I have a polygon layer which looks like this .
I used the QGIS
multiparts to singleparts tool and also
polygon to lines. In both cases i got this type of result
I want to extract polygon into individual lines like this
You could use line-to-polygon tool (See How can I transform a polygon to a linestring in QGIS?) followed by v.clean command (See http://grass.osgeo.org/grass64/manuals/v.clean.html).