January, 1929
IA\-D USTRIAL ALVDE,YGINEERIXG CHE-MISTRY
s compositions
of the alloys tested are marked in Figure 1. Those best suited for wiping purposes were found to fall on the line drawn from the lead vertex of the equilibrium diagram to the ternary eutectic point. These alloys, during equilibrium cooling, form no binary eutectic. The cooling is therefore very similar to that of a lead-tin solder. Several of these lead-tin-cadmium solders have longer cooling ranges than standard solder. This gives the splicer more time to wipe the joint. Of the satisfactory lead-tin-cadmium alloys that composed of 68 per cent lead-23 per cent tin-9 per cent cadmium is the cheapest. The substitution of this solder for the standard
19
62 per cent lead-38 per cent tin may effect a saving of several cents a pound. Conclusions
I-The addition of cadmium makes Possible the use of higher Percentages of lead in satisfactory solders. 2-These lead-tin-cadmium wiping solders are generally cheaper than corresponding lead-tin solders. 3-A solder containing 68 per cent lead-23 per cent tin, and 9 per cent cadmium is satisfactory as a substitute for standard 62 per cent lead-38 per cent tin solder.
Protection of Underground Pipe from Corrosion‘ A Method Used in Southern California E. 0. Slater SMITH-EMERY COMPANY, 920 SASTEE ST.,Los AXGELES,CALIF.
HE distributing systems of gas and water companies represent 65 to i 5 per cent of their invested capital and a large proportion of oil companies’ capital investment. The proper protection of this tremendous mileage of underground pipe-over 150,000 miles with its capital value of $1,500,000,000-is of vital and growing importance. The enormous annual repair bill represented by pipe-line corrosion mill probably increase rather than decrease, as a large amount of this pipe has been in the ground long enough for accumulated deterioration to demand attention. The average expenditure for protection is 1.6 cents per foot of pipe for each inch in diameter. This is a very small amount when compared with the cost of reconditioning or replacement while endeavoring to maintain efficient and dependable service. The methods suggested for protecting against corrosion are :
T
(1) Manufacture of corrosion-resistant pipe Progress is being made in this direction by the use of an all-alloy pipe or an ordinary pipe with a resistant shell, although costs, so far, are prohibitive. (2) Modification of the condition of soil, as placing the pipe in Portland cement or lime. (3) Use of protective coatings, This is the method most in use.
The rate of corrosion is determined in a broad way by the character or the soil and the soil mater. Therefore, any coating, t o be effective, must keep the soil and water from contact with the pipe. As one eminent chemist puts it, “Pipe will not corrode if you keep the moisture from it.” As soil corrosion falls within the scope of electrochemical theory, it follows that, if the pipe in only known bad soils is protected, then the rest of the line, even in good soil, will be more or less affected. Therefore, the whole line should be protected. Old lines or products of corrosion should not be placed in proximity t o the new lines, as electrochemical action is stimulated. There are several methods of determining the corrosive power of soil. Among these are chemical analysis; ability to conduct electric current; rate of giving off gas when mixed with iron; and loss of weight of iron placed in the soil. These tests are of value when checks are run a t the same time on soils of known corrosive power. 1
Received August 21, 1928.
Method of Application of Coating
If the protective coating is expected t o preserve the pipe, it must be applied t o a clean, hard surface with which it can form a permanent bond and to which it will adhere tenaciously. The surface of the metal must be cleaned of all mill scale, rust, dust, and all traces of oil, grease, and moisture. Mill scale is electronegative to iron and steel and this tends inevitably to stimulate pitting. Even on new pipe mill scale is only a thin, brittle, loose covering, and if painted over will crack off because of the different coefficient of expansion between it and the pipe. Pipe may be cleaned by wire brushing, scratching, filing, hammering, pickling, and sandblasting. Sand-blasting is the only method that gives a really clean surface with the least damage to the pipe. The cost of sand-blasting, as shown in a paper2 by Fred Benson, of Los Angeles Gas & Electric Company, runs less than 2 cents per lineal foot of pipe 4 inches in diameter. The unit cost reduces as the diameter increases. Note-Since this article was written one of the large companies has installed a plant especially equipped for sand-blastlng pipe commercially, which charges one cent per square foot of surface
The application of the protective coating is usually the last thing done t o the pipe before lowering into the ditch and backfilling. For this reason the job is hurried by the men and slighted by the contractor and the result is generally little protection. Quoting D. R. Hiskey, of the Engineering Department of the Southern California Gas Company, “If we cannot afford to apply properly, why try to protect a t all?” Pipecleaning and -coating crews should be hand-picked men who could be trained and relied upon to keep up the standard of the work. This part of the work should be dignified as an art for skilled labor as much as welding and should take its place as one of the important parts of pipe-lining. Inspection should be rigid and made by men familiar with the product being used. Types of Coatings
Protective coatings available for underground pipe lines are : (1) Bituminous, as native and residuum asphalts, coal-tar pitches, and gilsonite. These are applied cold as paint or hot by dipping or pouring.
* Western
Cas, 4 (May, 1928).
I N D U8TRIAL A N D ENGINEERING CHE.MISTRY
20
Wrap Applied to Joint in the Field Note perfect bond a t weld and oveilapp+a section: also ciiss-cros~ method 01 w r w p m g .
(2) Reenforcing wrawers of felt, cotton, or mineral fiber usually impregnated with bitumen. (3) Metal coatings.
K. H. Logan,3 U. S. Bureau of Standards, says:
Vol. 21,
so.I
Pan-American Line, rhrouah Salt Slough, near San Pedro, Calif. This line was givea a “McEverlart” wrap to protect from salt slush, se seen in bottom of trench.
of the bitumens and dissolved in a suitable volatile tbinner, is first applied, by hand-brushing or ragging on wit,h a c a n v ~ s sling. In either case it is rubbed well into the pipe and is put on immedi&ly after sand-blasting, whether in the field or
The test has already shown definitely that rapid corrosion may occur without the presence of stray currents and that electrolytic corrosion cannot he distinmished from soil action
z
Oil Gal 3.. P6, No. 4 (1928).
on the coating material (“McEverlast” Electrolysis Paint),
IhTD USTRIAL AND ENGINEERING CUEMISTRY
January, 1929
"McEverlsst" Osnaburg Wrap Beine Applied fo 8-Inch Plpe Coating underneath wrap ~oadrtsof one teat of ".McEuerlast" Penetration; and two coats of Elecriolyris ProofCoating.
using soil from this ditch as the electrolyte. This was done as indicated above: Three specimens of '/&mh pipe were painted with one coat of Electrolysis Penetration Coat and two coats of Electrolysis Cover Coat. Three days were allowed between coats for drying. These three specimens of painted pipe were used as one electrode and a battery carbon as the other electrode in a 5 per cent salt solution as the electrolyte. Current was furnished by three dry cells connected in series. The painted pipes were immersed 31/4 inches in the salt solution. 'The carbon (7/s inch in diameter) was immersed 31/4 inches in the same salt solution. The distance between eiectrodes was about 1'/2 inches. The dry cells were of a capacity of 30 ainperes and 2 volts-a total potential of 6 volts for the three cells in series. Analysis of Soil Silica . . . . . . . . . . . . . . . . . . . Ferric oxide.. Ferrous oxide.. . . . . . . . . . . Alunlinlrm oxide.. . . . . . . . Caldum oxide.. Magoesium oxide.. .......
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Mansanere oxide.. ....... g&d
