Cost Of CompromiseOr Why Titanic sank?

- Mahendra Patel, GNFC Ltd., Bharuch

Do not compromise when Quality is concerned, you never know the final cost of a smallcompromise. Being part of industrial community we can hardly underestimate the impact qualitystandards may have on the shape of end results. Sinking of Titanic is one such case in pointhere. Who could believe that compromise on quality of as small and trivial an item as a rivetwas the root cause of the entire catastrophe? But, as the investigations have revealed, this isthe reality that surfaced out from the wreckage of this vessel, once thought "Unsinkable" andnow resting on the sea bed in two pieces 12,600 feet apart.

An engineering tragedy consists of a series of events, some normal and some unusual,occurring in a sequence with a certain timing, for the accident to take place. What are thoseevents responsible for sinking of Titanic? How they occurred? Research investigations havebeen piecing together the details of what really occurred on April 14-15, 1912, after Titanicstruck an iceberg, broke in half and caused deaths of more than 1,500 people. Why did the46,000-ton ship sink in just two and a half hours? Well, the answer to this most elusive questioncomes in a report from NIST (National Institute of Standards and Technology, Maryland). AsNIST metallurgist, Timothy Foecke says in the report, the culprit is most probably one ofTitanic's smallest components -- the 3 million wrought iron rivets used to hold the hull platestogether.

Foecke performed metallurgical and mechanical analyses on steel and 48 rivet samplesrecovered from the Titanic's hull. His examinations revealed that the wrought iron in the rivetscontained high slag (the glassy residue left behind after the smelting of ore), more than threetimes the allowable amount, thus making it less ductile and more brittle hence prone to fracture.This finding provides strong evidence that Titanic's collision with the iceberg caused the rivetheads to break off, popped the fasteners from their holes and allowed water to rush in between

the separated hull plates, as published in various reports1, 2 from NIST.

Earlier in 1991 two groups in Canada suggested possibility of brittle fracture of the steelplates at ice brine temperatures, which was later on ruled out based on more relevant slow bend

testing of four hull plate samples, which showed average toughness of 55 MPa-m1/2 at 0° C,quite good for this application. Again, this confirmed that it was not brittle steel, but the rivetedseams that gave way under impact.

Titanic was built between 1911 and 1912 by well known shipbuilder M/s. Harland & Wolff,and she was designed to be ‘virtually unsinkable’, to stay afloat even if four of her 16 watertightcompartments would get flooded with water.

Titanic’s hull was triple riveted within the central 3/5th length using mild steel rivets, anddouble riveted using wrought iron in the bow and stern. This was done to assure strength in thecenter which gets the maximum wave flex stresses. Analysis of the steel rivets showed goodstrength, but the wrought iron rivets contained three times more slag than optimal levels. Inaddition, the slag was in large clusters. Both of these facts indicate fabrication by inexperiencedtradesman, as wrought iron was made by hand at the time.

Finite element models of rivets made from substandard materials show that they werealready loaded near their ultimate strength when installed. The source of this poor qualitymaterial became clearer during researching in the Harland & Wolff archives, they discoveredthat the shipbuilder's ambitious plans to build three large ships at the same time had put a hugestrain on its shipyard. "Not because of cost, but because of time pressures, they started usinglower-quality material to fill the gaps," says Foecke. It also became very clear from their minutesof meeting that the pressure to finish Titanic in hurry, caused the company to order wrought ironthat was one level below that generally specified for rivets and they had to use supplierspreviously uncertified for this application. The substandard rivets were pounded by hand into theship's bow and stern, where the large machines required to pound in steel rivets didn't fit. Steelrivets, meanwhile, which are much stronger than iron, were put in the more-accessible middle ofthe ship. So after collision with iceberg, the seams with wrought iron rivets opened up, and asFoecke says, it's no accident, that the flooding stopped at the point in the hull where the steelrivets began.

Titanic experienced a glancing impact with an iceberg roughly ten times her size alongher starboard bow, described by survivors as ‘slight’ and ‘a rumble’; a fairly minor impact. Thecollision opened six compartments to the sea, and she sank in two and a half hours. In the areaof the hull where most of the damage is contained, the seams consist of double rows of wroughtiron rivets. NIST believes that if the iron rivets had been of high average quality, or if thedesigners had opted for triple rows of rivets or to use steel instead of iron, then fewercompartments would have flooded. If it had been five compartments, with the Carpathia only sixhours away, she would have stayed afloat long enough for most people to have been rescued. Iffour compartments had flooded, she might have even limped into Halifax, thus avoiding thecasualties.

It is not to suggest that the ship would not have sustained significant damage in thecollision if she had been built differently, but rather she would have sunk more slowly. And withthe shortage of lifeboats, the time she spent afloat made all the difference in the tragedy. So, atthe end of the day, it is Quality that matters - even of a negligible component like a rivet.

References :

1. Materials Today, Elsevier, Oct-2008, Vol. 11, No. 10, p. 48

2. "Titanic Metallurgy" , in the Biweekly newsletter of NIST, Feb. 17, 1998.

3. Metallurgy of RMS Titanic, Report No: NISTIR 6118, Inquiries: mail to inquiries@nist.gov.

4. What Really Sank The Titanic - New Forensic Discoveries (Citadel 2008).