Q1. You state that it is your understanding that a pressure-indicating device (PID) must have an accuracy grade of 0.5%, and that if your PID exhibited an accuracy grade of 0.6% you would not be able to use that measuring device for pressure testing. You ask for confirmation of your understanding.

A1. For the purposes of this answer, and all other answers in this letter, it is important to note that the term accuracy grade is not a term used in the HMR. Your understanding is correct. As required by § 180.205(g)(3)(i) the PID, itself, must be certified as having an accuracy of ±0.5%, or better, of its full range. If your PID exhibited an accuracy grade of 0.6% you would not be able to use that measuring device for pressure testing.

Q2. You give an example of a 0 to 11,000 PSI PID with 0.5% accuracy grade (the PID is +/- 55 psi accurate at any point). You request confirmation of your understanding that you could not test any cylinder under the test pressure of 5,500 psi.

A2. Your understanding is correct. Section 180.205(g)(3)(i) states that the PID, as part of the retest apparatus, is accurate within ±1.0% of the prescribed test pressure of any cylinder tested that day. For additional tests to be conducted that day, PID, as part of the retest apparatus, must be accurate within ±1.0% of each individual test pressure to be tested that day. However, if the PID, itself, is not in compliance with an accuracy of ±0.5%, or better, of its full range, retesting is not permitted on that day.

Q3. You present a scenario where you are testing cylinders with a test pressure range of 3,000 to 10,000 psi on a daily basis. You note that you understand you should have a 0 to 11,000 psi gauge to comply with the +/- 10% range rule and ask if a PID with a 0.5% accuracy grade is not adequate, but if a 0.25% accuracy grade would be appropriate.

A3. In the scenario you provide the PID with 0.5% accuracy would not be appropriate for testing all cylinders within the psi range you have provided. A PID with 0.25% accuracy would be compliant.

Q4. Using the same scenario as described in Q3 above (0.25% accuracy grade), you ask if you are unable to prove your PID is +/- 30 psi accurate that it would be a violation to test cylinders with the pressure of 3,000 psi or lower.

A4. It is unclear as to intent of your question. Other than verification each day before retesting, there is no requirement in the HMR to retest the PID during the day.

Q5. You state it is your understanding that an expansion-indicating device (EID) must have an accuracy of +/- 0.5% or better of its full range. You ask if this means the accuracy grade of the EID has to be at least 0.5%.

A5. As required by § 180.205(g)(3)(ii) the expansion-indicating device, as part of the retest apparatus, gives a stable reading of expansion and is accurate to ±1.0% of the total expansion of any cylinder tested or 0.1 cc, whichever is larger. The expansion-indicating device itself must have an accuracy of ±0.5%, or better, of its full scale.

Q6. You provide a scenario in which you are using a 0 to 1,000 g (1 g = 1 ml) digital scale as an EID with 0.5% accuracy grade (1000 x 0.5/100 = 5 g accurate). You ask if it would be a violation to test cylinders producing total expansion of less than 500 g.

A6. Each day before retesting, the retester shall confirm that the expansion-indicating device, as part of the retest apparatus, gives a stable reading of expansion and is accurate to ±1.0% of the total expansion of any cylinder to be tested that day or 0.1 cc, whichever is larger. In the scenario you describe, testing cylinders producing total expansion of less than 500 g would be a violation.

Q7. You present a scenario where the total expansion ranges from 6 ml to 510 ml and you are using a 0 to 1,000 g scale. You state it is your understanding that you would need a 0.01% accuracy grade and not a 0.5% accuracy grade.

A7. The expansion-indicating device, as part of the retest apparatus, must be is accurate to ±1.0% of the total expansion of any cylinder to be tested that day or 0.1 cc, whichever is larger.

Q8. You ask several questions about verifying EID accuracy using Compressed Gas Association (CGA) Pamphlet C-1, Methods for Pressure Testing Compressed Gas Cylinders.

A8. CGA Pamphlet C-1 is not incorporated by reference and, therefore, is not a material made part of the regulations under the HMR and not enforceable.