There are two most common forms to elect tax treaty:

Form 8233 and Form W-8BEN.

Form 8233 is used to elect tax treaty for employment wages and must be made annually. Form W-8BEN is used to elect tax treaty for stipends and qualified scholarships (i.e. Tuition). The Form W-8BEN is valid for three years.

Note: it's Form 8233 (not 8223)