Testing explores SET for transport pipelines

March 19, 2007
Pipeline operators have begun considering the transfer of solid expandable tubular (SET) technology, widely used upstream, into pipeline repairs and restorations.

Pipeline operators have begun considering the transfer of solid expandable tubular (SET) technology, widely used upstream, into pipeline repairs and restorations. This article examines the potential benefits of this transfer and outlines its testing and progress to date.

Pipelines

Three pipe features determine maximum pipeline operating pressure: OD, WT, and metallurgy (SMYS). Adjusting this calculation to account for one (or more) safety factors yields maximum allowable operating pressure (MAOP):

MAOP = (2t × SMYS × SF) / OD
Where:
MAOP = Maximum allowable operating pressure
t = Wall thickness
SMYS = Specified minimum yield strength
SF = Safety factor
OD = Outside diameter
OD, WT, and metallurgy are all set when the pipe is produced, so that the only remaining variables affecting MAOP are safety factors. WT, however, can change in areas, primarily as a result of corrosion or third-party damage. Sleeves (steel as well as composite wraps) and liners (primarily plastics) were developed to restore wall thickness or reinforce pipe in isolated locations.

Few options existed for increasing MAOP outside of replacing, sleeving, lining, or wrapping the entire pipeline.

The pipeline could be hydrostatically tested to higher pressures, but stressing the pipe carries its own set of problems.

Decreasing safety factors is the final solution but is likely to be seen as a higher risk than use of more conservative safety factors and will require expensive risk remediation.

Local distribution companies (LDCs) have used lining technology extensively in settings where lines operate at much lower pressure than most transmission lines.

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Steel lining, however, is new. The concept is simple: insert a smaller pipe inside a larger pipe and, using pressure, drive a specially designed mandrel through the smaller pipe to accomplish a controlled expansion to fill the annular space between the two (Fig. 1).

But the expansion process is difficult. Driving the mandrel through the pipe cold works the steel, increasing its strength while decreasing its ductility. Extensive metallurgy, joining (girth weld), and expansion research have overcome these problems. Pipe joints, produced to rigid metallurgical specifications, can be welded together using qualified welding processes, tested, inserted, and expanded such that they meet API 5L and 1104 specifications after expansion (Figs. 2-3).

An end view of postexpansion pipe shows the completeness with which the annular space between the inserted steel tubing and preexisting pipe is filled during the cold-drawing radial enlargement process (Fig. 2).
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This side view of an end of pipe treated by SET technology shows how ID is maintained even as WT and strength are increased: by expanding the preexisting pipe. The left end of the pipe shows the inserted tubing (Fig. 3).
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The market

Market research shows this technology has ideal applications in areas where traditional excavate-and-repair techniques are impossible to use, cost prohibitive, or would attract significant public attention (Fig. 4). In such settings, the two broad categories SET technology would address most effectively are capacity restoration and anomaly repair.

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Capacity restoration includes areas that would be difficult or expensive to excavate.

Natural gas transmission lines in the US possess a class location (1, 2, 3, or 4) based on criteria established by the Office of Pipeline Safety (OPS). The class location assigned is essentially a function of nearby buildings and occupation levels.

Class location dictates the safety factor used to calculate the MAOP of a given section of natural gas pipeline.

When class locations change-usually due to population encroachment-the operator must use a more conservative safety factor, and unless it can take other measures to reduce the likelihood of pipeline failure, the operator must accordingly lower the MAOP of the pipeline.

Lower MAOP leads to lower capacity and therefore lower revenues for the operator. SET can restore MAOP and, through this, revenues (Figs. 5-6).

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Current industry options for maintaining capacity (and revenues) at the lower MAOP include looping the line or replacing it with a larger line or one with a greater WT or higher grade steel.

Operators may also request a waiver from the OPS to continue operating at the current MAOP. When such waivers are granted, however, the OPS requires the operator take additional protective measures to reduce the likelihood of a failure.

Looping, replacing line, and seeking waivers are all costly activities, and expandable technology has the potential to cut these costs, reduce permitting time, and increase operating time, while at the same time improving public perception.

Anomaly repair applications, especially in locations that are difficult or expensive to excavate, include:

  • Nonoffshore waterways.
  • Interstate highways, other highways, and roads.
  • Railroads.
  • Locations where disrupting the surrounding area would be logistically complex or expensive (such as environmentally sensitive areas, parking lots, and areas with nearby pipelines, buildings, cables, or other congested infrastructure).

Feasibility

The value propositions that attract the pipeline industry to SET include its permanent, steel, pipe-in-pipe ability to improve structurally at-risk or derated pipelines with only nominal ID loss. And because expandables would enable operators to increase pressures and thereby regain the pipelines’ more favorable classifications and throughput, several operators favor the concept.

Value proposition

The absence of trenches and minimal disruption to surrounding infrastructure and environment reduce operator costs, as does the reduced permitting time.

Cost, time, and risk are three key common components in evaluating various solutions to a problem. Like any other potential solution, expandables must outperform the next best alternatives.

Potential key benefits in using expandables in capacity restoration include cost and time savings stemming from:

  • Minimal environmental impact shortening permitting and solution cycle time.
  • Minimal public relations exposure.
  • Alternatives to waiver processes.
  • Flexibility for pipeline conversions.

Using expandables can also reduce risk and potential liabilities. Limited excavation minimizes exposure to potential environmental problems or damages to surrounding lines and infrastructure, leading to:

  • Less disruption to population and industry.
  • Increased operating safety factors and throughput.

Expandables also use environmentally friendly fluids and provide an alternative to abandonment.

In difficult-to-excavate areas, expandable pipeline repair often requires a smaller footprint than alternatives, allowing work within limited right-of-ways, minimizing permitting time, and reducing overall job time and risk.

Compared to a conventional re-drill that uses horizontal directional drilling (HDD), SET technology saves both cost and time by eliminating:

  • Geotechnical studies.
  • Containment pit for mud returns.
  • Pilot and back-reaming runs.
  • Drilling fluids.
  • Mud processing equipment.
  • Contaminated mud or water.

SET also reduces risk and potential liabilities by removing:

  • Environmental and regulatory concerns about drilling fluids containment and disposal.
  • Concerns about a structural fracture resulting in an uncontrolled fluid release and contamination.
  • Settlement damage to surrounding structures such as houses, highways, and railroads.

Upstream experience

Since 2000, operators have been successfully using SET technology in upstream applications, where it is subject to far harsher temperature and pressure parameters than are found in transport pipelines. Of the now hundreds of SET installations completed around the world, Burlington Resources’ application demonstrates the benefits of the technology well.

Burlington wanted to achieve a slimmer well profile while maximizing hole size at total depth (TD) in deep and ultradeep land gas wells, with the ultimate purpose of reducing field development costs of a multiinstallation program in a tight services market environment. Incorporating a 6 × 7.625-in. expandable openhole liner into the base well design let the operator drill a 14.75-in. surface hole instead of a 17.5-in. hole, allowing drillout of surface pipe 1 day earlier.

Below the surface pipe, the operator drilled a 9.875-in. hole (at a rate of 3 days/1,000 ft) vs. a 12.25-in. hole (4.8 days/1,000 ft). The operator reduced drilling time to TD by 21%; to 74 days from 94 days. Running the SET liner below this section allowed for 4.5-in. production casing at TD, allowing production at planned rates.

The value of using SET systems, rather than a conventional casing program, included:

  • Increasing the rate of penetration by 37%.
  • Lowering equivalent-circulation densities.
  • Increasing flow rates.
  • Saving more than $1 million/well by reducing drilling time for each well by about 4 weeks.

These savings translated into every sixth well being drilled at no cost.

Pipeline testing

Phase 1 testing of solid expandables for safety, reliability, and predictability in a variety of pipe grades has included:

  • Reviews to ensure expandables comply with Code of Federal Regulations, Canadian Standards Association, American Petroleum Institute, American Society of Mechanical Engineers, and National Association of Corrosion Engineers specifications.
  • An API 5L engineering study, for specification compliance pre and post-expansion.
  • An API 1104 pipeline weld assessment, to determine the expandability of specification-compliant defective welds.
  • A fusion-bonded epoxy coating study of 30% expansions of 10 coatings.
  • A 20° bend prototype laboratory test of a standard 1,400 km river crossing, to gauge the impact of bends on the pipe and expansion process (Fig. 7).
Testing has shown that SET technology can successfully be used in pipeline contexts through bends up to 20° (Fig. 7).
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JIP

Joint industry partnership (JIP) organizational meetings are under way between the expandables supplier and pipeline operators, aimed at addressing such key pipeline engineering issues as cathodic protection, annulus space treatment, hot tapping, piggability, and inline inspection.

The objectives of the JIP are to further develop, engineer, design, test, and deploy SET pipeline repair and construction technology, which is regulatory and code-compliant, providing the means to repair pipelines from the inside with steel tubulars. The JIP schedule consists of three phases: development; system design and proof testing; and field appraisal testing, which would initially involve installation in an abandoned pipeline, followed by field appraisals by participating operators in multiple operating pipelines.

The authors

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Kevin Waddell ([email protected]) is vice-president of expandable pipeline repair at Enventure Global Technology, a joint venture between Shell Technology Ventures and Halliburton Energy Services. Previously, Waddell was a business developer for Halliburton Energy Services. He earned a BS in geological engineering from the University of Arizona.

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Tom Miesner ([email protected]) spent 25 years working for Conoco Pipe Line Co. in a variety of positions, including serving as president for 6 years. In 2004 he formed Miesner LLC to provide expert consulting services to the pipeline industry. Miesner received his BS in engineering management from the University of Missouri-Rolla.