On completion a hydraulic test is performed and when the loco is finally ready, a steam test ensures that the various gauges and particularly the safety valves are working satisfactorily. A boiler certificate is then issued which is for 3 years for copper boilers and 2 years for steel boilers. The codes specifiy a maximum size for which they are applicable to. Beyond this, approvals need to be obtained from the State authoritites. The maximum pressure allowed for under the code is 100 pounds per square inch.
Some kits provide castings for many components.
In the usual engine castings are usually needed for the wheels, cylinders, cylinder covers and valve chests and the eccentric straps. Some other components such as chimneys, domes, axleboxes and hornways are usefully done with castings. Some of these may be of aluminium, while fabrication from steel or brass is often a good option and can reduce the cost. If you want to try your hand at pattern making, you can have castings done to your own patterns. The best place to get help is by joining a club.