A few days ago I saw the turret and the two Dahlgren guns undergoing a 7-year process of electrolyic reduction to remove chlorides from the iron. The massive parts are submerged in large tanks and every once in a while a bubble of gas breaks the surface. Without this procedure the iron deteriorates rapidly after exposure to air; an untreated cast iron deck plate is already breaking up despite washing and painting. http://www.monitorcenter.org/preserving/
Would the steel of the turret and guns of the "Bismarck" also require such an electrolytic reduction process after being hauled up? Are the untreated pieces of the Graf Spee starting to flake and split? http://bobhenneman.info/gss.htm
Electrolytic Reduction
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Ulrich Rudofsky
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Electrolytic Reduction
Ulrich
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Dave Saxton
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Hi Ulrich,
I don't know what to degree this kind of thing may be needed. I don't know the chemical composition of the gun tubes, but the composition of the armour plates is such that chloride corrosion would be greatly retarded. Chroride induced corrosion is greatly reduced by combining modest amounts of chromium with small amounts of molybdenum. This is why 316 stainless steel is often specified for extreme conditions in place of 307, 308, or 310 stainless. I have it on good authority that the USN began to sometimes use 316 in place of 310 for welding STS in the Pacific yards. 316 stainless steel combines a Cr eqivilancy of about 21%, and a Ni eqivilancy of 16%, with about 2-4% Mo. Copper is especially good at slowing corrosion, and this is amplified in the presense of MO an Cr. The German FoxA7 used weld Wh and Ww obtained these eqivilancies by using 5-6% Mn.
The Wh and KC plates used on German warships all contained these elements in high enough amounts to reduce corrosion significantly; compared to standard carbon steels, and especially cast iron. Even most ST52 structural steel usually contained significant copper and manganese. Some German ST52 compositions listed in German documents, from WWII, lists as much as .30% Cu.
I don't know what to degree this kind of thing may be needed. I don't know the chemical composition of the gun tubes, but the composition of the armour plates is such that chloride corrosion would be greatly retarded. Chroride induced corrosion is greatly reduced by combining modest amounts of chromium with small amounts of molybdenum. This is why 316 stainless steel is often specified for extreme conditions in place of 307, 308, or 310 stainless. I have it on good authority that the USN began to sometimes use 316 in place of 310 for welding STS in the Pacific yards. 316 stainless steel combines a Cr eqivilancy of about 21%, and a Ni eqivilancy of 16%, with about 2-4% Mo. Copper is especially good at slowing corrosion, and this is amplified in the presense of MO an Cr. The German FoxA7 used weld Wh and Ww obtained these eqivilancies by using 5-6% Mn.
The Wh and KC plates used on German warships all contained these elements in high enough amounts to reduce corrosion significantly; compared to standard carbon steels, and especially cast iron. Even most ST52 structural steel usually contained significant copper and manganese. Some German ST52 compositions listed in German documents, from WWII, lists as much as .30% Cu.
As a chemist, I don't believe Krupp used a long and expensive process of electrolitical passivation on they guns barrel to avoid corrosion, but I agree with Dave about the steel composition of the Wh and KC paltes of hardened steel: those material are designed specifically to resist corrosion in sea ambient (and you know salt and alogenous present in sea air, are catalizator of O2 reduction of metallic iron), apart the fact they are projected to improve rswsistance to blows, and explosions.
"Wir kämpfen bis zur letzten Granate."
Günther Lütjens
Günther Lütjens