The Critical Role Nondestructive Testing Plays in the Steel Utility Pole Industry

Garrett Ehler1, AWS-CWI, ASNT Level III

1Vice-President/General Manager, Texas Nondestructive Testing Academy

Phone: 281-231-0001; Email: Gehler@TXNDT.com

 

Abstract

Nondestructive testing has become an integral part of the process when determining the remaining lifespan of in-service steel utility pole structures and plays an essential role in the manufacturing of new replacement structures.  The nation’s critical utility infrastructure has come to rely on nondestructive testing even more as it ages and the service life of structures is pushed to its limits.  However, with the probability of detection of defects at an alarming low percentage, it is critically important for utility personnel to understand the various methods of nondestructive testing that can be employed and their limitations.  This paper/presentation will discuss the advantages and disadvantages of each method as well as their correct employment in a plant versus a field environment.  And finally, it will attempt to address some key points:

  • What are the appropriate training requirements and certifications necessary to insure that personnel inspecting your steel utility poles know how to perform these tasks correctly?
  • What types of defects should they be looking for?
  • How to properly evaluate findings to ensure critical defects are located.
  • Repairing defects while not doing more harm to the structure.

 

The Critical Role Nondestructive Testing Plays in the

Steel Utility Pole Industry

Introduction

When we flip the light switch, the light turns on 99.9% of the time. As a society, we have generally come to take this for granted.  The electrical grid in the United States consists of an estimated almost 400,000 miles of transmission lines, some of which date back to the 1880’s.[1]  With this aging infrastructure comes a need for forecasting the lifespan of existing utility structures along with the manufacture of utility structures for both new construction and replacement of in-service lines.  Nondestructive testing has become an essential component in the inspection of in-service structures while playing a critical role in the quality control during manufacturing.  As inspections are used to find discontinuities, cracks or other potential damage in a physical structure, it is important to know the strengths and weaknesses of each method of NDT as this will allow a properly trained and certified technician to select the right method to employ and then perform this testing accurately.  Electrical demand will continue to grow over the coming years, and with it, the need for proper Nondestructive Testing in the utility industry will continue to expand as well.

What is NDT?

There are numerous technical definitions of Nondestructive Testing (NDT), yet we feel that its simplest form is by far the best and most concise – NDT allows materials and components to be inspected and assessed without any physical damage to them.

NDT Methods

While the American Society for Nondestructive Testing (ASNT) recognizes nine major methods along with several other subcategories, this presentation will be focusing on the three primary methods used in the inspection and manufacturing of steel utility poles: Magnetic Particle Testing (MT), Ultrasonic Testing (UT) and the often overlooked Visual Testing (VT).

Magnetic Particle Testing (MT)

Magnetic Particle Testing (MT) uses magnetic fields to locate surface and near surface discontinuities in ferromagnetic materials such as steel.  In the steel pole industry, the magnetic field is applied indirectly, most commonly with a yoke.  Once the magnetic field is established, a fine pigmented ferromagnetic powder is applied to the surface of the part, which will be drawn into the magnetic leakage field caused by a discontinuity, causing a visible indication.

Magnetic Particle Testing (MT) Conducted on a Long Seam.

MT equipment is inexpensive to purchase and operate, is portable and it is relatively easy to train personnel in its use. MT does have its downsides as it is only suitable for surface breaking and near surface discontinuities, can only be used on ferromagnetic materials and can be misevaluated without proper training. Proper initial and ongoing training will teach a technician to tell the difference between a relevant indication and a false indication that could lead to hours of re-work during fabrication.

Relevant or Irrelevant Indication? Should this be Repaired?

Ultrasonic Testing (UT)

Ultrasonic Testing (UT) introduces sound waves to the part or item being tested via a transducer made up of a piezoelectric crystal that converts electrical current to sound waves.  The sound traveling through a part hits material with a different acoustical impedance and some of the sound will reflect back, be received by the unit and represented as an indication on the screen.  Knowing the velocity at which sound travels through a part, along with the time of travel results in a distance to the indication.

Ultrasonic Testing (UT) of a Newly Installed Gusset.

Ultrasonic testing is a portable method of inspection, gives consistent results and can detect both surface and subsurface indications. As such it is well suited for weld inspection in both manufacturing and field environments.  While significantly more expensive than MT to train and equip a technician, UT is still cost effective and can provide an extreme level of detail.  UT has significantly higher requirements for both classroom and field training than MT and without proper training, misinterpretation of findings can occur with dire consequences.

Visual Testing

The third method of NDT this paper will discuss is Visual Testing (VT). Visual inspection techniques rely on the aided and/or un-aided eye for the purpose of inspecting a part or weld.  VT is the most common testing method used across all industries as it is inherently part of all other test methods.  VT may be aided by the use of a magnifying glass or un-aided using the naked eye and many defects are able to be located using VT including cracks, corrosion, misalignment of parts and discoloration.

VT can be performed with little or no equipment but still requires training in the analysis of findings and the use of proper procedures.  VT’s limitations include only being able to detect surface breaking flaws and it is less sensitive to smaller flaws than other methods.

Even taking those limitations into account, as long as inspections are being performed, VT will be one of the most important tools an inspector can have in his arsenal.

Nondestructive Testing in a Manufacturing Environment

In any facility producing steel utility structures, NDT should be an integral part of nearly every stage of production.  With the emphasis on cost efficiencies, lower quality steel, and high deposit welding consumables, quality control has the difficult task of keeping all the variables within tolerances.  NDT is one of the key tools in ensuring that a quality product is received in the field by the end user.

UT is used to detect laminations in steel baseplates, to confirm weld penetration on long seams and is crucial for the confirmation of a complete joint penetration (CJP) weld.  UT is required on 100% of structures with large T-Joint welds such as base plates and flanges for the detection of cracks both pre and post galvanizing.[2]  Flaw detection in welding may be the single most important thing UT is used for and due to inconsistencies in training programs, many of those flaws are missed by improperly trained technicians.

MT and VT also aide in weld inspections – the identification of undercut, cold lap, crater cracks and poor starts/stops are just a few examples. Additionally, MT is often used during repairs to confirm that a crack is ground away prior to re-welding.  In many cases multiple methods may be needed to validate an indication or increase the probability of detection for small indications.[3]  This can be seen regularly with the use of visual testing to support all other forms of inspection.

Nondestructive Testing for In-Service Structures

NDT plays an integral role in the continued safe operation of in-service steel utility structures to determine if a structure is fit for continued service or needs to be repaired, strengthened or replaced. It is not uncommon to find a field technician using UT or MT inspection for the detection of fatigue in welds in the form of cracks.  Often located at the top toe of the base plate to pole shaft weld on the bend lines of a multisided pole, what begins as a stress riser, over time, becomes a crack due to cyclic stress on the structure.  In most cases, these toe cracks, cannot be seen by the naked eye and require some form of NDT to detect.

UT Transducer Gel Applied to A Weathering Steel Pole Prior to Testing to

Identify the Extent of “Pack-out” Issues at the Slip Splice.

Internal and external corrosion can cause catastrophic problems to in-service utility structures up to and including failure. As seen above, left undetected and unchecked, corrosion can cause wall loss that often leads to a significant decrease in the structural capacity.  Using UT inspection, a corrosion assessment can be completed giving an engineer the information needed to quantify the structural capacity of the effected pole.  Without the use of NDT techniques, estimating a lifespan or plan of action for repair would be a shot in the dark.

Proper Training Is Key

Training programs in the NDT industry are numerous and varied and range in quality from very poor to excellent. ASNT has given us an excellent guideline utilizing SNT-TC-1A as a recommended written practice for the qualification and certification of personnel, but it is only a guideline and some employers choose to provide only the bare minimum to qualify technicians.   It has been estimated that in some sectors the probability of detection is as low as 52% for a surface discontinuity with a length of .1”.[4]  Many variables that lower the detection rate can be eliminated with a high quality training program and a written practice following SNT-TC-1A or CP-189.

The process of qualifying technicians should be performed through formal classroom training with the recommended series of exams to prove knowledge and visual acuity.  In some cases, employers train in-house through the use of a “Corporate Level III” and bad habits can be passed on.[5]  A knowledgeable, properly certified educator using recognized course material is recommended and can prevent an internal “legacy” that utilizes those bad practices.

Following formal training, an apprentice technician needs quality on the job training meeting the minimum number of hours working under the direct supervision of a certified individual.  Once the trainee has met the requirements of his company’s written practice and proven his competency, the company can certify him in method.

Summary

As our countries infrastructure grows and ages, there will be an increased need for ongoing manufacturing quality control programs along with reliable monitoring and assessments of in-service steel utility structures.  As that need grows, so too does the demand for well trained and certified individuals to perform nondestructive testing in the utility industry.

To ensure the continued safe operation of your structures and extend their lifespans, NDT should be an integral part of both you and your pole manufacturer’s daily operations.

For further information, or questions, please contact:

 

Garrett Ehler, AWS-CWI, ASNT Level III

Vice-President/General Manager
Texas Nondestructive Testing Academy

Phone: 281-231-0001

Email: Gehler@TXNDT.com

About the Presenter: Mr. Garrett Ehler

Mr. Ehler is a 1998 graduate of Baylor University in Waco, Texas with dual degrees in Environmental Science and Psychology.  After spending several years in the heavy construction and utility industries, Mr. Ehler was one of the founding employees of ReliaPOLE Inspection Services Company, a Houston based inspection firm focused on the global pole and lattice tower industries. In 2015, Mr. Ehler and ReliaPOLE branched out to form Texas NDT Academy. As TXNDT’s Senior Instructor and General Manager, Mr. Ehler is committed to providing his students with the ideal curriculum consisting of both the theories and science behind each course offered, but also their use in real world applications and best practices.

Certifications:

AWS CWI – 13071361

ASNT Level III – 229488 UT/MT

Level II PT

ACCP VT Level II – 229488

AGA Certified Inspector

 

[1] ASCE – “2013 America’s Report Card for Infrastructure”

[2] ASCE/SEI 48-11 Design of Steel Transmission Pole Structures. 10.3.5 “Weld Inspection”

[3] “Verification of Indications” Bryan Lancon, ASNT Fall Conference and Quality Testing Show 2008

[4] “Probability of Detection”, Materials Evaluation, Vol. 58, No. 4, April 2000.

[5] “Misconceptions within Magnetic Particle Inspection”, George Hopman, ASNT Fall Conference 2007

0 replies

Leave a Reply

Want to join the discussion?
Feel free to contribute!

Leave a Reply

Your email address will not be published. Required fields are marked *