This one keeps on rearing its head. The idea is to put a band around the flange gap and squirt a corrosion inhibiting grease through grease nipples (Zerk’s in USA). The original intent of these devices was to contain high pressure leakage from the flange, it certainly was not intended as a corrosion control device. The photos show how the things generally work offshore. Two things absolutely amaze me. 1) These things are still offered for sale. 2) People actually buy and install them!