Are Mur-lok and or John Guest fitting reef safe if submerged?

[MoshJosh]

As I understand it, these fittings have a piece of metal inside of them. Being water tight that metal piece does not contact the liquid inside the tubing/fittings, however, what is the fitting is below the water line inside a tank? Are they still reef safe?

 

[KrisReef]

I don't think they normally use stainless steel, so I would expect the fitting to fail if it was submerged. I have found some that used plastic instead of metal, but finding a good supplier of these fittings has been in termoil since COVID