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Ultrasonic Testing

Ultrasonic testing, or UT as it is commonly called, is the procedure of introducing a high frequency sound wave into one exterior side of a material, and reflecting the sound wave from its interior surface to produce a precise measurement of wall thickness.  The round trip duration of travel, multiplied by the known sound velocity through that particular material divided by two, provides a wall thickness measurement equally accurate to a micrometer or caliper reading.

Ultrasound is a well proven and respected diagnostic tool routinely employed for weld and flaw detection in critical applications such as aviation, aerospace, military, and nuclear power.

Yet, while improvements in instrumentation have moved this technology into other areas such as manufacturing and quality control, its benefits to plant engineers and property owners as a diagnostic and predictive tool are still widely underutilized.

• Many Advantages Of Ultrasound

As a nondestructive method, UT offers obvious advantages over cutting out pipe for metallurgical inspection.  It is non-intrusive, accurate, reliable, safe to both building and inspection personnel, provides immediate results, requires no system shutdown, and is extremely cost effective.  As a nondestructive tool – it neither influences nor impacts the piping material or operating system in any way.

Depending upon the measurement technique, degree of testing, and data analysis method used, ultrasound can produce a general assessment of building piping condition, provide direction for capital projects, or focus in on a specific area of concern.  Establishing the condition of an aged piping system becomes especially important due to its critical function in any HVAC building environment, and due to the wide variety of problems which can potentially develop.

• Greater Threat Exists

Though not often recognized by building owners and operators, the corrosion threat to most piping systems has increased significantly over the past 25 years.  This is due to less effective chemical corrosion inhibitors, more corrosion susceptible steels, less tolerant engineering practices – and yet, always greater operating demands.

Compared to steel pipe installed in the 1950’s, and where a 1 mil per year (MPY) corrosion rate could be reliably assumed, most open water cooling or process water systems average 3-5 MPY or greater today.  Low pressure open water cooling tower systems, once exclusively constructed using schedule 80 or extra strong pipe until the early 1970’s, are now installed with schedule 40 and even ultra thin schedule 10 as a means to cut material and installation costs.

Chemical treatment programs are far less effective in all but the most strictly maintained and highly monitored piping systems, as a result they fail to equal the corrosion control of decades ago.  At the same time that microbiological agents are being recognized as a significant factor in many high corrosion rate scenarios, stricter environmental regulations have not only cut the effectiveness of many chemical biocides, but reduced their active half life as well.

Regular monitoring for corrosion and system life is often lacking for all but the largest or most critical building operations.  Even when employed, most testing methods provide little information relative to the true corrosion activity existing within the piping system.

• Corrosion Monitoring Lacking

Corrosion coupons, the most commonly used and widely accepted means of corrosion monitoring, exclude most of the environmental forces normally acting against a carbon steel pipe recirculating system.  Typically housed in an isolated loop separate of the main piping system, corrosion coupons never suffer the negative consequences of galvanic activity, flow rate, biofilm attachment, erosion, and most importantly – under deposit attack.

Although providing a relative indication of chemical effectiveness, corrosion coupons can significantly under report actual pipe losses by a factor of 10 or greater – this often to the surprise of building owners and operators years later, and after substantial piping damage has occurred.  Reviewing years of outstanding corrosion coupon results, therefore, can offer little true information relating to pipe condition and a hidden corrosion condition.  A Case History of corrosion coupon failure is provided in the handout at left.

• Serious Secondary Effects

While the threat of a piping leak is an obvious concern, a high corrosion condition can produce even more serious secondary effects which can often exist for years without being detected.

A low to moderate corrosion rate of 3 MPY at a 12 in. condenser water pipe for example, while seemingly minor, actually translates to a physical loss of 39 lbs. of steel per every 100 linear feet.  At 10 MPY, approximately 128 lbs. of metal is lost.  Multiplied by the number of years in service and overall length, the true magnitude of system corrosion takes on much greater significance than when reported as simply 1, 2, or 5 mils per year.

• System Dependent Problems

Corrosion affects all piping systems differently, and within any individual type of piping system, different impact to different areas of the system.  Open condenser water pipe typically produces the largest concern for any building property acquisition.  Pipe drained for winter freeze protection can exhibit 10 times the corrosion rate of basement pipe remaining filled.  By-pass and lead-lag equipment is a common site for substantially greater corrosion and pitting activity.  Threaded pipe is a common area of threat to condenser and all piping systems due to a thread cut which can remove 50% or more of the pipe wall.

Closed systems, such as chill water and dual temperature, are typically lower priority issues, but can be influenced by outer pipe corrosion due to poor insulation and outer surface corrosion.  Added factors such as direct free cooling, glycol deterioration, and poor water treatment can produce problems never expected otherwise.

Fire systems, traditionally viewed as being trouble free, have seen dramatic increases in failure rate due to the use of thin wall schedule 10 and schedule 7 pipe coupled with substantially greater testing and draining.  Add to thinner pipe materials the common use of lower quality foreign steel and fire pipe corrosion can become a very major issue.  All dry fire protection systems today are high priority threats and frequent sources of failure.

With all piping systems having their own specific corrosion based vulnerabilities, testing performed according to a defined procedure, and based upon a fixed interval, will often miss the most obvious problem areas.  Rather, ultrasonic testing must be performed at those areas most likely to show a vulnerability if present.  Performing ultrasonic testing to at least 25 or more examples of pipe within any piping system is always recommended.

CorrView International, LLC offers a detailed specification for ultrasonic pipe and tank testing which is available upon request.  Please contact CorrView for further information.

• Identify Building / System Status

Utilized properly, ultrasonic pipe testing offers tremendous benefits in any building acquisition.  An ultrasonic report will very often provide the very first suggestion of a corrosion problem or concern – and provide the advance notice required to address it during negotiations.

Ultrasonic pipe testing can provide irrefutable evidence of a suspected corrosion problem, or document that a piping system has fulfilled its useful service life and is in need of replacement.  In past investigation, discovery of a serious piping deficiency has resulted in either a reduction in the negotiated price, or the cancellation of the acquisition.

Where no problems exist, ultrasound will provide greater security, and most importantly, establish a solid baseline from which future and even more accurate and reliable estimates of corrosion rate and remaining pipe life can be made.

We offer an overview and interactive sample ultrasonic testing report above.  This level of reporting is provided by CorrView International, LLC to all clients and is based upon accurate and thorough field testing as well as a high level statistical analysis of that data.

© Copyright 2023 – William P. Duncan, CorrView International, LLC