Where is firebrick likely to break when raising the boiler furnace temperature too rapidly?

When raising the boiler furnace temperature too rapidly, firebrick is most likely to break at the anchor bolts. This is due to the thermal stresses that occur when the firebrick expands unevenly. The anchor bolts, which secure the firebrick in place, prevent natural expansion of the brick. As the temperature increases, the firebrick expands, but where it is restrained by the anchor bolts creates areas of stress concentration. This uneven expansion can lead to cracking or breaking of the firebrick at those points because they cannot move freely to accommodate the increase in temperature. Essentially, the integrity of the firebrick is compromised at locations where it is held in place, making the anchor bolts a critical point of failure in this scenario.