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Using Pipeline Coatings Instead of Casings

To meet today's pipeline construction challenges, a construction and/or design pipeline engineer must consider using more sophisticated equipment and materials. In the past, crossings were completed with pipeline casings. Now, their use is fast going the way of the dinosaur. The main reason is the concern of shorted casings, which leave the carrier pipe within the casing without cathodic protection.

The original reason for casings was to avoid having to open trench streams, roads, railroads, and various other obstacles. Some coatings were not always sufficiently abrasive resistant to be pulled directly through a bore hole without sustaining severe damage to the corrosion coating. Fusion-bonded epoxy offered the best solution because it has a harder and smoother finish, but this coating also suffers from damage when pulled through rocky areas. Most engineers reverted to casings using the same coating on the carrier pipe as that on the pipeline. Sometimes concrete coating over the corrosion coating was used to avoid casings, but this resulted in heavy, highly abrasive, and hard-to-pull protection. Other protective coatings over fusion-bonded epoxy were tried and worked well on pulls that were not too severe, but frequently tended to have a peeling effect when sharp rocks were present.


During the mid 1980's Shell Oil and Lone Star Industries jointly undertook a research project to develop an epoxy-based concrete. The product developed was a polymer concrete that was 10 times stronger than conventional concrete. It offered high compressive strength, high flexural strength, good abrasion resistance, very low water absorption, high dielectric strength, good resistance to acids, and high resistance to alkalies. Cure times were much faster than conventional concrete.

This joint venture was turned over to Lone Star Industries, Inc. The company patented a casing insulator using this product. They used this product to mold bars of polymer concrete, using a polypropylene non-woven mat at the base of the mold. An asphalt rubber adhesive similar to pipeline tape adhesives was used on the other side of the mat. This let workers apply the insulator by peeling off the plastic film mastic protector, heating the mastic until it became very tacky, and applying it to the pipe. This product did not contain any metal parts, and was definitely a step in the right direction.


Most pipeline design engineers wanted to eliminate pipeline casings wherever possible. To do this, they needed a better coating protector. A technique was developed to apply the epoxy-based polymer concrete product directly to the fusion-bonded epoxy coating. This bond provided a smooth outer shell with a toughness and abrasion resistance. The required thickness applied depends on terrain, type or hardness of the rock, length of the pull, size of pipe, and its weight. It can be applied in thicknesses from 0.38 mm minimum to as thick as needed. The maximum thickness to date is 3.2 mm. Experiences indicate that 1.6 mm minimum thickness of Powercrete® appears to be adequate for pulls up to 610 m on 61 cm pipe. The manufacturer recently coated 61 pipe with a 1.6-mm thickness for two directional drills totaling 1,190 m under the Niagara River near Niagara Falls, New York.


Impactresistance tests were performed according to ASTM G-14. No failures of the polymer concrete coating occurred at an average impact pass of 1.9 kg-m, where the polymer concrete coating ranged between 1.9 to 2.8 mm in thickness. The polymer concrete failed at a thickness of 1.3 mm, and an average impact pass 1.0 kg-m.

Taber abrasion was performed using abrader wheels H-18 (hardest available abrasion wheel for this test) with 1 kg of weight applied. The test was run for 1,000 cycles. Less than 1% weight loss of the polymer concrete was observed when the coating thickness was 3.6 to 3.9 mm.

In immersed acids, polymer concrete formulated as Powercrete® blisters and softens. Powercrete® was unaffected by alkaline solutions and salt water in both immersed and vapor phases.

Cathodic disbondment testing was performed according to ASTM G-8. Samples were tested at 25 degrees C over F.B.E. for 90 days. Sample thicknesses of 0.5, 1.0, 2.0, and 2.3 mm were prepared and tested. In 50% of the cases (Powercrete® 0.5 and 2.0 mm) resulted in a net disbondment area of less than 13.8 mm. The Powercrete® 1.0 and 2.3-mm samples averaged a net disbondment area of 119 sq. mm.

Powercrete® applied over bare steel at 2.0 mm thick, under the same conditions, resulted in a net disbondment area of 65.2 sq. mm.

Polymer concrete enhances the cathodic disbondment properties of the fusion-bond coating. A recent cathodic disbondment test was taken by Consolidated Pipe and Supply in Birmingham, Alabama, while performing a project with fusion bond coating and Powercrete® for Mobil Oil. A sample of pipe was taken with fusion-bond epoxy coating only, and another with fusion-bond and Powercrete®. After performing the cathodic disbondment test, the sample of fusion-bond protected with Powercrete® exhibited zero disbondment of the fusion-bond, whereas the fusion-bond by itself showed a disbonded area around the holiday.


Powercrete®'s flexibility is slightly less than that of the F.B.E. Powercrete® can be bent considerably, and there will be surface cracking, but the cracks do not extend through the F.B.E. Work is currently in progress to develop a new, more flexible Powercrete® product that should be available next year after testing is complete.

Because polymer concrete bonds chemically to the fusion-bond epoxy and does not require any surface preparation to new fusion-bond epoxy, and because it is harder than any alternative product that we have encountered to date, it is believed to be the best alternative available for slick bore.


Power Lone Star completed an 85 km field test in the high desert of Utah, Wyoming and Colorado. The pipeline ranged in diameters from 15.2 to 50.8 cm and was coated with 1.0 to 1.5 mm thick polymer concrete over fusion-bond epoxy. This pipe was laid on a production line basis, using three work stations. The first station was for welding, the second was for cleaning the weld splatter, and the third was for checking the weld. The pipe was on rollers at the work station area. When the signal was given to the awaiting tractor from each of the stations, the tractor would pull the pipe and advance another 18.3 m. All three stations would go back to work. In these cases, pipes were pulled out over the desert floor from a distance of approximately 0.80 km to as much as 1.60 km before moving the production line. Once the pipe was in place, 10 by 10 cm runners were situated under the pipe near the joint in order to allow Powercrete® application.