FredT
Guest
>You are pushing snake oil.
>>Aluminum is not all the same. Most aluminum plates are >made from 6061-T6.
>Pure baloney. 5000 series plate is used because it is more malleable without additional heat treatment. End of discussion.
NOPE! 6000 series failure mode in Cl ion environments is pitting. Once started this pitting is unstoppable unless the corrosion cell at the tip of the pit is mechanically removed.
The pits Ive seen in several Al plates indicate a 6000 series was used. 5000s, either 5053 or 5086, CAN be used for unwelded structural material uncoated in seawater long term. Use 5086 if welding is used inthe assembly. 6061 buoys will last about 3 years in seawater before pits start breaking through a 1/2" thick hull, but they do well in the great lakes. The National Data Buoy Center had a 6061 Nomad buoy hull # 6N10 I believe, its been a while. It pitted severely on its first deployment in cool seawater. After grinding out the thousands of pits and rewelding it to fill them it was relegated to the Great Lakes only.
5000 aluminums ARE easier to break severely since they are strain hardened, not heat-treated and don't have to be annealed between bends, but the overriding reason for using them in seawater is the corrosion resistance. The difference in fabrication effort in the plate thickness and bend angles used in plate manufacture is moot. I'm happy to hear you are using 5000s though.
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>>Note to the aluminum tank supporters: ALL aluminum tanks >>are/were manufactured of 6000 series aluminum. After 30+ >>years of throwing things in seawater I'm convinced the mix >>6000 series and seawater is not a good idea. The result has >>always been a bad thing for the aluminum.
>I guess we better all throw our AL tanks away. I have several bare AL80's that are going on ten years old, not pits, nothing but a dull surface oxidation. The insides are shiny as a new dime.
You obviously have a great fill station and rinse everything well on return from the sea. Moist air and Cl ions are bad news, as are Cl ions in a wet low oxygen environment. With the exception of a few neck cracks Al tanks will generally fail the visual before the hydro due to pitting, not the hydro itself. I estimate that 90% of all Al tanks Ive inspected that have been removed from service over the last 20 years failed due too pitting either internally or externally. Pitting internally is often due to poor fill station maintenance or fill technique. External pits are usually due to trapping saltwater against the tank or under the valve.
Aluminum tanks will work, for a while, even if not religiously maintained. If taken care of and cleaned EVERY TIME they are dove, and they are stored in a dry location (No such thing on the gulf coast unless in air conditioning) they will last quite a while. Never the less pitting is the primary failure mode. BTW many "bare" Aluminum tanks have a clear anodizing external coating.
>We'll put that aside as a spelling/grammar error. "pit in seawater, especially in area deprived in seawater"???
Sorry, it's been a long day.
That should be "in an area deprived of oxygen in seawater."
>90% of boat fittings are 304L. 90% of railings and tubular structures such as bimini supports, boat rails, davits, etc. are fabricated of 304 DOM tubing. These parts spend a lot more time in salt spray and immersion than any backplate ever will. Prop shafts, that are run through brass, fiberglass and other supports and hulls are made of 'Aquamet":
304 works fine, ABOVE THE WATERLINE and in spray zones. Below the waterline is a COMPLETELY different environment. I can't count the number of your tax dollars wasted due to someone putting 304 or 304L in a mooring. When an 18,000-foot moor is lost due to a 2" diameter 304 bolt pitting through and failing (even if it IS stamped 316!) there is close to $500K lost just in line! That doesn't count anchors, ground chain, floats, and the ship time to recover the buoy and replace it, or the lives lost and equipment damaged because the weather data wasn't available. We found that one by picking up a moor that had not _quite_ parted. A 2-4UNC nut weighed less than 2 ounces due to pitting and intergranular corrsion in less than 2 years exposure. Regrettably the vendor managed to stay out of jail even with the diffraction readings and chemicals proving it was NOT 316 as certified. I remember that one batch of hardware cost us several deep-water moors. Sorry, but I've been bit WAY too hard by 304 to ever use it for immersible parts. Even worse is the "dairy grade" 18-8 stainless hardware marked by two raised ticks on the bolt head 90° apart. The copper put in these parts to make them free machining is deadly in long-term seawater immersion. We even went so far as to surplus all 304 and dairy grade hardware (used in above deck applications) so we didn't even accidentally have a piece of 304 hardware used subsea!
BTW 316, or any other 300 series stainless, becomes more magnetic as it is cold worked or cut. That isnt the only way it gets magnetic, but it is the primary culprit for wrought shapes, machined parts and plate of known good alloy. If still magnetic after a pass through a reducing atmosphere annealing oven its time to spend the $s on checking the chemistry. I will agree that metals coming out of China, and to a lesser extent Korea, are often not what was specified though.
Aquamet is not used for shafting primarily for it's corrosion protection, even though of the high strength steels it is about the most resistant. It is used because it has roughly 3X to 5X the tensile and torsional strength of a similarly sized 316 shaft. 300 series stainless is the bubble gum of all steels. Using 316 for a highly stressed part subject to significant vibration is not a good thing.
>Glass beading addresses all these issues in a much more environmentally friendly manner. Compressed air and glass beads, not noxious chemicals that need to be disposed of.
That is a mechanical cleaning technique! I DID say that that worked.
>Pure baloney. If you arent using for explosive or other elicit production, you havent a worry.
As one of the 70% of FFL holders who got out of that business when Clinton did his "turn over your transaction documents or your civil rights" power and control grab, and a former FEL signatory at a site using over 8000 pounds of HE a day I have had way more than my fair share of dealings with ATF! I just don't want to ever waste another day with them.
Check your inorganic chemistry. HCl is not normally used to passivate for good reason, Muriatic is simply unpure HCl, and even concentrated phosphoric has to be disposed of. If you haven't tried the Coke trick, don't knock it. It works, but it's way SLOW! Its only real advantage is that the materials are available almost anywhere in the world, generally even at sea on US based ships, at a reasonable price and disposal is simple. Nitric is so much faster at the job it is used commercially, and I do specify that method for bulk parts. On a onsey twosey basis it's too expensive due to batch charges though.
Your only real "error" is assuming what works topside works subsea. The Thresher and its crew was lost due to that type of thinking. The discipline of Ocean Engineering was started in '65 to eliminate that possibility on future Navy projects as a direct result of the Thresher inquiry. Offshore oil recovery, mining, and fisheries have now all learned how valuable OEs can be, because the data you just got is NOT in the mainstream mechanical engineering texts. The understanding of corrosion of materials subsea is still in its infancy, even though we are a lot better at it than we were 40 years ago.
FT
>>Aluminum is not all the same. Most aluminum plates are >made from 6061-T6.
>Pure baloney. 5000 series plate is used because it is more malleable without additional heat treatment. End of discussion.
NOPE! 6000 series failure mode in Cl ion environments is pitting. Once started this pitting is unstoppable unless the corrosion cell at the tip of the pit is mechanically removed.
The pits Ive seen in several Al plates indicate a 6000 series was used. 5000s, either 5053 or 5086, CAN be used for unwelded structural material uncoated in seawater long term. Use 5086 if welding is used inthe assembly. 6061 buoys will last about 3 years in seawater before pits start breaking through a 1/2" thick hull, but they do well in the great lakes. The National Data Buoy Center had a 6061 Nomad buoy hull # 6N10 I believe, its been a while. It pitted severely on its first deployment in cool seawater. After grinding out the thousands of pits and rewelding it to fill them it was relegated to the Great Lakes only.
5000 aluminums ARE easier to break severely since they are strain hardened, not heat-treated and don't have to be annealed between bends, but the overriding reason for using them in seawater is the corrosion resistance. The difference in fabrication effort in the plate thickness and bend angles used in plate manufacture is moot. I'm happy to hear you are using 5000s though.
--------------
>>Note to the aluminum tank supporters: ALL aluminum tanks >>are/were manufactured of 6000 series aluminum. After 30+ >>years of throwing things in seawater I'm convinced the mix >>6000 series and seawater is not a good idea. The result has >>always been a bad thing for the aluminum.
>I guess we better all throw our AL tanks away. I have several bare AL80's that are going on ten years old, not pits, nothing but a dull surface oxidation. The insides are shiny as a new dime.
You obviously have a great fill station and rinse everything well on return from the sea. Moist air and Cl ions are bad news, as are Cl ions in a wet low oxygen environment. With the exception of a few neck cracks Al tanks will generally fail the visual before the hydro due to pitting, not the hydro itself. I estimate that 90% of all Al tanks Ive inspected that have been removed from service over the last 20 years failed due too pitting either internally or externally. Pitting internally is often due to poor fill station maintenance or fill technique. External pits are usually due to trapping saltwater against the tank or under the valve.
Aluminum tanks will work, for a while, even if not religiously maintained. If taken care of and cleaned EVERY TIME they are dove, and they are stored in a dry location (No such thing on the gulf coast unless in air conditioning) they will last quite a while. Never the less pitting is the primary failure mode. BTW many "bare" Aluminum tanks have a clear anodizing external coating.
>We'll put that aside as a spelling/grammar error. "pit in seawater, especially in area deprived in seawater"???
Sorry, it's been a long day.
That should be "in an area deprived of oxygen in seawater."
>90% of boat fittings are 304L. 90% of railings and tubular structures such as bimini supports, boat rails, davits, etc. are fabricated of 304 DOM tubing. These parts spend a lot more time in salt spray and immersion than any backplate ever will. Prop shafts, that are run through brass, fiberglass and other supports and hulls are made of 'Aquamet":
304 works fine, ABOVE THE WATERLINE and in spray zones. Below the waterline is a COMPLETELY different environment. I can't count the number of your tax dollars wasted due to someone putting 304 or 304L in a mooring. When an 18,000-foot moor is lost due to a 2" diameter 304 bolt pitting through and failing (even if it IS stamped 316!) there is close to $500K lost just in line! That doesn't count anchors, ground chain, floats, and the ship time to recover the buoy and replace it, or the lives lost and equipment damaged because the weather data wasn't available. We found that one by picking up a moor that had not _quite_ parted. A 2-4UNC nut weighed less than 2 ounces due to pitting and intergranular corrsion in less than 2 years exposure. Regrettably the vendor managed to stay out of jail even with the diffraction readings and chemicals proving it was NOT 316 as certified. I remember that one batch of hardware cost us several deep-water moors. Sorry, but I've been bit WAY too hard by 304 to ever use it for immersible parts. Even worse is the "dairy grade" 18-8 stainless hardware marked by two raised ticks on the bolt head 90° apart. The copper put in these parts to make them free machining is deadly in long-term seawater immersion. We even went so far as to surplus all 304 and dairy grade hardware (used in above deck applications) so we didn't even accidentally have a piece of 304 hardware used subsea!
BTW 316, or any other 300 series stainless, becomes more magnetic as it is cold worked or cut. That isnt the only way it gets magnetic, but it is the primary culprit for wrought shapes, machined parts and plate of known good alloy. If still magnetic after a pass through a reducing atmosphere annealing oven its time to spend the $s on checking the chemistry. I will agree that metals coming out of China, and to a lesser extent Korea, are often not what was specified though.
Aquamet is not used for shafting primarily for it's corrosion protection, even though of the high strength steels it is about the most resistant. It is used because it has roughly 3X to 5X the tensile and torsional strength of a similarly sized 316 shaft. 300 series stainless is the bubble gum of all steels. Using 316 for a highly stressed part subject to significant vibration is not a good thing.
>Glass beading addresses all these issues in a much more environmentally friendly manner. Compressed air and glass beads, not noxious chemicals that need to be disposed of.
That is a mechanical cleaning technique! I DID say that that worked.
>Pure baloney. If you arent using for explosive or other elicit production, you havent a worry.
As one of the 70% of FFL holders who got out of that business when Clinton did his "turn over your transaction documents or your civil rights" power and control grab, and a former FEL signatory at a site using over 8000 pounds of HE a day I have had way more than my fair share of dealings with ATF! I just don't want to ever waste another day with them.
Check your inorganic chemistry. HCl is not normally used to passivate for good reason, Muriatic is simply unpure HCl, and even concentrated phosphoric has to be disposed of. If you haven't tried the Coke trick, don't knock it. It works, but it's way SLOW! Its only real advantage is that the materials are available almost anywhere in the world, generally even at sea on US based ships, at a reasonable price and disposal is simple. Nitric is so much faster at the job it is used commercially, and I do specify that method for bulk parts. On a onsey twosey basis it's too expensive due to batch charges though.
Your only real "error" is assuming what works topside works subsea. The Thresher and its crew was lost due to that type of thinking. The discipline of Ocean Engineering was started in '65 to eliminate that possibility on future Navy projects as a direct result of the Thresher inquiry. Offshore oil recovery, mining, and fisheries have now all learned how valuable OEs can be, because the data you just got is NOT in the mainstream mechanical engineering texts. The understanding of corrosion of materials subsea is still in its infancy, even though we are a lot better at it than we were 40 years ago.
FT
