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The Largest Problem in Pipeline Infrastructure

The leading cause of pipeline failure is corrosion. The estimated capital investment needs for water & stormwater pipelines in the U.S. alone is $11.18B USD/ year, a majority of which is replacement cost due to corrosion.¹ The corrosion-related costs of the U.S. oil & gas industry pipelines is $7B USD/ year. ²

Internal corrosion accounts for approximately 60% – 75% of all pipeline incidents caused by corrosion.³

Combining the Benefits of Plastic & Steel Pipe

High Density Polyethylene pipe is widely used due to its excellent resistance to water, abrasion resistance, and flexibility. Its Achilles heel is its structural integrity and pressure limitations.

Carbon steel pipe provides the best overall structural properties with an excellent strength to weight ratio and high ductility that allows it to bend without breaking. Its Achilles heel is that it will corrode when exposed to water and other environments.

The optimum solution is polyurethane lined and coated steel pipe, perfectly blending the strength and ductility of steel with the flexibility and corrosion-resistance of plastic.

hdpe liner

HDPE pipe is widely used for low pressure applications.

Pipe pulled back during HDD operation. Polyurethane linings & coatings flex with the pipe and have no risk of cracking like epoxy.

Thickness, Impact-Resistance, & Flexibility

A main differentiator between polyurethane and epoxy is that it can better withstand the construction process and remains flexible at thicknesses sufficient to eliminate any chance of leaks in the lining (750+µm, 30+ mils). The thicker an epoxy is applied the higher the risk of it cracking when the pipe flexes during handling, suffers sharp impacts, and undergoes cold bends during construction.

It is inevitable during the handling of thousands of pipes for a project that some will experience impact and flex that push the limits of brittle epoxy linings. Polyurethane linings & coatings flex with the pipe and have no risk of cracking like epoxy. Epoxies will often crack in a tiny spider-web fashion that is difficult to visually detect.

Polyurethane: Thickness with Flexibility

Polyurethane is a relatively thick flexible plastic membrane that is aggressively adhered to the steel substrate. AWWA C222 requires that the material pass a bend test at a thickness of 500µm – 809µm. Epoxy becomes brittle at these thicknesses.

AWWA C222 specifies that, per ASTM D522, the polyurethane material be applied to a 0.8mm thick steel panel at a thickness of 508 – 809µm (.020 – .035”). The panel is bent 180º over a 3” mandrel and the polyurethane cannot display any cracking.

Typical polyurethane coatings have an elongation of at least 8% per ASTM D412.

Bendability Comparison: Polyurethane vs. Epoxy

  Flexibility / Bendability Testing Analysis

Polyurethane per AWWA C222

 Tested per ASTM D522. AWWA C22 requires bending a plate coated with 508 – 889 µm (20 – 35 mils) of polyurethane 180° over a 75mm (3 inch) mandrel. One typical polyurethane, Lifelast DS210, passed this test when bent over a 25mm (1 inch) mandrel. Elongation of polyurethanes are greater than 8%. Polyurethane applied at a much higher thickness than FBE does not exhibit cracking when bent over a mandrel 1/6 the diameter of the requirement for FBE in AWWA C213.
Fusion bonded (FBE) epoxy per AWWA C213 AWWA C213 requires bending a plate coated with 356 +/-50 µm (14 +/- 2 mils) of FBE 180° over a 159 mm (6.25 inch) mandrel.
Owner specifications often require bending the specimen over a mandrel that is 2.5° x pipe diameter at -30° C and then warming it to 20° C. (CSA Z245.20)
Elongation of FBE is generally not measured but is less than 5%.

Cold bending of pipe coated with epoxy is always a consideration. Epoxies applied at thicknesses below 400 µm (16 mils) onto properly prepared steel will withstand bending and flexing of pipe. However, higher thicknesses or sub-standard surface preparation may result in cracking. In summary, there is much less margin for error in epoxy application and a much higher risk of epoxies cracking than with polyurethane (where the problem does not exist at all).
Liquid epoxy per AWWA C210

AWWA C210 does not require bendability testing nor any testing of mechanical properties.
Elongation of LBE is not measured.

 Cold bending of pipe coated with epoxy is always a consideration. Epoxies applied at thicknesses below 400 µm (16 mils) onto properly prepared steel will withstand bending and flexing of pipe. However, higher thicknesses or sub-standard surface preparation may result in cracking. In summary, there is much less margin for error in epoxy application and a much higher risk of epoxies cracking than with polyurethane (where the problem does not exist at all).

Impact Resistance Comparison: Polyurethane vs. Epoxy

Impact Resistance Testing Analysis
Polyurethane per AWWA C222 Tested per ASTM G14 “Falling Weight Test”. Steel plates are coated with polyurethane thickness up to 1,905 µm (75 mils). Two-pound and four-pound weights dropped from various heights and coating is inspected microscopically for cracks. Impact strength above 8.5 Joules (75 in•lb) is required. Heights are increased until a crack or disbondment is observed. Measured strength of typical polyurethane, Lifelast DS210, is 180 in•lb, measured on plates with coating thickness ranging from 939 – 1270 µm (39 – 50 mils). Polyurethane is tested at a much higher thickness (in the case of Lifelast DS210 it was tested at ~300% the thickness of FBE per AWWA C213).
Fusion bonded (FBE) epoxy per AWWA C213 Tested per ASTM G14 “Falling Weight Test”. Steel plates are coated with FBE at a thickness of 305 – 355 µm (12 – 14 mils). Two-pound and four-pound weights dropped from various heights and coating is inspected using holiday detector for cracks.Impact strength above 11.3 Joules (100 in•lb) is required. The impact test is conducted on FBE applied at a thickness of 355 µm (14 mils). If the FBE was much thicker it would crack at a force much lower than 11.3 Joules (100 in•lb).
Liquid epoxy per AWWA C210 No impact test required per AWWA C210. A confidential 2020 specification from a prominent engineering company listed the minimum required impact resistance as 5 Joules. In the same specification it lists the minimum required impact resistance for FBE as 11.3 Joules (same as AWWA C213) Indicates that liquid epoxies have significantly less impact resistance than FBE.

Lining Thickness Matters: Corrosion Pitting

Polyurethane linings are applied at a thickness sufficient to essentially “bury” metal imperfections, sharp edges and irregularities. Thin epoxy linings run the risk of having pinholes form on isolated locations or scratches. Leaks through thin linings frequently occur on isolated thin spots over time AFTER having passed an initial holiday test.

Microscopic discontinuities in a lining are eventually catastrophic to the pipeline. “A small, narrow pit with minimal overall metal loss can lead to the failure of an entire engineering system… Fatigue and stress corrosion cracking may initiate at the base of corrosion pits.” ⁴

Corrosion is accelerated at the leak through the lining because it is constant contact with the electrolyte (water) while the adjacent surfaces are not. This results in the exposed steel serving as an anode and corrosion rates at this location are accelerated.

*Source: https://www.nace.org/resources/general-resources/corrosion-basics/group-1/pitting-corrosion

Impact & Abrasion Resistance

There are many different ways an internal lining can be scratched or impacted by a foreign object. Polyurethane provides superior impact resistance compared to epoxy. Its abrasion resistance is similar to epoxy, but the additional thickness provides a much larger buffer between the object and the steel.

 

Foreign objects: Experienced pipeline constructors have seen just about everything removed from a pipeline when a cleaning pig is sent through during commissioning. Whether its welding consumables, weld slag, nails, tools, rodents, rocks, etc., it is important that the lining withstand the impact and abrasion from potential foreign objects.

Silt and particles: At high flow rates minute particles and silt can wear linings thin. Polyurethane can be applied at any thickness required for the projected amount of abrasion.

Internal lineup clamps and bending mandrels: If used during construction, heavy internal lineup clamps and bending mandrels have the potential to scratch linings, particularly if they pinch or drag small pebbles through a pipe.

General Corrosion Resistance Properties

Polyurethane, liquid epoxy, and fusion bonded epoxy all provide excellent protection from steel corrosion as long as the steel is properly grit blasted and free of contaminants.

AWWA C222 (polyurethane), AWWA C213 (fusion bonded epoxy), and AWWA C210 (liquid epoxy) each have different standards for measuring water absorption and all are known to gain less than 2% weight from water absorption.

Cathodic disbondment testing is used to gauge a coating’s ability to remain bonded to steel despite introducing a discontinuity in the coating, immersing it, and subjecting it to an electric current. This is particularly important for pipeline coatings since cathodic protection is used. AWWA C222, C213, and C210 all specify a maximum distance the coating can disbond from the discontinuity (C222 is 12mm, C213 is 15mm, and C210 is 10mm).All three materials have sufficient adhesion to withstand coating disbondment. Excellent adhesion is important for a number of reasons, including withstanding the force of the water molecule to cause separation of the material after osmotic permeation. Per ASTM D4541 AWWA C222 requires 10,350 kPa (1,500 psi), AWWA C210 requires 5,515 kPa (800 psi), and AWWA C213 requires a shear adhesion test not directly comparable to the straight pull-off adhesion test per ASTM D4541. Reference white paper titled “Denver Water’s Assessment of Interior Polyurethane Coating of 108 inch Water Pipeline” (Bambei, Kelemen, Mielke) for long-term adhesion performance of an early version of polyurethane used for pipe lining.⁵

Polyurethane is more forgiving of sub-standard steel surface preparation and surface irregularities. Reference white paper titled “Denver Water’s Assessment of Interior Polyurethane Coating of 108 inch Water Pipeline” for information on polyurethane performance when applied over debris. While not applied per current standards, this demonstrates how polyurethanes can “bury” steel defects due to their thickness that epoxies cannot.⁵All three materials have extensive successful case history in immersion when the steel is properly prepared and when mechanical damage has not been introduced.

Polyurethane Linings: Current State of the Art

North American water agencies are rapidly increasing the use of polyurethane to protect their pipeline infrastructure for future generations:

Source: Northwest Pipe Company, the United States’ largest manufacturer of pipe for domestic water use

100 Year Design Life

Excerpt from “Longest Polyurethane Lined and Coated Steel Pipeline in North America” Budge, Rahman ASCE Pipelines 2012 ⁶

LPS Joint Technology Permits Use of Polyurethane Linings

LPS’ patented FlexSleeve® technology works with any internal lining.

Robots are the other main option to line the interior of joints after welding on pipelines larger than 18” diameter. They struggle with the quality of field-applied linings due to climate conditions, steel temperatures, and obtaining pinhole-free linings over jagged weld penetrations.

LPS technology completely avoids all issues with field-applied patches at joints and FlexSleeve® can be lined with the same material as the parent pipe.

pipeline corrosion protection

Sources

Specifications: AWWA C222, AWWA C213, AWWA C210, CSA Z245.20, ASTM D522, ASTM D412, ASTM G14, ASTM G95, ASTM D4541, Confidential Internal Lining Specification (2020), Technical Data Sheets for FBE from Axalta & 3M. Technical Data Sheets for polyurethane from Lifelast.

Technical Papers/Reports:

Additional white papers referenced on page 11 regarding 100 year design life:

  • ASCE Pipelines 2010 “Raw Sewage through Steel Pipe: A Unique Application on the Pima County Plant Interconnect” (Rivera, Lucie, Rahman, Ast)

  • ASCE Pipelines 2011 “Innovative Joint Proves Successful in Critical Slipline Project” (Baas, Gardner, Mielke)

Additional relevant white papers:

  • Middle East Corrosion Conference 2001 “100% Solids Polyurethane Coatings Technology for Corrosion Protection in Water and Wastewater Systems” (Guan)

  • ASCE Pipelines 2003 “100% Solids Polyurethane Coatings Technology and Its Application to Pipeline Corrosion Protection” (Guan)

“It’s what’s on the inside that counts”

State of the Art Internal Pipe Lining Material Polyurethane per AWWA C222

Download PU Lining per AWWA C222 PDF