API 1104 is the standard of the American Petroleum Institute (API) for welding procedure and welding operators qualification, issued specifically for oil and gas pipelines, which doesn' t mean at all that it can not be used for other piping systems, following agreement between the purchaser and the supplier.
You can order the standard directly from API, whose site is www.api.org
I'm not familiar with BS 4515, but I imagine that you can order it directly from BSI (British Standard Institution), whose site I don't know but shouldn't be that difficult to find.
Giovanni S. Crisi
Sao Paulo - Brazil