I haven't read Abercrombie. But yes, early steam engines were very limited by the strength of the available materials. The first, the Newcomen engine, was what is called an atmospheric engine. There was a very big pot boiler, which very likely was made of hammered copper sheets riveted together and tinned.. It was connected with more copper pipes to a steam cylinder that was cast brass. A weighted piston drew steam from the boiler into the cylinder, a valve flipped cutting off the boiler, a spray of water condensed that steam, and the collapsing steam created a vacuum. Because of that vacuum, there was atmospheric pressure sitting on top of the piston, which pushed it down. So the whole system was very low pressure. In fact, the only thing which had much pressure on it at all was the steam cylinder- and that was pressure from the outside and would never be greater than atmospheric pressure, or 14.7 psi (pounds/square inch). Almost certainly less, as the Newcomen engine typically had a little air left after every stroke. And the piston was sealed with oakum- greasey rope- held down with weights.

Bolton and Watt's improved steam engines were more efficient. For any steam engine, this means increasing the heat going in, and keeping heat from being drained off before it does work. To get hotter steam, the boiler was run at around 14 psi. But they were still atmospheric, running from a vacuum created in the steam cylinder.

It was quite difficult in the earlier 18th c. to make very good castings, and also very good to machine anything big. The rough bore of a newly-cast brass Newcomen steam cylinder was cleaned up not on a boring machine but by several men dragging an iron block, coated with emery powder, back and forth until the bore was smooth. James Watt would brag about finding a workman who could file-fit a piston for a steam cylinder to within a worn farthing's thickness... perhaps a millimeter. So, not only was there a problem with the strength of materials, but the tolerances needed to actually keep high-pressure steam from leaking.

The first engines that used steam in a compressive way would be created ( by Oliver Evans and Richard Trevithick) in the early days of the industrial revolution, around 1800. Stronger boilers could be made from iron plates ( or, better yet, iron pipes) and machining large things became easier. Even those, however, would run at a modest steam pressure, perhaps 70 psi, compared to the engines of the later 19th c., that would run at over 100 psi. And the early high pressure engines were regarded with some suspicion. Atmospheric engines would be used well into the 19th c. and some would still be pumping water from mines in the late 19th c.

And even when materials improved , so that boilers could be made from very heavy riveted steel plate, with steel tubes, there was always a risk of disaster. If the boiler was run dry it could get very hot, and if water was suddenly pumped into an overheated dry boiler the sudden pressure spike from the steam created could tear it apart, and a large steam boiler explosion released enough energy to not only blow apart a Mississippi steamboat ( like the one which killed Mark Twain's bother Henry Clement) but in a stationary powerplant in a factory could level buildings. To this day there are pretty stringent requirements for "pressure vessels" or boilers, requiring they be regularly inspected, and registered.

Metallurgical development was important but not as important as development in machine tooling. Early steam engine development was less an issue of keeping the boiler from exploding than keeping it from leaking. Comparatively, the casting of solid piecework like canon was much more trivial -- you can have tolerance issues on a field piece that would be fatal to a pressure vessel or its fittings.

Early steam engines -- both Abercrombie and Stephenson get this right as fictionalists -- were stationary replacements for traditional power sources like water. Because it was not technically feasible to build up big head pressure for quite a while, the steam provided power through contraction not expansion/pressure in these early devices. Abercrombies leap from the mine works to the (spoiler) in the timeframe in his books strains credulity, but maybe less than the Long Eye

Pieces were exploding all the time in the age of sail and early artillery, so I don't find that hard to credit in the fictional work, especially since the societies at hand had neither mastery of the powder technology or the metallurgy, but that's speculative in the literal sense that world does not in point of fact exist.

James Watt gets all the sexy rep and an SI naming credit, but check out "Newcomen: the prehistory of the steam engine" for the real real.