In Reply to: LA dive shops not filling tanks made of 6531 Aluminum alloy. Questions posted by Andy S on January 19, 2007 at 12:20:03:

Andy

Back in 1999 I informed the owner of a dive shop (still rents walter kidde aluminum cylinders today!) in Santa Monica about Luxfer Gas Cylinders warranty policy. Any Luxfer cylinder less than 10 years old, with a manufacturing defect, may be replaced at no cost. Defective cylinders between 10 and 15 years old may be replaced at a nominal charge. Cylinders older than 15 years having a manufacturing defect must have been inspected by a qualified inspector and, if made before May 1988, examined using an eddy current device.
BRIEF HISTORY OF ALUMINUM CYLINDERS

„« 1950 IMPORTED ALUMINUM CYLINDERS
„« 1956 U.S. NAVY BEGINS USE OF ALUMINUM (NON-MAGNETIC) CYLINDERS (6061 Alloy)
„« 1972 LUXFER U.S.A. BEGINS MFG OF E6498 ALUMINUM CYLINDERS (6351 Alloy)
„« 1982 (July) DOT Directs (SP/E) 6351 cylinders Be Over-stamped 3AL
„« 1983 Neck cracks discovered in cylinders manufactured with 6351 Alloy
„« 1986 CATALINA TANK COMPANY BEGINS MFG OF 3AL CYLINDERS (6061 Alloy)
„« 1988 (Jan) LUXFER U.S.A. BEGINS MFG OF 3AL CYLINDERS (6061 Alloy)
„« 1989 WALTER KIDDE DISCONTINUES MFG OF 3AL SCUBA CYLINDERS (6351 Alloy)

Sustained Load Cracking (SLC) ¡§6351¡¨
(formerly RTGBC ¡VRoom Temperature Grain Boundary Creep)

ALUMINUM CYLINDER ALLOYS

„« 6351 ¡VT6 1972 ¡V 1989
LUXFER BASE METAL UNTIL
JANUARY, 1988
Some cylinder sizes used 6351 until June 1988
WALTER KIDDE BASE METAL UNTIL 1989

„« 6061-T6 1986 ¡V Present
CATALINA BASE METAL SINCE 1986
LUXFER BASE METAL TRANSITION COMPLETED BY June 30, 1988

Luxfer Inspection Policy

Cylinders must be inspected by a trained inspector (ASSET or PSI)
„« ASSET- Assoc. of SCUBA Service Engineers and Technicians
Visually inspect all cylinders at least annually.
„« Recommend a 4 month inspection interval for cylinders in heavy use
Visual inspections of cylinders made prior to June of 1988 should include an eddy current test
„« Cylinders failing test should be removed from service

Eddy Current Policy
¡§Cylinders made from Luxfer¡¦s proprietary 6061 alloy are not susceptible to sustained-load cracks. Therefore, Luxfer does not deem it necessary to test these cylinders with eddy-current devices. ¡Kusing such eddy current devices with Luxfer 6061 alloy can result in misleading ¡§false-positive¡¨ readings.¡¨

Luxfer has authorized the use of the Visual Plus 3 on their proprietary 6061 alloy
THREE TYPES OF 3AL CRACKING

„« STRESS CORROSION CRACKING
CAN OCCUR IN ALL TYPES OF ALUMINUM CYLINDERS
CORROSION INDUCED OVER PERIOD OF TIME
LOOKS SIMILAR TO SMALL CRACK
Close inspection reveals rust patterns / stains

„« TORQUE CRACKING
DUE TO OVER TORQUEING VALVES IN CYLINDERS
FOLLOW CYLINDER MFG.¡¦S RECOMMENDATION
FOUND IN ALL TYPES OF ALUMINUM CYLINDERS

„« SUSTAINED LOAD CRACKING
FOUND ONLY IN 6351 ALUMINUM ALLOY

Sustained Load Cracking Issue

„« Discovered in SCBA¡¦s (1983)
„« 6351 Alloy Cylinders ( 1971-1988)
„« Develop Over Time
Luxfer 1982 & 1983 Higher Pb Content
Could be visible up to 7 years prior to becoming an explosive danger
„« Aggravated by warmer climates
„« Aggravated by hydrostatic test
„« Cracks Normally Form in Crown
Brittleness of 6351 Alloy

6351 Alloy Information

„« Luxfer manufactured 1,073,000 6351 alloy cylinders for the U.S. SCUBA industry
„« 1.25% of those cylinders have been found with SLC
„« There are 5.9 million cylinders worldwide made from the 6351 Alloy
„« .37% found with SLC
„« Out of 30 Million cylinders over a period of 30 years only 17 SLC Ruptures were reported to regulatory authorities (or Luxfer or PSI)
„« Only 14 of them have been SCUBA Cylinders
„« Most of the ruptures were during filling / all had a crack which could have been noticed by a trained cylinder inspector and taken out of service prior to the explosion.

Notice on 6351 Alloy Cylinders
U.S Department of Transportation RSPA-5143 (Notice 99-11)
„« Do not fill beyond marked service pressure
„« Do not fill or use if beyond the retest date
„« Insure a technical inspection on interior neck and shoulder
„« Between hydro retests perform additional examinations of neck and shoulder for SLC
„« Increase frequency of internal inspections to a minimum of annually (recommended)
„« Recommend PSI Standards

Hats off for Sport Chalet:

MESSAGE TO: SCUBA Dept Head DATE:OCTOBER 11,2005
FROM: SCUBA Operations Manager RE: Additional 6351 Cylinder Information

As you know we are no longer filling 6351 Aluminum cylinders. This decision was made to improve the safety of our employees and customers at our stores.
In keeping with that decision we will no longer provide visual inspections or any other cylinder services on them at any location including SCUBA Repair. The exposure to liability is just too great.
Do not send any of these cylinders to SCUBA Repair for service. They will only be returned to your store.
If you have any questions please feel free to contact me. In the meantime the only information that should be given to customers is the following:

As stated in our visual inspector courses the only SCUBA cylinders susceptible to possible neck cracks have been those manufactured with the 6351 Aluminum alloy. These cylinders were only manufactured by the following companies:
Luxfer (prior to May 1988)
Walter Kidde (prior to June 1989)

In an effort to eliminate the possibility of serious injury to our employees, our customers, and damage to our stores from these potentially dangerous cylinders I have decided that Sport Chalet should stop filling these cylinders.

So Andy, Just get your fills from Ocean Adventure Dive Co in Venice. Steve Ladd is a DIVER!

Have a great day!

Safe Diving
John V Corso
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