The cracking is most likely chloride induced stress cracking. When it is external, the most usual source for the chlorides is the insulation. Weld repair of major cracks can sometimes be done. However, usually the heat of welding will cause crack growth and/or new cracks to form. <br><br>If the cracking is extensive, it could lead to catastrophic failure of the vessel. In general, if a vessel has chloride stress cracking, it will need to be replaced.