In welding design what are the different applications of square-groove, V-groove, U-groove and J-groove?

When the base metal is thin (i.e. 0.125” to 0.25”), square-groove can be adopted. Where welding is carried out from one side of the joint, a temporary backup strip can be used to ensure proper joint penetration and to avoid excessive leakage of metal though the joint.

V-groove is commonly used for medium to thick metals (i.e. 0.25” to 0.375”). For even thicker metal plates, U-groove and J-groove can be adopted to provide good penetration of welded metal. One demerit of U-groove and J-groove is the preparation of the metal plates. For instance, air carbon arc and special mechanical cutting tools are required for preparing the joints.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.