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STAINLESS STEEL, Experience in Iwo Naval Applications corrosion resisting steel in war- ships of the United States navy have been circulating for several months, and finally reached publica- tion saying the navy had decided to eliminate such steel from vessels now under construction, This bad news (quite inaccurate) has traveled fast, and, although quickly denied by re- sponsible naval officers, has disturbed many consumers of the corrosion re- sisting steels, and raised some doubts as to the utility of these alloys for severe service. The facts are worthy of record: The bureau of construction and repair, United States navy, has been interested in corrosion resisting steels ever since their commercial production. They - offered opportun- ities for weight saving and perman- ence when replacing galvanized steel or wrought iron; the latter either had to be used in extra heavy section to provide for corrosion losses or re- placed before the ship became ob- sclete. R corres of serious failures of Weight Saving Important Weight saved on the top sides in- ereases the stability of the ship and permits an equal increase in power plant or armament. Consequently the navy has put an important tonnage of strip and sheet analyzing 18 per cent chromium, 8 per cent nickel (the so-called 18-8) into deck houses, floors, hatch covers, and a variety of other structures exposed to atmospheric corrosion in port and to dashing spray or water in a seaway. In these places the metal has served excellently, and the navy has no in- tention of avoiding such uses in the future. The same may also be said of some other applications of corro- sion resistant steel where the metal is attached to the hull so it is sub- merged almost continuously, such as rods and arms for operating diving fine on submarines, and stranded wire cabies for mooring. These satisfactory results encour- aged the naval constructors to pu: corrosion resisting steel into two ap- plications in which unfortunately it did not stand up—namely, gasoline stowage tanks and fire lines. Let us examine the circumstances surround- ing such failures. Salt water is pumped into the bot- tom of the tanks so the gasoline can be drawn off under hydraulic pres- Reprinted in part from an editorial published in the February issue of Metal Progress, the monthly magazine of the American Society for Metals. HE navy is continuing without interruption a very large use of stainless steel sheet and plate in floors, partitions, deck -h ou ses; hatches, and numberless other places where the metal is exposed only intermittent- ly to: sea: water. Abundant experience proves its remark- able resistance to such condi- tions. The navy is abandon- ing a much more limited use of stainless steel in pipe lines and tanks where sea water, more or less stagnant, is con- stantly in contact with the metal. Under these circum- stances deep pits are cor roded into the metal The Calise and cure are not vet discovered, although inten- sive research is under way. W. H. Eisenman, Secretary, American Society for Metals sure at all times; consequently the stowage tanks contain variable quan- tities of gasoline, doped with tetra- ethyl lead and ethylene dibromide, and sea water more or less fouled with marine organisms or diluted sewage. Tanks on the first aircraft carriers had been made of galvanized steel plate, welded, with welds tinned —a reasonably satisfactory construc- tion. On the newer ships the tanks were to be built into the hull in quite inaccessible locations, and the use of 18-8 promised absolute immunity frcm leakage (most dangerous in confined spaces aboard ship!) for the eutire life of the hull. Experience With Fire Lines The second unsatisfactory experi- ence was with fire lines of thin- walled seamless tubing, installed on the latest 10,000-ton cruisers. In older ships galvanized steel or iron pipe has been used, much heavier in wall thickness and of less life than the hull. It was anticipated that the 18-8 would resist sea water perfectly, and not only save considerable weight, but also the cost of expen- MARINE REVIEw—March, 1935 sive replacements. In both situations the stainless steel failed by pitting in as short a time as six months! These two are the applications which have given all the trouble, which are being removed from existing ships, and which will not be resumed until the cause is definitely known and cured. It would ke a dis-service to corrosion resist- ing steel to gloss over the facts, and allow other users to stumble into similar troubles, A multiude of laboratory salt spray tests and extensive naval ex- perience prove that commercial 18-8 totally resistant to common _ sgalt (sodium chloride), sea salt and sea water when moving vigorously and aerated, or to seashore and marine atmospheres. Trouble by pitting ap- parently exists only in stagnant sea er harbor water, and there is not the least cause for worry about a multi- tude of applications in dozens of in- dustries where chloride ions, stag- nant solutions, and foul deposits are not encountered or not permitted. Very serious study has been given to these failures, both by naval per- sonnel and various metallurgists. It would be well to list some of the find- ings to date. Heat Treatment Questioned The first gasoline tanks were of welded plate, and the heat treatment subsequent to fabrication was im- properly done. Damaging pits oc- curred in locations where the metal had not been quenched _ rapidly enough in final heat treatment, a condition which makes 18-8 suscept- ible to intergranular corrosion, as is well known. To avoid this condition on later tanks they were made of metal higher in alloying elements (approaching 19 per cent chromium, 9 per cent nickel), lower in carbon (below 0.06 per cent), and unusually clear of solid nonmetallic inclusions —-all matters which are believed to increase the stability of the alloy— yet serious pitting occurred in a few mecnths! Location of these pits could not be correlated with welds, bends, or position of plate. Large areas were unaffected. Some pits were so small or tightly closed as to elude careful inspection and were located only by “weeping’’ of gasoline outside. The under-surface cavities, when cut into, are of various shapes, and contain entrapped moisture so_ tenaciously that bubbles of corrosion products are exuded even after months in dry. warm storage. Others are open at (Continued on Page 36) Eve