I been using evergreen styrene strip to make wield seam.using the 0.25 x 0.5mm strip.but I am wondering if this is right size for making seams.
or is there an alternative other than styrene strip.

I use stretched sprue. Plenty of it on hand after a build. Plus, that way you can stretch to whatever thickness you need.

Steve

There is no "right" size. It would just depend on the seam you're trying to replicate.

Archer decals do 3D printed welds on decal film in a number of shapes and sizes.

. But it's not free .

You can use thick putty, white glue or ca glue. These won't make fancy welds, but work well for regular seams.

Archer weld seams are convenient and relatively easy to use. However...they're not particularly convincing as they are too regular in shape (too V-shaped) and spacing. They also don't take to curves well - they will wrap around a cylindrical shape, but not well around flat curves ie; bases of cupolas, etc. Stretched sprue, or putty, make more convincing weld seams. Use a round-headed tool (a burnisher, or even a toothpick sanded round, depending on the width of the seam) to press into the soft weld material to make the flow marks.

Here is my technique. I'm used to mask the area with paper tape, 1 or 1.5mm. I then apply 2 layers of Gunze Sangyo Mr 1000 liquid putty. The first layer is applied withut any modification and let dry for about 10 seconds. The second layer is then applied and after 5-10 seconds I'm used to remove the tape so the putty coat could easily sit down on the surface. After that I took an X-Acto cutter and made an irregular welding job. Let it dry for one hour at least and the carefully sandpaper the edges (not showed on the attached picture).