US2158771A - Means for preventing corrosion of metallic objects - Google Patents

Description

May 16, 19-39. L. B. BECKWITH 2,158,771

MEANS FOR PREVENTING CORROSION OF METALLIC OBJECTS Filed March 31,, 1956 WraPPzh (S 2 Sealing C0 1 1- rkmi g Coal- I Wrappin 6 1p ral) Enamel g r Wrapper h r- :3 2 5 I I Mu WATTO EY.

Patented May 16, 1939 MEANS FOR PREVENTING CORROSION OF METALLIC OBJECTS Lawton B. Beckwitli, San Pedro, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application March 31, 1936, Serial No. 71,922

4 Claims.

The present invention relatesto bituminous coatings for metallic objects, such -as' pipes and the like, and to a method for protecting such objects against corrosion, particularly pipes which are to be used in underground service and is a continuation-in-part of my copending application Serial Number 700,707, flied December 2, 1933. The present invention also relates to bituminous compositions which are particularly adapted to be used for protecting metallic objects,

such as pipes, against corrosion.

It is well known to protect pipes in underground service against corrosion by applying a coating to the pipe consisting .of asphaltic or bituminous 5 membranes sometimes used in conjunction with fabrics such as felt or cloth wrappers for reinforcing the bitumen comprising the membranes. However, the present common types of bituminous pipe line coatings are subject to damage by the soil since the action ofdrying mud, pressure of clodsor stones and other mechanical stresses tend to puncture the coatings so that direct electrical contact is established between the steel pipe and the surrounding soil. Although carefully applied asphalt or bitumen alone aflords protection against corrosion until such time as the bituminous membrane is punctured, it has been found necessary in making a more effective. and durable pipeline coating to introduce .into', the coating 50 some kind of mechanical reinforcing such as felt, cloth or other fabric in order to build up a finished coating having sufficient mechanical resistance to soil action to prevent pu'ncture. Even with such found that these ordinary asphalts heretofore employed have a relatively poor temperature susceptibility so that they are .quite brittle at ordi- 45 nary low temperatures and are, therefore, easily shattered from the pipe.

I have found an ideal coating for pipes to comprise one which is rigid and has a great resistance to mechanical action of the soil, 1. e. soil stresses,

50 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,

1. e. prevents corrosion of the pipe from elec-' trolysis operating through pinholes which develop from the imperfect application or production 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 nor be easily punctured; one which is" inert to chemical action, particularly the action of alka- 5 lies and acids; one which has a great resistance to wide ranges of temperature suchas when the pipe is used for conducting petroleum oils and the temperature of the oil being conducted through the pipe is varied between very wide limits and one which is convenient to apply either as a mill wrap or in the field as a hand wrap.

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

Various otherobjects and features of my invention will become apparent to those skilled in the art from the following detailed description of a preferred embodiment of this invention which is intended to be merely illustrativeand not limited.

In the drawing, Figure 1 represents a longitudinal view of a pipe which is protected against corrosion by the means embodying the feature of the invention. Figure 2 is a vertical cross section taken on line 2-2 of Figure 1.

In general, the pipe coating forming the subject of my invention comprises the following:

First, a primer which consists of an adhesive asphaltic paint or cut-back asphalt having a high degree of cementitiousness; second, a sealing coat which comprises a very adhesive asphalt and has a substantially high penetration and a relatively low melting point and a reasonable degree of duetility; third, a hard enamel layer or soil resistant enamel which comprises air blown asphalt containing a finely divided mineral flller such as 'diatomaceous earth which has the effect of lowering the penetration and increasing the melting point of the asphalt considerably; fourth, a wrap- 40 enamel; sixth, as many additionally alternating layers'of hard enamel and felt as desired, omitting the final layer of felt or substituting a wrapplng of Kraft paper for the final wrapper of felt. It is preferred to saturate the wrapper with a bituminous material, such as coal tar or asphalt, before use.

The primer which I desire to employ need not be confined to close limits; Gilsonite or any well refined asphalt having a melting point of F. to 250 F. dissolved in a suitable volatile hydrocarbon solvent may be employed. The primer may consist of a' synthetic base composed of suitable drying oils and solvents, as for example, Bakelite resins and China-wood oil dissolved in aromatic solvents with or without the addition of pigments. Preferably, however, the primer I desire to employ comprises an asphalt having a melting point of 185 F. to 195 F., a penetration at 77 F. of 18 to 22 which is dissolved in an aromatic solvent having approximately a boiling range of 275 F. to 375 F. and an A. P. I. gravity of 38 at 60 F.

As the sealing coat, I prefer to employ a layer of asphalt or bitumen which has a maximum adhesiveness to the steel, a minimum of brittleness and a minimum temperature susceptibility. I have found that these properties are obtained in an asphalt having a higher penetration for a given melting point than has ever before been used for pipe coatings. Such an asphalt is described hereinafter and is illustrated in the following specifications:

The purpose of the sealing coat of the special asphalt at the point is to serve as a cushioning layer between the hard enamel to be described and the steel, thereby preventing the scaling or peeling of the enamel which would occur if the enamel were applied directly to the metal. I have discovered that the adhesion of the coating to the metal is a function of the penetration of the coating and consequently an enamel of sufllcient hardness to serve as an armour coat against soil and other stresses would not have as great adhesion to the metal as would be desirable. I have discovered that at all times the metal should be sealed hermetically against water, electric currents, etc., and that this protection is afforded best by an asphalt of the type described above.

There are a number of methods for producing the sealing coat asphalt having the aforementioned characteristics. In one of the methods, an

asphalt residuum is subjected to oxidation with of producing a lubricating oil of a light or medium grade after chemical treatment. If desired, the lubricating oil may be chemically treated, such as with sulfuric acid prior to blending with the residuum and oxidation.

Also, the lubricating oil distillate may be subjected to solvent extraction with liquid sulfur diozddejfor example, in order to separate the aromatics and naphthenic hydrocarbons from the distillate and then the more parafiinic hydrocarbons are blended with the petroleum residuum prior to oxidation. In this connection it is desirable to reduce the asphalt by distillation as much as possible so as to remove a considerable amount of the oil fractions prior to blending with the solvent refined oil or acid treated distillate, or if desired the oil constituents may be separated from the asphalt by working it with a liquefied normally gaseous hydrocarbon such as liquid ethane, propane or butane.

I prefer to employ as the hard enamel coating an air-blown asphalt into which has been thoroughly incorporated a finely divided mineral flll- The hard enamel coating should have the er. following characteristics:

Minimum Maximum Melting int, F 235 250 Penetration at 77 F. (100 g. sec 2 6 Filler, percent by weight l3 17 Fire point, open cup, F 575 The asphalt which I desire to employ in the hard enamel coating should have the following characteristics:

Minimum Maximum Melting point, F 215 236 Penetration at 77 F. (100 g.5 sec.). 5' Flash point F 465 Bitumen soluble iii 6Q; Bitumen soluble in G014 The function of the hard enamel coating in combination with the felt wrappings is to carry the stresses imposed on the pipe by its surroundings. I have found that while the unique asphalt used as a sealing material has practically perfect water-proofing and corrosion preventing properties, it is necessary to protect the The hard asphalt enamel described above is characterized by a'high melting point, low penetration and low temperature susceptibility and high beam and tensile strengths. This material is very resistant to deformation even up to temperatures of 140 F. to 150 F. so that it is suitable for use on pipe lines carrying hot fluids. While the hard enamel is less resistant, per se, to shattering than the sealing coat, the latter acts as a cushion when the structure is subjected to sudden impacts. The hard enamel is more resistant to water penetration and to loss of oils to clay soil than ordinary air blown asphalts such as have been used in the past. It is thus obvious that the armor coat of hard enamel and reinforcing wrappers also protects the sealing coat against water penetration and loss of oil to the clay soil; consequently, the sealing coat maintains its eillciency over an indefinitely long period of time.

In choosing a wrapper, it is believed to be of entire area by capillary attraction.

paramount importance to select one that has been heavily saturated with asphalt because insufficiently saturated felts, either rag or asbestos, have an undesirable tendency in case of puncture from any cause, such as an inadvertent shovel cut, to transmit water throughout their Also, the saturant shouldbe free from oiliness and yet not impart brittleness to the wrappers. It is also considered essential that the surface of the wrapper be finished in such manner that a thorough bond will be established between the wrapper and the enamel. The coating of the saturated felt during manufacture by passing through a bath of coating asphalt of 210 to 225 F. melting point, having 12 to 20 penetration at 77 F., is beneficial provided the thickness of the coating is kept to a minimum and the surface properly finished. The use of mica or tale in finishing to prevent the rolls of the felt from sticking together is very undesirable in that these materials interfere with the establishment of a bond between the wrapper and enamel. A coarse silica finish on the surface oi. the wrapper is adequate to prevent the rolls from sticking to gether and has been found to ofier no obstacle to the fluxing of the coating or the wrapper and the enamel.

It will be observed that all mention herein of melting point, penetration and ductility is according to the methods outlined by the American Society of Testing Materials, as follows:

Penetration D- -25 Melting point (ball and ring) 1)- 3 -26 Ductzllity D-113-32T Flash point, Cleveland open cup method 13-9 -24 To produce hard enamel coating, the asphalt employed in the coating is heated to a temperature of about 450 F. and the desired amount of finely divided filler such as diatomaceous earth, rock dust, silica, slate dust, talc or mica, is gradually introduced into the melted asphalt maintained in the still by circulating the contents of the still through an intermediate mixing vessel equipped with an electrically driven propeller agitator in which filler is introduced continuously until the full quota of the filler has been incorporated into the still charge. The function of the filler in the asphalt is to increase the tensile strength of the asphalt. I have found that if diatomaceous earth is properly incorporated into the bituminous material, it has a remarkably greater reinforcing efiect that any of the other fillers for the same amount of filler. For example, to approximate the improvement made by incorporating by weight of diatomaceous earthin a particular bitumen, it is necessary to incorporate approximately 30% of talc or mica. During the addition of filler, steam or air is employed in the body of the still and is continued until after the incorporation of the filler is complete for approximately one hour. The purpose of the latter is to remove adsorbed air and moisture on the diatom structures and thus from the asphalt. The product thus produced is characterized by a smooth glossy appearance, a high density and a low porosity and is particularly adapted as the hard enamel coating of the pipe line. When applied to the pipe, the coating is rigid and has a great resistance to mechanical action of the soil. The coating also has a high electrical resistance, that is, it prevents corrosion of thepipe from the electrolysis operating through ent in filled asphalts which have not been subjected to the steaming operation heretofore de-' scribed. The coating is also characterized by=a great beam and tensile strength so that it will not be cracked nor easily punctured. It is also inert to chemical action, particularly the action of alkalies and acids and has a great resistance to wide ranges of temperature. Due to the absence of air bubbles in the filled asphalt and its high density, there is less tendency for the asphalt to absorb water and consequently when these are employed as waterproofing coatings, a structure is presented which effectively seals ofi tne part to be protected from the corrosive action of the water.

In order to describe more fully the manner in which the coating is applied to the pipe, the following is submitted:

The pipe, for example, one 8 inches in diameter, is first thoroughly freed on the outside from grease, rust and mill scale preferably by sand blasting. Immediately after the cleaning of the pipe, it is primed with the primer coating of a few thousandths of an inch in thickness and is then allowed to dry before further treatments are applied. After the primer coating has been dried, the pipe is then placed in a suitable lathe type wrapping machine. The pipe is then given a coating of thickness of the sealing asphalt which is applied at a temperature of about 325 F. to 375 F. and immediately following or simultaneously with the application of the sealing coat, a spiral wrapping of an asphalt saturated felt pipe wrapper made either of rag or asbestos is applied to the pipe. Over the wrapper thus described a coating of thickness of hard enamel described above is applied at a temperature of about 425 F. to 475 F. and immediately over this a second wrapper of felt is applied. Then a second layer of enamel, another wrapper of felt, a third layer of enamel and finally a layer of. Kraft paper are applied. All of the layers of the hard ena'mel are approximately in thickness and the wrapper used also has a thickness of approximately giving for the complete application as thus described a protective coating of a total of approximately to fi in thickness.

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 coated metallic pipe for use in underground service which comprises a metallic pipe, 9. layer of asphalt having a melting point of about 190 F.-200 F. adjacent said pipe and a layer of asphalt having a melting point of about 235 F.-250 F. over said first mentioned layer of asphalt, said asphalt of about 190 F. to 200 F. melting point having adhesive,- waterproofing and corrosion preventing properties and said asphalt of about 235 F. to 250 F. melting point affording great resistance to mechanical action of soil. Y

2. A coated metallic pipe for use in underground service which comprises a metallic pipe, a layer of asphalt having a melting point of about 190 F. to 200 F. and a penetration of about 30 at 77 F. adjacent said pipe and a layer of asphalt having a melting point of about 235 F. to 250 F. and a penetration of about 2 to 6 at 77 F. over said first mentioned layer of asphalt, said asphalt of about 190 F. to 200 F. melting point having adhesive, waterproofing and corrosion preventing properties and said asphalt of about 235 F. to 250 F. melting point afiording great resistance to mechanical action of soil.

3. A coated metallic pipe for use in underground service which comprises a metallic pipe, a layer of asphalt having a melting point of 190 F. to 200 F. and a penetration of about 30 at 77 F. adjacent said pipe, a layer of sheathing consisting of an asphalt saturated felt over said layer of asphalt and a second layer of asphalt over said sheathing, said asphalt having a melting point of about 235 F. to 250 F. and a penetration of about 2 to 6 at 77 F., said asphalt of about 190 F. to 200 F. melting point having adhesive, waterproofing and corrosion preventing properties and said asphalt of about 235 F. to 250 F. melting point afiording great resistance to mechanical action of soil.

4. A coated metallic pipe for use in underground service which comprises a metallic pipe, 9. primer coating of an adhesive asphalt having a melting point of about 185 F. to 195 F. and a penetration of about 18 to 22 at 77 F. adjacent said pipe, a sealing coat of asphalt having a melting point of about 190 F. to 200 F. and a penetration of about 30 at 77 F. over said primer coating, a hard enamel coating over said sealing coating consisting of an asphalt having a melting point of about 235 F. to 250 F. and a penetration of about 2 to 6 at 77 F., a felt wrapper over said hard enamel coating and a second coating of hard enamel over said felt wrapper, said asphalt of about 190 F. to 200 I

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