A firetube boiler is built to last a very long time, and for good reason; these are the boiler types used in the old steam locomotives, so they had to work well on long journeys with no repair resources in sight. They were built to last from the get-go.
Still, they eventually wear out beyond repair capability. When it's time to replace one, you have a chance to remedy any issues you had with your old boiler. For firetube boilers, increased safety is valuable, especially because you can never do too much to prevent damage and explosions.
Thermal Shock Protection
The heat of the water, flame, and gas that the insides of the boiler are exposed to can lead to thermal shock, damaging the material that comprises the boiler. Parts can corrode easily, leading to the need for repair. A boiler built to withstand thermal shock will have features such as a larger space for steam; instead of having all of the steam pass through a smaller space that can easily become damaged if the steam vent is blocked and the pressure too high, the steam now has a larger "waiting" space that reduces the pressure on the boiler material. The materials used to construct the innards of the boiler are also more corrosion-resistant now, leading to a longer life in use.
Vibration and Warping Prevention
The heat within the firebox, as well as vibration from the boiler and nearby equipment, can create warping in the metal housing of the boiler. Look for ties around the firebox that stabilize it and that have holes that allow warning leaks to appear. Once you see those leaks, you know you need to replace the ties to prevent warping. Otherwise, if you don't know the ties have corroded, the sides of the firebox can warp beyond repair before you know that anything is wrong.
Explosion Early-Warning Fittings
Look for fusible plugs. These melt when the firebox becomes too hot to be safe. This can occur if the water level drops below what is needed to keep the boiler at a safe temperature. If the firebox heats up too much, the boiler can explode. With fusible plugs, you get a warning. Fusible plugs aren't new, and you should have had them on your previous boiler. But the current technology to make the plugs may have improved substantially between the time you purchased your old boiler and now.
Industrial boilers are very good at what they do, and your workers and company deserve the safest boilers you can afford to get. It doesn't take much to make a boiler better to use. Be sure your new boiler has ample safety features. Contact local firetube boiler manufacturers for more information.