Overview of Thickness Measurement & Monitoring
Thickness Monitoring is the process of routinely measuring the material thickness of equipment such as piping, tubing, pressure vessels, or tanks. Thickness measurements are performed by using nondestructive examination techniques (NDE) on condition monitoring locations (CMLs) or other predetermined locations. Thickness monitoring is, generally, the most prevalent type of NDE conducted on CMLs in the oil & gas and petrochemical industries.
Thickness Measurements for Corrosion Rate Calculations
The following is from The 101 Essential Elements in a Pressure Equipment Integrity Management Program by John Reynolds. Download a free copy of the entire book now.
Accurate thickness measurements for corrosion rate calculations are fundamental to fixed equipment mechanical integrity (FEMI), yet it is a subject that is often considered so mundane that it does not receive the appropriate amount of attention. When that happens, the quality of thickness data can vary all over the map. Without accurate data for corrosion rate calculations, much time and money is lost on rework and inspections that are conducted more frequently than necessary, let alone the potential for equipment and piping failing prematurely due to the inaccurate data. An effective FEMI program needs to have appropriate NDE thickness measuring procedures in place to ensure that data will be accurate and reasonably reproducible for corrosion rate calculations.
In my experience, appropriate digital ultrasonic thickness testing (DUTT) procedures with a trained DUTT technician can yield reproducibility routinely within +/- 0.010” and profile radiographic (PRT) thickness data within ~6%. Some round robin tests that I am familiar with indicated that a lack of adequate procedures and training would yield ultrasonic accuracy variability, routinely of 3-4 times these numbers. And these tests included long-experienced inspectors and DUTT technicians. Hence, it is my belief that inspectors/DUTT technicians (company and contract) doing DUTT and PRT thickness measurements need detailed training and procedures in order to provide truly high quality data. And that does not mean simply making sure they are ASNT Level I or II qualified, unless the technicians have been specifically trained and qualified on DUTT. It means that they receive training covering the 8-9 variables that can affect DUTT data quality, including: calibration issues, cleaning, couplant issues, temperature monitoring and correction factors, hot measurement issues, doubling, minimum diameters of piping, effect of placement and rocking the transducer on curved surfaces, taking three readings in each examination point and averaging them, when to use A-scan equipment, dealing with coatings, and gauging through CML marking stickers. For a lot more information on DUTT, I recommend you read section 5.7.1 of API 570(1) and section 10.2 of API RP 574(2), both of which are currently being updated for their 4th editions.
Now that said, I recognize that not all thickness measurements needs to have the accuracy necessary for corrosion rate calculations. And as such, there are alternative methods to DUTT that can suffice under various circumstances including profile radiography, long range UT, guided wave UT, pulsed eddy current, and even the old fashion caliper method. But users of these techniques must recognize that some of these techniques are just screening techniques and understand their limitations in producing accurate UT thickness data.
Do you know if your thickness data accuracy is routinely good enough to allow your inspection data management system (IDMS) to function as well as it can, providing you with accurate corrosion rates, inspection schedules, and projected remaining service life for equipment that is subject to metal loss?
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BlogSeptember 12, 2019 By Olympus America
Here are 8 tips to help you overcome certain challenges encountered when taking thickness measurements at high temperatures.
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September/October 2018 Inspectioneering JournalBy Ashfaq Anwer
The best approach for better inspection confidence and long term asset integrity is to conduct baseline inspections upon receipt of an asset. Baseline inspection can save millions by providing accurate baseline information for later comparisons and...
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January/February 2018 Inspectioneering JournalBy Bruce A. Pellegrino at Sensor Networks, Inc., and Mark Feydo at Sensor Networks, Inc.
Over the past few years, network technologies have been developed to eliminate the need for long cables for UT thickness monitoring. Coupled with a software back-end, permanently-installed UT sensors have become much more competitive in the...
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January/February 2017 Inspectioneering JournalBy Israel D. Martinez at ORPIC
Evaluating remaining wall thickness of an asset is not enough to ensure its continued safe operation. Proactive strategies should be implemented to assess the entire environment affecting an asset’s condition, including the development of more...
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November/December 2016 Inspectioneering JournalBy Loganatha Pandian at Meridium, Inc.
This article summarizes seven key questions that an organization needs to answer to create a robust mechanical integrity program that is properly designed to monitor corrosion and indicate when issues increase to a level requiring review or...
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March/April 2016 Inspectioneering JournalBy Bruce A. Pellegrino at Sensor Networks, Inc., Dr. James N. Barshinger at Sensor Networks, Inc., and Michael Nugent at AEIS, LLC
While there are many methods for measuring equipment wall thickness, a predominant method used in the O&G and power generation industries is portable ultrasonic equipment. Ultrasonic testing is non-intrusive because it is applied to the outside of a...
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January/February 2016 Inspectioneering JournalBy Dr. Jake Davies at Permasense Ltd.
Fixed equipment in a refinery can be susceptible to corrosion from the process side, necessitating an inspection strategy to understand the condition of that equipment. Online measurement of pipe and pressure vessel wall thickness is made possible...
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September/October 2015 Inspectioneering JournalBy A.C. Gysbers at The Equity Engineering Group, Inc.
This article addresses a debate mechanical integrity professionals in the O&G and Chemical Processing industries periodically have about how thickness data gathered during a thickness monitoring inspection (TMI) should be recorded.
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BlogJanuary 6, 2014 By Nick Schmoyer at Inspectioneering
In 2013 Inspectioneering published content covering a wide array of topics, from risk-based inspection, to advanced nondestructive testing methods, to pipeline integrity management systems. Last year, we published more content than any year prior;...
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September/October 2013 Inspectioneering JournalBy A.C. Gysbers at The Equity Engineering Group, Inc.
This article is the fifth of a series of articles that will focus on one critical sub process within a PEIP that is key in managing the integrity of process piping; Thickness Monitoring Programs for Internal Corrosion.
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May/June 2013 Inspectioneering JournalBy A.C. Gysbers at The Equity Engineering Group, Inc.
Piping failures still represent a frustrating and ongoing problem for processing plants. Failures are still commonly reported and contribute to large losses. In the author’s experience, piping represents the highest percentage of fixed equipment...
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A Discussion on the Piping Thickness Management Process: Data Collection with Ultrasonics and RadiographyJanuary/February 2013 Inspectioneering JournalBy A.C. Gysbers at The Equity Engineering Group, Inc.
This article is the third of a series of articles that will focus on one critical sub process within a PEIP that is key in managing the integrity of process piping: thickness monitoring programs for internal corrosion. These articles will discuss...
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November/December 2012 Inspectioneering JournalBy A.C. Gysbers at The Equity Engineering Group, Inc.
Piping failures still represent a frustrating and ongoing problem for processing plants. Failures are still commonly reported and contribute to large losses. In the author’s experience, piping represents the highest percentage of fixed equipment...
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September/October 2012 Inspectioneering JournalBy A.C. Gysbers at The Equity Engineering Group, Inc.
Piping failures still represent a frustrating and ongoing problem for processing plants (example in Figure 1). Failures are commonly reported and contribute to large losses. As well per the author’s experience, piping still represents the highest...
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January/February 2009 Inspectioneering JournalBy Dan Carnevale at Danatronics Corporation
Ultrasonic thickness gages have progressed a long way since their early development in the 1960's. The first thickness gages were large and bulky although they used the same conventional longitudinal (compressional wave) techniques still in use...
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September/October 2000 Inspectioneering JournalBy T.C. Ridgeway & Staff at TCRI
In part 1 of this article we covered the importance of quality assurance of UT data, that is, understanding for each particular application, the accuracy required of the UT data, and new ways/graphical program to analyze and show the...
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July/August 2000 Inspectioneering JournalBy T.C. Ridgeway & Staff at TCRI
The American Paper Institute Recovery Boiler Reference Manual Volume 1, October 1979, indicates that the two main goals of conducting ultrasonic thickness (UT) inspections are to determine (1) the current tube wall thickness and (2) the rate of...
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July/August 1999 Inspectioneering JournalBy Art Leach at Krautkramer
Many digital ultrasonic thickness gauges have internal memory that allows the storage of thousands of thickness readings. Some instruments have "sequential" data loggers that store the thickness values in a numerical series. These data loggers are...
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May/June 1999 Inspectioneering JournalBy Art Leach at Krautkramer
Keeping critical equipment on-line can be a challenging task. Monitoring the wall thickness of equipment subjected to corrosive chemicals, temperature and operational changes is both a safety and manufacturing concern. Thus, on-line testing of...
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March/April 1999 Inspectioneering JournalBy Mike Sparago at CorrSolutions
Inspection data analysis tools, like risk-based inspection, help us to focus on quantitative reliability targets. When considering thinning mechanisms, there is a certain probability that a piece of equipment will reach retirement thickness before...
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January/February 1999 Inspectioneering JournalBy Joseph E. Pascente at Lixi, Inc.
One of the greatest challenges facing many of refining, fossil power, and pulp and paper industries is: How to effectively examine their insulated piping?
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January/February 1999 Inspectioneering JournalBy Mike Sparago at CorrSolutions
Ultrasonic thickness monitoring programs represent one of the most intensive inspection activities in refining and petrochemical facilities. Despite numerous improvements in ultrasonic testing equipment and inspection techniques, however, there has...
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September/October 1997 Inspectioneering JournalBy John Reynolds at Intertek
This is the fourth in a series of articles on piping inspection that I'm writing for the Journal. One of the previous ones dealt with improving thickness data taking accuracy with digital ultrasonic methods. This article is a "sister article" that...
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March/April 1997 Inspectioneering JournalBy John Reynolds at Intertek
This is the second in a series of articles on piping inspection. In the last article, I enumerated four inspection issues that I believe contribute to inadequate piping mechanical integrity in the hydrocarbon process industry.
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January/February 1997 Inspectioneering JournalBy John Reynolds at Intertek
It's probably more important to those of us who don't have a brain tumor. Unfortunately, it's precisely because piping inspection is not neurosurgery that it's often done poorly, which can lead to significant impacts on process unit reliability, or...
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