As a marine engineer of some 50 years or more, I can assure you all that the LP cylinder would not explode under any circumstances at the time of the sinking as the engines had not been used for some hours. In any case the term "low pressure" kind of gives it away, in that the steam from the IP cylinder entered the LP at 24psi and exited to the turbine or condenser at 9psia (below atmospheric), so around the pressure of a Manchester fog... The ship reported as having the "lp cylinder blow out" was probably the same exact reporting as when QE2 (whilst still a steamship) suffered an engineroom fire "when an oil pipe running through the boiler burst". I think we can all imagine the Board of Trade allowing oil pipes to pass through boilers...
Back to the LP cylinder lying on the seabed - when the ship broke in two
due to extraordinary stresses on the hull, it broke around the forward end of the engines, resulting in the LP cylinders being broken off, to fall with the rest of the wreckage to the ocean floor. Either that or they broke off as the stern spiralled to the bottom or when it eventually hit the deck (I don't know how far from the main wreckage the cylinders lie).
The engines themselves consist of a heavy bedplate that houses the main bearings, crankshaft and the oil sump. This is attached to the "tank top" by means of "holding down bolts" (which I have tightened on more occasions than I care to remember). The tank top is actually the top of the double bottom tanks which hold various fluids such as oil, fuel (though not in Titanic's case) and water, or left empty as "cofferdam spaces". If you turn the ship upside down, there is little chance of the holding down bolts keeping the engine in place, and it will likely tear itself loose and fall out, as they are only intended to hold the engine in place under normal (upright) forces. Even the propeller forces are not visited on the holding down bolts, as that is the job of the thrust bearing (or bearings in Titanic's case) which takes the thrust of the propeller to avoid shoving the engine through the forward engineroom bulkhead.
On top of this bedplate are mounted the engine cylinder columns, which are heavy items bolted to the bedplate at the bottom and on which the hp, ip and lp cylinders are mounted at the top. Whether the lp cylinder broke loose at bedplate, column or cylinder level I don't know as the photos are not that clear, but any of them are possible.
In this rather nice picture of a model Titanic port main engine from the Titanic Research and Modelling site (
Titanic's Portside Engine - Part 1) you can see the bedplate at the bottom (at the bottom level of the ladder). That's the tank top. Also bolted to the tanktop is the thrust bearing assembly, the row of collars seen at the after end (furthest right on the picture) with the flange that connects to the first line of shafting going to the propeller. The pump is likely to be the thrust bearing oil pump. The detail of the flywheel is interesting, where you can see the cylinder and worm gear of the steam engine that operated the "turning gear" to turn the engine at low revs during maintenance or warming through.
Working up, you can see the "A" frame columns that support the guides, reversing gear and other bits of kit. On top of the columns are the cylinders themselves, with the large LP cylinder at the after end, "sister" of the one of the same size at the forward end which is not visible on the picture.
(This model is really beautiful - wish I had it...) This is the inner side of the port main engine where you can see the LP cylinders more clearly at each end. The detail of the model is incredible - you can see the starting platform in the centre with the large wheel and the various gauges mounted on a stand. Looking at the forward LP cylinder, I would think that the likely break-up happened at the cylinder level rather than at the column level, or maybe somewhere in-between - who knows? Perhaps we will be lucky and further exploration of the wreck will concentrate more on the marvel of her propelling machinery than the inside of the 1st Class passenger spaces, all of which have been over-documented to infinity and beyond in this engineer's opinion!
