The topic of the test lecture, held on 24 January, was "Gas production and transport in the arctic environment of the Barents Sea".
Crack growth and subsidence
Ersdal's work addresses the possibility of extending the life of older structures used in the petroleum activities, exemplified by fixed steel framework facilities, so-called jacket facilities.
The thesis contains a review of the existing rules and standards for such life extension, and provides contributions for further development of such standards.
The problem associated with extending the life of older structures is that they must not represent an increased risk to health, the environment or financial performance.
At the same time, these structures can experience decay in the form of crack growth due to changing loads and corrosion.
In addition, several fields have experienced subsidence of the seabed as a consequence of oil and gas production. This increases the chance that large waves will reach the deck, thus entailing greater strain on the structure. Examples of this can be seen on the Ekofisk and Valhall fields.
Simulation program
As part of his doctoral research, Ersdal has constructed a simulation program. The purpose of this is to enable evaluation of crack growth as a result of variable loads, and overloading of the structure as a result of failure of parts of the structure. If the crack growth has been significant in one part of the structure, the strength of the structure has been studied without including this part.
The simulation program includes a statistical simulation of the probability that the remaining structure can withstand the load from large waves.
The simulation includes the parameter that the seabed subsides over time, which increases the likelihood of waves on the deck, and thus increased loads.
Ersdal has also studied parameters that are important to the safety of the platform, and the value these parameters should have if the platform is to be used longer. These parameters include strength of the structure, how high the platform deck is above the sea surface and the structure's ability to withstand damage to individual parts.
Ersdal has also examined how risk analyses can be used to make decisions on whether structures can be used longer than originally planned. The decision methods used here are weighed against ethical theories.
Ersdal's conclusion is that ethical dilemmas between economy and safety are hidden in some decision methods. Ersdal argues that decision methods must be selected where these ethical dilemmas emerge more clearly.
The title of the thesis is "Assessment of existing offshore structures for life extension". This work was carried out at the technical-scientific faculty at the University of Stavanger and financed through a grant from the Petroleum Safety Authority Norway.
Gerhard Ersdal is a chartered engineer who earned his degree in 1991 from the University of Trondheim (NTH), now the Norwegian University of Science and Technology. He is employed as a principal engineer with the Petroleum Safety Authority Norway.