing spatial context to corrosion data.

These technologies consistently evolve, with Simultaneous Localisation and Mapping (SLAM) algorithms being used to help the tank testing equipment cover more area in less time.

II] Predictive Maintenance

An essential part of Industry 4.0 concepts, predictive maintenance helps industries pre-emptively assess deformities in assets in order to streamline workflow.

1. Machine Learning Analytics

Data analytics tools process UT or MFL data using Random Forest algorithms for tank inspection data. This helps industries predict the remaining useful life. ML can also help highlight zones with a higher corrosion rate helping in the predictive maintenance of tank floors using NDT techniques.

2. Digital Twins

ANSYS-based digital twins use the data obtained from hybrid systems to stimulate stress distribution under various operational loads. NDT professionals can model repair options to optimise maintenance processes using this.

Image Credit: Sciencedirect

3. IoT-Enabled Monitoring

Wireless sensors that are erosion-resistant are embedded in high-risk zones to transmit real-time data for the continuous condition monitoring of storage tanks.

III] Human Validation

The third, yet vital prong, human validation brings the benefits of experiential knowledge to help discern the flaws detected using hybrid tank floor inspection methods. 

1. Anomaly Resolution

Level III NDT professionals classify defects by reviewing the results of automated tank inspections. They then correlate the data obtained with the operational history of the tank, like chemical exposure cycles which help them diagnose the corrosion mechanisms in the asset, such as microbiologically influenced corrosion (MIC) or SCC. Regulatory audits are met by human inspectors by double-checking the records from robotic UT or MFL scans. Adaptive Re-Scanning

2. Dynamic Re-routing

NDT technicians can redirect crawlers to perform higher-resolution PAUT scans when they detect anomalies in the test subject.

NDT methods like Acoustic Emission Testing (AET) are a vital hybrid approach to inspections. Used to screen tank floor, this method can be implemented on FRP tanks which cannot be inspected by techniques like MFL. 

Image Credit: Semanticscholar

The large volumes of data generated by hybrid tank floor inspections can be compressed by cloud platforms, which opens up avenues for increased global adoption.

Technical Advantages of a Hybrid Approach

A hybrid approach fills the gap in technology, aiding human operators to perform NDT inspections of complex asset scenarios, while, helping verify data obtained from advanced NDT techniques using human expertise. The many advantages of adopting a hybrid approach to tank floor inspections include: 

1. Mapping Gap

Hybrid systems employ the use of multi-modal tank testing equipment for thorough floor coverage which resolves the downfalls of conventional grid-based methods. High-resolution sensors, comprising PAUT, MFL, and LiDAR help in implementing the merits of multi-sensor fusion, which further eradicates this gap.

2. Cost Efficiency

Hybrid Tank Inspections help organisations save on downtime and expenses due to NDT inspection processes. This is because hybrid tank testing equipment like autonomous crawlers can perform UT inspections that cut short the entire inspection process. They also reduce the hours required for the technicians to be on-site during inspections.

Condition monitoring using AI techniques also helps predict corrosion which enables targeted repairs in advance, helping reduce the budget required for maintenance. Robotic tank testing equipment also eliminates the need for scaffolding setups.

Robotic Tank floor inspection equipment used in the nuclear industry

Image Credit: Diakont

3. Versatility

Hybrid NDT tank floor inspection methods are capable of adapting to various materials and work environments. A combo of MFL and PAUT techniques can be used to map corrosion in carbon-steel flooring, whereas Eddy Current Testing (ECT) can be used with MFL to inspect aluminium or FRP-based tanks.

4. Hazardous Environment

Hybrid NDT is efficient in hazardous tank inspections, with the use of EMAT probes for NDT inspection without any couplant in crude oil tanks. Remote visual inspections like drones also help bridge this gap by providing much-needed mobility in confined spaces.

5. Condition Monitoring and Predictive Analytics

Hybrid systems enable condition monitoring of storage tanks in real-time using wireless thickness sensors, and cloud-based dashboards for improved asset management. 

Hybrid systems are a pragmatic approach to the many hurdles in tank floor inspection, combining remote visual inspection, advanced sensors, and predictive analytics. Adopting such methodologies will help industries around the globe avoid waste during operations, directing their focus on improvement and growth.

Key Takeaways

• Traditional tank inspection techniques, such as manual visual inspections, ultrasonic testing, and magnetic flux leakage, have inherent drawbacks. These include restricted accessibility, human error, surface preparation needs, and limitations in detecting subsurface flaws or localised corrosion.
• A hybrid methodology incorporating robotic NDT, multi-sensor fusion, and predictive analytics optimises tank floor inspections. Techniques like phased array ultrasonic testing (PAUT), drones, electromagnetic acoustic transducers (EMAT), and machine learning models improve flaw detection while reducing inspection time and costs.
• AI-based analytics and IoT-enabled monitoring allow real-time tracking of corrosion and structural integrity. Digital twins and cloud-based platforms enable predictive maintenance, reducing downtime and improving asset longevity while minimising human exposure to hazardous environments.

FAQs

1. How does a hybrid approach improve tank floor inspections?

Ans: A hybrid approach integrates robotic automation, AI analytics, and human expertise, allowing for comprehensive corrosion mapping, enhanced data accuracy, and reduced manual intervention. This increases efficiency and safety while improving defect detection.

2. What industries benefit most from hybrid tank inspection methods?

Ans: Industries dealing with critical storage, such as Oil & Gas, Petrochemicals, and Power Generation, benefit significantly from hybrid tank inspections. These methods enhance safety, regulatory compliance, and operational efficiency in environments prone to corrosion and structural degradation.

References

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