Ceramic, two-piece, hybrid and metal ferrules, plus wear inserts for tube ends that see ash and dust.
A ferrule takes the heat at the tube inlet,
so the tubesheet and the weld behind it do not have to.
Waste heat boiler tubesheets are protected by ferrules: short sleeves that sit in the tube inlets and keep the hot process gas away from the tube end, the tube-to-tubesheet weld and the tubesheet itself. Below about 1,650 °F (900 °C) gas temperature a metal ferrule often does the job. Above that, the choice moves to ceramic: one-piece round or hex head ferrules, the two-piece ProLok, or a hybrid ferrule with a metal sleeve and a precast ceramic head for secondary reformer boilers.
Most waste heat boilers still protect the tubesheet with round ferrules set in a layer of castable that is held by metal anchors.
Four designs for the tubesheet of a waste heat boiler, from fully ceramic to a metal sleeve with a ceramic head.
Precast heads and stems that separate the structural job from the insulating one, with fiber where castable used to be.
Round heads for castable systems, hex heads that close into one surface at temperature, and when each one fits.
Head and stem in two pieces, joined by a bayonet lock so the stem cannot walk out of the tube under vibration.
A metal sleeve with a precast ceramic head for secondary reformer boilers, in place of refractory cast at the tubesheet.
A tubesheet rarely fails from the heat it was designed for: it fails where the layer in front of it cracks and lets the hot gas through.
Gas temperature at the inlet sets the material. Below about 1,650 °F (900 °C), metal ferrules protect the tube end at moderate cost. Above about 2,300 °F, metal is past its limits and an all-ceramic ferrule is the design to plan for.
Between the two, the boiler decides. Oxygen enrichment, acid gas and hydrogen-rich reformer gas favor ceramic, which does not suffer the metal dusting and carbon monoxide corrosion that alloy ferrules can see.
Particles change the question. Where fly ash, catalyst fines or clinker dust enter the tubes, abrasion wears the tube end long before heat does, and silicon carbide becomes the material to look at.
Not every tube end needs a ceramic head. These parts protect the inlet where the temperature is moderate or abrasion is the main attack.
Carbon steel, 300 series stainless, Hastelloy or Inconel sleeves for inlets below about 1,650 °F, replaced as a sacrificial part.
Thin-walled oxide bonded silicon carbide ferrules for heat exchanger tubes that see hot gas and particles at the inlet.
Silicon carbide inserts that take the fly ash erosion at the inlet of tubular air preheaters and keep the weld intact.
Silicon carbide tube end inserts for cement clinker cooler heat exchangers, in place of cast iron inserts.
Waste heat boilers after sulfur recovery units, thermal oxidizers and sulfuric acid furnaces. Process gas and syngas coolers in hydrogen and ammonia plants, including autothermal reformers and ammonia combustion boilers. Catalyst coolers and nitric acid boilers in refining and chemical processing. In power plants, the same tube end problem appears in air preheaters that burn abrasive fuels.
In the sulfur recovery unit of a US refinery, the first hex head ferrules went in during 1996 in half a shift, where the castable system before them had taken two days. Each later outage was 2.5 to 3 days shorter.
A sulfuric acid plant in Australia retubed a waste heat boiler with 859 tubes and a gas inlet temperature of 951 °C within a three week outage. Hex head ferrules went in 67% faster than round ferrules would.
No drawing is needed. The ferrules are designed from these values:
A short sleeve inserted into the inlet of each boiler tube. It carries the hot gas past the tube end and the weld, so the tubesheet sits behind insulation instead of in the gas stream.
Metal for gas temperatures up to about 1,650 °F (900 °C) and mild abrasion. Ceramic above that, and wherever metal dusting, carbon monoxide corrosion or oxygen enrichment is a concern.
Yes. Precast ferrules sit loose in their tubes, so one ferrule can be pulled for inspection or replaced without breaking out a castable layer.
No. Tube dimensions, pitch, temperatures and gas composition are enough to design the ferrules and the edge detail.
Tell us the tube size, pitch and inlet temperature, and a Blasch engineer suggests which ferrule and which material suit your boiler.
