The phrase "usage as a" is correct and usable in written English.
It can be used when discussing the function or role of something in a particular context.
Example: "The usage as a reference tool is essential for students in their research."
Alternatives: "function as a" or "role as a".
TO GOOGLE is now in broad usage as a verb for retrieving information from the internet.
To put it in even more context, the evaporation off Lake Mead alone is four times our annual usage as a community".
However, the Subcommission on Triassic Stratigraphy has recommended retaining its usage as a Triassic stage, and their recommendation has been followed in this article.
Youth culture will increasingly view soft-drug usage as a recreational choice on a par with use of tobacco and alcohol.
His training as a surgeon gives him an inherent literacy in some of the technical aspects of this complex subject, and he is certainly correct to identify drug usage as a threat to the integrity of the Games.
The media frequently make unfounded and exaggerated links between a diagnosis of schizophrenia and violent behaviour, while the bastardisation of the term "schizo" is in common usage as a particularly demeaning insult.
It is likelier to be far harder in the US for the defendant to argue that the word Kraftwerk is in common usage as a simple description of its product.
Rather, it is a provocative interrogation of Shakespeare's play, and most particularly of its antagonist, Shylock, whose name has passed into common usage as a byword for usury and malice or, conversely, antisemitism.
It used analysis of food bank usage as a way of determining the problem.
Often economists look to electric power usage as a reality check.
Plus-sign is used for indicating usage as a key in Cassandra database modelling.
