US3707450A - Coating for cathodically protected structures - Google Patents

Coating for cathodically protected structures Download PDF

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Publication number
US3707450A
US3707450A US61475A US3707450DA US3707450A US 3707450 A US3707450 A US 3707450A US 61475 A US61475 A US 61475A US 3707450D A US3707450D A US 3707450DA US 3707450 A US3707450 A US 3707450A
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US
United States
Prior art keywords
coating
primer
disbonding
current
inhibitor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US61475A
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English (en)
Inventor
Herbert E Townsend
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Bethlehem Steel Corp
Original Assignee
Bethlehem Steel Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Bethlehem Steel Corp filed Critical Bethlehem Steel Corp
Application granted granted Critical
Publication of US3707450A publication Critical patent/US3707450A/en
Anticipated expiration legal-status Critical
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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
    • F16L58/00—Protection of pipes or pipe fittings against corrosion or incrustation
    • F16L58/02—Protection of pipes or pipe fittings against corrosion or incrustation by means of internal or external coatings
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
    • C23F13/02—Inhibiting corrosion of metals by anodic or cathodic protection cathodic; Selection of conditions, parameters or procedures for cathodic protection, e.g. of electrical conditions
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04B—GENERAL BUILDING CONSTRUCTIONS; WALLS, e.g. PARTITIONS; ROOFS; FLOORS; CEILINGS; INSULATION OR OTHER PROTECTION OF BUILDINGS
    • E04B1/00—Constructions in general; Structures which are not restricted either to walls, e.g. partitions, or floors or ceilings or roofs
    • E04B1/62—Insulation or other protection; Elements or use of specified material therefor
    • E04B1/64—Insulation or other protection; Elements or use of specified material therefor for making damp-proof; Protection against corrosion
    • E04B1/642—Protecting metallic construction elements against corrosion
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S138/00—Pipes and tubular conduits
    • Y10S138/06—Corrosion

Definitions

  • This invention relates to an improvement in corrosion resistant coatings for metal structures and particularly for cathodically protected structures.
  • Underground pipelines such as those used for transcontinental transmission of gas, are protected throughout much of their length by cathodic protection.
  • This protection may be effected by means of an impressed current or by use of sacrificial anodes.
  • Gas transmission lines are generally subjected to high stress (up to 72% of the nominal yield strength) owing to high pressure. This fact, coupled with corrosive, low resistivity (less than 10,000 ohm-centimeters) soils encountered in the course of long pipelines, places heavy demands on any cathodic protection system.
  • Cathodic protection is effective for pipelines without the use of external coating.
  • the general practice is to coat the pipe with a relatively heavy coating of a bituminous material, usually with a thin primer coating adjacent to the metal substrate, in order to minimize the amount of current required for a given amount of protection.
  • organic compounds such as imidazolines, ethanolamines, sulfonic acids, etc., have been added to the coating in an attempt to retard disbonding.
  • this invention comprises coating the surface of, for example, a metal pipeline with a relatively thin primer coating of chlorinated elastomer, such as rubber or synthetic rubber.
  • the primer is coated with a bituminous material of the type preferably represented by coal tar.
  • the outer, bituminous coating is impregnated with at least 5% calcium carbonate, while the primer, preferably, also contains about 5% or more of calcium carbonate.
  • the suspension which contains from 50% to 55% solvent by weight, is applied to the outer surface of the pipe at a rate of one gallon of suspension for every 650 to 850 sq. ft. of pipe surface, resulting in a primer coating thickness, after evaporation of the solvent, of about 0.001 inch. Once the primer is dry and firmly set on the pipe surface, the pipe is ready for application of the bitumunous outer coating.
  • coal tar enamel-a mixture of topped coal tar, inert filler and, optionally, a plasticizer is heated to a freely flowing condition, and ground limestone (less than -mesh is incorporated with the hot tar in an amount equal to about 25% by weight.
  • ground limestone less than -mesh is incorporated with the hot tar in an amount equal to about 25% by weight.
  • the hot tar enamellimestone mixture at a temperature of about 450 F., is poured from a tank, downwardly onto a horizontal section of pipe which is rotating about its longitudinal axis, whereby the pipe is progressively completely covered with the mixture to a thickness of about 0.1 inch.
  • control of the thickness of the coating is maintained by applying an overlap of felt, fiberglass or kraft paper, to squeeze the coating to the desired thickness.
  • This overlap also gives protection to the coating during handling and installation of the pipe.
  • Coating materials of the type used for coating individual lengths of pipe are also used for coating any bare areas on the assembled pipeline, such as those areas existing where individual lengths of pipe have been joined by welding.
  • the anodes used in the impressed current protection system may be any conductive material such as copper, carbon, iron, etc. which will deteriorate slowly and provide long service.
  • the source of impressed direct current may be, for example, a rectifier, generator or battery.
  • a cathodic voltage of at least -0.85 volt with respect to a copper-copper sulfate reference electrode should be maintained at the metal surface.
  • a pipeline prepared in the manner of this invention will require less current to protect the pipe surface than is required of prior art cathodic protection methods.
  • the reason for the reduction in impressed current is due to a decease in disbonding, and to the inhibitive action of the coating of the invention in promoting the formation of protective calcareous films on any exposed metal surfaces and in pores in the coating.
  • Hydrogen can be a source of embrittlement if absorbed by pipe or tanks constructed of steels having a yield strength greater than 100,000 p.s.i.
  • This invention has particular application to gas transmission pipelines, as these lines are usually maintained under an internal pressure, and any corrosion which might Weaken the walls of the pipe to the point where rupture, and consequent explosion, could occur cannot be tolerated.
  • the invention is quite applicable to underground tanks, particularly those under pressure.
  • the coal tar enamel used for the outer coating may be plasticized, semi-plasticized or unplasticized, depending on the temperature conditions to which the structure is exposed. Plasticizing of the enamel is usually effected with ground coal. Bitumens other than coal tar are operative, for example, petroleum asphalt or natural asphalt can be used, although coal tar, in the form of coal tar enamel, has been found to be the most satisfactory.
  • Calcium carbonate in almost any form is satisfactory as the inhibitor in the coating, as long as the carbonate is of a degree of fineness adaptable for thorough and uniform mixing with the primer or outer coating.
  • ground limestone is quite suitable if of a fineness less than about lOO-mesh.
  • the calcium carbonate may be added in the form of ground dolomite.
  • Other alkaline earth metal carbonates, including barium and strontium, may be used alone or jointly. Any of these alternative inhibitor materials should be of a size less than 100-mesh in order to realize the greatest advantage from their use. The benefits of the invention may be obtained but to a lesser degree, with somewhat larger particle size inhibitor.
  • the maximum amount of calcium carbonate which can be used in primer or outer coating is that amount which permits the primer material or the bitumen to flow freely at the recommended application temperature.
  • the upper limit of calcium carbonate which can be used effectively in this invention will vary, depending on the exact nature of the coating material.
  • unplasticized coal tar enamel ranges, generally, between 375 and 475 F., and for plasticized coal tar enamel, the application temperature is between 450 and 550 F.
  • Calcium carbonate can be added to the primer in an amount equal to or greater than those shown for the coal tar enamel, for in the case of the primer, solvent is added to produce the proper fluidity.
  • a series of test panels for the comparative study of the behavior of inhibited and uninhibited coatings under simulated cathodic protection were prepared from 4-inch by 4-inch by fli-inch hot rolled carbon steel plates, sandblasted and cleaned in trichlorethylene vapor.
  • Primer chlorinated rubber
  • All primed and unprimed test panels were coated by dipping them into a container of molten coating bitumen (plasticized coal tar enamel) for a length of time (usually about 3 seconds) sufficient to result in a coating thickness of 0.09:0.03 inch when removed and allowed to drain in air.
  • Mixtures of coating bitumen and inhibitor were prepared by heating the bitumen to the application temperature of from 450 to 490 F. and adding the 'desired amount of inhibitor (25% by weight calcium carbonate for both primer and coating).
  • the procedure for the disbonding tests comprised the following steps:
  • a magnesium anode (1 inch by 1 inch by 4 inches) was electrically connected through a l-ohm resistor to a steel panel, and suspended in an electrolyte, about 1 inch above the holiday.
  • the anode was immersed in the electrolyte for a distance of about 2 inches to provide cathodic protection by means of the sacrificial magnesium anode.
  • the electrolyte comprised 1% sodium chloride (NaCl), 1% sodium sulfate(Na- S0 and 1% sodium carbonate (Na CO in 300 ml.'of distilled water.
  • Table I lists results for two eries of tests, the first series having no inhibitor and the second series containing inhibitor in both the primer and outercoating. Three specimens were tested for each series. Current is shown as an average of the weekly determinations.
  • the average reduction in current required for the inhibited specimens was 52%, while the average reduction results for a number of the different variables considered for this second set of tests.
  • Table I tests specimens were tested in triplicate and the current results averaged. While the differences in current and disbonding between inhibited and uninhibited specimens is not as great in Table II as in Table I, it will be appreciated that the 30- day tests are relatively short term as compared with those of four months.
  • Applicants invention is designed to give improved protection to pipelines and underground tanks for a matter of years, and it is over such long-range use that the greatest bene-fits from the invention are realized.
  • the tests used to supply results for both tables are accelerated tests with.the results of Table I showing the increasingly greater benefits obtained with longer use of the inhibited coatings.
  • test results in Table II is to provide a means of comparing variables, there being sufiicient showing of improvement in corrosion resistance shown by the inhibited specimens, even in the relatively short -day tests, to point up certain preferred practices in performing my invention.
  • the primer thickness was within the range of from 0.0005 to 0.0015 inch, and the coating thickness was within the range of from 0.065 to 0.120 inch.
  • a process for protection of the outer surface of a metallic article exposed to a corrosive underground environment which comprises applying to said surface an elastomer primer coating and an outer coating of a bitumen wherein each of the coatings contains more than by weight of an alkaline earth metal carbonate, and subjecting the thus-coated article as a cathode to an electric current sufficient to retard corrosion of the surface of said metallic article.
  • primer coating and outer coating each contains not less than 20% by weight of calcium carbonate.
  • a cathodically protected metal pipeline having the outer surface of the pipeline protected by a coating comprising: I
  • each of said layers contains a dispersion of more than 5% by weight of calcium carbonate
  • first layer has a coating thickness between 0.0005 and 0.0015 inch and the second layer has a coating thickness be-' tween 0.065 and 0.120 inch.

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  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Architecture (AREA)
  • Civil Engineering (AREA)
  • Electromagnetism (AREA)
  • Structural Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Paints Or Removers (AREA)
  • Prevention Of Electric Corrosion (AREA)
US61475A 1970-08-05 1970-08-05 Coating for cathodically protected structures Expired - Lifetime US3707450A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US6147570A 1970-08-05 1970-08-05

Publications (1)

Publication Number Publication Date
US3707450A true US3707450A (en) 1972-12-26

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Country Status (5)

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US (1) US3707450A (enExample)
CA (1) CA953681A (enExample)
DE (1) DE2139259A1 (enExample)
FR (1) FR2101255B1 (enExample)
GB (1) GB1362275A (enExample)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3992272A (en) * 1975-05-29 1976-11-16 Continental Oil Company Submerged offshore platform joint protection
EP0132332A1 (en) * 1983-07-09 1985-01-30 Webco Industrial Rubber Limited Cathodic protection system for pipes
US4941775A (en) * 1988-02-26 1990-07-17 Benedict Risque L Cathodic protection of critical offshore marine structure critical components by making the critical component noble (passive) to the balance of the platform
US20210071806A1 (en) * 2019-09-06 2021-03-11 Saudi Arabian Oil Company Reducing the risk of corrosion in pipelines

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4990231A (en) * 1981-06-12 1991-02-05 Raychem Corporation Corrosion protection system

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3992272A (en) * 1975-05-29 1976-11-16 Continental Oil Company Submerged offshore platform joint protection
EP0132332A1 (en) * 1983-07-09 1985-01-30 Webco Industrial Rubber Limited Cathodic protection system for pipes
US4941775A (en) * 1988-02-26 1990-07-17 Benedict Risque L Cathodic protection of critical offshore marine structure critical components by making the critical component noble (passive) to the balance of the platform
US20210071806A1 (en) * 2019-09-06 2021-03-11 Saudi Arabian Oil Company Reducing the risk of corrosion in pipelines
US11655929B2 (en) * 2019-09-06 2023-05-23 Saudi Arabian Oil Company Reducing the risk of corrosion in pipelines
US11655930B2 (en) 2019-09-06 2023-05-23 Saudi Arabian Oil Company Reducing the risk of corrosion in pipelines

Also Published As

Publication number Publication date
DE2139259A1 (de) 1972-02-17
GB1362275A (en) 1974-08-07
FR2101255B1 (enExample) 1976-02-13
CA953681A (en) 1974-08-27
FR2101255A1 (enExample) 1972-03-31

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