This project aims to develop field-applied alloy coatings, referred to as Field Protective coatings (FPC), to steel natural gas pipelines to mitigate corrosion from pipeline repair, poor initial construction, and pipeline burial conditions. The project focuses on girth welds that are generated during initial pipeline construction as the pipeline sections are welded together in addition to areas of pipeline repair or pipeline section replacement. The field applied coatings at girth welds and other repair areas do not perform as well as the factory-applied coatings on the rest of the pipeline, contributing to increased failures and maintenance. The metallic alloy coatings developed by this project aim to greatly augment the polymeric factory-applied coating that surrounds the length of each section of the pipe before being welded together, as well as the field-applied polymeric coating that is typically applied after the weld is completed. Specific objectives include:
Initially, the major focus will be to optimize the Field Protective Coating (FPC) composition through modeling and preliminary laboratory testing. Det Norske Veritas — Germanischer Lloyd, USA (DNV GL USA) will then conduct more extensive laboratory testing as well as testing in field-simulated conditions. The final focus will be on field testing and reporting results.
Det Norske Veritas — Germanischer Lloyd, USA (Katy, Texas)
Narasi Sridhar, MC Consult, LLC, Dublin, Ohio
Enbridge Gas Transmission, Houston, Texas
Lincoln Electric, Cleveland, Ohio
The gas transmission and storage sector contribute approximately 8% of the anthropogenic methane to greenhouse gas emissions. An industry association study states that 9% of the transmission and storage section methane emissions occur from pipelines, and most of this emission occurs during intentional venting to reduce pressure for maintenance. An unknown quantity of release also occurs due to pipeline failures, but this has not been quantified due to its sporadic occurrence. Pipelines are protected from external corrosion by a combination of polymeric coating and cathodic protection. The field-applied coatings at girth welds and other repair areas do not perform as well as the factory applied coatings on the rest of the pipeline, contributing to increased failures and maintenance. The methane release from pipelines can be reduced through improved field coatings.
The approach by DNV GL USA relies on the addition of a metallic FPC under the normal field top coat (FTC) made of polymeric materials. The FPC tested will be either a sacrificial type coating applied by brazing technique. or a corrosion-resistant alloy coating applied by weld deposition technique. The selection of the metallic coating compositions will involve the combined use of an atomistic model, experimental data generation, and machine learning techniques. The selected coating compositions will be thoroughly tested in the laboratory, and their compatibility with existing polymeric field coatings will be ensured. The project will verify the performance of the FPC-FTC combination using an instrumented disbonded coating coupon buried in the field next to an operating pipeline so that the coupon experiences the same external conditions as the pipe.
Successful completion of this project will provide a methodology for the developed coating system to be applied to an operating pipeline. The additional metallic FPC under the normal field top coat is expected to reduce the number of methane releases from gas transmission pipelines by better protecting the girth welds in the pipeline from corrosion. With lower corrosion rates, it is expected that the life of a pipeline can be extended and lower operating expense costs. If applied to oil pipelines, a similar improvement in lifespan, as well as a reduction in loss of product can be realized. If catastrophic failures are reduced, there is also improved public safety and environmental mitigation for both gas and oil pipeline operations.
Project activities were initiated on September 1, 2020, and an initial project kickoff meeting was held September 17, 2020. The Technology Maturation Plan, as well as the Data Management Plan have been submitted on time. DNV GL delivered their BP2 continuation presentation on 7/28/2021, which was well-received, and theTechnology Manager approved the DNV GL continuation to BP2. The Go/No-go decision point to proceed to BP2 was accomplished on time and within budget.
In Budget Period 2 (BP2), Two new density functional theory (DFT) models, developed for estimating corrosion resistance of alloys, were employed to further evaluate the hypothetical corrosion resistance provided by the proposed aluminum alloys and low alloy steels. The first model approach was designed to estimate the effect of alloying on changes in the corrosion potential (i.e., the potential on the galvanic series). The second model approach was designed to estimate the effectiveness of passivation processes on alloys (the chloride or corrosion susceptibility index, CSI). Specific alloys were selected from alloys which were commercially available, although some wider-ranging searches were also employed.
In BP2, DNV focused on fabricating and laboratory testing a field deployable and instrumented metal coupon that has a simulated repair area coated with a different coating. Several sacrificial and corrosion resistant alloys were tested and carried through to BP2. The best sacrificial alloy was found to be an Al-MG alloy and the best corrosion resistant alloy was a Fe-Cr-MO alloy. Laboratory testing of the corrosion resistant alloys was employed by both gas metal arch welding and flame spraying onto test coupons for laboratory corrosion testing. The corrosion resistant Fe-Cr-MO alloy was welded to a test coupon and the Al-MG sacrificial alloy was flame sprayed onto a test coupon. These were corrosion tested in the laboratory and found to be very good candidates for de-aerated soil slurry testing which was done in a lab-scale soil box. These coatings were tested and compared to pipeline steel grade X52 and the results for the spray coating were slightly better than the welded coating in the aerated and de-aerated soil slurry tests.
Work has started on optimizing the FPC composition, focusing on selecting the optimum metallic coating through a combination of modeling the FPC corrosion and testing the FPC alloy compositions. Two types of metallic coatings will be evaluated: a sacrificial coating consisting of brazed aluminum alloys and a corrosion-resistant coating consisting of iron-aluminum or iron-chromium alloys that will be arc weld deposited. A literature review to gather data on known materials suitable for the FPC and designing constraints on the coating composition have been initiated. In addition, candidates for the coating composition for the over-alloy and sacrificial FPC compositions have been selected.
After laboratory testing, the instrumented coupons will be installed at pipeline sites and tested for 6 months with some coupons are attached to the pipeline to assess cathodic protection. To that end, DNV has submitted an Environmental Questionnaire to obtain a CX for an Enbridge Pipeline site (industrial partner). The Huntsville Compressor Station site is located within an existing 24-inch pipeline compressor station surrounded by undeveloped property utilized for timber operations in San Jacinto County, Texas, which is near Houston. The CX was approved.