Towers, Poles, Lattice & Anchor Rod Inspections

The objective for pole, lattice, tower and anchor rod inspections and condition assessments is to gather data and provide information necessary to:

1. Ensure integrity and safety

2. Determine corrosion rate and life expectancy

3. Forecast and plan maintenance

4. Extend life of the systems

5. Achieve safety, integrity, and service life at a minimum cost

Circuit Prioritizing Methodology and Identifying High Risk Transmission Lines for Inspection

Matco Services has developed  a set of predictive protocols that are used to evaluate utility pole, lattice, tower and anchor rod strucutes. Using a combination of desk study, field inspection testing and evaluation of soil formations and corrosivity, Matco will go through your assest inventory and provide an inspection/repair plan which prioritizes the lines at risk based on:

1-Circuit Importance

2-Soil Formations,Topography, Aspect and Soil / Water Table Corrosivity

3-Time in Service (age)

4-Incidents, Accidents, Previous Inspection Reports

4-Materials of Construction, Metallurgy, Coating and Cathodic Protection

First, a desk soil formation study is conducted to predict the likelihood of corrosion taking place at each asset location. The asset inventory is tabulated and the geographic coordinates of each strucure are determined. Along with this data, the materials/coating or constructuion is noted and the age of each system is also listed. Then the local, regional,  national and Matco soils data is reviewd by Dr. Gibbon, Matco's senior geologist, to determine what pertinent information can be found.

Maps are made up within GIS framework so that each corrosion criteion is on an independent layer and can be queried in any combination with one another. Of course since the details of local conditions (topography, aspect , prior construction, etc) control the actual soil charateristics, each location will be placed within a range of predicted conditions. Then, transmission lines can be prioritized for field inspection.

Based on the results of the field checks, the predictive criteria are fine tuned and a preventive inspection/maintenance plan (immediate inspection, 5 year inspection and  10 year inspection) is developed to check and protect the entire asset base. This may involve design and installation of cathodic protection systems where necessary in most corrosive sites.

The field tier one inspection and tier two inspection methodology includes the following for pole, lattice, tower and anchor rod structure condition assessments: visual inspection, soil resistivity, electrochemical potential field evaluation, corrosion rate determination, ECN and dimentional measurments including pit depth and section loss. The test protocol will provide information as to excavation, repair, or no action subsurface structures.

Field Inspection

Matco Services will initialy assess the pole, lattice, tower or anchor rod by completing soil resistivity measurements directly on-site at different depths, therefore including the entire underground portion (including the water table, if present). The electrochemical  measurements will identify lattice legs, anchor rods or poles are corroded. The results will indicate if cathodic protection should be installed immediately to prevent further corrosion of the component. The electrochemical corrosion rate determination will provide further information on the life expectancy of the structure and plan future maintenance guidelines. More accurate measurement of the soil resistivity will also indicate the quality of the grounding system. Matco's electrochemical measurements will determine if partial excavation should be considered. If so the following methodology will be performed.

• Visual examination of above grade portions of towers,poles, ground anchors and CP assets; include appropriate digital photographic documentation.
• Electrochemical measurements at towers, poles and each ground anchor which will immediately indicate the genertal corrosion activity and identify any hot spots or areas of extreme corrosion.
• Partial excavation the backfill soil to a depth of three feet to allow for visual examination and thickness measurement on the ground anchors or tower legs.
• On-site soil resistivity measurements at three different depths, depending on the depth or design of the given tower.
• On-site determination and documentation of the moisture content of the soil.
• On-site electrochemical, ECN, potential and polarization resistance measurements
• On-site determination and documentation of the chloride/sulfate/sulfide.. concentration.
• Above ground and underground section loss and member thickness measurements

The on-site testing will provide information on the life expectancy, frequency of inspection(immediate action, five year inspection or ten year inspection),  and plan future maintenance guidelines for pole, lattice, tower and anchor rods. The maintenance may include coating, non-corrosive or passive backfill and cathodic protection.

In Matco's approach the testing will be in accordance with American Society for Testing and Materials (ASTM) standards and American Association of State Highway and Transportation Officials (AASHTO) standars. The testing will be perfomed by certified technicians and reviewed by a NACE Certified Corrosion and/or Cathodic Protection Specialist.

Inspection Services

Matco Services has years of experience in all aspects of on-site and laboratory inspection and assessment of utility pole, lattice, towers and anchor rods. Our team includes Ph.D.s, registered professional engineers, and certified inspectors from a variety of technical disciplines, including mechanical engineering, paint inspection, chemistry, metallurgy and materials science. We also have a comprehensive array of laboratory and field testing equipment, all calibrated on a routine basis in accordance with both national and international standards. This team is ready to be put to use at a moment's notice for inspection and investigation of poles, lattice, towers and anchor rods.

Corrosion on transmission-line towers and poles is directly related to the atmospheric and soil conditions present for the unique location of a given pole structure, as well as to the materials of manufacturing and the quality of these materials. Common failure modes:

• Internal corrosion due to the presence or entrapment of corrosive water (electrolyte)
• External corrosion due to corrosive atmospheric and environmental conditions
• Fatigue of Traffic and Light Poles due to wind loading and inadequate design
• Manufacturing defects and improper paint coating selection and application
• Little or no maintenance in corrosive environment
• Accumulation of debris and soil under base plate

Above:  Internal corrosion and wall perforation of a weaterhing steel pole exposed to a deicing salt containing environment.

Transmission Towers and Galvanized Utility Poles

Towers in submerged conditions are subject to a greater risk of corrosion because of the continuous presence of moisture – the electrolyte necessary to have the electrochemical corrosion reaction proceed. The specific chemical composition, resistivity and redox potential of the electrolyte in the soil will determine the relative corrosivity or risk of corrosion.

In addition to the soil characteristics, it is useful to measure the electrochemical potential of the structure in the electrolyte. This is done using methodologies developed by the underground pipeline industry and recognized by NACE International and other professional societies and regulatory organizations. The structure-to-soil potential of a buried asset can be related to the present state of corrosion, with less electronegative values of potential indicated an increasing likelihood of active corrosion. By using sacrificial (galvanic) cathodic protection, corrosion can be mitigated by shifting the structure-to-soil potential to more electronegative values where the corrosion reactions are not favored thermodynamically. The amount of galvanic current required to obtain acceptable levels of cathodic protection can be calculated.

Above:  Close up picture of pack-out (corrosion product build up) in a weathering (Cor-Ten steel) transmission tower.  Note deformation and bending of joint plate

A site investigation includes partial excavation for visual assessment of the underground structure. The visual observation complements the non-invasive structure-to-soil potential evaluation and, in the instances of active corrosion, allows direct assessment of the state of corrosion and material loss. It also allows for visual observation of mechanical damage (bent components) and the condition of protective coatings at and below the ground line. If sufficient material loss has occurred to compromise the design strength of the structure, replacement of the components may be required.

Matco's extensive experience with painted and unpainted galvanized steel towers provides specific knowledge and know-how  that can evaluate poles, lattice, towers and anchor rods from the coating point of view, the first defense against corrosion in these structures. We can evaluate the existing coating, predict its performance both under and above ground, and also recommend repair or select a new coating for that specific soil application. This knowledge comes from our experience in evaluation of numerous coated galvanized transmission structures in different soil environments and atmospheric conditions. This type of evaluation requires both metallurgical and polymer coating experience with painted galvanized steel. Very few firms have the specific knowledge required to evaluate aged painted galvanized poles, lattice, towers and anchor rods.

The first steps in a site investigation for transmission towers include recording the tower identification, type, and GPS location. Leg orientation will be confirmed and recorded before performing any inspection evaluations. The immediate area surrounding the structure must also be examined and documented to look for other structures or buried assets which may influence the evaluations which are to follow.

Soil resistivity will first be measured and recorded as specified at each leg of the structure before any soil is disturbed. Structure-to-soil potentials will also be profiled at each leg before soil disturbance. The profile length should equal the reported depth of the sub-surface structure. To the extent possible the profile should proceed radially away from the leg corner in order to minimize potential gradient influence from the adjacent legs.

As excavation proceeds, soil samples should be obtained from the near-surface and bottom of the excavation, or wherever different soil conditions are noted. Soil pH and redox potential should be measured on-site; samples will be procured for off-site analyses of sulfur and chloride content, with enough sample quantity retained for additional evaluations of pH, soil composition or soil resistivity per ASTM G 57 if required or requested at a later time.

Excavation of the buried structure to the required depth should be conducted. Dirt/rust removed should be removed from the structure by brushing and/or washing. Visual assessment may be complemented by holiday testing on coated structures; paint and zinc coating thickness measurements may both be required.

Fatigue of Traffic and Light Poles

Most pole designs prior to 2001 are suspect for fatigue cracking because the design procedures did not considered cyclic loading due to fatigue.  Pole structures should be designed so that the stress ranges due to the fatigue design wind loads are less than the fatigue thresholds for each detail, thus ensuring that fatigue will not occur even for a large number (hundreds of millions) of wind load cycles. In the Aashto 2001 Specification, the fatigue design procedures are based on control of the nominal stress range and knowledge of the fatigue threshold of the details.  Each of these details is assigned a "Stress Category"  and the fatigue threshold stress range for each category is given for this Specification.

If traffic poles are suspected of having crack(s), or if there have been catasrophic failures of the  at the weld toe locations in the past, poles with the same design at a project site should be  evaluated by ultrasonic testing or other forms of non destructive testing methods to identify additional suspect poles. Matco highly recommends that all similar pole structure be inspected immediately and that cracked poles be taken out of service as soon as possible. There is only a small window of time when the cracks are both large enough to detect, and small enough to not yet cause catastrophic failures. In most cases improper design and selection of poles play an important factor in ultimate failure. Fatique cylic  loads, vibration and wind  loading should be consider for the design. wind Matco can establish a program to inspect the poles with similiar design for fatigue cracking.

Above: Fatigue cracks at the toe of the weld is shown in top photo for a galvanized pole. The bottom photo exhibits the catasrophic failure of the pole. It should be noted that there is only a small window of time when the cracks are both large enough to detect, and small enough to not yet cause catastrophic failures.

Design calculations should be prepared and stamped by a professional engineer explicitly showing the fatigue design as well as the traditional allowable stress design for strength.

Corrosion Failures -The investigation of pole corrosion failures can be  complex, and usually requires multidisciplinary testing and analysis to determine the root cause of failure. The end determination must be able to be made with a high degree of certainty to ensure that proper design, replacement materials or adequate coatings are selected and that the most effective corrosion control methods are used. Experience is surely the most important ingredient to look for when choosing a materials firm to handle your corrosion control and failure analysis needs.

Above: Electrochemical cell for evaluation of corrosive soil and trapped water. Electrochemical corrosion testing provides information on corrosion rate in mills/year (mpy) and whether or not the soil is reducing (i.e. the corrosion rate will increase with time).

Pole structures that are to be stored prior to use should be protected from moisture retention and kept well ventilated. Immediate removal of all packing and shipping materials is recommended to prevent accelerated finish deterioration. A good stock rotation program (first in – first out) is recommended to minimize storage damage or deterioration. Foundation details should assure that water or excessive moisture cannot accumulate at the base of the pole. This includes providing drainage for any water caused by condensation inside the pole.

Above: Lack of drainage for water may result in acclerated corrosion.

All finishes are subject to gradual deterioration. The rate of deterioration is a function of many variables such as:

• Ultraviolet damage from constant sun exposure
• Corrosive elements in the atmosphere.
• Ground level exposure to mechanical damage.
• Salt spray from road surfaces, or a marine environment.
• Ground level exposure to corrosive materials and soil conditions.
• Moisture from rainfall or condensation

• Underground soil / ground water exposure

On-site Inspection & Condition Assessments -Our certified team of inspectors can perform non-destructive testing on project sites to evaluate the integrity of poles, lattice, towers and anchor rods.  Our team has performed such analyses nation and worldwide, and will travel to your project site at a moments notice for emergency evaluations.  Such large structure evaluations have included off-shore oil platforms, wind power generation towers, concrete poles, galvanized poles, cor-ten and alumnium poles, paint systems for c.steel and galvanized poles, and large elevated wind towers. Our projects have taken us from chicago, california, Pennsylvania, Hawaii to Alaska; from poles in Tennesse to Cor-ten poles in Chicago, IL.

We know that the most common failure modes for light poles is internal corrosionfrom build-up of moisture inside the pole, external corrosion due to deicing salts, and fatigure fracture from cyclic wind loading. Depending on complexity of project, on-site investigation and test protocol may include any or all of the following:

• Description of  pole installation including the base plate and weld toe examination for corrosion attack, cracks and photo-documentation of the project site
• Ultrasonic wall thickness measurment and thickness loss determination
• Non-destructive testing of the weldment at the base plate/pole connection
• Review of design, engineering and fracture mechanics calculations
• Evaluation of paint system (determination of thickness of paint layers, adhesion and % protection)
• Sampling of peeled paint and corrosion products for further laboratory examination
• Failure mode determination and determination of root cause
• Life expectancy determination
• Recommendations and determination of inspection frequency

If necessary, Matco personnel can  be on site almost immediately when requested during emergency situations. An illustrated formal report documents the results of the investigation.

Other MATCO's Services

The Matco team has experience working in many other diverse fields; from fracture mechanics, cathodic protection to paint inspection to failure analysis to remaining life determination. Some of our clients include Allegheny Energy, Valmont, California Edison, US Airways, First Energy and NY Power.

Corrosion Engineering & Failure Analysis

Experienced PE, PhD Scientists, NACE Certified in Corrosion, Coating, Design , Materials Selection & Cathodic Protection Specialists who will solve your corrosion problems at both initial design stages and in service. MATCO provides corrosion evaluation and failure analysis investigations for : (a) underground facilities (b) above ground facilities and (c) strcutres in marine environments. MATCO can investigate corrosion or corroso -related failures using state of the art techniques.Reports will be generated detailing corrosion failure causes and recommended means of prevention.

• Corrosion evaluation, life expectancy determination and cathodic protection of underground pipe lines, water mains, electrical poles and transmission lattices
• Corrosion mapping, detection of "Hot Spots", cathodic protection of reinforced concrete structures
• Coating/Paint  Investigations
• Electrochemical EIS , DC and AC Testing - Determination of cathodic protection criteria for non-ferrous alloys and stainless steels
• On-site Evaluation of tanks and corrosion mitigation by protective coatings and internal or external Cathodic Protection
• Corrosivity determination of soil, water and determination of corrosion mitigation techniques
• On-site coating evaluation and selection of coatings for specific corrosive environments by EIS

Our inspection crews are ready to be put to use at a moment's notice for inspection and investigation of towers, poles and anchor rods. Our team of experts includes NACE Certified Corrosion / Cathodic Protection / Materials Selection / Design / Coating Specialists (*) and other materials experts includes:

Dr. M. Zee (*)                                            Mr. Geoff Rhodes (*)

Dr. George Bayer                                      Mr. Tom Thomas (*)

Mr. Ed Larkin                                            Dr. Kasraie

Ms. Heather Groll (*)                                  Mr. John Mcardle

Mr. Sam Scheinman                                  Mr. Antonio DiNunno

 

Related Recent Publications:

Painted Galvinized Steel Case HIstories, by Dr. Mehrooz Zamanzadeh and Dr. George Bayer presented at PACE Conference 2006.

Laboratory and Field Corrosion Investigation of Galvanized Utility Poles, by M. Zamanzadeh, C. D. Kempkes, D. Aichinger and D. Riley

A Re-Examination of Failure Analysis, by Dr. Mehrooz Zamanzadeh, Dr. Donald Gibbon, and Edward Larkin, internally published by Matco Services.

Failure Analysis of Coatings, by Dr. George T. Bayer and Dr. Mehrooz Zamanzadeh, internally published by Matco Services.

Painted Galvinized Steel Case Histories, by Dr. Mehrooz Zamanzadeh and Dr. George Bayer presented at PACE 2006.

Final Words

We Value Our Customers... Throughout the years, we have noticed that much of our business comes from repeat customers. Our expertise and well-equipped lab can account for much of this, but we believe there is something more to it. We attribute it to the fact that we promote an open and friendly environment that is never too busy to meet your needs. At Matco Services, we value your business whether you are a large corporation or a small enterprise. We will provide you with the attention you need and deserve. We invite you to visit us and get to know our staff, and share in the learning experience.

Why Choose Matco Services? As one of the premier testing and failure analysis firms featuring state of the art equipment, Matco is able to provide a unique and diverse blend of services. Thousands of investigations have been performed at Matco, ranging from jet engines and boiler tubes, to computer components and implants. Projects are not only conducted on your schedule from initiation to completion with competent and experienced personnel, and conducted in a discrete manner that ensures confidentiality as well.