Metal tubing of steel; penstock pipes of steel for the transport of petroleum and natural gas; junctions of steel for pipes for oil and gas pipelines; gas-tight thread couplings of steel for oil pipelines and gas pipelines; pipe muffs of metal, in particular of steel; manifolds of metal for pipelines; threaded pipes of steel; pipe strings of metal for the extraction of petroleum and natural gas; oilfield pipes of metal; and drill strings of metal for oil and gas fields