Argentina. I'm pretty sure that gas installations wouldn't pass inspection with non-standard pipes. You could probably use whatever you want for water pipes.
https://www.totaline.com.ar/wp-content/uploads/2016/08/17-Ca...
My Spanish is rather bad, but I think this:
> Los tubos son producidos según los estándares establecidos por la norma internacional ASTM B88 y B88M.
Says that ASTM B88 and it's metric equivalent are accepted. As you'll see from the listed dimensions the latter is truly metric, while the former is imperial.
[1] https://www.enargas.gob.ar/secciones/normativa/pdf/normas-di... [2] https://www.enargas.gob.ar/secciones/normativa/pdf/normas-te...