Price in structural steel is discussed per tonne, but tonnage is only one input to cost. The same 500 tonnes can produce a difference of up to forty per cent between two projects.
The most common mistake in comparing quotations is to take the rate per tonne as the only measure. A fabricator's cost, however, builds up in hours: cutting hours, welding hours, blasting hours, painting hours, crane hours. Tonnage explains only part of those hours.
Piece count matters more than tonnage
A 500-tonne structure may consist of 1,200 pieces or of 3,500. Every piece is cut, drilled, marked, moved, welded, blasted, painted, labelled, loaded and erected separately on site. Most of these steps are fixed per piece and independent of weight.
As a result, the rate per tonne rises as the piece count per tonne rises. A roof made up of heavy columns and primary beams is markedly cheaper than a structure of the same tonnage dense with light purlins and connection components.
Connection complexity
A pinned fin plate connection is a few minutes' work. A stiffened, end-plated, preloaded moment connection requires many times as much preparation, welding and checking.
Knowing the distribution of connection types at the quotation stage is as important as knowing the tonnage. If the connection details have not yet been resolved, who owns that scope must be stated explicitly; otherwise two quotations are not pricing the same job.
Coating system and surface preparation
Between a single primer coat selected for C2 corrosivity under ISO 12944 and a three-coat system for C5 there is a difference in both material and labour. As the dry film thickness rises, so do the number of coats, the overcoating intervals and the number of check points.
Where hot-dip galvanising is involved the picture changes completely: the piece has to fit the galvanising bath, drainage and venting holes have to be designed in, and an allowance made for distortion after galvanising. If these are not discussed before quotation, a revision follows.
Execution class and extent of inspection
The difference between EXC2 and EXC3 is not merely a letter. The extent of non-destructive testing rises, welding procedures are approved over a narrower range, traceability descends to the piece and the documentation grows.
How much of this reaches the price varies by project, but it is never negligible. If the execution class is not stated in the design, every firm quoting makes a different assumption and the prices become impossible to compare.
Site conditions
Crane access, working height, whether existing production continues and any restriction on working hours all bear directly on erection cost. Working nights and weekends in a plant that does not stop production is markedly dearer than working on an empty site.
In the same way, the delivery location matters less for haulage distance than for transport gauge. Pieces exceeding gauge need special permits, escort vehicles and sometimes night transport, and that feeds straight through to the rate per tonne.
The five pieces of information a sound quotation needs
In our experience five headings are enough to establish the scope clearly: shop drawings or a concept design, a bill of quantities, the execution class, the coating system and the target erection schedule.
A quotation prepared from this is comparable. Quotations obtained on incomplete information, by contrast, are generally prepared on the lowest assumption, and the difference comes back as a variation once fabrication has started.
