Coal Tar Enamel Research Articles

Permeability of coal tar enamel coating to cathodic protection current on pipelines

Coal tar enamel (CTE) coatings are the primary coatings used for corrosion protection of oil/gas pipelines which have been usually in service for about fifty years. The compatibility of CTE coatings with cathodic protection (CP) is critical to integrity maintenance of the pipelines. In this work, the permeability of CTE to CP current was investigated in a simulated soil solution through monitoring potential, current and solution pH. Results show that the coatings are CP-impermeable. Even at the practically minimum thickness of 2.30 mm for the coating, the CP permeability is 0.541% only. As the coating thickness increases, the CP permeability reduces rapidly. For the coatings containing defects, the CP permeation depends on their size. In this work, the threshold diameter for circular coating defects present on CTE coating is 1 mm, below which more than 70% of CP current is shielded from permeation.

Fiber-Optic Leak-Detection Project

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 183137, “Fiber-Optic Leak-Detection Project,” by Marc Baqué, Total, prepared for the 2016 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 7–10 November. The paper has not been peer reviewed. The objectives of the Fiber-Optic Leak-Detection (FOLD) project, carried out in Verneuil-en-Halatte, France, were to assess the capability of fiber-optic sensing to detect a small gaseous leakage on a buried pipe, give guidelines regarding the best deployment positions of the fiber along the pipe, compare the performance of several methodologies, and assess the impact of the fiber-optic length on the detection performance. Buried Pipe and Nozzle Orifices The 30-m-long pipe used for the testing campaign was typical of those used for gas transportation. It was made of steel and had an internal diameter of 390 mm. As are many in-service pipelines installed during the last century, it was originally coated with coal-tar enamel. This coating was removed before burying the pipe. All leakages were simulated from the external surface of the pipe. As opposed to the real conditions, this pipe was not filled with pressurized gas but was rather used as a simple cylindrical envelope aimed at accommodating all lines feeding the different leakages with gas. There were 12 nozzle orifices on the pipe, thereby permitting investigation of four different release diameters (1, 3, 5, and 7 mm) and three different release directions (upward, sideways, and downward). For ease of tracking, each row of nozzle orifices along the pipe was attributed to a given release diameter. In addition, to avoid any important deterioration of the soil that may influence the experimental results between two neighboring orifices, the following sequence was adopted for the orifices: 1, 5, 3, and 7 mm. The first and last rows were located 5 m from the ends of the pipe. All rows were equally distributed along the remaining distance of the pipe. Main Line The main line was made of stainless steel and had a nominal size of 1 in. (Fig. 1). This corresponds to inner and outer diameters equal to 24.3 and 33.4 mm, respectively. A dome- loaded pressure reducer (DLPR) driven in by a driving pressure reducer (DPR) was used to adjust the gas pressure to the desired value at the nozzle orifice. Downstream of the equipment, there was a pneumatic remotely operated valve (ROV) that allowed triggering the release remotely. Gas then flowed through two different branches of the main line, depending on which nozzle orifice was being tested: one for Valve 1 and 5 mm and the other for Valve 3 and 7 mm. This was controlled by means of a manual valve (MV) located at the entry of each branch (MV3 and MV4 in Fig. 1). The vent line was used only during the main-line-purging operations. This purging was performed with nitrogen after each test.

Review of pipeline coating systems from an operator's perspective

Over the past 40 years, pipeline integrity has been maintained by the simultaneous application of protective coatings and cathodic protection (CP). There have been significant developments in pipeline coating technology over the last 30 years as the traditional coating systems such as coal tar enamel, asphalt and single- and two-layer polyethylene (PE) coatings have been replaced in favour of coatings such as single and dual layer fusion bonded epoxy and three-layer PE and polypropylene. New coating technologies inevitably bring with them new problems for pipeline operators. The present paper reviews the transition from the more traditional coating systems to the second and third generation of pipeline coatings and discusses the new challenges that pipeline operators face. The difficulties of selecting field joint coatings with similar performance to the newer mainline coating systems will also be discussed, as well as issues related to electrical interference (ac and dc) and CP shielding that have become more of a concern because of the high integrity and dielectric strength of some modern coatings. Lessons learned over the years will be reiterated, and how far the pipeline coatings industry has progressed will be reflected upon.

Stress corrosion failure of an X52 grade gas pipeline

In the present work, the failure investigation of a 45.72cm (18in.) diameter gas transmission pipeline (X-52 grade steel) has been described. The pipeline was shielded metal arc welded (SMAW) construction, and was welded in the form of spiral. The protective coating, applied on the pipeline, was made of glass fiber reinforced coal–tar enamel. The initial investigation showed that the failure of gas pipeline produced a big depression in the ground underneath. The produced depression was about 6.7m deep, 4.6m wide and 15m long. The visual examination of the pipe revealed the absence of the protective coating from the surface of the pipeline near the ruptured area at many places from 4 o’clock to 7 o’clock positions. On closer examination, pitting was also found at different portions of the bare areas (where the coating was absent) of gas pipeline. Furthermore, the soil in which the pipeline was buried had pH of ∼9–10 that promoted corrosion on the surface of gas pipeline. The microscopic examination showed that the ruptured portions of the pipeline contained intergranular type cracks. Moreover, the stresses produced due to lowering/submerging of the pipeline seem to have contributed to this failure. The detailed study of this rupture suggested that the possible reason for this failure was stress corrosion cracking (SCC).

Acceleration and quantitative evaluation of degradation for corrosion protective coatings on buried pipeline: Part II. Application to the evaluation of polyethylene and coal-tar enamel coatings

The pulsed potentiostatic polarization technique proposed previously has been applied to evaluate the electrochemical degradation of polyethylene and coal-tar enamel coated SS400 for buried pipeline. The degradation of coated systems was accelerated and evaluated using electrochemical techniques (pulsed potentiostatic polarization test, electrochemical impedance spectroscopy) and surface analyses (scanning electron microscopy and energy dispersive X-ray spectroscopy). It was found that polyethylene coating had better protective performance than coal-tar enamel coating due to its low porosity. It was confirmed that the electrochemically accelerated test is an effective technique in the evaluation of coating performance.

Laboratory Studies on Pipeline Coating Materials under Accelerated Weathering Condition

Laboratory test has been carried out to assess the rate of degradation of dielectric strength of different pipeline coating materials viz coal tar enamel, hot applied coal tar tape, cold applied polyolefin tape, coal tar epoxy, high build epoxy, polyurethane & 3LPE coating after accelerated weathering in QUV using 313 UVB lamp maintaining a cycle of 4 hour UV and 4 hrs. condensation and after 500 hours salt spray as per ASTM B117. This test is important since the corrosion control systems of most pipelines consist of the combination of coating and cathodic protections. It is desirable that the dielectric properties of the coating deteriorate at the minimum rate possible. Deteriorations of coating with time would lead to a constant requirement of additional cathodic protection current which would be both a technical & economic burden on the pipeline operator. This paper highlights to establish the suitability of proper coating material with respect to cathodic protection.

Role of hydrogen and hydroxyl ion in cathodic disbondment

The most economical way of protecting pipelines is through the application of organic coatings and wrappings. To make the protection foolproof at holidays and pores, cathodic protection is also applied. At coating holidays, the pipelines act as the cathode generating hydroxyl ion and hydrogen electrochemically. Extensive studies have been carried out using samples of mild steel pipe coated with reinforced coal tar enamel coating to investigate the role of hydrogen and hydroxyl ion on cathodic disbondment. The testing material is subjected to different environmental conditions like pH, aeration and addition of different anionic species. A mechanism has been proposed to describe the individual role of hydroxyl ion and hydrogen in the process of disbondment.

The use of polypropylene in pipeline coatings

Despite the fact that the pipeline coating represents only about 5% of the total cost, the choice of the most effective coating is a key point to guarantee the life of the installed pipelines. Since the eighties, polypropylene copolymer coatings have been used for the protection of the external surface of on-shore and off shore pipelines. Polypropylene is one of the most suitable coatings when high mechanical properties (impact resistance, penetration resistance, etc.) and/or heat resistance are required. Polypropylene has also been used in ordinary pipelines giving advantages compared with the standard coatings, e.g. fusion bonded epoxy resin, coal tar enamel and polyethylene. New applications for polypropylene copolymers such as pipeline coatings have recently been developed, these include an insulating coating obtained with foamed polypropylene and an internal coating obtained by spraying a polypropylene adhesive powder.

Evaluation of Principal Spillway Conduit Life

Visual inspection of soil and water sampling near 38 principal spillway conduits in Kansas PL-566 watershed dams were used to determine overall condition and obtain estimates of the expected average life of various conduit materials. Corrugated metal and C-76 reinforced concrete pipes had the lowest ratings and shortest expected average life of all materials in the sample. Expected life of corrugated metal was limited primarily by corrosion and leakage at joints. Most C-76 pipes were cracked. Lined welded steel and C-301 concrete steel cylinder pipes had the longest expected average life. Unlined welded steel pipes were usually corroded, while welded steel pipes lined with cement mortar or coal tar enamel were less corroded. C-301 steel cylinder concrete pipe was generally in excellent condition except for minor cracking of the lining and minor corrosion of the steel at a few joints. Some relationships between the expected life of conduits and environmental conditions were also found.

The surface preparation of steel linepipe prior to anticorrosion and weight coating for offshore service

Traditionally carbon steel has been used for both offshore and onshore pipelines and these have been coated with a variety of anticorrosion coatings including bituminous coatings such as reinforced coal tar enamel, asphalt enamel; fusion bonded epoxy powder and polyethylene. The use of more exotic alloys (e.g. Duplex stainless steel) had previously been limited to risers.

The protection of steel pipes with coal tar enamel systems: importance of specification and design

Summary The properties of coal tar systems and the mechanical requirements of pipeline protections before and after installation of the pipelines are defined. Correct specification related to the particular service conditions and adequate inspection are of paramount importance. With correct selection of primer, grade of coal tar enamel and glass reinforcements coal tar based systems are providing the most reliable protection under almost all service conditions.

Pipeline protection with hot‐applied coatings

After more than six years of operation carrying the hottest crude oil in the North Sea, the anti‐corrosion system of the Phillips Ekofisk pipeline is free from submarine decay. For the 212‐mile line, which stretches from Norway to Teeside, is protected with 120/5 glass‐reinforced coal tar enamel from Metrotect Ltd., of Cleckheaton, Yorkshire.

The protection of sub‐sea pipelines operating at elevated temperatures

An extensive investigation simulating the behaviour of coal tar protective systems on steel pipelines under concrete weight coatings has been carried out. In particular the study has been made of the behaviour of synthetic primer/high temperature coal tar enamel with glass reinforcement under the stresses caused by expansion of the steel pipe within its concrete weight coating. The possibility of shearing of the sacrificial anodes has been given special consideration. At high oil temperatures there tends to be an initial creep of the pipe which gradually ceases within 1/2 weeks, but the total movement amounts merely to a few millimeters. This has been found to apply up to temperatures in excess of 100°C. In order to establish this conclusion, laboratory studies were carried out by three different techniques and the effects evaluated. At elevated temperatures some coal tar oils pass from the enamel to the concrete, resulting in an increase in softening point of the coal tar enamel of up to 20°C. The resistance to creep of the enamel is thus greatly increased while the integrity of the corrosion protective coating is maintained. The conclusion that the coal tar enamel system provides a fully reliable protection at the highest submarine oil temperatures is borne out in experience. A North Sea line has been operating satisfactorily at 113°C, for the last four years.

North Sea pipeline coating seminar

Mallatite Plastics Ltd., of Stockport, sponsored a symposium on pipeline coatings for North Sea use at the Churchill Hotel in London on 18 April. Its purpose was to bring together the corrosion specialists and specifiers of the oil companies working in the North Sea and representatives of Bayer, A.G., makers of saponified polyethylene thermoplastic powder coatings, Helic van Cauwen bergtic, major European makers of epoxy powder coatings, as well as Metrotech Ltd. representing well tried coal tar enamel and wrap pipe coating systems, to discuss the new requirements arising in the North Sea Area where some of the oil is at temperatures up to 110°C with water temperatures as low as 5°C. These conditions are considerably different to those encountered in the Gulf of Mexico and elsewhere.

Occupational exposure to coal tar pitch volatiles at pipeline protective coating operations.

The results of industrial hygiene studies conducted at eight hot-applied coal tar enamel pipeline protective coating plants indicate that coating workers may be exposed to coal tar pitch volatiles (CTPV's) in excess of the established threshold limit value (TLV). The chemical characterization of CTPV samples shows a significant concentration of polynuclear aromatic hydrocarbons (PNA's), which lends support to the recommendation that exposure control measures be utilized pending a valid industry-wide retrospective epidemiologic study to determine the possibility of excess coating worker mortality.

Incrustation in Water Pipelines

Results are presented of an inspection of the water supply system of Boulder City, Nevada, with respect to problems caused by bacterial incrustation in portions of the pipelines of the system. Laboratory analysis identified the incrustation as an iron bacteriums Gallionella ferruginea, which feeds on iron and manganese in solution and if uncontrolled, builds up incrustations which reduce the carrying capacity of the pipeline, increases pumping, operation and maintenance costs, provides conditions conducive to corrosion-producing bacteria, and will necessitate the eventual cleaning or replacement of the pipeline. That part of the pipeline lined with coal-tar enamel is in good condition because it is difficult for the bacteria to attach themselves to the smooth lining. The coal-tar enamel lining also resists microbial attack. Analysis of electrical energy costs for pumps indicate that in 1 yr savings in electrical energy costs would exceed the costs of treating the pipe with coal-tar enamel.

鋼製水槽および温水器内面防錆塗料の性能試験

The present experiment has been executed with the purpose to choose a paint with high corrosion-resistance and durability which is suitable for repainting the interior of the water reservoir and the water heater made of steel plate which are provided on passenger cars.In the first report, some 30 commercial brands for the above-mentioned use were tested for their general properties, their durability under accelerated deterioration under passage of current, and long time immersion in distilled water and several of them for their durability under immersion in tepid to hot water in the water heater. The results show that coal-tar enamel, PVC or epoxy paints are relatively effective for painting the water reservoir; and epoxy enamel, PVC or saran paints have practical effect in the interior of the water heater.

水道鋼管コールタールエナメル塗覆装の密着性向上に関する研究

水道鋼管コールタールエナメル塗覆装の密着性向上に関する研究

Pipe-Type Cable Corrosion Protection Practices In the Utilities Industry

Abstract A summary is made on corrosion control practices on 301.2 circuit miles of pipe cable for the period 1953 and 1958. High pressure oil cables made up 245.9 miles of the total and high pressure gas cables the remaining 55.3 miles. Information contained in this report was supplied by 17 utility companies in response to a questionnaire distributed by an NACE Technical Committee. Asphalt mastic pipe coating was used by 14 of the 17 companies. Three companies used coal tar enamel, two asphalt enamel and one epoxy coating. Data given include number of circuits energized during year, approximate circuit miles and kilovolts, operating temperature design, average length between manholes, pressure medium (pipe miles), sizes of pipe used for pipe cables, type of external pipe coating used on buried pipe, type reinforcing and shielding used with enamel, coating thickness, precautions taken to prevent coating damage, material used to coat weld, and material used to coat cable joint sleeves in manholes. Also discussed were material used on non-buried sections, acceptable coating resistance, average soil resistivity, rate of coating deterioration, grounding and cathodic protection practices, performance of cathodic protection equipment, etc. The resistor-rectifier method of cathodic protection was finding wider application among companies operating pipe cables. 7.7

コールタールエナメルの吸水性, もろさおよび付着性について

水中構造物あるいは鉄管に使用されるコールタールエナメルの物性について, 特に常温形, 加熱形の吸水性, もろさおよび加熱形の被塗面温度とエナメルの加熱温度の相違による付着性とについて検討を行なった。(1) 常温形の吸水性は吸水量よりむしろ水中における剥落損失量が大である。(2) もろさは常温形より加熱形の方が低温度においては温度変化に対し鋭敏である。(3) 加熱形の付着性は被塗面温度を高くすることにより, エナメルの加熱温度を下げる事ができる。