1) Start a new part and start a new sketch.
2) Give dimensions and fully constrain you sketch.
3) Exit sketch and select the sketch from the Feature Manger Tree.
4) Keeping your sketch selected, go to File > Save as
5) Change the file type to Lib Feat part (*.sldlfp)
6) Go to location C:\Program Files\SolidWorks\data\weldment profiles\ and create you own folder or use the exiting folders. You can also set you own location and map the path in the File Locations. I have created a folder “Test” and created another folder named “Pipe” inside the test folder. SW will list the levels of the directory as Standard/Type/Size. In this case Test is my standard, Pipe is my type and size is the file name.
7) Give the file name as per your convenience. I have used 2.5OD x .125T.
8) Your file will look like this. Check for the green coloured L and the symbol. This indicates that this file is a SW library file.
9) For checking that everything has been done perfect, open a new part and draw a line. Exit sketch and go to Insert > Weldments > Structural Member.
10) Select Test as standard, Pipe as type and 2.5OD x .125T as size and then select the line. Select Ok.
Perfect. You can now make your own customized weldment profiles.