Intiger meta value with ‘>=’ returns posts with lower value

The meta type needs to be set as numeric.

'type'    => 'numeric',

The full Query:

Array
(
    [post_type] => post
    [posts_per_page] => 45
    [paged] => 0
    [orderby] => modified
    [meta_query] => Array
        (
            [0] => Array
                (
                    [key] => duration
                    [value] => 30
                    [type] => 'numeric';
                    [compare] => >=
                )

        )

);