Scared Silly
Contributor
Hopefully, this thread will become a sticky as it is an attempt to help educate divers on cylinders that were made from the AL6351 alloy.
Please do no add posts to this thread unless it is for factual information or corrections. I especially do not want discussions on what some dive shop policies are. I reserve the right to ask mods to delete superfluous posts as I would like to keep the thread as informational as possible.
Also I will not go into the details of sustained load cracking. Other than to say some cylinders burst catastrophically rather than leak. Luxfer has some info:
Luxfer: Sustained-load Cracking FAQ
------------------------
First, lets start off with the important part what are the affected cylinders? which are only those made from aluminum and specifically the alloy 6351 (steel cylinders are not affected).
Here is the official advisory that was published by DOT:
Notice No. 94-7; Safety Advisory; High Pressure Aluminum Seamless and Aluminum Composite Hoop-Wrapped Cylinders
Here is the summary for scuba cylinders:
All Walter Kidde DOT-3AL cylinders, of which production ceased in
January 1990, are made of alloy 6351-T6. Cliff Impact DOT-3AL cylinders
were made from alloy 6351-T6 before July 1990, at which time Cliff
Impact changed to alloy 6061-T6. Catalina Cylinders did not produce any
DOT-3AL cylinders from alloy 6351-T6; therefore, cylinders manufactured
by Catalina are not subject to this notice.
Until determined otherwise, any DOT-3AL or DOT-E 7235 cylinder
should be assumed to be made of alloy 6351-T6, if it was:
1. Manufactured by Luxfer USA before the applicable date listed in
the chart below;
2. Manufactured by Cliff-Impact before July 1990;
3. Manufactured by any other company in the United States,
excluding Catalina, before February 1990; or
4. Manufactured outside the United States.
Now lets focus on cylinders made by Luxfer as they are the most predominate scuba cylinder made with AL6351:
30 and 63 cu. ft............................. S30, S63 .... mfg date 5-88
40 cu. ft....................................... S40 ........... mfg date 6-88
50 and 92 cu. ft............................. S50, S92 .... mfg date 4-88
72 and 100 cu. ft........................... S72, S100 ... mfg date 8-87
80 cu. ft....................................... S80 ........... mfg date 1-88
80.8 cu. ft.................................... S80.8 ......... mfg date 5-87
By quickly scanning one can see that by July of 1988 Luxfer had quit making cylinders using AL 6351 and had fully switched over to AL6061. As importantly, given that the vast majority of aluminum scuba cylinders in use are AL80 for the most part one could "safely" say that any Luxfer AL80 made with a hydro year of 1988 were made using AL6061. Though I have seen a 1-88 hydro date for a Luxfer cylinder.
------------------------
Where did the 1990 date cut off for not filling a cylinder that many shops use come from???
In a nutshell it an arbitrary date. As noted, Luxfer quit using AL6351 18 months before hand. Yet Walter Kiddie and Cliff Impact made cylinders using AL6351 through Jan 1990 and July 1990 respectively. I suspect the date which is a nice round number came from the observation that Cliff Impact cylinders were few and far between and while Walter Kiddie were common that the chance of Jan 1990 sneaking in was remote.
Commentary regarding the 1990 date. I have heard the reason for the 1990 date is that it easy to remember for those filling cylinders. I do not buy it. Those filling cylinders are suppose to be knowledgeable and trained in hazmat rules and CGA recommendations for their job. Which requires the ability to read. I do not believe that having a quick lookup table such the one above is so difficult that substituting an arbitrary date is reasonable.
------------------------
So now that you have determined that you have a cylinder made from AL6351 what needs to be done with it?
The practical side. More and more shops are declining to fill cylinders made from AL6351. As such, before spending money on requalifying check to see if you can get it filled. Otherwise, it might just be a big wind chime.
What needs to been at the time of requalification? (aka hydro).
The hydro test is the same for any other cylinder except after Jan 2007 all cylinders made from AL6351 must also undergo an eddy current test at the same time. I.e. the hydro shop must perform the test. In addition, the cylinder must be mark with a "VE" after the hydro date to signify that the test was successfully passed. Here are the rules in all of their glory:
Hazardous Materials: Aluminum Cylinders Manufactured of Aluminum Alloy 6351-T6 Used in SCUBA, SCBA, and Oxygen Services--Revised Requalification and Use Criteria | Federal Register Environmental Documents | USEPA
------------------------
What about the annual VIP for a AL6351 cylinder?
While annual visual inspections for all scuba cylinders are recommended by the CGA and the scuba industry there is no law mandating them. That said they are a good idea.
Before 2007, AL6351 cylinders were typically inspected like any other scuba cylinder with the exception of an eddy current test. Now that the eddy current test is part of the re-qualification process there is no need for the test to be performed as part of the annual visual inspection. However, most shops continue to do the test as part of the annual visual inspection as they have the eddy current equipment on hand.
Historical note: before the 2007 rules went into affect Luxfer recommended that AL631 cylinders be eddy current tested at least every 2.5 years (Part 11):
Luxfer: Sustained-load Cracking FAQ
As a practical side the eddy current was incorporated into the annual inspection.
Commentary regarding performing the eddy current test on AL6061 cylinders. Many shops perform the test on all aluminum cylinders regardless of the alloy. Some of the early testers gave erroneous results. Some testers work on all alloys. Regardless eddy current is not needed on AL6061 as they are not prone to Sustained-load Cracking. Check to make sure you are not paying for a test that is not needed.
------------------------
Hopefully this information will be helpful to those who have a cylinder made from AL6351. Personally, at this point I would advise against buying one and if given one I would pass and make it in a wind chime or turn it in for scrap.
Please do no add posts to this thread unless it is for factual information or corrections. I especially do not want discussions on what some dive shop policies are. I reserve the right to ask mods to delete superfluous posts as I would like to keep the thread as informational as possible.
Also I will not go into the details of sustained load cracking. Other than to say some cylinders burst catastrophically rather than leak. Luxfer has some info:
Luxfer: Sustained-load Cracking FAQ
------------------------
First, lets start off with the important part what are the affected cylinders? which are only those made from aluminum and specifically the alloy 6351 (steel cylinders are not affected).
Here is the official advisory that was published by DOT:
Notice No. 94-7; Safety Advisory; High Pressure Aluminum Seamless and Aluminum Composite Hoop-Wrapped Cylinders
Here is the summary for scuba cylinders:
All Walter Kidde DOT-3AL cylinders, of which production ceased in
January 1990, are made of alloy 6351-T6. Cliff Impact DOT-3AL cylinders
were made from alloy 6351-T6 before July 1990, at which time Cliff
Impact changed to alloy 6061-T6. Catalina Cylinders did not produce any
DOT-3AL cylinders from alloy 6351-T6; therefore, cylinders manufactured
by Catalina are not subject to this notice.
Until determined otherwise, any DOT-3AL or DOT-E 7235 cylinder
should be assumed to be made of alloy 6351-T6, if it was:
1. Manufactured by Luxfer USA before the applicable date listed in
the chart below;
2. Manufactured by Cliff-Impact before July 1990;
3. Manufactured by any other company in the United States,
excluding Catalina, before February 1990; or
4. Manufactured outside the United States.
Now lets focus on cylinders made by Luxfer as they are the most predominate scuba cylinder made with AL6351:
30 and 63 cu. ft............................. S30, S63 .... mfg date 5-88
40 cu. ft....................................... S40 ........... mfg date 6-88
50 and 92 cu. ft............................. S50, S92 .... mfg date 4-88
72 and 100 cu. ft........................... S72, S100 ... mfg date 8-87
80 cu. ft....................................... S80 ........... mfg date 1-88
80.8 cu. ft.................................... S80.8 ......... mfg date 5-87
By quickly scanning one can see that by July of 1988 Luxfer had quit making cylinders using AL 6351 and had fully switched over to AL6061. As importantly, given that the vast majority of aluminum scuba cylinders in use are AL80 for the most part one could "safely" say that any Luxfer AL80 made with a hydro year of 1988 were made using AL6061. Though I have seen a 1-88 hydro date for a Luxfer cylinder.
------------------------
Where did the 1990 date cut off for not filling a cylinder that many shops use come from???
In a nutshell it an arbitrary date. As noted, Luxfer quit using AL6351 18 months before hand. Yet Walter Kiddie and Cliff Impact made cylinders using AL6351 through Jan 1990 and July 1990 respectively. I suspect the date which is a nice round number came from the observation that Cliff Impact cylinders were few and far between and while Walter Kiddie were common that the chance of Jan 1990 sneaking in was remote.
Commentary regarding the 1990 date. I have heard the reason for the 1990 date is that it easy to remember for those filling cylinders. I do not buy it. Those filling cylinders are suppose to be knowledgeable and trained in hazmat rules and CGA recommendations for their job. Which requires the ability to read. I do not believe that having a quick lookup table such the one above is so difficult that substituting an arbitrary date is reasonable.
------------------------
So now that you have determined that you have a cylinder made from AL6351 what needs to be done with it?
The practical side. More and more shops are declining to fill cylinders made from AL6351. As such, before spending money on requalifying check to see if you can get it filled. Otherwise, it might just be a big wind chime.
What needs to been at the time of requalification? (aka hydro).
The hydro test is the same for any other cylinder except after Jan 2007 all cylinders made from AL6351 must also undergo an eddy current test at the same time. I.e. the hydro shop must perform the test. In addition, the cylinder must be mark with a "VE" after the hydro date to signify that the test was successfully passed. Here are the rules in all of their glory:
Hazardous Materials: Aluminum Cylinders Manufactured of Aluminum Alloy 6351-T6 Used in SCUBA, SCBA, and Oxygen Services--Revised Requalification and Use Criteria | Federal Register Environmental Documents | USEPA
------------------------
What about the annual VIP for a AL6351 cylinder?
While annual visual inspections for all scuba cylinders are recommended by the CGA and the scuba industry there is no law mandating them. That said they are a good idea.
Before 2007, AL6351 cylinders were typically inspected like any other scuba cylinder with the exception of an eddy current test. Now that the eddy current test is part of the re-qualification process there is no need for the test to be performed as part of the annual visual inspection. However, most shops continue to do the test as part of the annual visual inspection as they have the eddy current equipment on hand.
Historical note: before the 2007 rules went into affect Luxfer recommended that AL631 cylinders be eddy current tested at least every 2.5 years (Part 11):
Luxfer: Sustained-load Cracking FAQ
As a practical side the eddy current was incorporated into the annual inspection.
Commentary regarding performing the eddy current test on AL6061 cylinders. Many shops perform the test on all aluminum cylinders regardless of the alloy. Some of the early testers gave erroneous results. Some testers work on all alloys. Regardless eddy current is not needed on AL6061 as they are not prone to Sustained-load Cracking. Check to make sure you are not paying for a test that is not needed.
------------------------
Hopefully this information will be helpful to those who have a cylinder made from AL6351. Personally, at this point I would advise against buying one and if given one I would pass and make it in a wind chime or turn it in for scrap.
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