US2158772A - Asphaltic coating and method for protecting pipe lines with same - Google Patents

Description

May 15 1939 L. B. BEcKwlTH 2,158,772

ASPHALTIC COATING AND METHOD FOR PROTECTING PIPE LINES WITH SAME Original Filed Dec. 2, 1933 Primm Coa g Molded Shz'UeZd ofAsphZ', Mineral Faller Fzbrous Maerzals INVENTOR. Lawton B. BecAW/v BY Maf ATTORNEY.

Patented May 18, 1939 I UNITED STATES ASPHLTIC OOA'I'ING': AND METHOD FCR' PMTECTING PIPE LINES WITH SAME Law-ton B. Beckwith. Ban Pedro, Calif., assigner to Union Oil Company of California', Los Anv golea. Calif., Y'a corporation of California Application December z, im, Bene Serial No. 700.707

Wod Allll 18, 193

, Claims.

The present invention relates to a bituminous coating for pipe lines and to a method for protecting pipe lines against corrosion. It is well known that pipe lines can be protected against 5 corrosion by applying to them a coating consisting of asphaltic or bituminous membranes sometimes used in conjunction with fabrics such as felt or cloth wrappers for reinforcing the bitumens comprising the membrane.

The present common types of bituminous pipe line coatings are subject to damage by the soil, since the action of drying mud, pressure of clods or stones, and other mechanical stresses tend to puncture the coatings so that directelectrical contact is established between the steep pipe and the surrounding soil. Although carefully applied asphalt or bitumen alone aiiords protection against corrosion until such time as the bituminous membrane is punctured, it has been found necessary in making really effective and durable pipe coatings, to introduce into the coating some kind of mechanical reinforcing such as felt, cloth, or other fabric, in order to build up a iln-ished coating having sumcient mechanical resistance to soil action to prevent ultimate puncture. Other mechanical stress resisting materials have also been used, for example, Portland cement concrete, metal strips or foil, Bakelite resin shields and the like, but each of these has inherent disadvantages well recognized by those skilled in the art of protecting pipe.

An ideal mechanical shield for constructing pipe coatings comprises one which is rigid and has a great resistance to mechanical action of the soil, i. e. soil stresses, or in other words, one which Will not be stretched or distorted by the mechanical action of drying mud; one which has high electrical resistance, i. e. prevents corrosion of the pipe from electrolysis operating through pin holes which develop by the imperfect application of the asphalt or other bituminous coating on the pipe line; one which has great beam, tensile and compressive strengths so that it will not crack or be easily punctured; one which is inert to chemical action, particularly the action of alkaliesand acids; one which has a great resistance to wide ranges of temperature, and most important of all, one which is convenient to apply either as a mill wrap or in the field as a hand wrap.

In order to produce a pipe line coating which is durable and resistant to puncture or other damage, it has been proposed to cover the pipe with the following coating: First, a primer which comprises an adhesive asphaltic paint or cut-back asphalt having a high degree of cementitiousness; second, a seal coat which comprises a very adhesive asphalt and has a substantiallyhigh penetration and high melting point and a reasonable degree of ductility; third, a hard enamel layer which comprises air blown asphalt conl taining a mineral filler such as diatomaceous earth which decreases the penetration and increases the melting point of the asphalt considerably; fourth, a wrapper of felt or fabric such as rag felt, burlap, cotton or asbestos fabric having open spaces between strands, which is wrapped spirally around the pipe; fth, a second layer of enamel; sixth, another wrapper of fabric; seventh,'a third layer of enamel; eighth, another wrapper of fabric and ninth, a final enamel layer or plurality of such layers.

A coating for pipe lines as described in the preceding paragraph will have substantially all of the desired characteristics. However, it is apparent that the plurality of applications necessitated in applying such a coating makes this type of a job inconvenient and expensive.

It is, therefore, an object of my invention to produce a coating for protecting pipe lines which is durable and. highly resistant to puncture or other damage.

It is a further object of my invention to produce a shield for pipe line coatings which will have all of the desired advantages of resistance to mechanical action, high electrical resistance, great beam, tensile and compressive strengths, great resistance to lWide ranges of temperature change and yet which is convenient and inexpensive to apply, in conjunction with suitable bituminous cements and/or enamels.

In the drawing, Fig. 1 represents a longitudinal View of a pipe which is protected against corrosion by the means embodying the features of the invention. Parts of the various elements are broken away to reveal the elements underlying. Fig. 2 is a vertical cross section taken on line 2-2 of Fig. l.

Brieily stated, my invention resides in a coating for pipe line protection which includes the use of shields molded into hollow half-cylinders and adapted to be placed around the pipe to be protected. the molded shields comprising a mixture of asphalt, ilnely divided mineral filler and fibrous material. The invention valso includes a method for protecting pipes with the aforementioned hollow half-cylindrical shields or shells which are disposed in such manner as to cover the entire pipe. The half-cylindrical shields are cemented to the pipe by means of a bituminous cement; preferably, an application of bituminous cement ork paint is made on the pipe and on the interior surface of the molded hollow half-cylinders which are then pressed onto the pipe. Preferably, the edges and ends of the half-cylinders are formed with grooves so as to present adequate Joints when alternate half-cylinders are placed on the top and bottom of the pipe. 'I'he invention also includes the application of a hard asphaltic or bituminous enamel over the half-cylinders after having been amxed to the pipe.

I have discovered that an ideal coating for pipe lines may be made by the aid of compressed mechanical shields having the shape of semi-cylindrical shells which are adapted to be disposed around the pipe to afford suiiicient protection against corrosion. These shields may be made of any desired length and thickness. Generally, I have found that shields approximately 4 ft. long and from l/a to V4 inch thick and having an internal diameter from l/s to inch greater than the external diameter of the pipe to be protected are well adapted for the intended purpose of protecting the pipe line. If desired, the shape of the shields may be one-third or one-quarter of a hollow cylinder or any desired segment of a cylinder, the only important requirement being that when the shields are placed around the pipe to be protected, there is an even distribution of shields without' over-lapping. However, I prefer to employ shields of hollow 4half-cylinders so that only two of these may be disposed around the pipe. 'Ihe internal diameter of the shields is somewhat larger than the `external diameter of the pipe to which they are to be applied.in order to leave an annular space between pipe and shield which may be filled with bituminous cement so that the pipe is protected against the intrusion of water, not only by the shields themselves but also by the layer of the bituminous cement which i'ills the annular space.

The hollow half-cylindrical shields are produced from an asphaltic composition which has a high tensile and compressive strength and resistance to impact and which is inert to chemical action. 'Ihe composition which may be molded into shields as aforesaid may comprise from 30 to '15% by weight bitumen, 10 to 30% by weight of mineral filler and from 5 to 25% by weight of ber.

As bitumen, I may employ either steam blown or air blown asphalt, or natural asphalt, such as Gilsonite, Trinidad or Burmudas asphalt, cracked residues, coal tar, coal tar pitch or stearin pitch. I may also employ the asphalt precipitated from topped asphaltic crudes by means of such liquened normally gaseous hydrocarbon solvents as propane. In other words, I desire to employ as the bituminous content of the asphaltic mixture a material which exhibits a reasonably high degree of cementitiousness.

As a mineral filler for the mixture, I particulark desire to employ diatomaceous earth or pulverized silica, or I may employ finely divided clay, slate dust, rock dust, marl, barytes or mixtures thereof. The function of the mineral filler is to increase the tensile and compressive strength of the bitumen and to produce bitumen of high melting point and low penetration and reasonable ductility.

As fiber, I may employ any cheap fibers, such as cotton linters, asbestos, woolfibers or other vegetable and animal bers.

Preferably, I desire to employ moldable asphaltic mixtureof approximately 65% by weight of diatomaceous earth and about of cheap aisavva bers such as cotton linters. To produce the asphaitic mixture, I first melt the asphalt at a temperature of about 500 F. and then mix the mineral filler with the melted asphalt in any suitable vessel employing mechanical agitation until a smooth illled asphalt or mastic is obtained. I then add the cotton linters or other fibrous material to the filled asphalt in a pug mill and mechanically agitate at a temperature of about- 350 F. until a smooth, thick mastic is obtained. Portions of this hot mastic are then placed in a suitable metal mold and compressed heavily, preferably, at160 F. or whatever other temperature is found most suitable, by hydraulic pressure into the form of hollow half-cylinders having the desired thickness and inside diameter to conform to the outside diameter of the pipe to be protected. 'I'he practice of molding the asphaltic mastic is well known and understood by those skilled in the art. This operation perhaps may be likened to the process employed in the manufacture of mud storage battery cases in the storage battery industry. The finished hollow half-cylinders can be cut with a saw, Whittled or machined, if such an operation would be desirable.

Preferably, I desire to shape the edges, that is, both the longitudinal edges and the serni-circular ends so that when a plurality of the hollow half-cylindrical shields are placed on the pipe to be protected, suitable joints are presented which prevent the asphaltic coatings applied to the pipe from oozing through the joints. Thus, I may employ tongue and groove, ship-lap or beveled joints. y'l'hejoints may be formed on the asphaltic shield subsequent to its molding by machining or preferably the mold may be provided so as to present the grooves or joints on the iinished shield.

The following is a method for protecting pipe lines employing the asphaltic shield described above. However, it is to be understood that this method is not to be construed as limiting my invention but is to be considered as merely illustrative of one way of carrying out the invention.

After cleaning and priming the pipe with a priming coat of an adhesive asphaltic paint, such as a cut-back asphalt having a high degree of cementitiousness, a hot sling coat of asphalt is applied over the dried primer having a high melting point, as for example, greater than 190 F. and a minimum penetration of 35 at 77 F. and exhibiting very adhesive powers. 'I'he inner surfaces and edges of the hollow half-cylindrical vshields are then mopped with hot asphalt, preferably an adhesive asphalt similar to the one employed over the priming coat on the pipe. While still hot, the shields are ilrmly pressed into place over the coated pipeA so that all air is pressed out. 'I'he hot pipe sling coat will also be pressed out through the narrow joints between the hollow half-cylinders. In placing the shields on the pipe, it is preferable to stagger the alternate hollow half-cylinders on the top and bottom of the pipe in order'to eliminate circular joints passing all the way around the pipe. To hold the cylinders firmly in place until subsequent layers of asphaltic enamel can be applied and to permit the asphaltic cement to set, a wide spiral of narrow adhesive, such as friction tape, may then be applied after which two successive flood coats of a hard asphaltic enamel are applied. As asphaltic enamel, I prefer to employ an air blown asphalt containing a finely divided mineral filler, such as diatomaceous earth and having a minimum melting point of approximately 250 F. and a penetration of 2 to 4 at 77 F. Upon hardening, the pipe is deemed sumciently protected against soil stresses or other mechanical stresses or other forces which normally destroy the asphaltic coatings on the pipes.

' It is to be understood that the above description is merely illustrative of preferred embodiments of my invention of which many variations may be made within the scope of the following claims by those skilled in the art without departing from the spirit thereof.

I claim:

1. A method for protecting pipe against corrosion which comprises coating said pipe with hot bituminous cement, placing preformed hollow half-cylindrical shields containing a mixture of asphalt, finely divided mineral iiller and fibrous materials `on'said pipe to completely cover said pipe and subsequently coating said half cylindrical shields with asphalt.

2. A method for protecting pipe against corrosion which comprises coating said pipe with not bituminous cement, placing preformed hollow half-cylindrical shields containing a mixture of asphalt, finely divided mineral filler and ilbrous materials on-said pipe tot completely cover said pipe and subsequently coating said half-cylindrical shields with asphalt, said-last mentioned asphalt comprising an asphalt having a high melting point and low penetration.

3. A method for protecting pipe against corrosion which comprises coating said pipe with a bituminous cement, placing upper and lower preformed hollow half-cylindrical shields on said pipe in staggered relationship to prevent the ends of said upper and lower half-cylindrical shields from coinciding, the interior of said half-cylindrical shields having been previously coated with a bituminous cement and subsequently coating the outer surface of said cylindrical shields with asphalt of high melting point and low penetration.

4. A method for protecting pipe against corrosion which comprises coating'said pipe with a bituminous cement and placing preformed hollow half-cylindrical shields on said coated pipe to completely cover said pipe, said preformed shield containing approximately 30% to '75% by weight asphalt, 10% to 30% by weight finely divided mineral ller and 5% to 25% by weight of fibrous material and subsequently coating said halfcylindrical shields with asphalt.

5. A method of protecting pipe against corrosion which comprises applying to said pipe a layer of asphalt having a melting point of approximately 190 F., placing preformed half-cylindrical shields onsaid pipe over said layer of asphalt completely covering said pipe and comprising a mixture of asphalt, finely divided mineral iiller and fibrous material, and applying over said shields asecond layer ofvasphalt having a melting point of approximately 250 F.. said first mentioned asphalt layer having adhesive properties and said second mentioned asphalt layer affording great resistance to mechanical action of soil.

LAWTON B. BECKWITH.

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