There may be a Acier Mannesman, but I'm leaning toward it noting a Mannesman process or processes that make a tube.

Laminage des tubes mtalliques sans soudure par le procd Mannesmann. - Rolling tubes by the Mannesman process.

http://www.vallourec.com/FR/group/ABOUTUS/HISTORY/Pages/default.aspx

Cheers,

Raimey
rse