Thread and neck inspection criteria for 6061 scuba cylinders

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 mirror or other acceptable 2X method.

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 are listed under that item.

Minimum Number of Threads

The minimum numbers of complete threads required in Catalina Scuba Cylinders’ cylinders are:

Service Pressure Minimum # of 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, 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:

  • it interrupts the required minimum number of complete threads and
  • it creates a thread imbalance of 6 threads or more

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:

  • It interrupts the required minimum number of threads in a cylinder, or
  • It measures an imbalance of 6 threads or more

Replacement Policy:

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

Folds

A fold is a 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 (an alloy never used to manufacture Scuba Tanks by Catalina Cylinders).

Rejection Criteria: (in accordance with CGA 6.1 2013-6th edition Paragraph 5.9.2

A fold is unacceptable if:

  • it interrupts the required minimum number of complete threads, or
  • it interrupts two complete threads, or
  • it causes loss of contents of the 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. 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:

  • it interrupts the required minimum number of complete threads, or
  • it interrupts two complete threads, or
  • it causes loss of contents of the cylinder

Replacement Policy:

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

Rejection Criteria:

Any linear indication that interrupts two complete threads is reason for reject (not condemned). Cylinder 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.

Cylinders that exhibit unacceptable manufacturing conditions (i.e. folds, or lack of complete threads) that extend two threads are covered by Catalina Cylinders Return Authorization Policy.

Tool Stop Marks

Tool Stop Marks appears as linear indications in the threads of a cylinder. 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.

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:

  • it causes loss of contents of the cylinder, or
  • It interrupts the required minimum number of complete threads in 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 properly mark or placarded the cylinder and then contact Catalina Cylinders immediately and ask to speak with a Catalina Cylinders Return Authorization (RA) representative. Our RA office hours are Monday through Friday 8:00am – 5:00pm. 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.

Posted in: Scuba