US1948007A - Means for preventing corrosion of metallic objects - Google Patents

Description

J. F. PUT-NAM [nwntar Febhzo, 1934.

MEANS FOR PREVENTING CORROSION OF METALLIC OBJECTS Filed June so. 1951 Patented F eb. 20, 1934 UNITED STATES PATENT OFFICE MEANS FOR PREVENTING CORROSION OF METALLIC OBJECTS 6 Claims. (01. 154-41) This invention relates to the provision of means for coating and protecting metallic objects such as pipes, tanks, and the like, from corrosion or other injury. I

The invention particularly relates to a protective coating which consists in part of bituminous materials, such coating being particularly applicable to cylinders, tanks, pipes, and other metallic equipment used either above or below ground level, which equipment is subjected to changes in temperature.

It is the general object of this invention to disclose a protective coating for metallic objects such as pipes, which will resist changes in temperature wthout deformation, cracking, or movement on the body to which the coating is applied, and which will also resist deformation, flow or penetration due to pressure exerted upon localized sections of the covering or due to the action of changes in atmospheric conditions.

For purposes of lucidity, the subsequent description will be particularly directed toward the adaptation of the means to the covering of pipes,

particularly oil pipes in underground service.

Although many substances have been employed in protecting pipe lines from corrosion, among them being coal tar residues, natural asphalts and petroleum asphalts, these substances have several disadvantages.

While the pure bitumens have good waterproofing and insulating characteristics, they are incapable of completely protecting the pipe from corrosion when subjected to mechanical abrasion, soil pressure and/or temperature fluctuations. Pure bitumens have a tendency to flow when subjected to heat and/or pressure whereas hard bitumens which do not flow readily in moderately high temperature have a tendency to crack when cool.

For this reason, if pipes or the like are coated with the usual types of bitumen, the bitumen will not remain on the pipe under pressure and temperature conditions encountered in practice.

This invention employs as one of the protective coatings a bituminous mastic composition de-' scribed in a co-pending application Serial No. 504,726. By bituminous masticfas hereinafter used, reference is made to a-bitumen composition containing a rather large percentage of inert aggregate and a relatively minor portion of a bitumen such as asphalt. For example, the bituminous mastic particularly adapted for use in a protective coating made in accordance with this invention employs more than 75% by weight of a mineral aggregate made of small, crushed rock, gravel, sand, limestone dust, Portland cement, and the like. The preferred aggregate preferably passes an 8 mesh screen but is partially retained on a 16 or 28 mesh screen, from about 15% to 20% of the aggregate passing a 200 mesh screen. In addition to this relatively coarse aggregate, a small quantity of finely divided filler such as any finely comminuted inert material, stone dust, limestone dust, etc., may be employed. Furthermore, a relatively small amount of reinforcing agent such as asbestos fiber or finely pulverized diatomaceous earth or the like, may be added to the mastic composition in amounts not exceeding about 3% by weight.

It has been found, however, that when a bituminous mastic such as has been described hereinbefore is applied to the exterior surfaces of 'a metallic body such as a tank or pipe, and such mastic coating then covered with a fibrous sheathing such as a spirally wound strip of paper, there is a tendency for the coating to crack, due to the stresses set up in the covering. These stresses set up in the fibrous covering are apparently due to changes in atmospheric conditions including changes in humidity and temperature. The mastic coating itself is relatively hard and resists depression remarkably well, but when the fibrous sheathing is aplied to the mastic covering, it becomes bonded thereto and when the protected pipe is exposed to varying atmospheric conditions such as are encountered during any 24 hour period, the stresses set up in the fibrous covering are sufficient to cause craclm to appear in the mastic. These cracks necessarily impair the effectiveness of the coating and its capacity to protect the pipe from corrosion. Although at first it was believed that the deformation and stresses set up in the fibrous wrapping were due to variations in temperature or moisture conditions, it has actually been found that apparently such deformation and stress is due to the effect of light, possibly the ultra violet rays in sunlight.

It .is an object of this invention, therefore, to disclose and provide means whereby metallic objects may be covered with a protective coating which is unaffected by changes in atmospheric conditions and/or light.

Another object of this invention is to disclose and provide means whereby amastic bituminous protective coating may be prevented from cracking after application to a metallic body due to stresses set up in a fibrous exterior covering.

A further object of this invention is to disclose and provide-means for protecting metallic llO objects from corrosion, said protecting means being resistant to mechanical abrasion, changes in temperature or atmospheric conditions.

These and other objects, uses and advantages of this invention will become apparent to those skilled in the art from the following detailed description of a preferred embodiment of this invention, referencebeing had to the appended drawing, in which Fig. 1 is a plan view of a section of pipe covered with a protecting coating made in accordance with this invention.

Fig. 2 is an enlarged transverse section of a portion of a coating made in accordance with this invention and applied to a metallic cylindrical body.

In the drawing and in the subsequent description, it will be assumed that the coating of this invention is to be applied to a metallic pipe such as a pipe for use in conducting petroleum oils. Pipe lines for this purpose are subject to strenuous conditions inasmuch as the temperature of the oil being conducted through the pipe is varied between very wide limits. Furthermore, in view of the length of oil lines, it is impossible to economically lay the pipe with a great deal of care so that the ditches are not carefully smooth nor are they very deep. The pipe, therefore, will probably rest on a rocky, uneven bottom and be subjected to wide temperature changes due to its proximity to the earths surface. The entire weight of the pipe resting upon a few sharp rocks, there will be a tendency for the rocks to displace the coating and expose the metal of the pipe to the action of soil moisture and its electrolytic and corrosive effect. Its proximity to the earths surface will cause the pipe to become hot during the summer months, softening the protective coating and thus facilitating the deformation and displacement of the coating.

A pipe coated in accordance with this invention, however, will successfully resist these strenuous conditions, not only after it is placed in the ground but even if the pipe is exposed to direct sunlight.

Preferably, the pipe or.-other metallic object 10 is covered with a bituminous mastic 11 which may vary in thickness depending upon the size of the pipe or other metallic object which it is desired to protect. Ordinarily, the mastic coating 11 is from about to 1" in thickness; A," coating has. been found sufficient for usual pipe lines. Just prior to the application of the mastic coating 11, the exterior surface of the pipe 10 is preferably coated with a primer 12. Such primer may be made from an asphalt similar to that used in the mastic 11, cut back to the proper consistency for application as a cold paint, with a suitable bitumen distillate. The mastic coating may be applied to the pipe 10 in any suitable manner as, for example, by means of extrusion methods or by being spirally wound upon the pipe while the mastic is in a heated and plastic condition. The preferred mastic coating 11 is, as has been stated before, composed of a mineral aggregate and contains notmore than 25% and preferably less than 15% of asphalt.

It has been found that a bituminous mastic containing from about 10% to 25% by weight of asphalt, 75% to by weight of graded mineral aggregate between 8 and 200 mesh, and not more than about 20% of a mineral filler and reinforcing agent or dust, will withstand deformation and maintain its form at temperatures as high at 170 F.

The mastic coating 11 is preferably covered with a sheathing 13 spirally applied to the exterior surface as indicated in Fig. 1. The sheathing 13 may be in the form of a stri-pfbf fibrous material such as paper, the edges of the strip being placed either in abutting relation or in overlapping relation.

When a pipe is covered merely by a mastic 11 and a sheathing 13, the mastic 11 will crack when the pipe is exposed to light due to stresses set up in the sheathing 13. The sheathing 13 adheres to the mastic coating 11, particularly when the sheathing 13 is applied over the mastic while the latter is still warm. Cracks which develop in the mastic 11 necessarily reduce the effectiveness of the protective coating 11.

Ithas been found, however, that if this sheathing is covered with a relatively thin layer of bitumen such as asphalt 14 and an outer layer or covering of any suitable material 15 then placed over or around the pipe, thecracking of the mastic 11 will be effectively prevented.

Preferably, the intermediate layer 14 of bitumen is applied hot to the sheathing or supporting material 13 after such sheathing has been wrapped around the mastic 11. The bituminous layer 14 may consist of air blown asphalt of about 30 penetration, or it may consist of any other bituminous material capable of becoming flexible or readily deformable at temperatures of between 120 and 170 F. so as to absorb the stresses set up in the exterior coating 15 and prevent the development of stresses in the sheathing 13. The thickness of this layer need not be great, layers or 1 g in thickness being sufficient. The exterior covering 15 may be composed of paper and when spirally wound around the pipe, such exterior covering is preferably wrapped in overlapping relation to the joints or marginal edges between strips of the sheathing 13.

Instead of applying the bituminous layer 14 to the supporting material 13, the bituminous layer 14 may be applied to a strip of the outer covering 15 and such coated strip then wrapped around the pipe sheathing and supporting material 13. The exterior covering 15 may have stresses set up in it due to the exposure of the pipe to sunlight or varying atmospheric conditions but such stresses are apparently absorbed by the asphaltic or bituminous layer 14 and thus transmitted to the supporting material, tape or sheathing 13. In this manner the sheathing 13 is protected and stresses not transmitted to the elastic coating 11, thereby preventing the development of cracks or distortion of the mastic coating 11.

Although the invention has been described in detail as it pertains to the protection of pipe from corrosion, it is to be understood that a similar combination of elements may be employed in protecting any other metallic body from corrosion. Numerous changes and modifications may be made in the composition of the mastic and in the particular quality, weight, strength, etc.,- of the sheathing and covering materials. For example, the sheathing 13 may be either composed of relatively heavy paper such as 40 pound paper, or it may consist of a very lightweight paper and under certain circumstances, it might be desirable to employ a metallic foil for this purpose. The exterior covering 15 is preferably inexpensive and its main purpose lies in maintaining the asphaltic or bituminous layer 14 distributed over the sheathing 13 and preventing sticking in handling and adhesion of clods, dirt, etc., which cause soil stress.

All such changes and modifications as come within the scope of the appended claims are embraced thereby.

I claim:

l. A protecting coating for metallic bodies comprising a layer of bituminous mastic adjacent the metallic body, a spirally wound sheathing covering said mastic, and a separate spirally wound fibrous covering exterior of said sheathing, a layer of flexible asphaltic material being interposed between said sheathing and fibrous covering.

2. A protecting coating for metallic bodies comprising a layer of bituminous mastic adjacent the metallic body, said mastic containing not less than about by weight of a mineral aggregate and not more than 25% by weight of asphaltic material, a spirally wound sheathing covering said mastic, and a separate spirally wound fibrous covering exterior of said sheathing, a layer of asphaltic material adapted to become readily deformable at temperatures of l20-170 F. being interposed between said sheathing and fibrous covering whereby relative movement between the fibrous covering and sheathing is permitted.

3. A protecting coating for metallic bodies comprising a layer of bituminous mastic capable of resisting deformation adjacent the metallic body, a coating of bituminous primer between said mastie and metallic body, a spirally wound fibrous sheathing covering said mastic, and'a separate spirally wound fibrous covering exterior of said sheathing, a layer of readily deformable asphaltic material being interposed between said sheathing and fibrous covering.

4. A protecting coating for metallic bodies comprising a layer of bituminous mastic capable of resisting deformation adjacent the metallic body, a. spirally wound sheathing covering said mastic, and a separate spirally wound fibrous covering exterior of said sheathing, said fibrous covering overlapping the joints in said sheathing, and a layer of flexible and readily deformable asphaltic material between said sheathing and fibrous covering.

5. A protecting coating for metallic bodies comprising a layer of bituminous mastic capable of resisting deformation adjacent the metallic body, said mastic containing not less than about 75% by weight of a mineral aggregate and not more than 25% by weight of asphaltic material, a spirally wound sheathing covering said mastic, and a separate spirally wound fibrous covering exterior of said sheathing, said fibrous covering overlapping the joints in said sheathing, and a layer of flexible asphaltic material adapted to become readily deformable at temperatures of between 1201'70 F. between said sheathing and fibrous covering.

6. A protecting coating for metallic bodies comprising a layer of bituminous mastic capable of resisting deformation adjacent the metallic body, a coating of bituminous primer between said mastic and metallic body, a spirally wound fibrous sheathing covering said mastic, a separate spirally wound fibrous covering exterior of said sheathing, said fibrous covering overlapping the joints in said sheathing, and a layer of deformable asphaltic material between said sheathing and fibrous covering.

JOSEPH F. PUTNAM.

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