An Overview On Ultrasonic Pipe Testing

Ultrasonic testing, or UT as it is commonly called, is the procedure of introducing an ultra high-frequency sound wave into the exterior side of a pipe or some other type of material, and reflecting the sound wave echo from its interior surface to produce a measurement of wall thickness.  The two way duration of travel, divided by the known sound velocity through that particular metal, provides a wall thickness measurement equally accurate to that of a dial caliper.

Ultrasonic testing is a nondestructive discipline termed NDT – meaning that it does not damage, alter, change, degrade, influence, or impact the material under evaluation in any possible way.  It is also safe to anyone nearby as well as sensitive electrical equipment, and contains no safety, radiation, or other emission concerns.

Since UT quickly allows the precise measurement of the pipe wall dimension from the outside surface, it is ideally suited as a diagnostic tool for piping, tanks, and pressure vessels.  Accurate and reliable results require high quality instrumentation, a skilled and knowledgeable technician, knowledge to the varying corrosion threats specific to different piping systems, a thorough mechanical understanding of piping systems and their components, and the ability to analyze and translate an otherwise meaningless spreadsheet of numbers into a useful and informative final report.  Employed correctly, an ultrasonic evaluation will produce a thorough and extremely reliable fitness for service assessment within a short period of time and at very reasonable cost.

• Different Test Methods Available

Investigative methods such as x-ray, spool pieces, linear polorization resistance (LPR), and selective metallurgical analysis will provide some information related to pipe condition and corrosion activity for one or a few specific locations.  Robotic video inspection (RVI) is another useful tool when the interior condition of the pipe is of interest – such as to define the volume of internal rust deposits, find blockages at fire lines, investigate a defective ERW weld seam, or confirm premature galvanized steel pipe failure, etc.

Corrosion coupons, the industry standard and most commonly used testing method for HVAC systems, produce a corrosion rate estimate of thickness lost over time in MPY, which stands for Mils Per Year or alternatively, Mils Penetration per Year.  While somewhat beneficial, they fail to present a reliable assessment of piping conditions, and are typically inaccurate by a factor of at least 5 to 10 times.

Compared against confirmed pipe wall loss measured ultrasonically, and even more definitively where pipe failure has occurred, we have documented corrosion coupons to have an error rate of up to 1,000 percent.  Technically, and by their true definition, corrosion coupons do not measure wall loss occurring at the pipe as most property owners and operators either believe or are led to believe, but instead only provide an indication to the corrosivity of the water itself.

We provide substantial documentation on this site for the benefit of those who are under the misassumption that a corrosion coupon report defines the wall loss occurring inside their piping system, or that it is a statement of system health.  To be accurate, the official definition of a corrosion coupon rate is that it only indicates the potential corrosivity of the liquid against a specific metal.

In terms of usefulness, all such methods fail to provide sufficient information upon which to base an accurate and reliable overall piping evaluation.  Most importantly, none of the above diagnostic methods can produce the most important information necessary – which is the actual wall loss occurring at the inside pipe surface.

For many building properties, corrosion monitoring is generally inadequate, mostly inaccurate, installed and then ignored, or simply nonexistent.  In the worst examples often encountered, an absolute and blind reliance on corrosion coupons, even despite multiple tell-tale indicators of a severe corrosion problem, will conceal the fact that substantial pipe deterioration is occurring.

• Reporting Detail
  

Equally important to taking an accurate wall thickness measurement and knowing the most corrosion susceptible areas of each piping system to investigate is the final analysis of the raw thickness data.  Rather than present a spreadsheet of meaningless wall thickness values for the reader to try to decipher, CorrView invests substantially more time in the analysis and presentation of accumulated wall thickness into a thorough and meaningful report.

For most investigations, it requires a 3-4 times greater number of hours to transform a day’s worth of investigation into a final report – a full presentation typically assembled into a 2 or 3 inch 3-ring binder.  Perhaps most colorfully described by one client as “An autopsy of my building,” we strive to provide the most complete building piping assessment possible.  As of this date, we are closing in on our 1,060th building investigation; having taken over 4,184,800 wall thickness measurements at more than 2,947 different piping systems.

Always striving to provide the maximum information and benefit to our clients, we have added new enhancements to our reporting format which are now featured on our also new and upgraded Internet site.

• Applicable To All Piping Systems

If performed properly, ultrasonic testing offers multiple benefits to the property owner / operator / engineer by providing extremely accurate data across a wide sampling of test points.  Combined with statistical analysis, UT can define the extent of a corrosion problem and/or provide excellent advance prediction of remaining service life.

Ultrasonic testing is commonly employed for:

• • • Condenser water
    • Chill water
    • Secondary water
    • Other closed systems
    • Hot water heating
      
    • Steam supply
    • Domestic water
    • Process cooling
    • Steam condensate
    • Tanks and pressure vessels

Less frequently tested piping applications are:

• • • Sanitary waste
    • Vent stack
    • Storm drain
    • Fan coil condensate
    • Gas and fuel oil
    • Compressed air

Ultrasonic testing does hold some disadvantages, however, by not being able to provide or identify the following:

• • • The volume or location of internal deposits
    • The mechanism or cause of some piping failures
      
    • Deposit composition
    • Microbiological type and volume

• Decades Of Experience

Our involvement in the field of corrosion began in 1982 in chemical water treatment, with prior involvement in research and development as an inventor for a major think tank.  This early dedication to pure science and unbiased investigation in the pursuit of solutions to problems and questions continues to this day.  In addition to advancing and improving our level of service and benefit to our clients, our firm reliance upon the hard facts has led to our better understanding and criticism of many established beliefs and procedures within the HVAC field that we so commonly document as the cause of the most serious piping failure events.  As we have proven in case after case, taking corrective steps based upon a thorough and complete understanding of the problem, and the causes leading up to it, provides a far greater chance of success than following unsubstantiated speculation, inaccurate assumptions, incorrect data, and worst of all – politically driven demands.

• The Best First Step

A properly performed and thorough ultrasound inspection will provide a full understanding of the piping system in question, its areas of weakness, immediate threats, and corrective actions if necessary.  Although limited in some respects, ultrasonic testing continues to offer the best all around piping valuation service if performed properly, and if reported using the appropriate data analysis tools.  Substantial information related to the ultrasonic analysis of both piping as well as tanks and pressure vessels is presented throughout this site.

Investigations are typically initiated in order to:

• • • Investigate a leak or failure
    • Determine the extent and severity of a corrosion issue
    • Assess fitness for service and remaining service life
    • Define existing piping conditions prior to renovation
    • Due diligence prior to building acquisition
    • Monitor corrosion activity / water treatment effectiveness
    • Establish a baseline condition assessment
    • Confirm wall thickness prior to welding
    • Response to a visual corrosion threat

• Nationwide / Worldwide Testing Service

CorrView International, LLC provides ultrasonic testing in our local New York area, as well as throughout the United States.  Frequent cities of interest are Chicago, Washington, DC, and Boston, with services provided from Miami, FL to Anchorage, AK; Long Island, NY to San Francisco, CA.  Foreign based investigations have taken us as far as Australia, Lybia, and Guam.  We also have highly qualified affiliates in various cities that can provide the same service locally.  Our fees for out of state projects are extremely reasonable in comparison to metallurgical testing and most other testing services.

Fees are in the range of $100-$150 per each general piping location tested, with any necessary travel expenses additional.  Data from each location is analyzed and presented in a full-color report as detailed in our pipe testing specifications, and illustrated throughout this Internet site.  Most ultrasonic testing evaluations involve between 50 and 150 test locations; providing to the client the highest degree of information and analysis unavailable anywhere else.

Typical UT testing costs to address 50 examples of pipe will range between $4,500 and $9,500 depending upon the location and travel; the equivalent of cutting out and metallurgically testing 1-3 pipe samples.  We recommend dedicating at least 25 test areas at any individual piping system in order to provide a representative and reliable final assessment.  Typically, 40-50 individual locations can be tested during a normal work day – with our progress generally determined by building and piping layout, insulation, pipe surface quality, and most importantly, on-site cooperation and assistance.

Where budget is an issue or where the pipe has already been removed and an assessment desired, we can provide the same level of statistical analysis for pipe samples sent to our office.   Please contact CorrView for further details.

© Copyright 2024 – William P. Duncan, CorrView International, LLC