What sort of equipment? Is this arc or gas welding? Electrical equipment needs periodic inspection and, for welding equipment, I would strongly recommend testing because of the hostile environment in which it is often operated. Gas equipment needs inspection and periodic replacement of regulators, flashback arrestors. Exhaust ventilation requires inspection and testing. The accessories and personal protective equipment should also be inspected.

Gas equipment. What do most people do - have inspection performed by outside experts or always go with in-house trained folk?