Steel — themain component

Why the wall thickness is 30% above the industry minimum

The main material for shells, furnaces and tube sheets is pressure-vessel steel, P355NL1 and P265GH to EN 10028-2. These grades are intended for pressure equipment: they keep their ductility in the cold, tolerate cyclic loading from start-ups and shutdowns, and are not prone to embrittlement in the heat-affected zone of a weld.

The calculated wall thickness required by the codes is the minimum at which the structure passes on strength in the as-new condition. Service adds what the codes allow for only in part: oxygen in the make-up water, deposits on heating surfaces, daily thermal cycles. We add 30% over the industry minimum and spend that margin not on strength but on service life.

Corrosion allowance

Wall thinning does not take the boiler outside its design strength after a few years in service.

Resistance to cycling

A thicker wall responds more gently to temperature swings during frequent start-ups.

Less distortion

A stiff shell breathes less as it heats up, and the lining holds its geometry for longer.

Repairability

There is metal to weld in a patch or a branch without losing section.

Where a boiler needs creep-resistant steel and what a creep calculation is

Not every part of the structure works under the same conditions. Furnace-space components, screens and supports close to the flame run considerably hotter than a wall cooled by water. Ordinary pressure-vessel steel loses strength there under prolonged heating and deforms slowly under its own load.

In such components we use the creep-resistant grades 13CrMo4-5 and X11CrMo5-1: alloying with chromium and molybdenum preserves the structure of the steel at operating temperatures for tens of thousands of hours. That is why we calculate these components not only for strength but also for creep — the accumulation of strain under sustained load. The calculation shows whether a part will hold its geometry to the end of its assigned life or become a consumable.

Thermal insulation: how λ ≤ 0.04 W/(m·K) turns into your gas bill

Losses through the cladding do not show on the nameplate, but they show in annual fuel consumption: every degree on the outer surface is heat that went into the boiler house rather than into the working fluid. The insulation system is designed for λ ≤ 0.04 W/(m·K) and is built up in layers.

Basalt wool

High-density boards, not rolls: loose wool settles and leaves an uninsulated band at the top of the shell.

Reflective screens

They return the radiant component of the heat flow to the wall — without them the heat passes through the insulation as radiation.

Galvanised cladding

Galvanised steel with a protective coating holds its shape and does not rust from condensation.

Joints and branch penetrations get particular attention: that is where thermal bridges form. We design the cladding to be removable, because insulation that cannot be taken apart without damage stops working after the first repair.

Furnace lining: refractory castable and fireclay

The furnace is the most heavily loaded part of a boiler: the material works at temperatures unattainable for steel and takes a thermal shock at every start-up. For lining combustion chambers we use heat-resistant refractory castable rated to 1,600 °C — it allows complex geometry to be formed without building it up from individual pieces, and therefore without unnecessary joints.

In the more demanding zones we back the castable up with fireclay brick: local repair of brickwork costs less than recasting the chamber. The first heat-up schedule, with a controlled rate of temperature rise, is supplied with the boiler — departing from it during installation remains a common cause of early cracking.

Components: a short list of suppliers instead of the cheapest quotation

We build the boiler body ourselves, while the burner, the pumps and the control system come from manufacturers that specialise in those items. We have deliberately kept the list of brands short: the shorter it is, the better our engineers know the equipment, and the more predictable the supply of spare parts years later.

Burners

Weishaupt, Riello, Oilon — for gas, oil and dual-fuel arrangements. The model is selected for the operating regime of the site, not for rated output.

Pumps

Grundfos and Wilo in the circulation and make-up circuits. Selected against the actual system curve so that the pump runs at its duty point.

Controls

Siemens and Schneider, along with regional alternatives approved by our engineering team — they give independence in delivery times and cost of servicing.

Key items come with authorised service: if something fails, you deal not with a reseller but with an organisation that has access to original spare parts. If you need an approved equivalent, or a specific brand to match an installed base, we build the specification around that condition at the approval stage.

What the QC department checks before a plate reaches the cutting table

Every batch of material goes through incoming inspection by the QC department. A fault in the metal missed at the store costs incomparably less than the same fault at the hydrostatic test of a finished boiler, or on your site. The laboratory has a spark spectrometer and a hardness tester, so we check material on the day it arrives.

• Cross-checking the quality certificate against the actual batch marking.
• Spectral analysis of the composition — confirming the grade of steel as it is, not as it is stamped.
• Hardness measurement to assess the as-delivered condition.
• Dimensional checks: plate thickness, deviations from flatness, condition of the edges.
• Surface examination for laminations, corrosion and transport damage.

A batch that fails inspection is returned to the supplier. The results are tied to the order — at handover those documents are available to your specialists.

Stock for 90 days of production is really about your delivery date

The most common reason for missed deadlines in boiler making is not slow manufacturing but the absence of material: the works waits for plate of the right thickness or for a burner, and the customer receives a letter about a new date. We hold stock for roughly 90 days of the programme.

Plate

1,200 tonnes of pressure-vessel steel in the common thicknesses.

Tubes

8,500 metres for heating surfaces and pipework.

Insulation

320 m³ of basalt boards.

Refractory

180 tonnes for furnace linings.

Fasteners

65 tonnes of fixings — usually the very item that brings assembly to a halt.

Burners

120 units — the item with the longest lead time.

The stock works for you twice over. On time: production starts with cutting in the first days after the drawings are approved. On price: buying in large batches ahead of time protects the price agreed with you from movements in the steel market. If the material you need is not in permanent stock, we quote the lead time including procurement straight away, in the offer, rather than moving the date later.