Validated Research

Validated Research

For many years, those working with fiberglass reinforced plastic (FRP), including owners, fabricators, inspectors, have been looking for a method to inspect that meets the following criteria:

  • Non-Destructive – Measurements are made without causing any damage to the material inspected
  • Non-intrusive – Measurements are made while the pressure boundary is intact
    • Minimize Space Entry
    • Possibly in Operation
  • Reliable – The inspection will get the same results no matter who the inspector is
  • Valid – Measurement relates closely to standardized destructive testing
  • Predictive: Able to give a good estimate of when repairs or replacements are required, ideally within budget cycles.
  • Reasonable cost: Cost for the service, limiting shut down requirement.

In 2000, while working at an oil refinery in Indiana, Geoff Clarkson, the developer of the UTComp System, took on this challenge.  He was asked “How do we create the curve for FRP like we have for steel thickness measurement?” The question evolved to “how can we predict when FRP is going to fail?”  At this time there was no method to do this, and this started Geoff on a quest to find this answer.

Understanding the Scientific Method

The first step was to determine the best route and use a scientific method.  This method requires:

  1. Identification of the problem
    1. A method of providing remaining service life of FRP.
  2. Gather relevant data
    1. Other methods
    2. Past Published Research
    3. Possible Methodologies
  3. Develop a hypothesis
  4. Empirically Test Hypothesis
  5. Repeat

What are the Alternatives?

Geoff took a long look at what was available and systematically evaluated each of them in turn. He wanted to make sure that a better system was based on science, was an objective measurement and had the needs of the customer at its core.  This process has taken more than 16 years and continues today. There are many reviews of these types of methods of evaluating FRP, including most recently Swerea Kimab. Below is a summary of the methods initially evaluated BEFORE he developed the UTComp System.

Inspection Method

 

 

 

 

 

 

 

*Cost Ranking: 1 (least expensive) to 5 (most expensive).  Consideration is given for both direct (cost of inspection) and indirect costs (shut-down, loss of production, outage time, opportunity cost).

The majority of these systems, listed above, do not measure the structural capacity of the FRP, which is essential to being able to determine remaining service life. Intuitively, ultrasound became the most reasonable method of evaluating FRP however being able to show results proved to be challenging.  Ultrasound can be done from outside of the equipment and while it is in operation. The next questions were: Can we overcome the challenges of collecting data on FRP?  Can this be done reliably? Can validity be achieved?

Reviewing the Research and Gathering Information

The second step in the research is to gather all relevant data. Research began to identify how FRP changes from use. The image below shows the Damage Mechanisms and Failure Modes that contribute to the change of FRP over time. From this, it can be seen that the development of a tool that can measure changes in laminate mechanical strength needed to be the focus of this research.

Image 1.

damage mech

 

A review of the published peer reviewed papers, showed that many other engineers and researchers had attempted to do this with limited results.  There were two issues that were identified:  the focus of most prior work was primarily on defect defection and there was so much “noise” that there was no ability to determine valuable information from the screen, which is how we have come to think non-destructive testing works.  Some early work by NASA pointed the research into a direction that provided creep information.

Historically, inspection of FRP has focussed on visual detection of features on the surface.  This is very limited as surface condition has little relationship to the structural capacity of the equipment.  With broader use of FRP in structural and corrosion applications, understanding of damage mechanisms and failure modes has grown.  Development of pressure ratings for FRP pipe, for example, is based on this broader understanding.  This has also shown that damage development in FRP is very similar to corrosion in mild steel: in the case of steel, there is general loss of thickness from corrosion and in FRP there is general reduction of strength properties (with no appreciable change in thickness), especially where chemical attack and stress are highest.  Note that corrosion of stainless steel is different, usually showing as localized pitting and corrosion that is not easily detected using thickness changes.  Inspection of stainless steel must focus on detection of local defects and damage.

Inspection of FRP has focussed on visual detection of features, flaws and defects in the corrosion barrier, similar to the inspection needs for stainless steel.  It became evident that inspection of FRP requires techniques that find generalized damage, similar to thickness testing of mild steel.

As part of the data gathering, an investigation in to the best tools to use was under taken.  From this work, it was verified that reading from the screen was limited and post processing of the raw data would be required.  To get this information, a number of ultrasonic instruments were explored. The initial instrument was the Olympus EPOCH 4 (now discontinued due to mercury in the keyboard) with an M2008 Transducer. This combination was able to get through the complex material of FRP, show a back wall and return.

Developing the Hypothesis

Once the instrument was determine and the beginnings of the post processing analysis was developed. The next step was to formalize the hypothesis.  The hypothesis that:

“Ultrasonic testing method and post processing of ultrasonic data will be the same as destructive testing results using primarily flexural values provided through ASTM D790.”

Proving it Works: Reliability and Validity

A variety of samples (new and in-service) were provided to UTComp for this initial testing.  To get a statistically significant result, UTComp initially started with 30+ samples.  Some of the assumptions that were considered was the variation in the FRP due to cutting, the variety of materials resin/glass), methods of construction (hand lay-up, filament wound, etc.) and diameter of the samples. Flexural values were chosen as this is the best representation of how FRP changes while in service. The flexural tests were completed at an independent third party certified lab, Cambridge Materials Testing

In doing this testing and comparing the results, UTComp was able to see there was great promise in the data collection and post-processing of the data. Chart 1 shows the results from when compared side-by-side of the destructive testing and UTComp System.  The correlation for this testing is for this testing is 0.88 with an ideal of 1. This is show in Chart 2.

These charts have shown there is close relationship to the flexural modulus, as shown by destructive tests, to the non-destructive, non-intrusive testing as developed by UTComp.

Chart 1: Destructive v. UTComp Results

Destructive results

 

 

 

 

 

 

 

 

 

 

Chart 2: Correlation Results

correlation

 

While there are still outliers in this data, the UTComp predicted the results of the destructive tests +15% 95% of the time.  This was a significant advancement on any other method that has been commonly used.

Now that validity was shown, the next step was to determine if this can be done reliably.  Can independent data collectors get the same results? As the system developed UTComp hired a number of Engineering Analysts to the team.  To show reliability, more samples were acquired and the Engineering Analysts were trained.  And again, UTComp was able to show that they were able successfully collect data and achieve the same results. This extended beyond the collection of data.  Testing was run to determine if these same employees were able to analyze the data and achieve the same results as the developer of the system – and they were.

In ideal circumstances the UTComp System can be used as a procurement to retirement tool and is able to predict remaining service life. Data can be collected on new pieces of equipment and then on regular intervals more data can be collected to monitor the change in the equipment over time. This enables customers to project the curve and estimate when the equipment will need to be repaired or replaced.  However, there are a great deal of FRP assets currently in operation.  Faced with this dilemma, UTComp developed a “calculated baseline” of what the equipment should have been when it was new.  While not ideal, it does provide a starting point to estimate the remaining service life predictions.

UTComp also researched the need for a calibration sample, as is commonly used in non-destructive testing.  The simplest use of a calibration sample is to establish sonic velocity for the measurement of thickness.   Each test method and procedure, such as ultrasound, acoustic emission, and radiography, has different calibration methods and requirements.

Through extensive testing, UTComp has found that the analysis only requires a reference reading from the transducer with delay line.  There is no need for calibration to a specimen.

In the past year, we have focused on developing methods to provide corrosion barrier damage information from outside of the equipment.  UTComp again looked at about 50 samples of equipment with known corrosion barrier damage and some without any damage (e.g. new). The UTComp System has shown that damage to the corrosion barrier can be seen.  It is important to note that the interface between corrosion barrier and structural layers will not normally be detected, so detailed reporting of corrosion barrier thickness is not considered to be reliable

The primary focus of the UTComp research has been on defining the overall strength of FRP and providing remaining service life predictions based on structural considerations.  As the focus of most ultrasonic testing is to find defects and delaminations it became a natural extension of this work. UTComp investigated this and found that this was possible if the transducer was at the location of the delamination or defect.  This was validated by the work completed by Dr. Ahmed Hassan at the University of Alabama at Birmingham. In this case, he prepared the samples for a round-robin testing.  He collected the data using the UTComp technique and sent it to our offices for analysis.  There was no visual evidence of the defects that were built in.  It should be noted that  UTComp identified the defects based on local reduction  to the overall structural capacity of the equipment. It is only with the post-processing of the data that the structural capacity can be revealed.

This work has also continued beyond FRP.  Many customers will use dual laminates as part of their systems for particular applications.  Ultrasonically, FRP and dual laminates are very similar and as such the UTComp System can be used on Dual Laminates equally as well.

Our research has also identified a number of limitations. The system operates best at 10⁰C or 50⁰F and warmer.  This was discovered when the equipment keypad froze at cold temperatures and we saw changes in how the ultrasound moved through the delay line at the end of the transducer.  We also learned that when working close (within 2400mm or 8feet) to very high magnetic fields (120,000+Amps), prevents readings from being taken. Another limitation is that ultrasound does not travel through foam cores or thick (75mm or 3inch) balsa cores. While the UTComp System has been developed to be used while the equipment is in operation, there are circumstances when it will be necessary to go inside: e.g. to test internal structures and the floor, when insulation cannot be removed.  Finally, UTComp has not tested pipe with diameters <50mm or 2inches.

Other Testing

In addition to these lab exercises, many customers were learning about the UTComp System and wanted to know more. Since this system has been developed more than 30 blind tests have been conducted with customers to show that this system works.  Many of these case studies and examples are listed here.

To give our customers even more confidence in this system, UTComp has worked with two (2) unrelated and independent universities to research and test this system for reliability and validity.  The pipe research was conducted at University of Alabama at Birmingham, Alabama, USA and the work on vessels was conducted at York University in Toronto, Ontario, Canada. In both cases, the data and destructive testing was completed by PhD candidates, under the supervision of their professors.  This work, once again showed that the UTComp System was able to meet its initial stated objectives.

Continuing the Research

To date, UTComp has conducted over 500 customer blind and lab tests to show the results of the UTComp System are achieving a high degree of correlation to destructive testing.  Moreover, significant advancements have also been achieved and expanded this work.  In April 2014, UTComp was able to release the analysis for pipe with diameters between 50mm/2inches and 350mm/14inches. At the same time, we also released reporting on the corrosion barrier condition and the use in composites with sand cores, etc.

Further work has gone into the relationship of bonding of FRP to FRP for repads, etc. as well as the expansion of this system into Wind Turbine Blades, High Speed Train Cabs, and more. Moreover, the UTComp data base is growing and more information is being gleaned from this data that can provide the industry with real life examples of what happens to equipment over time.

UTComp is currently, following over 2000 assets in North America, South America, Europe, Africa, and Asia.  We work with some of the largest food processing, mineral processing, chemical processing, oil and gas companies around the world. We have trained over 20 people around the world to offer this service to ensure that owners are able to control costs.

The UTComp System has met, and in many ways exceeded, the expectations of its developers. More is being learned every day about how this system is able to non-destructively, non-intrusively, reliably, validly predict remaining service life of FRP assets. UTComp has successfully predicted failures in 5 tanks, some with up to 4 years warning.

So what is the Pudding?

Proving any technology is a challenge as each person and company will have their own ideas about how to determine what is best for them.  UTComp has successfully:

  • Independently tested, using third party independent lab, over 500 samples
  • Completed third party testing at 2 universities
  • Predicted failures in advance
  • Demonstrated defect and delamination detection
  • Developed methods to determine the condition of the corrosion barrier
  • Verified over 30 blind testing demonstrations with customers
  • Monitored over 2000 assets globally
  • Trained over 20 people to collect data using the UTComp method
  • Gotten the support of some of the world’s largest customers.
  • Identified limitations
  • Adopted a system of continuous development and research

With this work done, the earlier chart can now include the UTComp System, showing that it has met all of the criteria as set out by the industry for a significant improvement on the existing methods of inspecting fiberglass reinforced plastic assets.

with UTC

 

 

 

 

 

 

*Cost Ranking: 1 (least expensive) to 5 (most expensive).  Consideration is given for both direct (cost of inspection) and indirect costs (shut-down, loss of production, outage time, opportunity cost).

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