Question Regarding Titanic’s Rivets During Stress Testing

[Steven CParticipant @stevenc95127]

Hello everyone, I’d like to ask a question that has been at the back of my head for some time now. When some of Titanic’s rivets and hull plating were recovered from the wreck and tested in order to observe their tensile strength. Would the fact the rivets and hull plating being underwater for nearly a hundred years when the test was conducted along with metal-eating bacteria have had any bearing as to the lack of ductility of Titanic’s rivets that was found when they when tested after being raised? I imagine some corrosion would’ve taken place before the wreck was found. I hope someone who knows a bit more about metallurgy might be able to help me.

[Michael GilliganParticipant @michaelgilligan61133]

I’m sure it must all have had some effect … but surely trivial compared with the fundamental problem revealed here:

https://www.nist.gov/nist-time-capsule/nist-beneath-waves/nist-reveals-how-tiny-rivets-doomed-titanic-vessel

MichaelG.

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Foecke performed metallurgical and mechanical analyses on steel and rivet samples recovered from the Titanic debris field at the bottom of the ocean. His examinations determined that the wrought iron in the rivets contained three times today’s allowable amount of slag (the glassy residue left behind after the smelting of the iron ore). The slag made the rivets less ductile and more brittle than they should have been when exposed to very cold temperatures—like those typically found in the icy seawater of the North Atlantic. This finding strongly suggested that Titanic’s collision with the iceberg caused the rivet heads to break off, popped the fasteners from their holes and allowed water to rush in between the separated hull plates.

[Steven CParticipant @stevenc95127]

Forgive me if I am wrong in thinking this but aren’t the rivets on these big ocean liners flush with their plating to minimize any hydrodynamic drag while underway? There would need to be considerable pressure applied from the Berg to not only shear the rivet heads but to pop them from their fasteners as the article suggests, since they are tapered in the middle. The rivets illustrated in the article I think would’ve been placed high above the waterline since they appear to still have their round heads.

[Nigel Graham 2Participant @nigelgraham2]

Strange how so many vessels were built in the same way and served for 20-40 years without problems. Strange how many bridges and other structures built even decades before the Titanic and her two sister-ships, are still going strong despite diurnal and annual (seasonal) temperature cycling for well over 100 years.

The only possible way to ascertain exactly how the iceberg pierced the hull is to examine the entire collision area, which is buried deeply in the sediment, more closely than by “simple” sonar imaging. The sonar will show the overall damage below the silt, but not the reason for lost rivets, and may not even show the difference between rivet-hole and rivet.

A quick calculation suggests the sonar need work at >30kHz just to show a 50mm diameter object as a “something”, be it rivet head or hole, and having seen quite a number of sides-scan sonar images it would take a very skilled sonar operator indeed to identify it from something similar in appearance.  I doubt sufficient definition by increasing the frequency because the higher the frequency the shorter the range and greater the possible loss by absorption and scattering. So spotting rivet-holes from rivet-heads under a deep layer of mud seems far-fetched.

Consequently I also doubt the survey convincingly “saw” all the damage, but what has long been suggested is that the ship flooded enough initially to put the watertight bulkhead tops under the water.

‘

I do question this though:

The slag in the rivets being “(the glassy residue left behind after the smelting of the iron ore)”.

No: wrought-iron is made by re-melting and processing the raw cast-iron, then rolling that. The slag fibres are layers of oxide that form in the rolling. So although some smelting slag might have carried over, generally that explanation does not help the case.

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I think it far more likely that the rivetted joints failed by forces overwhelming the structure, not because any of the metal was fundamentally weak. The hull breaking in half a long way aft would have been an effect of the stern portion lifting from its supporting water.

Though I do wonder what happens to all the contraction stresses in hot-set rivets: do they slowly relieve by age and natural temperature-cycling? If not could they contribute to failure?

I cannot of course presume to question the researcher’s knowledge of his subject but wonder if he has really identified what happened to the ship, or proposes this as a hypothesis.

 

I don’t know if they Rivetted-joint designing was well-established by Edwardian times, and texts I have show joints tended to fail by the plates tearing from the rivet-holes rather than by the rivets breaking. Though once that started the action might well shear further rivets.

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As an aside a biography I read of Isambard Kingdom Brunel said the problem of breaking up the Great Eastern’s huge hull was solved by inventing the demolition-ball, whose blows started the rivets enough for the joints to be dismantled. It did not say how, but this probably bent the plates enough to spring the rivets so they could be cut by hammer and cold-chisel.

 

[Michael GilliganParticipant @michaelgilligan61133]

Speaking only for myself …

I was rather impressed by the 1998 paper

MichaelG.

[Steven CParticipant @stevenc95127]

“Though I do wonder what happens to all the contraction stresses in hot-set rivets: do they slowly relieve by age and natural temperature-cycling? If not could they contribute to failure?”

Regarding your question if rivets do relieve by age and natural temperature-cycling. I’m inclined to say that they don’t. We have all but one surviving ship built by Harland & Wolff in Belfast, most others being sunk during the world wars or subsequent scrapping. The Nomadic was built in 1911 to be a purpose-built tender for the Olympic class ships in the same yard and using the same steel. She still has most of her original 1911 rivets in place and remained largely watertight even after her conversion to a floating restaurant on the seine river, receiving little to no maintenance during that period of years before being preserved.

 

I imagine a modern ship of welded construction and similar tonnage going at a speed of 22 knots and colliding with an iceberg in the same fashion as Titanic did would not sustain similar damage.

[Steven CParticipant @stevenc95127]

Forgive me for my poor wording. What I meant to say in my last sentence. I would think a modern ship with welded construction and tonnage going at a speed of 22 knots and colliding with a berg in the same fashion Titanic did would sustain similar damage Titanic did.

[Harry WilkesParticipant @harrywilkes58467]

Interesting link Michael thanks

H

[David AmbroseParticipant @davidambrose86182]

I remember that at college we were taught how to calculate the shear force on rivets, but were then told that was largely academic, as the contraction of the rivet meant that friction between the plates would mean that such shear forces would not occur.  Tensile failure of the rivet was more likely, although whether this would be true if the hull was ripped open by an iceberg is a moot point.

[Michael Gilligan]

On Michael Gilligan Said:

I’m sure it must all have had some effect … but surely trivial compared with the fundamental problem revealed here:

https://www.nist.gov/nist-time-capsule/nist-beneath-waves/nist-reveals-how-tiny-rivets-doomed-titanic-vessel

MichaelG.

.

Foecke performed metallurgical and mechanical analyses on steel and rivet samples recovered from the Titanic debris field at the bottom of the ocean. His examinations determined that the wrought iron in the rivets contained three times today’s allowable amount of slag (the glassy residue left behind after the smelting of the iron ore). The slag made the rivets less ductile and more brittle than they should have been when exposed to very cold temperatures—like those typically found in the icy seawater of the North Atlantic. This finding strongly suggested that Titanic’s collision with the iceberg caused the rivet heads to break off, popped the fasteners from their holes and allowed water to rush in between the separated hull plates.

“Wrought iron in the rivets”?   By the time the Titanic was built I would have thought wrought iron well obsolete.  Superseded by proper steel but nowhere near as pure (refined) as the steel we use.  I’m guessing that the steel the Titanic was made from was made by the open hearth process, maybe Bessemer process as well.  This would likely account for the impurities in the rivets.

Anyway, reading this thread reminds me I must paint my “wrought iron” gates this year.

[Michael GilliganParticipant @michaelgilligan61133]

Did you read the 1998 paper, John ?

… it is quite explicit regarding the rivets

MichaelG.

[John MCParticipant @johnmc39344]

Michael, if you mean the link you provided, then yes.  Wrought iron began to go out of fashion in the last third of the 19th century, Titanic was built 1909/12.  Therefore almost certain that the rivets were steel rather than wrought iron.

I would like to read Foecke’s paper on the subject rather than someone else’s interpretation.

[Michael GilliganParticipant @michaelgilligan61133]

No John, I mean the actual paper … which is hyperlinked within the brief article.

MichaelG.

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For your convenience … here is the URL extracted from that source:

https://www.nist.gov/publications/metallurgy-rms-titanic

… which then gives you the facility to have a Local Download:

https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=852863

 

[derek hall 1Participant @derekhall1]

Interesting read, however I read the following…

“…..Helping support the rivet theory are two bits of supporting evidence. First, sonar mapping of Titanic’s starboard hull buried in the ocean floor revealed only six thin tears from the iceberg with a total area open to the sea of only one square meter (12 square feet), or less than that of two sidewalk squares. This dispelled the long-believed myth that the iceberg ripped a 90-meter (300-foot) gash in the side of the ship. The actual damage could not have resulted in the flooding that overwhelmed Titanic’s watertight compartments.

I highlighted the bit in bold, so if this did not contribute to the sinking then what did?

[SillyOldDufferModerator @sillyoldduffer]

Tricky question, because it bears on the state of metallurgy and the ship-building methods applied by Harland and Wolfe in 1908.

Metallurgy was far from perfect!  Contemporary magazines like ‘Engineering’ contain many complaints of poor steel quality, such as ‘plates that shatter like glass’.   The Bessemer Process revolutionised mild-steel production, but the product was inferior to modern steels because the purifying blast was done with compressed air, nearly 80% Nitrogen, which didn’t clean fully, and left Nitrides behind in the steel causing brittleness.  Cured later by blowing with pure Oxygen and by eliminating impurities by detecting and removing them chemically, a process that took decades.   But in 1908 steel quality varied mysteriously because the raw materials weren’t pure and the chemistry wasn’t fully understood.  Further, the science of the day had only touched on the effect of low temperatures on metals, which turned out to be significant.

And in 1908 shipbuilding was dominated by riveting plates to girders and columns.  This type of structure is rather weak and excessively heavy, difficult to keep watertight, and the rivets are weak in shear.   Shear strength matters when a plate is struck a sideways blow, or the rivet head is over stressed upwards,  as might happen when a plate is dished by hitting a rock.  It’s possible for seams to break completely open, or for a blow to cause multiple small leaks by popping or stretching rivets during a collision.

Mostly likely cause of the Titanic sinking was about a third of the submerged hull being scraped at high-speed along an iceberg weighing much more than the ship!   Didn’t create a single massive hole, rather a line of serious leaks that bypassed 5 or 6 bulkheads and couldn’t be controlled.   Then it didn’t help that the bulkheads were open at the top, allowing flooding to spread into undamaged compartments as the bow sank.

It’s been suggested that itanic would have survived had she hit the iceberg head-on.  She was designed to do that, allowing the bow to fold, and protecting the bulkheads further back.   Up to 3 flooded compartments were survivable, not 5 or 6.

The collision occurred during unusually cold weather, so the hypothesis that steel-plates and/or rivets were weakened by brittleness isn’t daft.   And if they failed prematurely during the collision, the leak would have been bigger than otherwise, perhaps ending all hope.  However, although they might have made the situation worse, brittle rivets didn’t sink the ship!

As the disaster occurred in modern times, the Titanic’s construction is well documented.  Tom McCluskies “Anatomy of the Titanic” is worth a read.  Thus we know that the ship was built with Wrought-Iron rivets, not mild-steel, and which sizes and head types were used in each section.   Briefly, the shell was held to the frames with pan-head, flush point rivets, that is the outside of the rivet was hammered fairly flat to the plate, as Steven’s diagram above shows.   Looking at the photos, long-shots of the lower hull don’t have obvious rivet heads, but close ups show them distinctly rounded above the plate. I don’t think exact shape would make much difference in this accident – when a 50,000 ton liner swipes an iceberg, the entire structure bends.

Wrought-Iron was made from Pig-Iron, not Cast Iron.   Pig-iron is poor stuff full of slag (mostly silicates) but repeatedly turning and hammering it tended to beat the slag out, improving the Iron whilst imparting a grain structure like wood.   The best Wrought Iron is about as strong as mild-steel, but only along the grain.   It forges and welds easily and resists corrosion.   On the down side, very expensive to make, difficult to machine and the quality is unpredictable.  It improves the more it is reheated and beaten, more art than science.

Thirty years later several Victory ships fell apart due to low temperature brittleness during WW2.   A combination of problems: making the ships from a mild-steel that was low temperature sensitive; squaring off hatchways etc as a welding opportunity introduced stress raisers; and then the ships were routed far north into the stormy Atlantic to avoid U-boats.   The pictured example broke in harbour, others weren’t so lucky!

 

We can’t know for sure exactly what happened to the Titanic.  The US Inquiry was a politicised shambles that failed to ask the right questions, and the British Board of Trade Inquiry didn’t do well either!  Concentrating on blame and emotion rather than the technology left the door wide open to conspiracy and other theories.   The NIST report is more credible than most though.

Dave

[Steven CParticipant @stevenc95127]

Then it didn’t help that the bulkheads were open at the top, allowing flooding to spread into undamaged compartments as the bow sank.

It should be noted the reason why Titanic’s bulkheads weren’t sealed at the top, was because it was and still is against maritime shipbuilding law to fit a passenger vessel with watertight bulkhead decks above passenger spaces with no means to escape. The only reason as to why modern cruise ships are fitted with watertight bulkhead decks is because there is no passenger accommodation below the waterline or anywhere near any of the subdivision on modern vessels. There are various other reasons why Titanic’s watertight subdivision was the way that it was. Titanic wasn’t the first nor last liner with open bulkhead “roofs” take a look at the S.S. United States, Queen Mary, and Queen Elizabeth.

[John MCParticipant @johnmc39344]

Thanks for the link Michael.  I would still doubt the rivets are “wrought iron”.  Steel of the time contained much impurity.  As the paper says, the exfoliated rivets have allowed the slag within to spread (expand?), no doubt giving the appearance of wrought iron in a micrograph.

The report also suggest further analysis is continuing on the rivets, interesting to see the results of that.

I really enjoyed reading the paper, brought back very happy memories of the 10 years I spent working in a metallurgical laboratory.

[Michael GilliganParticipant @michaelgilligan61133]

You’re welcome, John

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

As a slight digression from ship-building, there are a couple of interesting pages here:

https://fet.uwe.ac.uk/conweb/commercial/ironandsteel/section4.htm

MichaelG.

[Steven C]

On Steven C Said:

Then it didn’t help that the bulkheads were open at the top, allowing flooding to spread into undamaged compartments as the bow sank.

It should be noted the reason why Titanic’s bulkheads weren’t sealed at the top, was because it was and still is against maritime shipbuilding law to fit a passenger vessel with watertight bulkhead decks above passenger spaces with no means to escape. The only reason as to why modern cruise ships are fitted with watertight bulkhead decks is because there is no passenger accommodation below the waterline or anywhere near any of the subdivision on modern vessels. There are various other reasons why Titanic’s watertight subdivision was the way that it was. Titanic wasn’t the first nor last liner with open bulkhead “roofs” take a look at the S.S. United States, Queen Mary, and Queen Elizabeth.

From a safety point of view the ideal bulkhead completely seals each watertight compartment from the next.   But this is like a fire prevention solution where all the doors and windows of a house are bricked up, the power disconnected, and Oxygen excluded by filling the rooms full of Halon.  Not practical because a building fireproofed that way is unusable.

Same problem with ships: many practical requirements make it necessary to penetrate bulkheads – pipes, propeller shafts, coal bunkers, power cables, ventilation, and crew/passenger access.    Only warships tend to be fully compartmented, and they’re imperfect too.

Doesn’t matter why the Titanic’s bulkheads were open at the top, the fact is they were! It’s known they were overtopped, causing the stern to rise steeply out of the water as the bow went under.  The section of stern lifted out of the water has no buoyancy, so it’s weight is transferred to the bow end, increasing the flood rate by forcing the holes deeper underwater.    Above a certain angle open topped bulkheads become ineffective and the ship sinks rapidly.

Dave

[John MC]

On John MC Said:

I would still doubt the rivets are “wrought iron”.

…

John doubt’s are probably because his training and experience are too modern!  Later rivets were almost always made of mild-steel, not least because Wrought Iron went rapidly out of production once mild-steel improved.    But the Titanic was built starting in 1908, a slightly old-fashioned design, at a time when Wrought-Iron rivets were still common.

Not much room for doubt: the evidence in favour of Wrought-Iron is pretty solid.  First, Harland and Wolff’s riveting plan specifies Wrought-Iron, and that’s what examples retrieved from the wreck are made off.

Had mild-steel been used instead, the rivets might not have suffered from cold-brittleness, but we don’t know that!  As the Victory Ship failures show, mild-steel can also become brittle!    There’s a suggestion the Titanic’s plate-work also have suffered brittle failures, but we can’t prove that – the plates are too corroded to tell.

Dave

 

[GreensandsParticipant @greensands]

An interesting article in Today’s Times on the Titanic

[Howard LewisParticipant @howardlewis46836]

Was always under the impression that the plates were sheared along a length of the ship, past several bulkheads.

Given the size and speed of the ship, the forces involved must have been ENORMOUS, far in excess of what anyone could have envisaged, for the plates or the rivets.

Like R101, another example of publicity taking precedance over caution.

It’s not speed that kills, it’s the forces involved to decelerate the mass over a short distance.

Many years ago, when in digs in Brighton, the van behind my car was sliced open, end to end, like a food  tin with an opener (Must have missed my car by millimetres!)  The early morning refuse truck was suspected, but after the event impossible to prove.

Howard

[noel shelleyParticipant @noelshelley55608]

Having had the problems of faulty steel plate to deal with in the 70s I would believe anything of steel plate of the 1910s ! Consider the angle of the bow/hull to the iceberg, the speed and the weights of the 2 objects and then calculate the forces on the hull and iceberg. Torn plate,sheared or popped rivets, all are very likely. Why did the aft section not continue to float ? Was the speed of the disaster such that the aft water tight doors were not closed ? How was the shaft tunnel sealed ? So many ifs and buts ?

Small faults and human error all contributed to the loss of many poor souls. Noel

[Steven CParticipant @stevenc95127]

Why did the aft section not continue to float ? Was the speed of the disaster such that the aft water tight doors were not closed ? How was the shaft tunnel sealed ? So many ifs and buts ?

As I understand it when the ship broke in two just aft of the third funnel, her double-bottom keel still attached to both sections dragged the stern under allowing water to flow over the bulkheads.

I think the steel and rivets used to build the Titanic were more than adequate, one must remember she was traveling at an approximate 30 knots before she slammed into the sea floor and still remained largely recognizable until they found her in 1985.

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