Corrosion of steels and irons immersed in natural seawater for up to 600 years

Marine immersion corrosion observations for archaeological and other data, including from shipwrecks, wrought iron anchors and cast iron bridge piers are used to estimate corrosion losses in natural unpolluted coastal and near-coastal seawaters for exposures up to about 600 years. Empirical functions for the development of corrosion loss with time were then developed, standardized to 20˚C mean seawater temperature. The resulting slightly non-linear corrosion loss trend, represented by a modified form of the power law, is consistent with Phase 4 of the previously proposed bi-modal corrosion model. These observations support the notion that the rate of long-term corrosion is controlled by outward diffusion, through the rust layers, of gaseous hydrogen generated by the cathodic hydrogen evolution reaction under predominantly anaerobic corrosion conditions. The power-law trend also provides good extrapolation from shorter- term data. For practical purposes for exposures < 100 years in seawaters with mean temperature around 20˚C, a linear model, with longer-term corrosion rate 0.06 mm/y at 20˚C, is sufficiently accurate.

LOCKING SYSTEMS IN BULGARIAN LANDS IN THE 16- 19 CENTURIES

В статье исследуются замковые системы на болгарских землях XVI - XIX вв. Замки рассматриваемого периода в основном изготавливались из кованого железа и отличались главным образом своим декором. Несмотря на свою уникальность, они представляют собой всего один базовый тип -замок с поворотным ключом. Существует несколько разновидностей этого замка, но их основная конструкция оставалась неизменной на протяжении веков. Модель была широко распространена в болгарских землях, замки этого типа предпочитали из-за простоты, надёжности и прочности. Из-за их относительно высокой цены очень немногие люди могли себе их позволить, и поэтому сохранившихся экземпляров этого периода не так много. Чаще всего их использовали для запирания общественных зданий, церквей, а также домов самых богатых купцов. Дешёвый импорт замков промышленного производства и навесных замков, импортированных из Западной Европы, которые широко использовались в конце XIX в., привёл к отказу от традиционных металлических замков ручной работы. The present article researches the locking systems in Bulgarian lands during 16-19 centuries. The locks during the considered period are mainly made of wrought iron and are distinguished mainly by their decoration. Despite their uniqueness, they are just one basic type - a rotary key lock. Several varieties of this lock exist, but their basic construction remains unchanged over the centuries. The model is widespread in the Bulgarian lands. It is preferred for its simplicity and reliability. The main requirement for the locks of this period is their physical strength. Therefore, they are always made of solid wrought iron. Due to their relatively high price, very few people could afford them and therefore there are not many preserved specimens from this period. Most often they are used to lock up public buildings, churches, as well as wealthiest merchants’ houses. The cheap imports of industrially produced locks and padlocks imported from Western Europe -which were widely used at the end of the 19 century - led to the abandonment of traditionally hand-made metal locks.

Long-term immersion corrosion of irons and steel in seawaters with calcareous deposition

The marine immersion corrosion of irons and steel under calcareous deposition (principally calcium carbonate) is known to be relatively low for shorter exposures (e.g. a few years). Herein the effect of calcareous deposition on corrosion is considered for exposures up to 1300 years. The data are derived from archaeological steel and iron shipwrecks, cast iron cannons and cannonballs, and wrought iron anchors in locations where there was direct evidence, in and on the corrosion products, of calcareous deposition. Such deposition promotes formation of calcium and ferrous carbonate layers of low permeability on and within rusts. These tend to inhibit both early and long-term corrosion rates. The data show that up to about 200y exposure corrosion losses as a function of time can be approximated closely by a linear function of time. Longer exposures follow a moderate power-law function, consistent with diffusion considerations. Comments are made about the likely interplay between calcareous deposition and microbiological corrosion.

The Rakaia Gorge bridge deck replacement and seismic strengthening

<p>The Rakaia Gorge No. 1 Bridge on SH77 is a Category 1 Historic Place constructed circa 1882. The 55m span ‘Bollman-like’ truss is recognised as unique in the world and is also one of the oldest wrought iron bridges in New Zealand. To ensure that this important structure continued to provide a safe and resilient transport route, the deteriorating timber deck required replacement. Some innovative solutions were required to resolve the numerous challenges presented by this unusual structure related to load capacity, heritage effects, operational safety, seismic resilience, constructability and traffic management. The project sensitively balanced the conflicting objectives of state highway operations and heritage preservation – refurbishing the deck and providing seismic resilience to this strategically important structure, whilst respecting the heritage significance and successfully preserving the exceptional landmark appearance of the bridge.</p>