Is it standard to use a sleeve to protect a copper pipe from rubbing against the wall?
It is probably sweat/condensation covering. We use isolators,
hangers, plastic sleeves, 10 mil vinyl tape, and other items like
those to prevent noise caused by temperature change
(expansion/contraction) in water lines, and to prevent damage from
abrasion when in contact with harder materials, and to protect from
chemical damage when in contact with concrete, and to protect from
electrolysis when in contact with dis-similar metals.