Lxperiments on
Pipe Coatings CHARLES FITZGERALD AND M. G . JOHNSON Sinclair Refining Company. Fort Worth, Texas
hlOS(,; the inany nnd uarious coating materials teated a t Gpinrtle To11 Golly there lias emerged one shield of soiiic ~~~i~iriist-nar,iel~;, ct:Ilriloid or cellulose iiitratc plastic. On tlie original specimen, tlie celluloid was apFilied i n two spiral maps of transparent stock 5 mils thick and lmiiled to t,lre pipe rvitli an adliesive. After three years in a liiglrly corrosive mil, and oiie that subjects a coating to extreme stresses, thc results were so satisfactory that tests on ail operating line appeared to lie warrnrited.
Celluloid Applications The first application was iiiarlc in February, 1934, using clear stock celluloid :i inils tliick, arid black stock celluloid 8 m i l s thick, over a hot asphidt coating on a (;-inch lime in a soil kiiirwii to be enrrosivt:. In the past three years this coating lias treeii inspected several times; the results of the .July, 1937, inspection are illustrated in Figure 1, clear celluloid, and Figrrre 2, black celluloid. A s a result of these first inspections, a quantity of eell~il~~irl lias been rirecl in nee there t as no clreniical or physical diiTereiice; except, d , R concolor, iietweii tile Clear nriri black stock c e ~ l ~ i h ibut si(lcr:tl,le diffen:nce in pice, the latter was selected. A 10clioseri iii prefrw?ncoto the original 5- or 8. to reduce tlic proldility of breakage from clrxls or I Y J C ~ Sin the trerieli bottoin. The first repair nrarle 7%-itlia IO-mil I)lack celluloiii sliielii v a s over two eoats of cold black paint with a flood coat of the same paint. The first coat, was thinned for a primer and allowed to dr>- Iiad, Ijut to the second coat a11 oil was adrietl to delay dvyiiig. In order to keep the paint soft for an iiiMiiiite period, tlie celluloid \vas wrapped a few minotcr d t e r applying the secoiiil paint, coat., :toil the spiral butt, joint was sealed with a 1.5-incli strip of celluloid, as illustrated i n Figures 3 aiiil 4. At first a special et:lluloiii cement was iiretl to s e d t,lie strip hut later this was discontinutxl Irecause of difficulties ericoiintered in preventiirg foreign matter froni contaminating the cement and iiestroyiiig its bonding properties. In Vigiire 3 tlie strip is being sealed with an ap~)licationd the cold paint. l'liis proved to be uiisatisfactor?. in:iiause it was difficult to obtaiii a slricld tight enough to iireiwt drying; as a result, the Irlack paint cracked and did not prixiile coverage of tlie pipe surface. Considerable
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I n the softening process it will expand 5 per cent and, upon drying, will shrink 12 per cent, which accounts for the tight fit around obstacles such as collars, girth welds, edges of half-soles, and over pit welds. The softening solution will cause disintegration if it contains too much ethyl acetate or alcohol, which is apparent when softening progresses unevenly. Each mixing of the solution is a n experiment and must be regulated to soften the celluloid uniformly in about thirty minutes, so that it may be easily formed without tearing. The softening action may be retarded by adding water and accelerated by adding alcohol. Figures 6 and 7 illustrate the perfect fit obtained over collars and welds. These photographs were taken after the coating had been underground for two years. The condition in Figure 7 is most difficult to wrap because it is at the end of a whole sole, or sleeve, and near a girth weld having a n adjacent pit weld. The edges and ends of form-fitted sheets lap the adjacent smooth-wrapped celluloid and are cemented, forming a tight joint.
Methods of Repairing Pipe Lines After successful results over a period of more than two years, the method now in use on repair work is as follows: COATING.One application of No-Ox-Id “A” Special applied by hand on pipe that has been cleaned, as well as possible, with hand scrapers and gasoline. The only variation is that No-Ox-Id “A” grade is used during midsummer instead of “A” Special because it has a heavier body and thereby provides a heavier coating. SHIELD. One spiral lapped wrap of 0.010-inch thick black stock Pyralin 8.5 inches wide, over smooth pipe surface, half-soles and whole soles with a lap of about 1 inch. The same material is softened in a solution for application over collars, girth welds, and ends of half-soles or whole soles. In locations where the line may be buried very deep, or across creeks and rivers where it may be inaccessible during flood periods, two wraps of Pyralin are used. The second layer is wrapped spirally directly over the first without a n intermediate coating and in such a manner that the center of the sheet on the second wrap is a t the lap of the first wrap. Cementing of the outer wrap is advisable if there is liable to be sufficient line or soil movement to slip the shield the length of the lap. The slipping of the shield has been found on only two inspections, and experiments are now in progress to devise a method for preventing it. Since the lapped joint next to the coating cannot be satisfactorily sealed, it is believed that a strip about one inch wide laid along the top
of the line and cemented a t the center of each turn will hoId the shield in place indefinitely.
Rubber Another coating with some promise, although as yet in the early experimental stage, is pure rubber. It is made up in rolls of any length backed by parchment paper to prevent the successive layers from bonding. Figure 8 illustrates the method of application. The pipe is cleaned, and a special rubber adhesive is applied and allowed to dry for about fifteen minutes, or until it becomes tacky. The rubber is then spirally lap-wrapped over the adhesive with a 50 per cent lap which results in a coverage of two thicknesses or about 40 mils; this coating is shown in Figure 9. A curing solution is then applied by brush, followed by a wrapping of the original parchment paper. In Figure 8 one man is applying the curing solution ahead of two wrapping the paper. After nine months underground on a 6-inch line in a red clay soil, a considerable portion of the paper had rotted and the coating was wrinkled from stressing, but it is still providing excellent protection. Nipple samples which have been buried at Spindle Top Gully for two years show as little deterioration as the line installation described above. The rubber coating has the particular advantage over more rigid shields in that the wrapping angle may be altered at will, as it is very pliable and will stretch. Obstacles such as pit welds, ends or edges of half-soles, and girth welds present no wrapping difficulty; the spiral may be continued over them without bulging or tearing. Figure 9 shows the perfect fit around edges and over-lapping ends of two halfsoles. Contrary to expectations, it is not easily punctured by rocks or clods. Its ductility is comparable to that of rubber used in automobile tires, although it may be permanently elongated before it is cured. The curing solution now used requires about seven days to complete its action. This fact makes it necessary to use the parchment paper to protect the rubber from soil contact while curing progresses. If it were possible to leave the line exposed for seven days the paper would not be necessary. No cement or adhesive is used a t the laps because the joint is self-bonding. This product is not yet ready for the market as laboratory experiments are being conducted to develop an adhesive which will bond the rubber to the pipe even though the pipe is not cleaned to bright metal. RECEIVED December 31, 1937. Presented before the 4th Conference on Underground Corrosion, Washington, D. C., November 15 to 17. 1937.
Coal Hydrogenation-Correction’ I wish to correct a misinterpretation of the data of Horton, King, and Williams [J.Inst. Fuel, 7, 85 (1933)] made in my paper on the chemistry of coal hydrogenation which appeared in the December, 1937, issue of INDUSTRIAL AND ENGINEERING CHEMISTRY.
J. C. King has called my attention to the fact that in experiments 1 t o 4 of Table I (page 1368) the rotation of the converter served t o agitate the contents, and that a loose metal stirrer was also employed t o assist in the mixing. In experiments 5 t o 7 the converter itself was not rotated, but a mechanically driven “: 1 Published by permission of the Director, Bureau of Mines, United States Department of the Interior.
(Not subject to copyright.)
stirrer was used to agitate the contents. Comparisons of any of experiments 1 to 4 with any of experiments 5 to 7 cannot yield reliable information as t o the effect of agitation since there was some agitation in both sets of experiments. There were also other essential differences in procedure which make comparisons between the two groups unsound. However, all comparisons made between experimentsof the same group-that is, 1 t o 4 or 5 to 7are sound since they are not affected by the experimental differences between these two groups. H. H. STORCH CENTRAL EXPERIMENT STATION, BUREAUOF MINEB, PITT~BURQFI, PA. February 1 , 1938
