THE EVOLUTION OF LEAD-LINED PIPING ON SHIPBOARD.
By Naval Constructor R.D. Gatewood, U. S. Navy.
There is probably nothing on a modern man-of-war that causes as much constant trouble both for the ship's force and the navy yard as the various piping systems. Certainly there is nothing upon which "all the law and the prophets" have so often disagreed both as to the cause of the failure of the pipes and as to the means for preventing it.
Before describing the process which is believed to be the last, or rather the latest, word toward the removal of the difficulties, it may be of interest to review the history of the corrosion on board ship of the non-ferrous metals used in these systems together with the results of some of the leading investigators of this subject.
Instances are on record in the early 18th century of serious corrosion of the iron fastenings of vessels sheathed with lead, which sheathing was accordingly abandoned and copper, with copper fastening, used in its place.
Occasional cases of serious corrosion of copper sheathing still arose and Sir Humphry Davy about 1820 conducted some experiments along preventive lines, the results of which were to show that the sheathing was perfectly protected when the ratio of its area to that of the protective metals, iron or zinc, was approximately 1000 to 1. For a while this form of protection was used but it was found that the iron or zinc required very frequent renewal and the sheathing thus protected was much more easily fouled by marine growth than when not protected, and the scheme was abandoned.
In 1832 Muntz metal replaced copper as sheathing, and for a long time there was comparatively little trouble with sheathing or piping except in isolated instances and many officers now living can well remember the pride with which the chief engineers of the old navy would exhibit the highly burnished copper piping in the bilges at Sunday captain's inspection.
When iron and steel came to be universally adopted for hull construction a new problem arose. The copper pipes, bilge water, and steel floors and angles and the shell formed an excellent electric battery and very serious corrosion of the electro-positive steel resulted as a consequence of which copper pipes in the bilges were reduced to a minimum. There is an instance of a vessel that was run ashore to prevent her sinking from a hole in her shell caused by a copper strainer in a bilge suction pipe.
Another period of comparative immunity ensued until the general introduction of electricity on shipboard, and from that time until the present the trouble has been constantly increasing. The increased steam pressures occurring about the same time were frequently blamed for some of the difficulties, but in the light of the modern electrolytic theory of corrosion they may safely be eliminated as a cause.
Nature of the Action
The action occurs in the valves and piping of the fire, flushing, drainage and fresh-water systems, and in the tubes of condensers and distillers. It takes several characteristic forms, among the most common of which are as follows: Sometimes the pipe is eaten through in pin-holes; sometimes the holes are as large as one-half square inch in area with sharp, clean-cut edges as though punched; again they are pitted and honeycombed as though the pipe had a disease similar to smallpox; and still again there are long clean-cut longitudinal grooves in the tubes or pipes. Corrosion is found generally at or near the bends, branches and valves In the case of ordinary piping the pits or holes are usually found in the top of the pipe and near the flanges while in condenser tubes about 80 per cent of the pitting is found in the bottoms. Throughout the whole phenomenon the action has been found to be exceedingly erratic. Under conditions where corrosion has been found to be most virulent cases are encountered which, while apparently similar in every respect, show most excellent states of preservation.
The Principal Facts Established by Early Observers
The causes for the above observed results are the subject of much controversy and the literature on the subject while voluminous is contradictory and confusing in the extreme. Out of the maze of it all the following may be considered as the facts established prior to the exposition of the electrolytic theory of corrosion:
- Corrosion is due largely to electrolytic action. ( No adequate cause was assigned for this fact.)
- Corrosion is accompanied in practically all cases by dezincification, that is the zinc that was in the metal is eaten out.
- Pitting is due to any one or all of the following causes: (1) local segregation of impurities in the metal. (2) the presence of deposits of impurities such as carbon, lead, iron, etc., derived from outside sources, and (3) the presence of stray electric currents.
- Tin, when present in brass or copper in solution up to 1.5 per cent, or when plated, retards corrosion.
- The longitudinal grooves are due to the fact that certain impurities are drawn out along the surface of the tube during the process of manufacture.
- Electrolytic copper although the purest of metal (the writer has had analyses made that show it to be 99.96 per cent pure), is more readily corroded than brass or copper made by the usual process. This is a striking fact because other things being equal, the purer and more homogeneous a metal the less liable is it to corrosion.
- Electrolytic copper should not be used in the manufacture of Muntz metal.
- When material is strained as in unequal cooling of the surface or where the metal is upset and bruised as in riveting, corrosion is much more rapid.
- Thick tubes or pipes are more resistant than thin ones.
- Corrosion is accelerated by increasing the temperature of either the metal or the solution in which immersed, hot sea water being much more effective than cold.
- The presence of air and carbon dioxide increases corrosion.
Means of Prevention
A knowledge of these facts has resulted to produce many and varied recommendations as to the best means to be adopted to prevent corrosion, the most important of which, up to about 1905, are the following:
1. The use of the more electro-positive metals such as sheets or slabs of iron and zinc in direct metallic contact. Our navy uses zinc slabs inserted in zinc boxes installed in pipe lines from 30 to 40 feet apart. A photograph of this type of box is here shown. The British use cast iron freely. This they say is equally as effective on account of better metallic contact and being much cheaper and easier to insert, which they do by means either of cast strips and rods let in among the tubes in condensers or short lengths of cast iron pipe in their piping systems.
2. The use of some form of coating to protect the surface of the metal from contact with sea water. One school of engineers and chemists advocated the use of non-metallic coatings, such as marine glue, varnish, lacquers, asphalt, porcelain and special forms of cement and wax. The best known form of this type was that called the Sabin process, named from its inventor Professor A. H. Sabiu, and used extensively for several years in our navy. The process was expensive, involving as it did very careful cleaning of the pipe, dipping into a patented hot liquid coating and baking in a special oven at a constant temperature with the pipe on end Properly applied it did protect the piping but like all other coatings of this nature, it eventually cracked, scaled or eroded off with consequent clogging of small branches, valves and strainers, and further, in those spots where this occurred the corrosive action was materially intensified. For these reasons it was abandoned
Another school advocated the use of metallic coatings and the most common were tin, lead, and tin-lead alloys. Until the present lead-lining process was perfected it was very difficult to apply these as entirely unbroken coatings free from pin-holes that seriously increase the corrosive action. Also they were not durable owing to their slight thickness.
3. It was recommended that the tubes or pipes be kept free from foreign particles by being constantly cleaned out, a proceeding as difficult as it is expensive.
4. Every care was to be used in preventing the access of stray electric currents to the piping or tubes.
5. Care was to be taken in the manufacture (1) to obtain a homogeneous mixture, (2) to prevent the presence of any impurities, and (3) to produce metal with an absolutely smooth surface, free from air holes and strains due to cooling or mechanical working.
Electrolytic Theory of Corrosion
The above was about the extent of knowledge on the subject prior to the advent, about 1906, of that very satisfying theory of corrosion known as the electrolytic theory which was largely due to the researches of the American investigators, Cushman, Gardner, and Walker. It was about this same time that the present process of lead-lining was begun in earnest and since then very considerable progress can be reported.
The most important additions to our knowledge of corrosion phenomena due to the application of this theory are:
1. All metals and alloys when in contact with dilute acid or water, either pure or containing salts in solution, tend to pass into solution in the form of ions.' This tendency is known as the solution pressure of the metal and each one has a definite and characteristic solution pressure in a given solvent which depends only on (1) the temperature and (2) the number of its own metallic ions in the solution.
2. Ordinary metals dissolve or are corroded because they are not chemically and physically homogeneous.
3. A perfectly homogeneous metal will not corrode appreciably in pure water. The reason for this will be given in a later paper. It is practically impossible to obtain an absolutely pure metal free from strains by any means now employed. It will corrode slightly. but so slightly that the amount cannot be measured. (For explanation of corrosion of pure electrolytic copper see later.)
4. Metals and alloys may with some minor exceptions be arranged in a definite order in which they tend to pass into solution. This order corresponds, interestingly enough, with the order of electro-positiveness of the metals and for the ordinary metals and oxygen and hydrogen is as follows: Zinc, iron, tin, lead, hydrogen, copper and oxygen.
5. Opposing solution pressure there is another real pressure of considerable magnitude known as osmotic pressure, which is that due to the tendency of the ions dissolved off to pass back into their former state of metallic atoms, and may be readily pictured as corresponding to the pressure of a gas on the walls of its containing vessel. The pressure tends thus to prevent the entrance of more ions into solution.
6. A metal or alloy will be corroded by a solution that contains ions of a more electro-negative nature than the metal or alloy itself. Thus, referring to the above list of metals, zinc will corrode rapidly in a solution of copper ions, iron will corrode slowly in a solution of lead ions (on account of the nearness of the two metals in the electro-positive scale), etc.
7. When an ion of a metal passes into solution it takes on a positive electric charge leaving a negative one on the corroding metal. Now this negative charge sometimes, as in the case of water, attracts a positively charged hydrogen ion that is in the water and tends to form on itself a plating of hydrogen which will hinder further action. If though there be present in the metal or solution a substance such as oxygen, or air, which will combine with the hydrogen to form water and thus remove it from the surface of the corroding metal, it will give up its positive charge when it thus combines with oxygen, thus neutralizing the negative charge on the zinc, another ion of the zinc will be thrown off at this point and the action will thus be accelerated. Such a substance which removes hydrogen is called a "depolariser."
8. Our old conception of corrosion by means of galvanic action must thus be completely reversed. Ordinary corrosion is not primarily the effect of an electric current but is rather the cause of the current.
9. The conceptions of solution pressure and osmotic pressure may be likened to those of gravitation and a resisting medium in space. By means of the two latter the theory of the formation of the worlds has recently been practically solved.
By means of the two former much will be accomplished toward the attainment of that other goal toward which so many minds are now bent—the conservation of our national resources.
10. The new idea of the function of the impurities is (1) that they act to raise or lower the solution pressure of the metal or (2) as depolarisers and increase corrosion, or even in the opposite sense and so retard corrosion, or (3) to produce negative and positive areas in the metal.
11. The rapid corrosion of electrolytic copper has not yet beer satisfactorily accounted for. Analysis of this copper made at Mare Island Navy Yard shows:
Iron, .02
Arsenic, trace
Lead, trace
Copper 99.97
And it would be an ideal material for resisting corrosion. The most plausible theory so far advanced is that of Bengough: "Such copper almost invariably contains a certain quantity of hydrogen gas, absorbed, or in solid solution, or present in a definite compound, and the presence of this gas may, perhaps, be the cause of a greater tendency to corrosion than that shown by ordinary best select copper." The same investigator, however, admits that the ordinary less pure copper may be protected by the presence of small quantities of a protecting impurity such as tin or arsenic.
Practical Tests of Bureau C. & R.
Keeping the above facts in mind it will be of interest to see the results of certain practical tests that have been made.
(a) Comparative test on three different vessels.—In this connection the Bureau of Construction and Repair about 1905 instituted the following test to determine the relative merits of the three forms of piping: (1) pure copper uncoated, (2) pure copper sabined, (3) pure copper tinned. The three armored cruiser Milwaukee, California and South Dakota were fitted with fire and flushing systems installed throughout in one of the above ways. Tinning proved to be the best but when the coating once began to wear off the pipe corroded as readily if not more readily than either of the others and required extensive repairs at the end of 18 months. The sabined copper and the pure copper were about equally bad, leaving out of account the very considerable inconvenience caused to a vessel in full commission by the constant clogging of small branches and valves due to particles of the sabine coating.
(b) Sabined copper pipe and copper pipe with iron wire inside.—In June, 1905, tests were made at the New York Navy Yard with copper pipe protected by the insertion of an iron wire in the form of a helix in contact with the pipe. A 6-foot length of standard copper pipe 6 inches in diameter was fitted with a helix of wire, size ¼ by 1/16 inch with 6-inch pitch, the end of the wire being soldered to the inside to avoid lateral movement. The ends of the pipe were flanged and blank flanges fitted. These blank flanges were tapped for ½-inch galvanized-iron pipe connections. Sea water furnished the circulating pump of the power plant was run through the copper pipe continuously by means of the small end pipe connections. The test was started June 23, 1905. On November 25 the pipes were removed for examination. The iron wire had disappeared entirely except for a section about 18 inches in length near the outer end of the pipe, which was corroded so that the size was reduced to 1/8 by 1/64 inch. The interior of the pipe contained about 1 quart of muck and a thin film of iron oxide remained on the inner surface. The copper itself was in practically the same condition as at the start, there being no loss of weight.
The test was continued and made a comparative one between similar sections of copper pipe, one plain and the other sabined. The original pipe was fitted with a new helix of iron wire and all three were set up with blank flanges and i-inch inlet and outlet pipes as originally arranged. The new test was started on April 15. 1906. On November 9, 1906, the pipes were examined. All three pipes were half filled with muck and small shells. The plain copper pipe showed a moderate amount of corrosion near the ends, but was in good condition along the middle. The pipe coated by the Sabine process was in as good condition as when installed; the interior was, however, covered with barnacles and shells. The copper of the pipe fitted with the iron helix was in excellent condition, showing practically no pitting, but the iron wire had disappeared completely except for a length of about 3 inches, which on being touched crumbled into rust. In view of the fact that the wire helix disappeared in so short a time, and to the consequent impracticability of renewing the wire on board ship at such short intervals, no further tests were made.
(c) Lead-lined pipe at the Norfolk Yard.—In 1906 experiments were made by Naval Constructor Stocker at the Norfolk Navy Yard that resulted in the present method of lead-lining. Experience with lead- and tin-lined linings had been confined to screwed connections which had proven more or less unsatisfactory at the joints. Mr. Stacker's idea was to use seamless drawn steel tubing, galvanized to increase life against external corrosion, lined with an unbroken coating of lead forced by high pressure into intimate contact with the tubing, using throughout only flanged joints. The success of this method was clearly demonstrated by the following facts:
(d) Electrolytic tests of various pipes at the navy yard, Sett York.—At the New York Navy Yard extensive electrolytic tests were undertaken in 1906-7 with various kinds of protected pipes. These included plain copper, sabined copper, galvanized iron, galvanized iron with zinc box, and plain brass. All the pipes were connected to a brass header at one end, the other end being blank-flanged with a small screwed outlet connection. Water was supplied the header through a rubber hose. The pipes were supported on wooden chocks insulated with sheet rubber. The five pipes were connected in parallel with a storage battery of 300 ampere hours' capacity. The voltage of this battery varied from 2 to 1.8 volts from charge to discharge, but by means of the resistance wire and the rheostats in the circuit it was possible to maintain practically a uniform current. The connection of the pipes to the header was made to resemble as nearly as possible the conditions on ship, these connections being of composition, representing the pump and pump cylinders. In each case a large globe valve was connected to the pipe at the header end. The following was the calculated division of current in the pipes (it being assumed that the resistances of the pipes remain unchanged) during the first period of the test:
Pipe No.
| Amperes
|
1. Copper pipe
| 1.00
|
2. Galv. iron pipe without zinc box
| .378
|
3. Galv. iron pipe with zinc box
| .359
|
4. Brass pipe
| .608
|
5. Copper pipe sabined
| .191
|
In December, 1907, the pipes were examined and showed the following results of test: The brass pipe at the valve end had an almost continuous circle around the extreme edge of large pits about 1/8 to 3/16 inch deep by ¼ to ½ inch long in addition to a number of well-defined deep pit-boles, some as large as 1/8 by 3/16 inch deep. The entire length of pipe had a bright surface similar to brass treated with acids, due probably to the zinc of the composition being eaten away and leaving the bright copper lustre. The outlet end of this pipe was not noticeably affected. The large brass globe valve lying between the pipe and header was badly eaten around the valve seat, especially at right-angles to the direction of the pipe. This pitting had the appearance of wormholes about 3/16 inch deep by ¼ inch wide by ½ to ¾ inch long, showing bright red metal. The valve proper was not so badly affected but was pitted around its contact surface. The galvanized iron pipe protected with zinc box was in excellent condition and even some of the galvanizing still existed. The valve end was in excellent condition and even some of the galvanizing still existed. The valve end was not affected, there being only a very thin coating of rust. There was no pitting, and the threads were in perfect condition. At the outlet end there was a very slight pitting and a somewhat thicker coating of rust. The pipe was in practically perfect condition as regards pitting, although the galvanizing was, except in a few places, gone. The zinc ring in the box was eaten away more than when last examined, especially where the two halves meet, but was still serviceable. The large globe valve was in excellent condition. The unprotected galvanized-iron pipe was in a badly corroded condition at the valve end. The thread was practically all eaten away, and a coating of rust about 1/16 inch deep extended toward the interior of the pipe. At the outlet end the thread was in good condition, and there was only a very little pitting with only a very thin coating of rust. The globe valve leading to this pipe was slightly pitted around the valve seat and around the contact surface of the valve proper, but not near so badly as in the case of the brass-pipe valve. The plain copper pipe at valve end showed slight pitting around the edge of same, also a thin coating in spots of green oxide of copper which when scraped off showed a bright surface underneath. The other end showed slightly more needle-like pitting, but no green oxide. There were about 6 pit-holes about 1/16 inch diameter by 1/32 inch deep. The globe valve leading to this pipe was in excellent condition, there being only very slight pitting on both the valve seat and the valve proper. The sabined pipe coating was in poor condition, especially near the ends where the pipe was nearly entirely exposed. Through the middle of the pipe the coating was in better condition, but was broken in spots. The coating could be easily peeled off in large sheets and showed considerable flexibility. The valve and seat were in good condition. This pipe had been in actual service since April 15, 1906, having been taken from the former test in comparison with the pipe fitted with the iron helix. It was in such excellent condition at that time that it was not resabined, but connected up with the above pipes at the start of the present test on December 3, 1906.
3. There had also been connected up in parallel a length of pipe lined with lead as per process described as in vogue at the Norfolk Mavy Yard. This pipe had been in service from February to December and showed no signs of deterioration.
Reviewing these tests it is evident that aside from lead-lined pipe, the most serviceable and economical method for protecting pipes is to employ zinc boxes in connection with galvanized-iron piping. In connection with this method it is to be noted that since the above pipes had been in service the small composition valves and fittings connected with the outlets of the pipes had to be renewed because of corrosion causing bad leaks, except in the case of the iron pipe with the zinc box. The outlet valve on the brass pipe would require renewal before connection could again be made. The above tests indicated that the Sabine coating was unsatisfactory compared with the excellent results obtained from using a zinc box, or even of employing a plain copper pipe. The plain brass pipe and the galvanized-iron pipe without zinc box were unsatisfactory because of excessive pitting and corrosion.
4. On further examination in May, 1908, it was found that the lead-lined pipe had suffered no injury, the lead lining being in perfect condition.
From the above it is clear that lead-lined pipe is superior to all others for use on shipboard. The next in importance is galvanized-iron pipe with zinc boxes. The other pipes are distinctly inferior.
Further test was made by installing the same length of leadlined piping on the Tacoma in May, 1908. When examined a year later it was found to be in perfect condition.
(e) Tests on Kentucky, Kearsarge and Louisiana.—Three sections of lead-lined flushing pipe were fitted in the crew's head of the Kentucky in December, 1906, and when removed and examined in April, 1909, were found to be in good condition, with the exception of a slight deposit on the surface of the lead pipe. There was no sign of corrosion or pitting.
On the Louisiana five sections of lead-lined flushing pipe were fitted in the crew's head and one section in the fire main between frames 9 and 11 under the protective deck, port side, in December, 1907. These when removed were found to be in excellent condition with the exception of the same slight deposit as cited above on the Kentucky. Four sections of lead-lined pipe were installed in the fire main and flushing main on the Kearsarge in November, 1906, and on examination in April, 1909, were found to be practically in as good condition as when installed, and it is believed that the lead lining will be good for at least five years more. In one or two of the sections examined it was noted that there was a slight tendency of the lead lining to draw toward the ends of the pipe, caused, no doubt, by the expansion and contraction of the pipe and lining.
The marked superiority of lead lined pipe having been thus clearly shown, it was adopted by the Bureau of Construction and Repair for all salt-water pressure piping above 1 ½ inches in diameter.
Description of Its Manufacture
In repairing pipe lines brass, iron and copper piping may be lined, but for new work lap-welded steel casing (being much cheaper than seamless drawn tubing and equally as satisfactory) is used. The inner surface of this casing is first made entirely smooth by a revolving chain mop on a flexible spindle attached to a pneumatic drilling machine. In the case of old piping this is first cleaned and the pits closed by solder, wiped off smooth, and tested to a pressure of 300 pounds.
All joints are made with flanges. When repairing a pipe having several different bends it is sometimes necessary to cut the pipe at the bend and fit flanges. The flanges are counter-bored to about Vi, inch from the face of the pipe, depending on the size of the flange, and about 1/10 inch deep, or the thickness of the lead which is to be flanged over, care being taken that the edge of the casing over which the lead is bent is carefully rounded with a file.
The lead tubing used is about ¼ inch smaller than the pipe to be lined. Where bends are encountered it is necessary to pull the lining through. This is done by means of a rope led through the lead tube and then through a plug and secured by a knot. The lead tubing is then filled with dry sand by means of the machine shown in Fig. 1, covered with tallow and while the outer tube H tapped with a wooden mallet, pulled through by means of the machine shown in Figs. 2, 3 and 4.' operated by air or water pressure at from 15 to 100 pounds pressure according to the nature of the bend. Bad bends are warmed slightly by means of a gasoline torch.
The plug, sand and rope are then removed and the lead examined by inserting a small electric portable. If no defects appear the tubing is tapped over into the recess of the flange at one end of the pipe only. The other end of the lead pipe is sawed off about 6 inches longer than the pipe that is to be lined and the plug shown in Fig. 5 is fitted.
The air cock shown is opened and the pressure turned on slowly. When the air is all out the plug is closed and the pressure very gradually run up to 300 pounds. The lead pipe becomes shorter under this pressure which is then removed and the lead fitted into the recess of the flange at the other end of the pipe. The piece of piping is then blank-Hanged and treated to a final pressure of 600 pounds per square inch. See Fig. 6.
Weight and Cost
In order to reduce weight the lining should be no thicker than absolutely necessary. For sizes given in the following table the weight and thickness there given have been found very satisfactory:
Outside diameter of pipe
| Weight of pipe
| Thickness
|
1 ½"
| 2
| .088
|
2
| 3
| .099
|
3
| 4
| .088
|
4
| 5 ¾
| .095
|
The weight of such a system is about 5 per cent less than that of a similar installation of copper piping. The cost is about 50 per cent less.
Further Points of Interest Thus Far Determined.
1. The lead piping should be shipped from the works of the manufacturer very carefully packed on wooden mandrels to prevent crushing and distortion.
2. In the case of galvanized iron, wrought iron or steel tubing, the elbows, tees and other fittings are not lead lined. It has been found necessary to lead line fittings under no circumstances.
3. Old pipe has been lined with lead where the radius of the bend was twice the diameter, but it is better practice to bend the tubing to be lined to about 4 or 5 times the diameter.
4. In relining old copper pipe it is much cheaper to reline the old pipe even though it is necessary to cut out the brazed flanges and substitute flanged fittings.
5. The process does not work well on pipe above 5 ½ inches on account of the crushing of the lead tubing when drawing it into the steel casing.
6. Lead-lined piping is not adapted to suction pipes. The suction pulls the lead away from the walls of the steel casing.
7. Lead-lined piping is not adapted for use with very hot water or steam service such as bottom blow piping for evaporators, on account of the large expansion in those cases.
8. Thickness of tubing thinner than that given in the above table should not be used. Considerable difficulty has been experienced on recent torpedo boat destroyers in the attempt to save weight in this manner.
9. Special care should be used to give no crown to the lead where expanded over the recess of the flange. Unless a perfectly flush surface is thus obtained it has been found that in setting up the joint the pressure comes on the lead causing it to separate from the flange recess or to crack where bent over the steel casing.
10. Several cases of severe lead poisoning have occurred at Mare Island due to the milky oxide of lead on the outside of the tubing getting into the pores of the skin of the workmen and all the usual precautions should be taken to guard against this form of poisoning.
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