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In North America, the material and size of pipes that make up water and sewer networks range widely. Because these pipeline systems are so complex, it requires a strategic approach based on risk and real data for effective long-term management.

Worker inspecting pipe

Historically, however, it has been challenging to gather real data that can shape defensive capital decisions for an entire system. The assessment of metallic pipelines — which make up most water and pressurized sewer networks — differs from prestressed concrete cylinder pipes (PCCP), both in terms of failure modes and in the fact that metallic pipe materials are featured in both transmission and distribution networks.

While PCCP assessment and management have been successfully used by utilities for years, effective assessment solutions for ferrous pipe have only recently been commercialized.

In 2011, Pure Technologies began an initiative to help close the gap in metallic pipe assessment technologies, and focus attention on gathering honest feedback from proactive utilities on what solutions are needed to effectively manage metallic pipe.

Seven years later, Pure Technologies reports that notable progress has been made with the development and advancement of assessment technologies for metallic pipeline networks.

Team of workers with a metallic pipe

Many proactive utilities involved in guiding Pure’s research efforts

Proactive utilities have been involved in the metallic pipe initiative, and instrumental in the development of new inspection tools for metallic pipe, both by providing feedback that helps guide research and development, and by providing opportunities that allow solution testing in live operating conditions. As a result of these efforts, there has been significant improvements to the technologies available to utilities for assessing the condition of metallic pipelines in both transmission and distribution networks.

For large-diameter transmission mains, there is a well-developed business case for assessing these mains as they approach the end of their useful life. These pipelines typically carry a high replacement cost and are higher risk — due primarily to their size and criticality — making it important for utilities to fully understand the condition of the asset.

Armed with real condition data, utilities can make a defensible renewal or replacement decision about the pipeline. Based on well over 14,000 miles of data, Pure Technologies has found that only a small percentage of pipes are in need of immediate renewal.

Small diameter metallic pipe leak

Case for using inline tools for small diameter pipelines

In distribution networks, however, the case for condition assessment is more challenging as smaller pipelines can sometimes be replaced cost-effectively. Despite this, the process for making a replacement decision should be based, whenever possible, on risk and real data.

With the EPA suggesting that between 70 and 90 percent of pipes being replaced have remaining useful life, the case is even stronger for collecting condition data to drive the decision making to help utilities spend their replacement dollars more efficiently and avoid replacing pipe with remaining useful life.

In some instances with smaller diameter pipes, it is often cost-efficient to use inline tools to gather detailed screening data on a pipe-by-pipe basis to determine if replacement is necessary.

A new approach to metallic pipeline management

While there is no silver bullet technology for assessing metallic pipelines, Pure has developed a flexible, risk-based approach to help utilities better understand their infrastructure, gather actionable data and prioritize both short and long-term management efforts.

Over the past few years, Pure has worked along proactive utilities to develop its data-driven Assess and Address® approach, which focuses on four main areas:

  • Understand
  • Assess
  • Address
  • Manage

Through the implementation of programs across North America, Pure has found that the majority of pipelines 16 inches and above can be cost-effectively managed for between 5 and 15 percent of the replacement cost.

Starting an effective pipeline management program

The first step of any pipeline management program is understanding the system-wide risk along with the benefits and limitations of assessment solutions. This allows for the development of a defensible management strategy that can be implemented to maintain and extend the life of the assets.

Many technologies now exist to provide a snapshot of a pipeline condition at various levels of confidence. It is therefore prudent for utilities to approach technology selection and subsequent analysis based on the risk of each pipeline.

A more thorough risk assessment involves estimating the Consequence of Failure (CoF) and the Likelihood of Failure (Lof) of each pipeline based on internal knowledge, operational history and pipeline characteristics. This initial risk assessment determines which areas of the system require further assessment to acquire real condition data and provides the utility with the necessary information to make an informed technology selection.

By using risk to guide management strategies, owners can ensure they are implementing the right approach, at the right time, with the lowest financial impact. The goal of a management program should always be o focus resources on managing the asset while safely getting the most service life out of the pipeline.

Sinkhole in a street

Reducing the Consequence of Failure

Reducing CoF comes down to improving emergency events through field operations efficiency. Studies have shown that the time to shut down a pipeline had more impact on the consequence of failure than the diameter of the pipeline.

Utilities can reduce CoF — and in turn risk — by gaining a better control on their system, which can be achieved two ways:

  • 1. Adding valves and redundancy in the system
  • 2. Knowing the location, condition and operability of control points

For example, if a pipe fails and utility operations staff are unable to locate valves — or the valves are inoperable when they are located — it will take longer to isolate a pipe failure. This will result in greater damage, more water loss and longer outages and repair times as a result of the failure. Implementing a proactive program for control assets that focus on providing better data for field staff reduces CoF by decreasing emergency response time.

Reducing the Likelihood of Failure through condition assessment

Many factors influence the likelihood that a pipeline will fail. Metallic pipelines, specifically, have a variety of failure modes and require a wide array of technologies to accurately assess their condition. Until recently, technologies for metallic pipe assessment have been unavailable or limited in their viability.

As a result, lower risk metallic mains have historically been prioritized for replacement using age, material and break history, while higher risk mains have sometimes been assessed with test pits along the length of the pipeline. After test pitting, statistical methods are used to extrapolate the condition of the test pit locations along the entire pipe length.

Through the development of metallic assessment solutions, condition data shows that pipe distress is often random and localized, meaning that an area of distress identified during the test pit method may inaccurately identify the entire pipeline as distressed, conversely, identify the entire length of pipeline as in good condition.

The development of reliable inline condition assessment tools provides owners with pipe-by-pipe data that gives a more complete picture of the actual condition of the pipeline. This allows for a more targeted management of small sections of pipe instead of generalizing the condition of an entire pipe length. It also allows for the collection of real data to drive pipeline renewal, which allows for more defensible capital decision making.

Staff members behind an open pipe

When you’re a regional water authority with a sound way to identify problems with your aging water pipeline before the problems get bigger, it’s cause for a celebration, highlighted with speeches, live demonstrations and cake included in the ceremony.

In late November 2016, a delegation of government officials, special guests and educators gathered in London, Ontario Canada  to celebrate the successful funding, installation and commissioning of a 60 km (37 miles) Acoustic Fiber Optic (AFO) system installed on the Lake Huron Water System’s water transmission pipeline.

Map with pipeline location

Pipeline draws water from near Grand Bend to terminal reservoir north of London

The pipeline, which supplies drinking water to more than 500,000 people in southwestern Ontario, draws water from the Lake Huron water treatment plant near Grand Bend to the terminal reservoir just north of London. Constructed of 1200mm (48-inch) prestressed concrete cylinder pipe (PCCP), the Lake Huron-to-London pipeline has ruptured four times, most recently in 2012.

To mitigate the chance of a future catastrophic failure on such a critical line, the water authority for the Lake Huron Primary Water Supply System collaborated with Pure Technologies (Pure) to install an acoustic-based monitoring system, designed to ensure the success of the Region’s long-term comprehensive pipeline management program.

The $7.5 million upgrade to the Lake Huron-to London water line is part of $179.1 million in water safety infrastructure investments across Southwestern Ontario.

SoundPrint® AFO Fiber Optic wire

SoundPrint Acoustic Fiber Optic technology tracks and records pipeline deterioration

Pure’s SoundPrint Acoustic Fiber Optic (AFO) monitoring technology is an industry-leading system that that listens, identifies and locates pipeline deterioration in real time. Once installed on a pipeline, the SoundPrint AFO system remotely detects the acoustic signature of wire breaks or “pings” in prestressed concrete cylinder pipe, and records their specific pipe location. If break activity increases, utility staff are alerted and can intervene on the deteriorating pipe in advance of failure.

Under the new system, “We will get an email to say a section of pipe has a break, and they even give us the map location of where it happens,”

John Walker

Operations Manager, Lake Huron and Elgin Area Primary Water Supply

The AFO system remotely detects the acoustic signature of breaks in the pipeline structural reinforcement and records the specific pipe location of the deterioration, alerting operating staff who can intervene in advance of a catastrophic failure of this regionally significant water transmission pipeline.

“A snapping wire or two won’t sound an alarm bell,” says Heather Edwards, project manager at Pure. “But when our monitoring team listens and identifies a large number of pings from wires breaking in a concentrated location, that’s when we focus attention on the acoustic anomalies to determine whether remedial action needs to take place.”

By managing their pipelines with innovative technologies, utilities can save millions of dollars

The project was special for Pure as it showcased the innovative SountPrint AFO technology upon which the company was founded more than 20 years ago.

“We love partnering with forward-thinking utilities like London Region to save money by using innovative technologies like the AFO system,” said Mike Wrigglesworth, senior vice-president of Pure Technologies, who spoke at the ceremony. “Instead of budgeting for an expensive replacement program or dealing with disruptive bursts, London Region has saved millions of dollars by actually managing their pipeline.”

Pure surpasses 700 miles (1,100 km) AFO monitoring milestone

Globally, Pure has surpassed 700 miles (1,100 km) of active AFO monitoring. Currently within North America and China, Pure monitors 56 mains from a combined total of 17 clients, including London Region. Pure’s active AFO system has recorded more than 43,600 wire breaks from its managed roster of pipelines located in North America and China alone.

With the installation of AFO technology in place, the London Region utility ensures active management of their most valuable buried assets, for the life of the asset.

That’s a comforting thought, well worth celebrating.

City of Baltimore

Over the past decade, the City of Baltimore has seen vast improvements in control point operability and system sustainability of its water distribution assets. The report card is looking better each year.

The Baltimore City Department of Public Works shoulders a big responsibility. The Department provides 265 million gallons of water daily to 1.8 million people in the greater Baltimore region, and maintains 3,400 miles of water mains, 19,000 fire hydrants and more than 64,000 pipeline valves.

For more than ten years, Wachs Water Services has partnered with Baltimore and surrounding counties to deliver GIS data, coax non-functioning valves and hydrants back to operational life and reduce the probability of failure. The ongoing program is a showcase for Wachs Water Services to demonstrate how its unique approach, field experience and mechanical advantage could give Baltimore new confidence in managing their water distribution assets.

Broken water mains propel utility to investigate distribution system

Many of Baltimore’s water distribution system assets are decades old, with some pipes dating back 100 years and more. Since 2000, large-diameter pipeline failures were occurring more frequently, resulting in extreme flooding in some urban areas. Emergency response was often delayed because of difficult to locate or non-operational valves.

The water utility decided it was time to locate, assess and repair or replace the critical pipeline valves within their distribution system. They turned to the industry leader in valve management solutions, Wachs Water Services, a division of Pure Technologies.

WachsWater Workers

Valve management delivers operational intelligence to mitigate risk

Collaborating closely with field crews from Baltimore Public Works, Wachs Water Services technicians immediately went to work to locate and test the thousands of pipeline valves and water assets within the distribution system.

Valve management involves integrating field-verified valve status details into the GIS system, the vital “operational intelligence” utilities need in mitigating operational risk, and accelerating emergency response to major pipeline failures.

After physically locating each valve, Wachs Water Services field technicians recorded the valves’ precise GPS position, operational and service history, and current functional status into Baltimore GIS (geographical information systems) and CMMS (computerized maintenance management systems), ensuring the vital asset information could be easily accessed during an emergency response.

Damaged or questionable valves were expertly serviced, replaced or updated to verify compliance with industry specifications, and Baltimore field crews were trained to deal with operating valves to respond to an array of emergency situations.

Damaged valve

Valve training pays dividends sooner than expected

The emergency valve training paid dividends much sooner than expected. In September 2009, a 72-inch PCCP water main suffered a catastrophic failure near a busy Baltimore street intersection, flooding the area with 175,000 gallons per minute. Field crews from Baltimore Public Works, Wachs Water Services and emergency service workers converged on the scene as water submerged residential areas and threatened 6,000 homes.

Working closely with Baltimore Public Works, Wachs Water Services provided detailed maps and plans for shutting down the broken pipeline main, including information on all valves involved, and the specific pattern to execute the shutdown in a manageable way.

The utility knew exactly what crews to deploy, where to deploy them, and what they needed when they arrived on location, successfully shutting down all pipelines feeding the ruptured main in a fraction of the time.

Baltimore proves its commitment to municipal water stewardship

Tremendous progress has been made by Baltimore City and surrounding counties, and they have set industry benchmarks for control point operability and system sustainability. In the ongoing program, more than 64,000 valves and 22,000 fire hydrants have been GPS-located and mapped over more than 2,000 miles of mains.

The City has earned high marks, not only for its diligence, but also for its commitment to municipal water stewardship.

Tech analysing data
Hydrant inspection

This large Midwest utility maintains and operates water collection, treatment, and distribution systems, as well as wastewater collection and treatment systems and stormwater management systems for its residential, business and wholesale customers in the region.

To ensure the accessibility and quality of water services to meet the growing needs of the region, the Utility needed to conduct a complete assessment of their water distribution system.  The limited internal resources and need for quick results were more than the department could handle on their own.

To kick-start the process, and ensure success of the project, the Utility needed to identify the most economical solution that would provide the greatest impact on their distribution system in the shortest period of time.

The long-term project called for highly specialized valve maintenance expertise, equipment and technology, and the Utility elected to partner with the industry leader in valve management solutions, Wachs Water Services.

Inserting tools for inspection

Collecting valve status information critical for improving quality of water service

Because of its experience in the field, Wachs Water Services (WWS) was chosen to collect valve status information to assist in operational planning and speed of response, with the ultimate goal to improve the quality of water services in the growing region.

The comprehensive project called on WWS to dedicate an onsite team for the 5-year project, which included water valve assessment, mapping, and data management – including fire hydrant assessments.

During the course of the project, more than 35,000 valves were accessed, assessed and repaired where necessary. During these inspections, WWS discovered almost 2,000 valves with packing leaks, which were subsequently corrected by snugging up the valve to the seal.

Service included raising buried valves to grade to provide easy access

In addition to locating and assessing the valves in the distribution system, the WWS team took 1,065 valves buried in asphalt and raised these to grade in order to provide easy access and shut off during an emergency. Additionally, 5,387 valves buried in non-asphalt environments (dirt-grass-gravel) were raised to grade and are now accessible.

Almost 2,000 damaged or missing operating nuts on valves were repaired or replaced.  This represented by far the largest number of operating nut anomalies that WWS had ever encountered in the field.

This was due, in part, to the use of over-sized tooling.  While some of the operating nuts were over-sized, those that were not (the majority) were damaged by the over-sized tools.

As part of the condition assessment and repairs, more than 10,000 valve boxes were vacuumed and cleared of debris so the valves could be accessed and assessed for damage/need of repairs.

Finally, more than 7,400 fire hydrants were accessed, with a least 20 percent requiring some repairs. Hydrants were also pressure tested, and those with a low-flow reading were corrected.

Inspecting valves

 

System operability increased from 55 percent to 84 percent

Overall, the system operability increased from 55 percent to 84 percent, which added up to an increase of 53 percent more valves now accessible and operable than before the assessment.

The Utility’s GIS was updated to increase the accuracy and include additional attribute information. In addition, WWS provided the Utility with assistance on numerous construction shut-downs for the duration of the contract.

The operating nut repairs eliminated more than 1,300 dead ends caused by inoperable valves, a solution that increased water quality, increased fire-fighting capacity, and corrected system pressure problems.

Wachs Water Service also performed a leak sounding pilot on all the valves accessed during the first 5 months of the program.

Overall, tremendous progress has been made, and the Utility has set industry benchmarks for control point operability and system sustainability.

*Published in World Pipelines Magazine

Oil and gas pipelines have been around for well over a century, and some of the earliest constructed are still in service today.  Although early pipelines were made of wood, and in the past few decades plastics and composite materials have increased in popularity, the vast majority of pipelines in service today are constructed with steel.

Like any pipe material, steel pipe has its downfalls. Steel has a propensity to dent, buckle, corrode and crack when exposed to the environment.  Steel pipeline’s carrying combustible hydrocarbons are buried underground with typically ~1 meter (3 feet) of cover to protect them.  In order to mitigate corrosion, pipelines are covered with a protective coating, utilize cathodic protection (CP), and have their pressure regulated to reduce crack formation and propagation.

Despite all of the design innovations made over the past century, it has not been enough to prevent failures – even the most recently constructed pipelines.  Weather cycles, frost heaves, and road loadings cause physical damage to the pipeline and protective coating.  Operational errors and material defects cause the steel to succumb after years of relentless pressure cycles from the pipeline product itself.  Therefore, proactive pipeline inspections are needed to identify defects, before they cause a leak or rupture.

Pipeline integrity can be validated and assessed using three primary techniques: hydro-testing, the use of Inline Inspection (ILI) tools, and Direct Assessment.

Hydro-testing

Hydro-testing became common practice for pipelines in the 1940s. The process involves taking the pipeline out of service and purging the product, then the pipeline is pressurized above the maximum operating pressure (MOP) with the intent to determine the ability to operate the pipeline at MOP.  While hydro-testing is still widely used today, there are several drawbacks to the process. The water used in hydro-testing is considered hazardous material after being used, meaning owners incur the additional risk and cost associated with disposing of the water after testing. The information gained from the test is also limited in that it provides no information of the actual condition of the pipe, coating, or surrounding environment.

Hydro-testing can also promote internal corrosion of pipelines, especially if the water used is not properly treated for microbiologically influenced corrosion (MIC) and chlorides. Internal corrosion usually occurs if the pipeline is not properly cleaned and dried after the test.  Hydro-testing can also result in pressure reversals, which worsen the integrity of the pipeline [1].  Finally, the pipeline may be required to be out of service for a significant amount of time, resulting in a significant loss of revenue.

Inline Inspection

ILI tools – which are commonly referred to as smart pigs – were developed in the 1960s and commercialized in the 1970s.  These tools are designed to survey the conditions of the pipeline wall with limited disruption and can identify and quantify the corrosion and cracking in steel pipelines [2].  Magnetic flux leakage (MFL) and ultrasonic testing (UT) are common ILI tools used widely by owners today.

ILI is a significant part of pipeline integrity management, and promote safe, efficient and cost-effective pipeline operation [2].  However, it is important to remember that ILI is just a subset of a family of inspection tools used to verify pipeline fitness for service.  As with any inspection technology, ILI tools have a threshold for detection – the tools are unable to reliably detect anomalies that are below their design specifications’ detection ability. Also, internal pipeline inspections are primarily reactive, requiring the damage or wall loss to occur before defect detection is possible.

Direct Assessment (DA)

The most recently developed solution for pipeline integrity management is Direct Assessment (DA), which is a structured, iterative integrity assessment protocol used by pipeline operators to assess and evaluate the integrity of their pipelines.

Adoption and demand for DA is increasing in modern integrity programs due to more stringent industry regulations, aging pipeline networks, limitations of alternate inspection techniques, and the fact that roughly 70 percent of pipelines within North America are difficult to pig.  Direct assessment surveys provide pipeline owners with important information on both the pipeline’s condition and its surrounding conditions, both of which can lead to degradation and eventual failure.

The Stages of Direct Assessment

It should be noted that geotechnical, dent, and buckle threats are not specifically addressed with any of the DA techniques.  All DA protocols are four-step iterative processes which include a Pre-Assessment, an Indirect Inspection, a Direct Examination and a Post-Assessment.  Inspections involve the integration of as much pipeline available integrity data as possible, which includes physical characteristics and operational history, historical and multiple indirect inspections, and direct pipe surface examinations.

In the pre-assessment step, historic and current pipeline data is collected to determine whether DA is feasible, define DA regions, select indirect inspection tools and determine if additional integrity data is needed.

The second step in DA methodology involves the use of non-intrusive and aboveground techniques. These tools assess the effectiveness of the coating and cathodic protection for pipeline external corrosion assessment (EDCA an ECCDA), and predictive modelling, or critical angle calculations for pipeline internal corrosion assessment (ICDA) to identify and define areas susceptible to internal corrosion.

For external corrosion assessment, the state of cathodic protection, coating and soil resistivity are critical factors in determining high-risk areas. For internal corrosion assessment, fluid flow, mass transfer, solid accumulation, mineral scales, corrosion products, and MIC are critical components [3].  For stress corrosion cracking, critical factors include operating stresses, operating temperatures, distance from a compressor station, age of the pipeline, and coating type.

The direct examination step involves the analysis of pre-assessment and indirect inspection data to select sites for excavation and examination of pipe surface. This process validates the inspection data and provides a first-hand evaluation of the pipe surface and surrounding environment.

Finally, the post-assessment phase involves the analysis and integration of integrity data collected from the previous three steps to assess the effectiveness of the DA process and determine the necessary reassessment intervals.

There are six DA standards developed by National Association of Corrosion Engineers (NACE) and they include:

2002 -NACE SP0502-2010 ECDA (External Corrosion Direct Assessment)

2004 -NACE SP0204-2008 SCC-DA (Stress Corrosion Cracking Direct Assessment)

2006 -NACE SP0206-2006 DG-ICDA (Dry Gas Internal Corrosion Direct Assessment)

2008 -NACE SP0208-2008 LP-ICDA (Liquid Petroleum Internal Corrosion Direct Assessment)

2010 -NACE SP0110-2010 WG-ICDA (Wet Gas Internal Corrosion Direct Assessment)

2010 -NACE SP0210-2010 ECCDA (External Corrosion Confirmatory Direct Assessment)

DA is also covered in ASME B31.8S (Section 6.4).  In the United States, DA is covered in US Code of Federal Regulation CFR 49 Part 192.923 (for natural gas pipelines) and 195.888 (for liquid hazardous pipelines).  It is now one of the three accepted inspections (ILI and Hydro-testing being the other two) allowed for oil and gas pipelines.

Identifying Pipeline Anomalies Using Directing Assessment

When completing a DA inspection, there are three types of anomalies that owners are aiming to identify:

1.         External Corrosion (EDCA and ECCDA)

2.         Internal Corrosion (dry gas, wet gas, and liquid petroleum ICDA)

3.         Stress Corrosion Cracking (SCCDA).

Due to the serious consequences of corrosion and leaks in underground pipelines, external corrosion direct assessment (ECDA), and external corrosion confirmatory direct assessment (ECCDA) – as described in ANSI/NACE SP0502 and NACE SP0210 – were developed in an attempt to proactively prevent external corrosion and ensure the integrity of oil and gas pipelines that are difficult to pig.

ECDA is a continuous improvement process intended to identify and address locations at which corrosion activity has occurred, is occurring, or might occur. For instance, ECDA identifies areas where coating defects have already formed, and can ascertain where cathodic protection is insufficient and corrosion is possible, before major repairs are required.

The success of any ECDA requires strong knowledge of the soil/environment, pipeline material, coating, cathodic protection, and foreign/interference current on the pipeline. Also, the accurate selection of susceptible areas for external corrosion relies on using at least two complementary advanced aboveground inspection techniques. These aboveground indirect inspection techniques may include: direct current voltage gradient (DCVG) or alternating current voltage gradient (ACVG) surveys, a cathodic protection close interval potential survey (CP CIPS), alternating current—current attenuation (ACCA) and side drain (for bare or ineffectively coated pipelines) surveys. Normally these aboveground inspections are used in conjunction with pipe locating.

The development of internal corrosion in pipelines is partly because of its complex nature and interaction between constituents that are found in transported gas and liquid products (e.g., oxygen, carbon dioxide, hydrogen sulfide, chloride, bacteria, etc.). When in the presence of water, these contaminants can lead to conditions conducive to the occurrence of internal corrosion. The susceptible locations for internal corrosion are usually where liquids, solids and gas accumulate. In order to ensure that susceptible locations along the pipeline are prevented from internal corrosion, internal corrosion direct assessment methodology is implemented.

Internal Corrosion Direct Assessment (ICDA) methodology has been developed to verify pipeline integrity, especially for pipelines that are not able to accept inline inspection (ILI) tools. ICDA includes Wet Gas Internal Corrosion Direct Assessment (WG-ICDA), Dry Gas Internal Corrosion Assessment (DG-ICDA) and Liquid Petroleum Internal Corrosion Direct Assessment (LP-ICDA). WG-ICDA (NACE SP110-2010) is used in pipelines that assumes that water, or a combination of water and hydrocarbons can be present in the pipeline. It is intended for onshore and offshore systems where liquid to gas ratio is small. It tends to identify locations in the pipeline where corrosion is expected to be severe. DG-ICDA (NACE SP206-2006) is applicable to pipelines that transport gas that is normally dry, but may suffer infrequent upsets, which may introduce water to the pipeline. LP-ICDA (NACE SP208-2008) is employed to assess the susceptibility of internal corrosion on pipelines that transport incompressible liquid hydrocarbons that normally contain less than 5 percent base sediment and water. The success of any ICDA process is dependent on using an accurate corrosion model to predict a precise elevation profile in order to determine susceptible locations for internal corrosion.

DA technology has also proven successful in stress corrosion cracking direct assessment (SCCDA), offering pipeline operators a comprehensive pipeline integrity management portfolio. SCCDA (referenced in NACE SP0204-2008 and ASME B31.8S) is a proactive structured process that seeks to improve pipeline safety by assessing and reducing the impact of stress corrosion cracking. Stress corrosion cracking can occur at neutral or high pH when susceptible pipeline material is exposed to stress, specific susceptible temperature, and a corrosive environment.

The Benefits of Direct Assessment

Direct Assessment is non-intrusive and inspections can be completed during normal operation of the pipeline.  DA is also a proactive integrity management tool that can find anomalies before they become critical defects, while traditional ILI tools are reactive in that they identify existing pipeline damage.

While hydro-testing and ILI tools are an important part of integrity management, the development of DA provides pipeline owners with another solution to identify at-risk areas of pipe before they become a major problem. A combined integrity approach that employs DA can help pipeline owners ensure containment and prevent costly, reputation-harming pipe failures.

References

1.    Pipeline Research Committee, American Gas Association, NG-18 Report No. 111 (Nov. 3, 1980)

2.    NACE 35100, In-Line Inspection of Pipelines, NACE International, May 2012

3.    NACE Training Course, Direct Assessment, NACE International, November 2012

Hamilton sign

In late 2015, the City of Hamilton, Pure Technologies (Pure) and Robinson Consultants worked together to perform an external investigation of a pipe section in the Woodward Greenhill Transmission Main (WGTM) to gain understanding of what was causing degradation in a specific geographical area.

A 2014 condition assessment performed by Pure had identified a cluster of damaged pipes on the WGTM, which is comprised of prestressed concrete cylinder pipe (PCCP). Pure used electromagnetic (EM) inspection technology to identify which pipes in the WGTM had broken prestressing wires, a sign of deterioration in PCCP. When prestressing wires break, the pipe loses compression. When enough wires break the pipe becomes at risk of failure.

Understanding the root cause of why pipes deteriorate

Pure’s condition assessment of the WGTM included finite element analysis (FEA) to determine the number of broken wires a pipe can safely operate at given the pressures of the pipeline. Although each pipe reported with broken wires had total wire breaks well below the threshold, and not in any immediate need of rehabilitation, further investigation of the pipeline was undertaken to understand the root cause of the degradation.

The City of Hamilton’s pipeline management plan is comprehensive, going beyond identifying and managing damaged pipe sections. By understanding why the pipes are deteriorating, expectations on future degradation can be made.

The investigation included testing the soil and mortar to determine if aggressive soil conditions were contributing to the distress, and confirming the pipe properties and actual number of wire breaks, factors key to the structural analysis of the distressed pipe.

External EM scan confirms correct pipe excavated

On October 20, 2015 Pure performed an external investigation on one of the pipes identified with wire breaks. Pure’s external investigation included an external EM scan to confirm the correct pipe was excavated. This was accomplished by comparing the data from the external EM scan to the data from the internal EM data collected from the 2014 inspection. The comparison confirmed the correct pipe was found.

The next step was an external and visual sounding inspection of the exposed pipe. The mortar was inspected for cracks, spalls, corrosion staining and other signs of distress that would indicate advanced deterioration. None of these signs were found.

Process for verifying number of broken wires

The process of verifying the number of broken wires on PCCP involves removing an approximately 2-inch wide strip of mortar across the length of the pipeline to expose the prestressing wires, and using a multi-meter to measure the electrical resistance from wire to wire (this process is specific for PCCP without shorting straps). If an electrical discontinuity is identified, it confirms that a break exists between the two points of contact. Upon completion of the tests, the mortar is patched to protect the wires and prepare the pipe for burial.

Workers with measurements tools

The electrical continuity measurements on the exposed pipe section in the WGTM confirmed the two regions that were identified by the electromagnetic inspection. No other wire breaks were found across the pipe length.

 

 Comparison Of Estimated Versus Actual Wire Breaks
Estimated Position Actual Position Estimated No. of WB Actual No. of WB
4 feet 3 feet 5 2
8.5 feet 8-8.5 feet 10 6

 

Results used to recalculate FEA analysis

The results of the investigation were used to recalculate the FEA analysis, adding to a slight increase in the number of wire breaks that the pipe can withstand under pipeline pressures. Ultimately the findings concluded that the pipe can remain in service with no repair or changes to operating pressures.

The City of Hamilton’s condition assessment program for PCCP pipe is an example of their comprehensive approach to pipeline management. Beyond locating the damage, the City strives to understand the root cause. The use of the EM inspection technology allows the City to pinpoint damaged pipe sections. FEA analysis provides a means for determining if a pipe requires rehabilitation.

For this project, further investigation through external testing will provide insight into the root cause of pipe deterioration (the results of the soil and mortar testing will be presented by Robinson Consultants at a future date). This project showed how collaboration between the City, Pure Technologies, and Robinson Consultants resulted in a comprehensive condition assessment of one of Hamilton’s critical watermains.

Water and sewer utilities across North America are facing a major funding gap related to their buried pipeline infrastructure. Based on current estimates, utilities do not have enough capital available to fix or replace their aging assets. In addition to the funding gap, utilities are under scrutiny because of increased incidences of pipeline failures that are disruptive to communities and expensive to mitigate.

This new reality has forced utilities to squeeze more remaining life out of existing assets, creating more demand for condition assessment programs that allow utilities to identify specific areas of damage and selectively repair pipelines in favor of full replacement.

Historically, condition assessment has been in the realm of a few specialized firms that respond to high profile pipeline failures; however, the industry has changed and condition assessment is becoming widely used and trusted. This approach has been adopted by many utilities that have successfully managed risk and extended the life of assets for a fraction of the cost of a replacement program.

According to a study by Pure Technologies, the majority of pipelines 16 inches and above can be cost-effectively managed for between 5 and 15 percent of the replacement cost. The study found that pipeline damage is typically not systematic across an entire pipeline, but is usually localized due to factors such as design, manufacturing, installation, environmental, operational or maintenance factors.

Equipped with this information, utilities can be assured that assessing the majority of their mains before replacement can reduce their infrastructure gap and extend the useful life of assets.

However, one question that often gets asked about condition assessment programs is how a utility should choose the right condition assessment solution.

The easiest way to solve this challenge is to employ a risk-based approach to condition assessment using a variety of tools that offer different resolutions.

Staff inserting tools

Defining Risk and Pipeline Priorities

Risk is a measure of the probability and consequence of uncertain future events, in this case, potential pipeline failure. A basic approach can be used to define risk even in complex systems; simply, risk is a product of Consequence of Failure and Likelihood of Failure (CoF x LoF).

Consequence of Failure (COF) refers to the damage a failure would cause based on factors like its location, the amount of users it supplies, and its size and operating pressure. Likelihood of Failure (LOF) refers to the probability of a failure occurring based on factors such as age, pipe material, soil conditions, operating pressure, failure history, among others.

Generally, the Consequence of Failure is well defined by the potential damage a pipeline failure would impose on the surrounding environment and is generally fairly static – or – once defined, it is unlikely going to change rapidly.

With this in mind the key to managing risk, or the possibility that a pipeline could fail, is in understanding the Likelihood of Failure. This can be achieved by quantifying the physical condition of the pipeline and understanding and quantifying the factors that affect the potential for deterioration of the assets.

Once risk is defined, the pipeline inventory can be prioritized which helps in the selection of condition assessment approaches and the application of the appropriate technologies. In general, high-risk pipelines warrant a detailed assessment while low risk pipelines can use lower resolution alternatives.

Using Risk to Select Condition Assessment Techniques

When selecting condition assessment techniques, qualifications and technical judgment should be used in lieu of price. High resolution tools come with a higher cost, but saving money on a low resolution condition assessment is not a responsible alternative for a high-risk main.

For example, the savings gained by selecting a low resolution technology for a large-diameter pipeline with a high CoF are often miniscule in comparison to the repair and capital programming decisions that result from the low resolution condition assessment data. If the data is inconclusive or inaccurate, a utility may unnecessarily invest millions in a capital replacement program that was not required, easily eliminating the savings achieved by selecting the less expensive condition assessment option.

Tech monitoring results

Additionally, the cost of a failure should be considered when selecting a lower-cost assessment for a critical pipeline. The average cost of a large-diameter pipe failure is between US $500,000 and $1.5 million; money saved on lower-resolution assessments can easily be negated by the cost of mitigating a single failure and the resulting reputational damage.

One method of selecting a technology is to compare uncertainty to risk. As mentioned earlier, risk is a measure of the probability and consequence of uncertain future events. When dealing with a high-risk asset, it is important that the solution allows the utility manager to minimize the uncertainty of the condition assessment. More importantly, it is crucial that the utility manager knows the condition of the asset to the best extent possible, particularly in areas where there is a high Consequence of Failure.

Pure Technologies has a suite of condition assessment tools with different resolutions. Our low resolution solutions can provide basic condition data on leaks, air pockets and areas of pipe wall stress that could represent damage. This is a valuable prescreening option for high-risk mains, or alternatively for lower risk mains, can be enough detail for a utility to manage the asset.

Pure’s medium and high resolution tools provide more comprehensive data for higher risk pipe. Our high resolution tools can provide detailed accuracy, for example, locating small pits on metallic pipe. The data collected from both medium and high resolution tools is often used by utilities to create rehabilitation plans for critical mains.

Regardless of the solution provider, it is important that utilities employ a balanced, risk-based approach to condition assessment that uses appropriate tools. The most important factor a utility owner can remember is that there is no silver bullet to assess an entire system.

Sewer pipes below a road

A critical component of Queensland Urban Utilities’ sewerage network is a series of large-diameter sewer rising mains – also known as force mains – which are responsible for transporting 50 per cent of raw sewage in the Brisbane area for treatment. The mains are made of mild steel cement-lined (MSCL) pipe and prestressed concrete pipe (PCP), of diameters ranging from 1295 to 1840 millimetres (52 to 74 inches). The reliability of these sewer rising mains are important from both a customer and environmental perspective.

Building upon previous assessments conducted by Pure Technologies’ Engineering Services, Queensland Urban Utilities sought to identify industry best practices for assessing these critical large-diameter rising mains. The goal of the assessment was to understand the current condition of the mains and identify what remedial works or condition monitoring approaches would help maintain the safe operation of the mains, while extending the life of the assets in accordance with management plans.

In consultation with Pure Technologies, a comprehensive assessment methodology was developed which included: SmartBall® leak and gas pocket detection; ground surveys to determine residual ground cover; isolation, dewatering and cleaning of the mains; CCTV and laser profiling to determine internal deterioration; valve inspections; PureEM™ inspection to determine structural deterioration of the pipe walls; internal visual inspection to confirm and further document findings; transient pressure monitoring to identify loading conditions; and an engineering assessment with rehabilitation recommendations.

PureNET Overhead

A customised EM tool was designed to assess the condition of QUU’s
steel pipe.

Field Data Collection

The inspection provided QUU with actionable information about their assets.

 

Related Topics

“Queensland Urban Utilities is keen to embrace new technologies to improve our customer service and the reliability of our water and sewerage network,” says Jonathan Farrell, Design Manager at QUU. “The technical expertise provided by Pure has allowed us to undertake an accurate condition assessment and have the appropriate data to make an informed decision on the current condition of the mains. This will allow us to plan cost-effective, timely upgrades to ensure the asset reaches its design life.”

This was a first-of-its-kind assessment in Australia applying new inspection technologies, including the customisation of a 48-detector PureEM tool, as well as a new risk assessment technique for metallic pipes. Detections from the PureEM inspection (i.e. discrete areas of structural deterioration) were validated utilising alternate electromagnetic and ultrasonic techniques, which provided supplemental condition information for the structural assessment.

Inspection and assessment work on two of these critical mains has been completed at this point. The inspection identified specific pipes along the mains with deterioration; but more importantly, the engineering assessment with structural modeling determined that less than 1 per cent of pipes are at a higher risk of failure, meaning the main is in primarily good shape. This data coupled with engineering recommendations is enabling Queensland Urban Utilities to make informed decisions on the mains, including: selective repair or replacement, condition monitoring, and operational changes (i.e. safe working pressure), all for a fraction of the capital replacement costs.

In addition, the work associated with the assessment has provided Queensland Urban Utilities with some valuable lessons learned on the safe management and operation of the mains.

 

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Cast Iron Pipes

Managing Metallic Pipelines

Pure offers a number of leading edge technology options for assessing the condition of ferrous water and wastewater mains.

Padre Dam Municipal Water District Assesses Steel Pipeline with Advanced Inline Technology

In November 2012, PDMWD wanted to assess the condition of a 1.2-mile (2-kilometer) stretch of 20-inch (500-mm) mortar-lined steel pipeline that was thought to be in poor condition and may need replacement. Before committing to the large capital project, PDMWD completed a non-destructive inline assessment.

Steel Pipes

Steel Pipe

In an article from the August 2013 Issue of Municipal Sewer and Water, the author explores how Baltimore City Public Works (BPW) is managing its again water system using Acoustic Fiber Optic Monitoring and free-flowing electromagnetic (EM) technology.

hese distinctions can make assessing BWP challenging for pipeline operators attempting to renew their large-diameter water transmission mains, since the methods for determining baseline condition in the similar-looking pipe types are different.

PCCP is a concrete pipe that remains under compression because of the prestressing wires, with the thin-gauge steel cylinder acting as a water membrane. With BWP, the cylinder plays a much larger role in the structural integrity of the pipe. BWP is essentially designed as a steel pipe with mild steel used to manufacture the steel cylinder and steel bars.

The high strength steel wire in PCCP is smaller in diameter and wrapped under higher tension, therefore corrosion makes it quite vulnerable to breakage. The mild steel bars in BWP are thicker in diameter and wrapped under less tension, therefore corrosion takes significantly longer to lead to breakage.

This was the case for Trinity River Authority of Texas (TRA), who owns and operates 8.5 miles of 30-inch BWP and PCCP that supplies raw water from Lake Arlington to the Tarrant County Water Supply Project Water Treatment Plant in Euless, Texas.

The 30-inch pipeline, in conjunction with a parallel 54-inch pipeline, conveys raw water to TRA’s 87 mgd Water Treatment Plant (WTP). Treated water produced at the WTP is then supplied to five cities in the mid-cities region between Dallas and Fort Worth including Bedford, Colleyville, Euless, Grapevine and North Richland Hills.

TRA had originally planned to replace this pipeline, but chose to assess and selectively rehabilitate the pipeline by finding solutions that could identify the most distressed areas. The pipeline, constructed in 1973, is made up primarily of BWP, although there are some sections of PCCP.

In November 2012, TRA began a condition assessment program with Pure Technologies that included transient pressure monitoring, acoustic leak and gas pocket detection, internal electromagnetic inspection, and structural condition assessment including finite element analysis.

Pure Technologies staff verify the pipe condition

Pure Technologies staff verify the pipe condition

Crew verify and reveal corrosion on three pipe sections

Verification revealed corrosion on three pipe sections

After completing the inspections, TRA has verified and repaired three sections of BWP that were beyond the yield limit determined by BWP structural performance curves. During the verification, TRA and Pure determined that the distress areas identified in the structural assessment were accurate and the excavated pipe sections had bar breaks and corrosion.

The condition assessment project also identified four leaks and three gas pockets and although the four identified leaks were small (less than 2 gallons per minute), one was located in the front yard of a brand new church building and could have caused significant water damage had it not been repaired immediately by TRA. Water from this leak was visible at the surface 325 feet away from the actual leak location.

Through the use of condition assessment, TRA was able to selectively rehabilitate its assets for roughly 4 percent of the estimated $25 million replacement cost. The project has also allowed TRA to increase service reliability for customers in the region.

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Assess & Address Pipeline Management Program

Assess & Address Pipeline Management Program

Pure Technologies is helping utilities manage their buried infrastructure through its Assess & Address which can often be implemented for only a fraction of the capital replacement cost.

Case Study

Case Study: Trinity River Authority of Texas

After completing leak detection and structural condition assessment on 8.5 miles of PCCP and Bar-Wrapped Pipe, Trinity River Authority verified the results of inspection, finding three distressed pipe sections.

Technical Paper

Failure Risk of Bar-Wrapped Pipe with Broken Bars and Corroded Cylinder

This study investigates the behavior of a deteriorating BWP under various levels of distress and various internal pressures. The results based on a 24-inch pipe transmission main, are used to define criteria to evaluate the performance of a damaged BWP. Based upon the finite element results obtained in this study, suggestions for future work are presented and discussed.

In April 2012, the District signed a Federal Consent Decree requiring improvements to the collections system aimed to eliminate illegal discharges of untreated raw sewage. As part of the requirements outlined within Consent Decree, a force main non-destructive testing and condition assessment program must be developed and implemented. The force main condition assessment program incorporates an asset management approach and risk categorization scale that classifies each of its force mains as high, medium, or low risk based on a previously conducted prioritization. The District and Jason Consultants (a wholly owned subsidiary of Pure Technologies) have developed individualized assessment strategy for each high and medium risk force main including the implementation of various inspection techniques and technologies.

Condition assessment and management of wastewater force mains has historically proven difficult for pipeline owners and operators. Conventional gravity sewer inspection methods (e.g. visual inspection, sonar and laser profiling) do not provide a full condition assessment of most pressure pipes since the loss of structural capacity cannot be quantified with these methods. As part of the condition assessment of force mains, leak and gas pocket detection is crucial since their presence is often a preliminary indicator of a potential failure location. Gas pockets in force mains are of significant concern as they are the primary failure mode for these critical pipelines. Hydrogen sulfide gas within the wastewater may be converted to sulfuric acid by bacteria in the slime layer on the pipe wall, which may cause corrosion and eventual breakdown of the pipe’s exposed surface.

SmartBall Insertion
Tool Tracking

Based on Pure Technologies’ assessment of over 8,000 miles of pressure pipe, including over 400 miles of wastewater force mains, our clients have found that pressure pipes typically do not deteriorate or fail systematically along their full length. Rather, pipe condition is usually related to localized problems due to design, manufacturing, installation, environmental, operational, or maintenance factors. By identifying the localized areas of deterioration and performing “surgical” repair techniques, utilities can manage their pressure pipelines for often less than 10% of the replacement cost.

After completion of the SmartBall inspection and other screening techniques such as pressure transient monitoring and external corrosion evaluations, the District and Jason Consultants have identified locations for external evaluation for several force mains to determine the condition of the pipe wall. These evaluations will be conducted using various techniques including visual, physical measurements, and ultrasonic testing with the goal of District staff providing most of these inspection services. Jason Consultants will then work with District staff to deliver force main specific management strategies including:

  • Repair, rehabilitation, or replacement recommendations;
  • Recommendations for modifications to the force main including future inspection needs and air release valves;
  • Re-evaluation of force main risk based on inspection results and condition assessment;
  • Remaining useful life estimations;
  • Emergency response planning for high and medium risk force mains.

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Sewer access

Sewer Force Main Inspection

Pure Technologies has the complete portfolio for sewer force main and large diameter gravity main inspection. As the trusted global leader, we have successfully inspected thousands of miles of pipeline.

Assess & Address Pipeline Management Program

Assess & Address Pipeline Management Program

Pure Technologies is helping utilities manage their buried infrastructure through its Assess & Address which can often be implemnented for only a fraction of the capital replacement cost

Case Study

Case Study: Baltimore County Department of Public Works

Baltimore County Department of Public Works (DPW)has been working with Pure Technologies to manage its force main inventory since 2011. Through proactive and regular assessment, DPW has been able to identify select areas of pipeline deterioration, thereby avoiding unnecessary pipe replacement.

In January 2013, Lake Huron Primary Water Supply System (LHPWSS) verified the results of a condition assessment project completed in October 2012 that included leak detection and electromagnetic (EM) assessment. The verification allowed LHPWSS to proactively repair of three sections of Prestressed Concrete Cylinder Pipe (PCCP) along its major transmission main.

While the majority of Pipeline A – LHPWSS’s major water transmission that runs 47 kilometers (29 miles) – was found to be in good condition, the inspection showed seven pipe sections had a relatively high level of distress. Of these seven pipes, two were located within a twinned section and therefore had a lower consequence of failure.

The remaining five high-distress pipes were located within 3.5 kilometers (2 miles) of each other and are in the same vicinity of failures that occurred in 2010 and 2012. LHPWSS has since verified and replaced the three most distressed pipes from the five that didn’t have redundancy to mitigate the risk of another failure.

Although the pipeline is primarily in good shape, the identification of several highly-distressed pipe sections has allowed LHPWSS to proactively plan targeted rehabilitation to ensure the continued delivery of quality service and the prevention of a major pipeline failure.

Verification Tool
Excavated Pipe

By determining the baseline condition of their entire primary large-diameter pipeline, LHPWSS now has a better understanding of the overall health of their system and can make informed decisions as they move forward with their pipeline management program and the rehabilitation of their assets.

LHPWSS serves about 500,000 people in eight different municipalities in the London Region and provides about 170 million liters (44 million gallons) of water per day. Its major transmission main, the Lake Huron Pipeline A, runs from the Lake Huron Water Treatment Plant near Grand Bend, ON to a terminal reservoir located near the community of Arva, North West of the City of London and features mostly 1200-millimetre (48-inch) Prestressed Concrete Cylinder Pipe (PCCP).

 

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 Electromagnetic Pipeline Inspection

Electromagnetic Pipeline Inspection

Electromagnetic testing provides the best condition assessment data for large diameter PCCP (AWWA C301) and BWP (AWWA C303) pressure pipelines.

 SmartBall® – Leak Detection for Water Trunk Mains

SmartBall® – Leak Detection for Water Trunk Mains

SmartBall® is an innovative free-swimming in-line leak detection technology designed to operate in a live water mains.

Introduction

Underground pipelines are among the most valuable, yet neglected, assets in the public arena. They provide essential services such as supply of energy and drinking water and collection of wastewater. But we install the cheapest we can, bury it and forget about it – at least until something goes wrong. Then we are faced with having to fix the problem under emergency conditions, often considering only immediate needs and not the future operation of the pipeline in question.

This infrastructure must be seen as an asset, and managed as such. Properly maintained the pipe networks are valuable assets that are critical to delivering services to customers, and in any business the means of connecting product or service to customers is a major link in the business value chain. Not to maintain this network is negligent bordering on criminal.

Pipeline operators from around the world are discovering that simply replacing their aging pipeline assets is cost prohibitive and that advanced condition assessment services from Pure can help them confidently make informed decisions that drastically reduce capital and operating costs.

There are many ways in which a pipeline can deteriorate to a state of failure; countless sources of stress both inside and outside the pipe can take their toll.

Single-step blowouts of pipe walls are quite rare; pinhole leaks, hairline cracks, corrosion and leaking gaskets tend to occur first. Most catastrophic failures are caused by a sudden unexpected stress such as a water hammer acting on an existing weak point in the pipe. There is a widely held belief that the failure process is a simple one, where a pipe corrodes to the point at which it can no longer withstand the applied internal and external forces, resulting in a main break. However, research has shown that the failure process is more complex than expected. Corrosion plays a significant role in water main failures, but soil-pipe interactions, manufacturing techniques and human error are also important factors. Failures also take place in multiple stages rather than in a single episode. Early damage not only weakens portions of the pipe, it also allows water to escape, causing corrosion and washing out of the supporting soil.

Pipes at highest risk are typically constructed using dated materials or methods, running through an area with heavily vehicle traffic. Urban centers typically represent significant loss potential from damage caused by water main breaks as a result of high density buildings, underground infrastructure, important traffic thoroughfares, and economic loss potential of power, gas, water utilities and legal cases.

Older pipes that face stresses such as heavy traffic, construction activity, pressure transients or advanced age are more likely to fail. However there are other factors at work such as installation or material defects that may surface over a shorter period of time. The net result is that age alone can not be relied on as an indicator of a high risk pipe.

Types of pipe material and typical causes of failure:

Prestressed Concrete Cylinder Pipe (PCCP) has a unique failure mechanism: high strength steel pre-stressing wires that provide strength to the pipe can become distressed and reduce the structural integrity of the pipe. Broken wires can be caused by physical damage to the pipe, corrosion, or hydrogen embrittlement. Regions of broken wires may be accompanied by leaks, especially in pipelines smaller than 48 inches in diameter, where the internal steel cylinder corrodes at the same rate as the wires or where water escaping through the joint encourages corrosion. Leakage has been proven to be a key indicator of structural condition in lined cylinder pipe, a type of PCCP in which the prestressing wires are placed directly on the steel cylinder. These types of leaks can create voids around the pipe and introduce added stress at an existing weak point.

Corroded Wires, Embrittled Wires, Cylinder Perforation

Cast iron pipes corrode, become brittle and are prone to cracking. Many older North American cities have cast iron pipes that were installed in the 1800s, prior to the existence of pipeline standards, when methods of construction were not uniform and advanced quality control programs did not exist. Consequently, many pipelines were installed using what are considered poor construction practices by today’s standards.

Tuberculation, Bell Cracking, Longitudinal Cracking, Corrosion

Ductile iron pipes have failure mechanisms similar to those of cast iron pipes; however they become less brittle and consequently degrade at a slower rate. These pipes may be capable of supporting large leaks for longer periods of time without failing immediately.

Plastic and polyvinyl chloride (PVC) pipes are less prone to corrosion and less brittle than iron pipes. Failures in these pipes are often traced to leaking joints where the escaping water creates voids around the pipeline, causing unplanned stresses on the pipe.

Leadite is a sulphur-based joint-sealing compound commonly used in the 1940s and 1950s that appears to produce pipe failures due to the difference between its coefficient of thermal expansion and that of the metal in the pipes it seals. Leadite in pipe joints expands at a different rate than the pipe itself, causing added stress near the joints. This undesirable behaviour has resulted in particularly destructive joint ruptures on otherwise strong iron pipes.

Steel pipes primarily fail due to loss of integrity at welds, and external corrosion causing severe pitting and weakening the pipe wall. Both losses of joint integrity and through-wall corrosion pits lead to leakage long before failure. Older steel pipes in aggressive environments are capable of sustaining massive levels of leakage for decades before failing.

Introduction

A significant percentage of the United States force mains have been in use for several decades and never been assessed or proactively managed. To safely rely on these pipelines, their condition should be periodically checked to ensure there are no locations susceptible to failure.

In addition, many wastewater agencies are faced with EPA consent decrees that require condition assessment of force mains. As a result, many agencies are now faced with the daunting task of assessing their sewer force mains—a task that until recently was often not feasible due to operational constraints. However, Pure Technologies continues to improve technology and can now obtain a realistic assessment of a force main within the common constraints of most wastewater agencies.

Authors

  • Michael S. Higgins, P.E.; Pure Technologies, Columbia, MD, USA.