The retest pressure is 5250psi for all SP 12079 steel SCUBA cylinders.
All Department of Transportation (DOT) Special Permit (SP) 12079 steel SCUBA cylinders must be requalified at a retest pressure equal to 3/2 (1.5) times the design service pressure of the cylinder. This may be confusing to some who are in possession of SP 12079 steel SCUBA cylinders marked with a service pressure of 3442psi, “DOT-SP12079-3442”. Following is an explanation of how cylinders marked with the same special permit number, “SP 12079”, and marked with two different service pressures, “3500” and “3442” are to be requalified at the same retest pressure, “5250psi”.
The United States (US) DOT requires that all specification cylinders be periodically requalified as identified in 49 CFR section 180. In 49 CFR 180.205 (c); Periodic Requalification of Cylinders it states,” Each cylinder bearing a DOT special permit number must be requalified and marked in conformance with this section and the terms of the applicable special permit (SP 12079).” To perform requalification in conformance with the terms of the special permit, it is interpreted that a copy of the special permit is on hand or can be accessed electronically. Copies of special permits can be attained by accessing the US DOT PHMSA webpage.
All steel SCUBA cylinders marked with DOT-SP 12079 have been designed with a service pressure of 3,500psi as noted on page 4 of the SP 12079 regardless of when they were manufactured. The original steel SCUBA cylinders marked against this specification were marked with “DOT-E12079-3500”. The next generation of these steel SCUBA cylinders were marked slightly differently, “DOT-SP12079-3500” due to a change by the DOT in identifying these cylinders now as special permit (SP) cylinders replacing the exemption (E) cylinder identification. Even though all E or SP 12079 steel SCUBA cylinders have been designed with a service pressure of 3500psi, cylinders manufactured since late 2007 have been marked with a lower service pressure of 3442psi, “DOT-SP12079-3442”. These cylinders are marked with the lower service pressure of 3442psi so that standard SCUBA valves can be used on these cylinders. Cylinders marked with a service pressure of 3442psi must not be used in service at a pressure greater than 3442psi.
As stated earlier, special permit cylinders must be requalified in accordance with the requirements of the DOT regulation and the special permit. In SP 12079 section 8; Special Provisions paragraph (f) it states, “Each cylinder must be requalified for use every 5 years in accordance with 180.205 as prescribed for DOT specification 3AA cylinders except the minimum retest pressure must be 3/2 (1.5) times the service pressure.”
In conclusion, since the design service pressure of all SP 12079 cylinders is 3500psi, regardless if they are marked at 3500psi or 3442psi, the requalification (retest) pressure must be 5250psi.