this

code/game/objects/items.dm

@@ -1,4 +1,5 @@
 GLOBAL_DATUM_INIT(fire_overlay, /mutable_appearance, mutable_appearance('icons/effects/fire.dmi', "fire"))
+GLOBAL_DATUM_INIT(welding_sparks, /mutable_appearance, mutable_appearance('icons/effects/welding_effect.dmi', "welding_sparks", GASFIRE_LAYER, ABOVE_LIGHTING_PLANE))
 
 GLOBAL_VAR_INIT(rpg_loot_items, FALSE)
 // if true, everyone item when created will have its name changed to be

code/game/objects/items/tools/weldingtool.dm

@@ -119,6 +119,11 @@
 	dyn_explosion(T, plasmaAmount/5)//20 plasma in a standard welder has a 4 power explosion. no breaches, but enough to kill/dismember holder
 	qdel(src)
 
+/obj/item/weldingtool/use_tool(atom/target, mob/living/user, delay, amount, volume, datum/callback/extra_checks)
+	target.add_overlay(GLOB.welding_sparks)
+	. = ..()
+	target.cut_overlay(GLOB.welding_sparks)
+
 /obj/item/weldingtool/attack(mob/living/carbon/human/H, mob/user)
 	if(!istype(H))
 		return ..()