|
Diligent external visual examination |
required |
required |
|
Diligent internal visual examination |
not required |
required |
|
Physical testing principle |
High-frequency sound waves traveling at a high velocity are used to interrogate the cylinder sidewall and sidewall-to-base transition areas. |
A pressure test designed to check the elasticity (expansion and contraction) of the cylinder wall thickness is used to test the entire cylinder. |
|
Valve removal |
not required, eliminating processing steps and potential damage to cylinder neck threads. |
required |
|
Risk of introducing any sources of contamination into the cylinder's interior. |
None |
High. Necessary to introduce water (contamination souce) into the cylinder's interior in order to pressurize the cylinder as a means of measuring elasticity. |
|
Necessity to drain and dry the cylinder interior. |
None |
Necessary to drain and dry the cylinder's interior after expansion testing is completed; otherwise, internal oxidation could occur. |
|
Necessity to bake out the cylinder to remove potential contaminants, maintaining gas purity. |
None |
Bake out of the cylinder is necessary to remove potential contaminants, requiring additional labor, processing time, and resources. |
|
Ideal for testing of |
seamless high-pressure metallic cylinders. |
high- and low-pressure cylinders and test cylinders made of fiber wrapped or other composite materials |
|
Productivity and quicker turnaround time |
High - results in the need for less cylinder assets. |
Lower - results in the need for more cylinder assets. |
|
Extension of re-qualification periodicity |
Allowed - requires greater exam sensitivity and detection of smaller potential flaw sizes. |
Re-qualification periodicity not allowed. |
|
Detection and measurement of potential flaws that reduces the strength and structural integrity of a cylinder wall. |
Possible |
Cannot detect and measure potential small flaws that may result in reduced wall strength and structural integrity of a cylinder wall. |
|
Detection of metallurgical conditions |
May not associated with overheat, improper heat treatment, or annealing of cylinders normally associated with manufacturing processes. |
Can detect certain metallurgical conditions associated with overheat, improper heat treatment, or annealing of cylinders normally associated with manufacturing processes. |
|
Water moisture detection |
Probe head designs are capable of detecting empty cylinders with moisture droplets within the cylinder's interior. |
Requires filling the cylinder completely with water and then pressurizing it. |
|
Detection of non-droplet froming contaminants |
May not detect non-droplet forming contaminants within a cylinder, such as oily residues. |
Visual examination after valve removal could detect non-droplet forming contaminants such as oily residues. |
|
Aluminum alloy cylinder neck threads and internal shoulders |
Per 49CFR 180, 3A, 3AA, and 3AL 6061-T6 or 6351-T6 aluminum alloy cylinder neck threads and internal shoulders that are not susceptible to sustained load cracking are required to be visually inspected and receive eddy current examination. |
Per 49CFR 180, 3A, 3AA, and 3AL 6061-T6 or 6351-T6 aluminum alloy cylinder neck threads and internal shoulders that are not susceptible to sustained load cracking are required to be visually inspected and receive eddy current examination. |
|
Regulations |
Testing is permitted in accordance with specially issued government approvals (special permit or equivalency certificate) or 49CFR 180 existing UN standards (ISO). |
Already approved per DOT and TC government regulations. |
|
Cylinder rate failures due to external visual inspections are |
consistent when diligently completed. |
consistent when diligently completed. |
|
Inspection of sidewall-to-base transition (SBT) zone |
SBT region is required to examined using a more sensitive detection technique due to possible line corrosion, cracking, and pitting. |
Internal visual inspection of areas near the SBT region are difficult to detect the presence of line corrosion and pitting due to extremely limited depth of field and observation angle given the neck opening size and cylinder length. |
|
Risk of moisture entering during test |
No need to submerge cylinder under water to test. No water enters through cylinder valve. |
Valve needs to be removed and cylinder filled with water prior to testing. |
|
ISO Acceptance |
Accepted by ISO for the purposes of requalifying high pressure seamless cylinders per ISO-6406 and 10461. Certain high pressure cylinders must be tested using UE. |
Accepted by ISO for the purposes of requalifying high pressure seamless cylinders per ISO-6406 and 10461. Certain high pressure cylinders must be tested using UE and cannot receive hydrostatic testing. |
|
Risk of personnel injury |
Since the valve does not need to be removed from a potentially charged high-pressure cylinder, there is less likelihood of personnel being injured performing this action or the release of gas into the environment. |
Since the valve needs to be removed from a potentially charged high-pressure cylinder, there is potential to injure personnel or release gas into the environment. |
|
Risk of cylinder condemnation due to valve thread damage.
|
None. Eliminates removal and replacement of installed cylilnder O-ring seals. |
High. Requires removal and replacement of installed cylinder O-ring seals. |