US3402742A - Pipe coating methods and coated pipe - Google Patents

Description

United States Patent Oliice 3,402,742 Patented Sept. 24, 1968 3,402,742 PIPE COATING METHODS AND COATED PIPE Harold C. OBrien, Jr., Pittsburgh, Pa., assignor to Royston Laboratories, Inc., a corporation of Pennsylvania No Drawing; Filed Aug. 27, 1964, Ser. No. 392,639 5 Claims. (Cl. 138-143) ABSTRACT OF THE DISCLOSURE A method is provided for coating pipe with an elec trically insulative and physically protective coating by the steps of cleaning the pipe, applying a coating of organic vehicle filled with finely divided organic resins insoluble in said vehicle and wrapping said coated pipe with a tape made up of two layers of resin dispersible in said vehicle, one layer on each side of a film material insoluble in said vehicle.

This invention relates to methods of coating pipe and to a coated pipe and more particularly to amethod of coating pipe using a quick setting cold applied mastic and compatible insulative outer wrap.

The practice of coating underground pipes and the like for providing resistance to corrosion is old and well known. It has been for many years the practice to coat pipe before burial in the earth with a hot applied coating of tar or asphalt and thereafter to apply afelt or like wrapper to protect the hot applied .coating. Usually the tar or asphalt is loaded or filled with an inorganic filler such as asbestos, talc or clay in order to maintain a sufiicient thickness in the coating to protect the pipe. Unfortunately these inorganic fillers, while giving body to the liquid coating material also drastically reduce its electrical insulative properties. This difficulty is well recognized and is accepted as a necessary evil in order to achieve the requisite coating thickness which must approximate 25 mils when dry. The outer felt wrap is provided to protect the hot applied coating against abrasion. It adds little or nothing to the insulative quality of the materials.

I have discovered a method of coating pipe which provides the necessary thickness and insulative qualities and at the same time provides abrasion resistance of exceptional quality.

Preferably I abrasively clean the surfaces to be coated as, for example, by brushing, followed by applying a coating of a cold applied mastic comprising an organic vehicle filled with a finely divided organic resin insoluble in said vehicle as described in my copending application Ser. No. 294,942, filed July 15, 1963, after which I wrap an insulative tape around the cold applied mastic which tape comprises an inner and outer resin layer compatible with and softened by solvent of the vehicle of the cold applied mastic, said layers being separated by a fibrous layer, preferably permeable to and saturated by the inner and outer layer resins. Preferably the cold applied mastic and the resin of the tape mutually diffuse at the contact surface to form an integral continuous insulative layer of high electrical resistivity.

The method of this invention can perhaps best be understood by the following examples.

Example I A 3" pipe was brushed to remove all mill scale, and was coated with a mixture of 50% coal tar pitch ground to less than 100' mesh as the pigment in 50% of a vehicle made up of 63 parts by weight of asphalt washed free of ionizable substance, parts by weight of aromatic solvent, and 27 parts by weight of aliphatic solvent to 50 mils thickness which would dry to 25 mils of thickness. A tape (6" wide) was tightly wrapped about the coating mixture with /2" of overlap. The tape was made up of 15 ,mils of unfilled asphalt washed and treated to remove all water and ionizable substance on each side of a- 5 mil layer of fiberglass filament impregnated with the same asphalt. The total thickness of cold coating and tape averaged 60 mils. The resultant coating was physically tested and compared with standard hot applied asphalt pipe enamel coating and standard modified coal tar enamel coatings.

Penetrometer needle tests at 77 F. (50 grams, 5 seconds) gave a penetration of 5.3 almost identical with that of the coal tar and asphalt coating.

Deformation and recovery using a load equivalent of 1200 lbs./in. gave 65% less deformation than that of hot applied asphalt'pipe coating and 83% less than the modified coal tar enamel.

Electrical resistivity tests showed that the 60 mil coating yielded an electrical resistivity equal to that of mil hot coating and far greater than any practical cold coating.

Example II A 6" pipe was cleaned of mill scale and dirt by brushing and was coated with the same cold mixture of vehicle and pigment as in Example I followed by a wrapping of 9" tape with /2" overlap. The tape was made up of a polyethylene tape (5 mils thick) coated on each side with 15 mil of asphalt as in the case of the tape of Example I. The physical tests showed substantially identical results to those of Example I.

Example III A 4" pipe was brushed and coated with a cold coating mastic at the rate of 24 gallons/ 1000 ft. (about 50 mils of thickness). The coating was composed of 23% by weight of mixed aromatic and aliphatic solvent, about 33.6% by weight of asphalt, and about 43.4% by weight of insoluble phenolic resin powder. A tape 6" wide was wrapped over the mastic coated pipe with /2 overlap. The tape was made up of 20 mils of a mixture of washed asphalt and milled rubber on either side of a 5 mil sheet of perforated polyester film. Physical tests showed results comparable to those of Example 1.

Example IV A 16" pipe was brushed and coated with a cold mastic at the rate of 84 gallons per thousand feet. The cold mastic was composed of 26% by weight of mixed aromatic and aliphatic solvents, 39% washed asphalt, 28.5% of insoluble polyethylene powder and 6.5% of talc. An 18" wide tape was wrapped over the coated pipe with a 1" overlap. The tape was made up of 20 mils of coal tar resins on either side of a 5 mil layer of polypropylene film (imperforate). The physical properties of the resulting coating were substantially the same as those of Example I.

The tape used in wrapping the mastic coated tape may be made of two layers of any appropriate resinous materials such as asphalt, coal tar resins, bitumens, rubber, vinyls, and other synthetic resins soluble in the solvent of the mastic on opposite sides of a base reinforcing film of fiberglass, polyethylene, polypropylene, perforated polyester, etc.

The use of the method of this invention materially reduces the equipment and men required as compared with conventional hot coated applications at a much lower cost and at greater rates of speed. Moreover the resulting physical properties are far superior to any conventional hot or cold coating now available.

While I have illustrated certain presently preferred practices and embodiments of my invention, it will be understoodthat this invention may be otherwise embodied withinthe-scopeof the following claims.

1. A coated pipe comprising a metal pipe, a coating of organic vehicle filled with finely divided organic resins insoluble in said vehicle on said pipe and an outer wrapping oftape made up of two layers of resin selected'from the group consisting of bituminous resins, epoxy resins, hydrocarbon resins, coal tar resins, rubber, vinyl and synthetic resins soluble in the vehicle, said layers being separated by a reinforcing film of polyethylene.

2. The method of coating a pipe to provide electrical and physical protection comprising the steps of cleaning said pipe, applying a coating of organic vehicle containing an organic resin and a solvent therefor filled with finely divided organic resins insoluble in said vehicle and wrapping said coated pipe with a tape made up of two layers of resin soluble in said vehicle, said layers lying on opposite sides of a reinforcing film of material insoluble in said vehicle.

3. The method of coating a pipe to provide electrical and physical protection comprising the steps of cleaning said pipe, applying a coating of organic vehicle containing anorganic resin and a solvent therefor filled with finely divided organic resin particles less than 50 mesh in size and insoluble in said vehicle and wrapping said coated pipe with a tape made up of two layers of resin soluble in said vehicle, said layers lying on opposite sides of a reinforcing film of material insoluble in said vehicle.

4. The method as claimed in claim 2 wherein the organic vehicle is a material selected from the group consisting of bituminous resins, epoxy resins, hydrocarbon resins dissolved in an organic solvent and the finely divided insoluble organic resin filler is a member selected from the group consisting of coal tar pitch, bituminous pitch, residue petroleum distillate pitch, insoluble esters of pinetar," buta'die'ne styrene resins,"polyst'yrene, vinyl wrapping said coated pipe with a tape made up of two layers of resin selected from the group consisting of bituminous resins, epoxyresinsfhydrocarbon resins, coal tar resins, rubber, vinyl and synthetic resins soluble in the vehicle of the coating, said layers lying on opposite sides of a flexible reinforcing film of material "insoluble in said vehicle. 1

References Cited UNITED s ATEs PATENTS 1,474,423

11/1923 Maynard 1567-1 1,805,739 5/1931 Moeller et al 156 71 2,158,772 5/1939 Beckwith 156-187X 2,161,036 6/1939 Gremmel et al 156-187 2,192,517 3/1940 Ciinnington 15671 X 2,598,090 5/1952 Yung et al. 16192 2,815,043 12/1957 Kleiner et al 138-76 3,005,742 10/ 1961 Kennedy 156308 X 3,231,443 1/1966 McNulty' 1 56187 3,245,856 4/1966 Morain 156l87 2,677,165 5/ 1954 Copenhaver et a1. 138-144 X 3,247,869 4/1966 Boegershausen et al. 138-144 3,321,357 5/1967 Kennedy 161 236 HAROLD ANSHER, Primary Examiner.