The work of flanging usually warps a plate more or less, though the work of straightening can frequently be done before it goes to the annealing furnace. Flanged plates are placed in a large coal or oil-burning furnace, heated red, and drawn out on a level floor of cast-iron slabs to be straightened by mauls and flatters.

Annealing also takes place in a large furnace. The annealing heat is best gaged by a pyrometer, and it is the best practice to allow plates to cool gradually in the furnace by shutting off the fuel supply.

After annealing, flanged plates are then ready for marking with the location of rivet, tube and stay-bolt holes, which could not be marked before flanging, as a slight distortion of the plate would warp these marks out of position.