Web API timespan format issue

Hi,

I am migrating web services from WCF to WebAPI. In WCF we are exposing an element of type TimeSpan, and in the response we are getting it in ISO 8601 lexical format like.

PT14H10M

But the same element in web api is giving me as 14:10:00

I need to expose these attribute in lexical format (ISO 8601) from web api, can you please let me know how can we do it.