The present invention relates to methods for a long-term and sustained release of flavonoids, in particular rhamnose-containing flavonoids, and for prolonging the uptake of said flavonoids in the gastro-intestinal tract. and oil country tubular goods obtained by this method of production. The apparatus further comprises a reversal preventing device F which, contacts and limits the engaging link pairs and to an outwardly bent position where flexing pivotal portions of the engaging link pairs project radially outward. The conduit device constitutes a tubular path for the intervention string.