Corrosion and Material Forum are a useful source of information, suggestion, previous experiences. On the net there are several Forum dedicated to Corrosion Engineering that can be accessed simply registering and where you can post your question on Materials Selection and Corrosion or search trough the previous topics for what you're looking for. Approx  20.000 question have been asked in these forum in the last years.

These links will guide you to the Forum page, or you can try a search directly into some of these the forum using the Corrosion Search Engine above and selecting the FORUM.

NACE Corrosion Network (NCN)

The Forum of NACE (National Association of Corrosion Engineer). There are several Forum dedicated to different aspect of Corrosion and Materials Selection: Cathodic Protection, Coating.. Select the NACE forum if you are looking for topics on Corrosion & Materials

ENG-TIPS

Eng-Tips site contains several Forums dedicated to all the aspects of Engineering. There are also Forums dedicated to Corrosion Engineering, Stainless Steel and Metals & Materials

HG-HOUSTON

HG-Houston has a section dedicated to Forums. There are three categories: General Topics on Corrosion, Materials Selection and one dedicated to Corrosion & Materials in Refinery.

Materialsforum has a forum dedicated to Engineering Topics where there are also some question on Corrosion & Materials