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Technical Support Document

Thread and Neck Inspection Criteria
for SCUBA Cylinders

(Eddy Current Device Thread Inspection Rejection Criteria Included)

April 10, 2006


All SCUBA cylinders should be subjected to an annual visual inspection under normal use. A cylinder subjected to an average of one fill a day or more is considered a cylinder subjected to high use. A cylinder subjected to high use should be visually inspected, both externally and internally, a minimum of every six months. Annual visual inspection includes the inspection of the threads and neck of a cylinder. Thread and neck inspection can only be performed with the valve removed from the cylinder and all foreign material (i.e. dirt, corrosion, etc.) removed from the o-ring gland and threads. Thread and neck inspection is performed visually with the aid of a light source and a 2X dental mirror and can be supported by the use of an eddy current thread inspecting device.

Eddy current inspection of 6061 aluminum alloy cylinders is not mandated by the Department of Transportation (DOT). Catalina Cylinders has only manufactured its cylinders from 6061 aluminum alloy. Only 6351 aluminum alloy cylinders are required to be inspected at the time of requalifcation, every 5 years, by the DOT.

Catalina Cylinders recommends that the items defined below be included in the thread and neck inspection of Catalina Cylinders' SCUBA cylinders subjected to annual visual inspection. The rejection criteria for each item is listed under that item.

Minimum Number of Threads

The minimum number of complete threads required in Catalina Cylinders SCUBA cylinders are:

Service Minimum #
Pressure Threads
3000 psi 8.0
3300 psi 9.0

The minimum number of complete threads is counted from the top thread down. The minimum number of complete threads cannot be interrupted by any discontinuities (i.e. valleys, folds, corrosion, cracks, or damage).

Rejection criteria:

Cylinders with less than the minimum number of complete threads required for the above noted service pressures are unacceptable.

Replacement Policy:

Catalina Cylinders Return Authorization Policy covers cylinders manufactured with less than the minimum number of complete threads required.

Valley

A valley is a lack of metal condition at the bottom of the threads. A valley is created during the crown forming operation. A valley has an inverted "U" appearance in the bottom of the threads. The contour of a valley is generously rounded.

Rejection Criteria:

A valley is unacceptable if:

A valley can be detected by, but is not rejected singularly by the use of an eddy current thread inspection device. A valley will not appear as a spike on a Visual Plus Unit.

Replacement Policy:

An unacceptable valley is a manufacturing related defect covered by Catalina Cylinders Return Authorization Policy.

Thread Imbalance

A thread imbalance is the count of partial threads in a cylinder. A thread imbalance is the difference between the number of complete threads and the number of total threads (complete threads and partial threads) in a cylinder.

Rejection Criteria:

A thread imbalance is unacceptable if:

A thread imbalance can be detected by, but is not rejected singularly by the use of an eddy current thread inspection device.

Replacement Policy:

An unacceptable thread imbalance is a manufacturing related defect covered by Catalina Cylinders Return Authorization Policy.

Folds

A fold is a lack of metal condition at the bottom of the threads or in the shoulder of a cylinder. A fold is created during the crown forming operation and is actually the metal folding over on itself during the forming operation. A fold is a static condition - not propagating or growing in magnitude. A fold has an inverted "V" appearance in the bottom of the threads. Typically a fold will have a linear indication running down the deepest part of the fold. The contour of a fold is sharp at its deepest point. A fold is similar in appearance to and often mistaken for a crack, a dynamic condition, which can occur in 6351 alloy cylinders.

Rejection Criteria:

A fold is unacceptable if:

An eddy current thread inspection device can detect folds in the threads of a cylinder.

Replacement Policy:

An unacceptable fold is a manufacturing related defect covered by Catalina Cylinders Return Authorization Policy.

Corrosion

Corrosion can occur in the threads of a cylinder if moisture, possibly by charging the cylinder with wet air, enters the cylinder. Corrosion will typically start in the 9th or 10th threads, at the location where the bottom of the threaded portion of the valve ends in the threads of a cylinder. A scuba valve that is not fully chrome plated may accelerate the corrosion process in the thread section of a cylinder. Corrosion can occur on the top surface of the cylinder and in the o-ring gland of the cylinder.

Rejection Criteria:

Corrosion is unacceptable if:

An eddy current thread inspection device can detect corrosion in the threads of a cylinder.

Replacement Policy:

Corrosion is not a manufacturing related condition and is not covered by Catalina Cylinders Return Authorization Policy.

Thread Cracks

A crack is a linear discontinuity that typically runs linearly top to bottom in the threads. A crack typically starts at the bottom of the threads and propagates upward. A crack can, but rarely does, start at the top of the threads. A crack is a dynamic condition - propagating or growing in magnitude over time, typically when the cylinder is under pressure. A crack in a 6351 alloy cylinder is similar in appearance to a fold, a static condition.

Rejection Criteria:

A crack is unacceptable.

Cracks can be identified and rejected by an eddy current thread inspection device. It is recommended that cylinders, in which a crack has been identified by an eddy current thread inspection device and cannot be identified visually, be returned to Catalina Cylinders against a Return Authorization (RA) for evaluation prior to condemning.

Replacement Policy:

A crack that is determined to be a manufacturing related defect is covered by Catalina Cylinders Return Authorization Policy.

Eddy Current Device "Spike" Indications

Eddy current inspection of 6061 aluminum alloy cylinders is not mandated by the Department of Transportation (DOT). Catalina Cylinders has only manufactured its cylinders from 6061 aluminum alloy. Only 6351 aluminum alloy cylinders are required to be inspected at the time of requalification, every 5 years, by the DOT.
Eddy Current Device "Spike" indications measuring two threads long. These indications are measured after the unit has been calibrated, is operated in the 1X mode, and the trace line has been reset and centered below the threshold line.

Rejection Criteria:

Any linear indication that interrupts two complete threads and is identified by the Eddy Current Device as a spike indication is reason for reject (not condemned). Cylinder with Eddy Current Device reject conditions should have the reject condition visually verified before condemning the cylinder.

Replacement Policy:

Corrosion pits, an acceptable valley, and 1 thread fold are not covered by Catalina Cylinders Return Authorization Policy.

A cylinder that exhibits unacceptable manufacturing conditions (i.e. folds, cracks, or lack of complete threads) that extend two threads as identified by the Eddy Current Device are covered by Catalina Cylinders Return Authorization Policy.

Tool Stop Marks

Tool Stop Marks appears as linear indications in the bottom 1 - 3 threads of a cylinder. Typically there are six equally spaced tool stop marks visible at the bottom of the threads in a cylinder when the threads are complete. The tool that cuts the threads into a cylinder creates tool stop marks. A tool stop mark is a slight build-up of metal at the location where the thread cutting tool stops, hence the name tool stop mark. Tool stop marks are not a rejectable condition.

Eddy current thread inspection devices typically do not detect tool stop marks.

Rejection Criteria:

None.

Replacement Policy:

Tool stop marks are not an unacceptable manufacturing condition covered by Catalina Cylinders Return Authorization Policy.

Damage

Damage to the top surface, the o-ring gland, or the threads of a cylinder can be created during the manufacture of a cylinder and after the cylinder has been in service.

Rejection Criteria:

Damage to the top surface, the o-ring gland, or the threads of a cylinder is unacceptable if:

An eddy current thread inspection device may or may not detect damage to the threads of a cylinder.

Replacement Policy:

Catalina Cylinders Return Authorization Policy covers unacceptable damage created during the manufacturing of the cylinder.

If at any time the integrity of a cylinder stamped with "CATALINA" and/or "M4002" on the crown is in question, we request you contact Catalina Cylinders immediately at (714) 890-0999 and ask to speak with a Catalina Cylinders Return Authorization (RA) representative. Our RA office hours are Monday through Friday 8:00am - 5:00pm PST. Before calling, please have available the cylinder crown marking (stamping) and an explanation of your concerns about the cylinder. Having this information available at the time of the call will help expedite the resolution to your concerns. The information you provide the RA representative will determine if a RA report should be generated and the cylinder returned to Catalina Cylinders.




Catalina Cylinders - West
Corporate Headquarters

7300 Anaconda Avenue
Garden Grove, California 92841 USA
Phone: (714) 890-0999
Fax: (714) 890-1744
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Catalina Cylinders - East
Cliff Impact Division

2400 Aluminum Avenue
Hampton, Virginia 23661 USA
Phone: (757) 896-9100
Fax: (757) 896-9143
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