A bit of clarification here...the VIP has always been part fo the hydro test and for 6351-T6 alloy tanks an eddy current / visual plus inspection has been part of the hydro test / recertification process as well ever since Luxfer released eddy current inspection protocols for 6351-T6 tanks.
Dive shops became involved in eddy curent testing at the same time as Luxfer recommended the edy current test every 18 months - which effectively meant annually as part of the dive industry standard annual VIP.
Most shops have pretty much always ripped off divers by requiring a VIP on tanks that were freshly returned from hydro as the VIP and eddy current test were part of the recertification process and the dive shop VIP on a just hydro tested tank is redundant. (I agree shops shoud be abel to do one if it makes them feel better, but they should limit the charge to the cost of the sticker as it is for their piece of mind, not because it is needed.)
Based on 8 years of test data and field results the DOT recently ruled that an eddy current examination is only required at the time the tank is recertified (the legal term for the process of hydro testing, eddy current and visual inspection). If the tank successfully passes the eddy current test it is to be stamped with a V next to the hydro test date indicating the test was completed. That mark then notifies the dive shop that the tank has passed a visual inspection, just as the hydro test date notifies them it has passed the hydro test.
Obviously this also means shops have no real justification in charging for a eddy current inspection on a just returned from hydro test 6351-T6 tank. It does not however change the scuba industry standard of doing an annual VIP on scuba tanks. And since the eddy current inspection has become part of this ritual for 6351tanks (and in some shops for all aluminum tanks over 10 or 20 years old) shops will probably still insist they be done.
The test data and field results have been very clear in documenting that a sustained load crack from the time it is detectabel until the time it propogates to the point of potential failure takes well in excess of the 5 year hydro test requirement, so there are at least two opportunities for the crack to be detected with eddy current inspections done by the hydro test facilties.
I agree with Luis that a hydro test facility could subcontract the eddy current test to a dive shop, but doing so would create a documentation problem. Technically the tank could not be retured to service and stamped with the V or the test date until the shop completed the eddy current exam, and the testing records have to be maintained by the hydro test facility, so the test results would have to be returned to the test facility and technically the tank would have to be returned as well to be stamped. It's possible the shop could inspect the tank prior to sending it to the facility for the hydro test, but a percentage of the cracks I have observed were not observable prior to the hydro test, but were observable after the hydro test. So prudence seems to dictate doing the VIP and eddy current inspection after the hydro test. In addition, the hydro test facility is liable if a tank explodes and the DOT WILL track down the test records. I don't know of any hydro test facilities that will accept the liability of having a dive shop perform the eddy current inspection.
The irony here is that local dive shops will still insist on doing an eddy current exam every year as they do not trust the hydro facility testing (even though the test facility will do thousands of tanks per year and multipel tanks per day and become very proficient compared to tens or at best hundreds per year done one or two per day or week by the average LDS. Paranoia and ignorance regarding 6351-T6 tanks plays a major role here as LDS's worry about exploding 6351-T6 tanks but there has never been a documented case of a properly inspected 6351-T6 exploding since eddy current test protocols were adopted over 8 years ago.
The short version of the story is that:
1. There is now no longer any reason for a shop to do an eddy current inspection other than that it is now customary and as they already have the equipment to do it.
2. It is now required by law that any hydro test facility do the test as part of the recertification process (and it does nto really matter if the dive shop does one or not) and a sop completed eddy current inspection has no bearing on the requalification requirements.
3. Eddy current inspection is not rocket science and the latest visual plus equipment is just about idiot proof so getting a bad inspection from a hydro test facility is extremely unlikely. False positives requiring more in depth inspection and expertise are far more likely, and many LDS staff lack this expertise.
