Tor Hemmingsen | University of Stavanger (original) (raw)

Papers by Tor Hemmingsen

Corrosion science, Jul 1, 2024

Structural integrity, 2024

A straightforward method was established for the determination of migration contaminants in olive... more A straightforward method was established for the determination of migration contaminants in olive oil with a special focus on the two can-coating migration compounds bisphenol A diglycidyl ether (BADGE) and bisphenol F diglycidyl ether (BFDGE). The preferred sample preparation was a single liquid-liquid extraction of compounds from the oil into 20% (v/v) methanol in acetonitrile, followed by clean-up with solid-phase extraction on aminopropyl bonded to silica. This purification procedure selectively removed all free fatty acids from the extracts without removing phenolic compounds of interest. The solid-phase extraction columns were used many times by implementing a procedure of washing out the strongly retained fatty acids with 2% acetic acid in methanol. Gas chromatography coupled with full scan (m/z 33-700) electron ionization mass spectrometry was used for the determination of several model compounds in olive oil samples. BADGE and BFDGE could be determined in the 0.05-2 mg kg(-1) range in oil samples with a relative SD of <6% (six replicates). The method was used in an enforcement campaign for the Norwegian Food Control Authority to analyse vegetable oil samples from canned fish-in-oil.

IOP conference series, Nov 1, 2021

Several chemical problems can occur during the production of oil and gas through flow lines. This... more Several chemical problems can occur during the production of oil and gas through flow lines. This includes corrosion, scale deposition and gas hydrate plugging. Three separate chemicals may be needed to treat these issues. Kinetic hydrate inhibitors (KHIs) are used in cold oil or natural gas production flow lines to prevent the formation and plugging of the line with gas hydrates. They are often injected concomitantly with other production chemicals such as corrosion and scale inhibitors. KHIs are specific low molecular weight water-soluble polymers with amphiphilic groups formulated with synergists and solvents. However, many corrosion inhibitors (CIs) are antagonistic to the KHI polymer, severely reducing the KHI performance. It would be preferable and economic if the KHI also could act as a CI. We have explored the use of maleic-based copolymers as KHIs as well as their use as film-forming CIs. KHIs were tested using a natural gas mixture in high pressure rocking cells using the slow constant cooling test method. A terpolymer from reaction of vinyl acetate:maleic anhydride copolymer with cyclohexy lamine and 3,3-di-n-butylaminopropylamine (VA:MA-60% cHex-40% DBAPA), gave excellent performance as a KHI, better than the commercially available poly(N-vinyl caprolactam) (PVCap). CO2 corrosion inhibition was measured by Linear Polarization Resistance (LPR) in a 1 litre CO2 bubble test equipment using C1018 steel coupons. The new terpolymer gave good CO2 corrosion inhibition in 3.6 wt% brine, significantly better than PVCap, but not as good as a commercial imidazoline-based surfactant corrosion inhibitor. The terpolymer also showed good corrosion inhibition efficiency at high salinity conditions, (density 1.12 g/cm3). VA:MA-60% cHex-40% DBAPA shifted the open-circuit potential to more positive values and significantly decreased the corrosion rate.

IOP conference series, Nov 1, 2021

Recently, a novel Subsea Shuttle Tanker (SST) concept has been proposed to transport carbon dioxi... more Recently, a novel Subsea Shuttle Tanker (SST) concept has been proposed to transport carbon dioxide (CO2) from ports to offshore oil and gas fields for either permanent storage or enhanced oil recovery (EOR). SST is a large autonomous underwater vehicle that travels at a constant water depth away from waves. SST has some key advantages over subsea pipelines and tanker ships when employed at marginal fields. It enables carbon storage in marginal fields which do not have sufficient volumes to justify pipelines. Further, in contrast to ships, SST does not require the use of a permanently installed riser base. This paper will evaluate the key challenges of using such vessel for CO2 transportation. It discusses the most important properties such as thermodynamic properties, purity, and hydrate formation of CO2 at different vessel-transportation states in relation to cargo sizing, material selection, and energy consumption.

IOP Conference Series: Materials Science and Engineering, 2017

Structures exposed to aggressive environmental conditions are often subjected to time-dependent l... more Structures exposed to aggressive environmental conditions are often subjected to time-dependent loss of coating and loss of material due to corrosion; this causes reduction in the cross-sectional properties of the members, increased surface roughness, surface irregularities and corrosion pits, and degradation of material strengths. These effects have been identified and simulated in different research studies. However, time and corrosive media dependent fatigue strength curves for materials have not been discussed in the design or assessment guidelines for structures. This paper attempts to review the corrosion degradation process and available approaches/models used to determine the fatigue strength of corroded materials and to interpolate corrosion deterioration data. High cycle fatigue and full range fatigue life formulae for fatigue strength of corroded materials are proposed. The above formulae depend on the endurance limit of corroded material, in addition to the stress-life fatigue curve parameters of the uncorroded material. The endurance limit of corroded material can either be determined by a limited number of tests in the very high-cycle fatigue region or predicted by an analytical approach. Comparison with experimentally measured corrosion fatigue behavior of several materials is provided and discussed.

ChemInform, Aug 22, 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

IOP Conference Series: Materials Science and Engineering

Models for predicting top-of-line corrosion (TLC) rates on carbon steels are important tools for ... more Models for predicting top-of-line corrosion (TLC) rates on carbon steels are important tools for cost-effectively designing and operating natural gas transportation pipelines. The work presented in this paper is aimed to investigate how the corrosion rates on carbon steel is affected by acids typically present in the transported pipeline fluids. This investigation may contribute to the development of improved models. In a series of experiments, the corrosion rate differences for pure CO2 (carbonic acid) corrosion and pure organic acid corrosion (acetic acid and formic acid) on X65 carbon steel were investigated at starting pH values; 4.5, 5.3, or 6.3. The experiments were conducted in deaerated low-salinity aqueous solutions at atmospheric pressure and temperature of 65 °C. The corrosion rates were evaluated from linear polarization resistance data as well as mass loss and released iron concentration. A correlation between lower pH values and increased corrosion rates was found for ...

IOP Conference Series: Materials Science and Engineering, 2021

This paper presents a framework based on a recently proposed fatigue strength curve of corroded s... more This paper presents a framework based on a recently proposed fatigue strength curve of corroded steel to assess the life of an existing steel bridge exposed to environment-assisted fatigue. Environment-assisted cracking (EAC) and how it affects the structural integrity of steel bridges are introduced by the framework. Determination of both corroded and uncorroded details in a corrosive environment are also included in this framework. To conform the applicability and significance, a fatigue life of a railway bridge was assessed by methods given in the framework. The obtained fatigue lives were compared. The difference of the estimated fatigue lives emphasizes the importance of having this framework to consider the interaction of corrosion and fatigue mechanisms.

Fatigue & Fracture of Engineering Materials & Structures, 2020

A formula for stress-life curve is proposed to predict the fatigue life of riveted bridges locate... more A formula for stress-life curve is proposed to predict the fatigue life of riveted bridges located in corrosive environments. The corrosive environment-dependent parameters of the S-N curve are determined based on the corrosion fatigue testing results of different types of steel specimens in air, fresh water, and seawater. Eurocode detail category 71 and UK WIrivet detail category represent the fatigue strength of riveted members. The proposed S-N curve formula is compared with full-scale fatigue test results of riveted joints, plate girders, and truss girders, which were tested in a corrosive environment. Thus, the validity of the formula is confirmed. The formula does not require any material parameter other than the code-given fatigue curve of riveted details. The fatigue life of a riveted railway bridge is estimated by using the proposed formula, and the results are compared with conventional approaches. The applicability and significance of the proposed curve are confirmed.

The pH stabilization technique is a widely used corrosion protection method for multiphase gas pi... more The pH stabilization technique is a widely used corrosion protection method for multiphase gas pipelines with glycol as hydrate inhibitor. It implies to increase the pH by addition of 3HCO in order to enhance the formation of protective iron carbonate films. The protection mechanism at ~20°C is of concern because the conditions for precipitating protective corrosion film are less favorable compared to higher temperatures due to the increasing solubility of FeCO3 with decreasing temperature. The scope of the ongoing work is to investigate whether corrosion mitigation of pipelines at ~20°C relies on the formation of protective corrosion films or if the corrosion rate is sufficiently lowered by the elevated pH. This paper discusses the corrosion rate and corrosion potential observed on carbon steel exposed to varying concentrations of 3HCO and Fe2+ at 20°C in a 1wt % NaCl and 50wt % glycol solution purged with CO2 at 1 atm partial pressure. The objective was to promote protective FeCO3...

Journal of Offshore Mechanics and Arctic Engineering

A novel subsea shuttle tanker (SST) concept was proposed as a cost-effective alternative to subse... more A novel subsea shuttle tanker (SST) concept was proposed as a cost-effective alternative to subsea pipelines and tanker ships for liquid CO2 transportation between a source facility and a subsea well. The SST will be deployed to transport CO2 to marginal subsea fields with an annual CO2 storage capacity of around 1 million tonnes. A baseline design was recently developed by the authors to support research work aimed at assessing large and ultra-efficient subsea cargo drone technology. One crucial aspect is the development of SST's operation envelope, i.e., the safe depth versus speed regions. The development of this envelope entails comprehensive and detailed studies of SST's dynamic load-effects under all expected operating scenarios which in the early concept development phase can be performed using suitable computational models. In this technical brief, the initial development of such a model is unveiled. This fully coupled 2D planar model considers the most relevant load...

International Journal of Electrochemical Science, 2019

The oxygen reduction reaction on nitrogen doped multiwalled carbon nanotubes (N-MCNTs) is studied... more The oxygen reduction reaction on nitrogen doped multiwalled carbon nanotubes (N-MCNTs) is studied for its application for deoxygenation of seawater. N-MCNTs were synthesized using commercial MCNTs and polyaniline as nitrogen precursor and annealing at a high temperature. The ORR was studied on N-MCNTs in 0.5 M sodium chloride solution using a rotating disk electrode, and physical characterization of the electrocatalysts was performed using X-ray diffraction, mass spectroscopy and transmission electron microscope techniques. The material showed high activity for the ORR in the chloride electrolyte. The onset potential for N-MCNTs was 0.94 V vs RHE. Koutecky-Levich analysis showed that the electrons transfer mainly followed the four-electron pathway, and the electrocatalyst showed good stability during a 15-h stability test.

2020 International Conference on Unmanned Aircraft Systems (ICUAS), 2020

Industrial use of multirotor drones is gaining traction, and fuel cell based power sources have b... more Industrial use of multirotor drones is gaining traction, and fuel cell based power sources have been identified as a way of improving the flight endurance from what is possible to achieve with current lithium-based battery options. The state-of-technology and barriers for further adoption are presented. It is found that there are lightweight options commercially available and that the viability of powering multirotor drones for long-range and high endurance missions is demonstrated. The barriers mainly relate to the future required level of certification, technical improvements, and operational aspects. For advancing the state-of-technology, liquid-cooled fuel cells are identified as an attractive alternative that can expand the environmental flight envelope. However, a high system mass of these fuel cells remains a constraint. Hydrogen storage is a central challenge, and storage alternatives are investigated. To further improve the adoption of fuel cell based power sources for multirotor drones, operational and financial rewards must be well proven for realistic operations and relevant operating conditions.

Volume 5: Ocean Space Utilization, 2021

A novel subsea shuttle tanker (SST) concept was recently proposed as a cost-effective alternative... more A novel subsea shuttle tanker (SST) concept was recently proposed as a cost-effective alternative to subsea pipelines and tanker ships for liquid CO2 transportation between a source facility and a subsea well. It is envisioned that the SST will be deployed to transport CO2 to marginal subsea fields with an annual CO2 storage capacity less than 1 million metric tons; volumes that do not justify a full subsea field development. The SST is designed to be a fully autonomous underwater vessel with a cargo capacity of over 17,000 metric tons. It is 155 m long and it has a 17 m diameter hull. The vessel may operate at a water depth of between 50 to 200 m in a weather-independent environment. Furthermore, it travels at a slow speed for minimal energy consumption and maximal range. During the offloading process, the SST will approach the subsea well and land on the seabed just outside the safety radius of the well. After that, a remotely operated vehicle (ROV) will mate the offloading flowli...

Ocean Engineering, 2021

This paper presents the baseline design of a 34,000-tonne subsea shuttle tanker (SST). The SST is... more This paper presents the baseline design of a 34,000-tonne subsea shuttle tanker (SST). The SST is proposed as an alternative to subsea pipelines and surface tankers for the transportation of liquid carbon dioxide (CO 2) from existing offshore/land facilities to marginal subsea fields. In contrast to highly weather-dependent surface tanker operations, the SST can operate in any condition underwater. The SST is an electric-powered autonomous underwater vehicle with a length and beam of 164 m and 17 m, respectively. It has a cargo carrying capacity of 16,362 m 3. This capacity is sufficient to allow the SST to fulfil the annual storage demands of ongoing carbon capture and storage (CCS) projects in Norway. It travels with a slow speed of 6 knots at 70 m constant water depth for maximum energy efficiency and offloads CO 2 via a connected coupling to the subsea well where CO 2 is directly injected. To be economically attractive, the SST has a high payload of 50% displacement which makes a low structural weight design extremely crucial. This is achieved by employing a double hull design for the SST with active pressure compensating systems to cope with the large collapse pressure loads underwater.

Fatigue & Fracture of Engineering Materials & Structures, 2019

A formula is proposed to predict fatigue strength of corroded members and joints of steel structu... more A formula is proposed to predict fatigue strength of corroded members and joints of steel structures. The concept of the formula is first studied from recently identified mechanism of corrosion fatigue. Hence, the corresponding fatigue strength curve (i.e. S-N curve) of corroded steel is presented. It is further improved to derive linear, bilinear or trilinear S-N curve for corroded constructional details of steel structures. The parameters of the corroded steel S-N curve are determined based on the corrosion fatigue testing results of different types of steel specimens in air, fresh water and seawater. Hence, the parameters for the derived S-N curve of corroded constructional details are predicted based on the above parameters and tabulated for the detail categories given in the Eurocode and DNVGL code. The proposed S-N curve formula is compared with full-scale fatigue test results of several constructional details, and the validity of the formula is confirmed. KEYWORDS corrosion fatigue, joints and connections, S-N curve, steel structures 1 | INTRODUCTION Corrosion is one of the main structural degradation processes that affect integrity. Fractures due to cyclic stress in corrosive media are designated as corrosion fatigue (CF) which is a type of environmental assisted cracking. The forty percent failures in oil and gas pipelines and 8% of failures in offshore steel structures are reported to be caused degradation/deterioration due to corrosion. Corrosion commonly takes place in the splash zone area of offshore structures as the coating in this area disappears a few years after installation. 1 Recent collapses of steel bridges due to corrosion are reported and some examples are the Silver Bridge in 1967, the Mianus River Bridge in 1990 and the Minnesota Bridge in 2007. 2-4 Though many bridges are located onshore, de-icing salt may simulate marine environment to the bridges in snowy regions. 2 These failures emphasize the importance of more accurate simulation of CF strength of structural joints and connections (i.e. constructional details) in different corrosive environments. 3,5,6 Corrosion pit induced stress concentration models and fatigue notch factor are commonly used to determine structures integrity. 7-10 Fatigue crack initiation life is determined when micro-cracks propagate to certain critical length. Fatigue crack propagation life is determined by fracture mechanics approach. Accurate determination of modified corrosion-fatigue stress intensity threshold and the critical length has been reported as challenging and difficult. 2-4 Therefore, limited amount of published

International Arctic Petroleum Cooperation, 2015

Corrosion science, Jul 1, 2024

Structural integrity, 2024

A straightforward method was established for the determination of migration contaminants in olive... more A straightforward method was established for the determination of migration contaminants in olive oil with a special focus on the two can-coating migration compounds bisphenol A diglycidyl ether (BADGE) and bisphenol F diglycidyl ether (BFDGE). The preferred sample preparation was a single liquid-liquid extraction of compounds from the oil into 20% (v/v) methanol in acetonitrile, followed by clean-up with solid-phase extraction on aminopropyl bonded to silica. This purification procedure selectively removed all free fatty acids from the extracts without removing phenolic compounds of interest. The solid-phase extraction columns were used many times by implementing a procedure of washing out the strongly retained fatty acids with 2% acetic acid in methanol. Gas chromatography coupled with full scan (m/z 33-700) electron ionization mass spectrometry was used for the determination of several model compounds in olive oil samples. BADGE and BFDGE could be determined in the 0.05-2 mg kg(-1) range in oil samples with a relative SD of <6% (six replicates). The method was used in an enforcement campaign for the Norwegian Food Control Authority to analyse vegetable oil samples from canned fish-in-oil.

IOP conference series, Nov 1, 2021

Several chemical problems can occur during the production of oil and gas through flow lines. This... more Several chemical problems can occur during the production of oil and gas through flow lines. This includes corrosion, scale deposition and gas hydrate plugging. Three separate chemicals may be needed to treat these issues. Kinetic hydrate inhibitors (KHIs) are used in cold oil or natural gas production flow lines to prevent the formation and plugging of the line with gas hydrates. They are often injected concomitantly with other production chemicals such as corrosion and scale inhibitors. KHIs are specific low molecular weight water-soluble polymers with amphiphilic groups formulated with synergists and solvents. However, many corrosion inhibitors (CIs) are antagonistic to the KHI polymer, severely reducing the KHI performance. It would be preferable and economic if the KHI also could act as a CI. We have explored the use of maleic-based copolymers as KHIs as well as their use as film-forming CIs. KHIs were tested using a natural gas mixture in high pressure rocking cells using the slow constant cooling test method. A terpolymer from reaction of vinyl acetate:maleic anhydride copolymer with cyclohexy lamine and 3,3-di-n-butylaminopropylamine (VA:MA-60% cHex-40% DBAPA), gave excellent performance as a KHI, better than the commercially available poly(N-vinyl caprolactam) (PVCap). CO2 corrosion inhibition was measured by Linear Polarization Resistance (LPR) in a 1 litre CO2 bubble test equipment using C1018 steel coupons. The new terpolymer gave good CO2 corrosion inhibition in 3.6 wt% brine, significantly better than PVCap, but not as good as a commercial imidazoline-based surfactant corrosion inhibitor. The terpolymer also showed good corrosion inhibition efficiency at high salinity conditions, (density 1.12 g/cm3). VA:MA-60% cHex-40% DBAPA shifted the open-circuit potential to more positive values and significantly decreased the corrosion rate.

IOP conference series, Nov 1, 2021

Recently, a novel Subsea Shuttle Tanker (SST) concept has been proposed to transport carbon dioxi... more Recently, a novel Subsea Shuttle Tanker (SST) concept has been proposed to transport carbon dioxide (CO2) from ports to offshore oil and gas fields for either permanent storage or enhanced oil recovery (EOR). SST is a large autonomous underwater vehicle that travels at a constant water depth away from waves. SST has some key advantages over subsea pipelines and tanker ships when employed at marginal fields. It enables carbon storage in marginal fields which do not have sufficient volumes to justify pipelines. Further, in contrast to ships, SST does not require the use of a permanently installed riser base. This paper will evaluate the key challenges of using such vessel for CO2 transportation. It discusses the most important properties such as thermodynamic properties, purity, and hydrate formation of CO2 at different vessel-transportation states in relation to cargo sizing, material selection, and energy consumption.

IOP Conference Series: Materials Science and Engineering, 2017

Structures exposed to aggressive environmental conditions are often subjected to time-dependent l... more Structures exposed to aggressive environmental conditions are often subjected to time-dependent loss of coating and loss of material due to corrosion; this causes reduction in the cross-sectional properties of the members, increased surface roughness, surface irregularities and corrosion pits, and degradation of material strengths. These effects have been identified and simulated in different research studies. However, time and corrosive media dependent fatigue strength curves for materials have not been discussed in the design or assessment guidelines for structures. This paper attempts to review the corrosion degradation process and available approaches/models used to determine the fatigue strength of corroded materials and to interpolate corrosion deterioration data. High cycle fatigue and full range fatigue life formulae for fatigue strength of corroded materials are proposed. The above formulae depend on the endurance limit of corroded material, in addition to the stress-life fatigue curve parameters of the uncorroded material. The endurance limit of corroded material can either be determined by a limited number of tests in the very high-cycle fatigue region or predicted by an analytical approach. Comparison with experimentally measured corrosion fatigue behavior of several materials is provided and discussed.

ChemInform, Aug 22, 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

IOP Conference Series: Materials Science and Engineering

Models for predicting top-of-line corrosion (TLC) rates on carbon steels are important tools for ... more Models for predicting top-of-line corrosion (TLC) rates on carbon steels are important tools for cost-effectively designing and operating natural gas transportation pipelines. The work presented in this paper is aimed to investigate how the corrosion rates on carbon steel is affected by acids typically present in the transported pipeline fluids. This investigation may contribute to the development of improved models. In a series of experiments, the corrosion rate differences for pure CO2 (carbonic acid) corrosion and pure organic acid corrosion (acetic acid and formic acid) on X65 carbon steel were investigated at starting pH values; 4.5, 5.3, or 6.3. The experiments were conducted in deaerated low-salinity aqueous solutions at atmospheric pressure and temperature of 65 °C. The corrosion rates were evaluated from linear polarization resistance data as well as mass loss and released iron concentration. A correlation between lower pH values and increased corrosion rates was found for ...

IOP Conference Series: Materials Science and Engineering, 2021

This paper presents a framework based on a recently proposed fatigue strength curve of corroded s... more This paper presents a framework based on a recently proposed fatigue strength curve of corroded steel to assess the life of an existing steel bridge exposed to environment-assisted fatigue. Environment-assisted cracking (EAC) and how it affects the structural integrity of steel bridges are introduced by the framework. Determination of both corroded and uncorroded details in a corrosive environment are also included in this framework. To conform the applicability and significance, a fatigue life of a railway bridge was assessed by methods given in the framework. The obtained fatigue lives were compared. The difference of the estimated fatigue lives emphasizes the importance of having this framework to consider the interaction of corrosion and fatigue mechanisms.

Fatigue & Fracture of Engineering Materials & Structures, 2020

A formula for stress-life curve is proposed to predict the fatigue life of riveted bridges locate... more A formula for stress-life curve is proposed to predict the fatigue life of riveted bridges located in corrosive environments. The corrosive environment-dependent parameters of the S-N curve are determined based on the corrosion fatigue testing results of different types of steel specimens in air, fresh water, and seawater. Eurocode detail category 71 and UK WIrivet detail category represent the fatigue strength of riveted members. The proposed S-N curve formula is compared with full-scale fatigue test results of riveted joints, plate girders, and truss girders, which were tested in a corrosive environment. Thus, the validity of the formula is confirmed. The formula does not require any material parameter other than the code-given fatigue curve of riveted details. The fatigue life of a riveted railway bridge is estimated by using the proposed formula, and the results are compared with conventional approaches. The applicability and significance of the proposed curve are confirmed.

The pH stabilization technique is a widely used corrosion protection method for multiphase gas pi... more The pH stabilization technique is a widely used corrosion protection method for multiphase gas pipelines with glycol as hydrate inhibitor. It implies to increase the pH by addition of 3HCO in order to enhance the formation of protective iron carbonate films. The protection mechanism at ~20°C is of concern because the conditions for precipitating protective corrosion film are less favorable compared to higher temperatures due to the increasing solubility of FeCO3 with decreasing temperature. The scope of the ongoing work is to investigate whether corrosion mitigation of pipelines at ~20°C relies on the formation of protective corrosion films or if the corrosion rate is sufficiently lowered by the elevated pH. This paper discusses the corrosion rate and corrosion potential observed on carbon steel exposed to varying concentrations of 3HCO and Fe2+ at 20°C in a 1wt % NaCl and 50wt % glycol solution purged with CO2 at 1 atm partial pressure. The objective was to promote protective FeCO3...

Journal of Offshore Mechanics and Arctic Engineering

A novel subsea shuttle tanker (SST) concept was proposed as a cost-effective alternative to subse... more A novel subsea shuttle tanker (SST) concept was proposed as a cost-effective alternative to subsea pipelines and tanker ships for liquid CO2 transportation between a source facility and a subsea well. The SST will be deployed to transport CO2 to marginal subsea fields with an annual CO2 storage capacity of around 1 million tonnes. A baseline design was recently developed by the authors to support research work aimed at assessing large and ultra-efficient subsea cargo drone technology. One crucial aspect is the development of SST's operation envelope, i.e., the safe depth versus speed regions. The development of this envelope entails comprehensive and detailed studies of SST's dynamic load-effects under all expected operating scenarios which in the early concept development phase can be performed using suitable computational models. In this technical brief, the initial development of such a model is unveiled. This fully coupled 2D planar model considers the most relevant load...

International Journal of Electrochemical Science, 2019

The oxygen reduction reaction on nitrogen doped multiwalled carbon nanotubes (N-MCNTs) is studied... more The oxygen reduction reaction on nitrogen doped multiwalled carbon nanotubes (N-MCNTs) is studied for its application for deoxygenation of seawater. N-MCNTs were synthesized using commercial MCNTs and polyaniline as nitrogen precursor and annealing at a high temperature. The ORR was studied on N-MCNTs in 0.5 M sodium chloride solution using a rotating disk electrode, and physical characterization of the electrocatalysts was performed using X-ray diffraction, mass spectroscopy and transmission electron microscope techniques. The material showed high activity for the ORR in the chloride electrolyte. The onset potential for N-MCNTs was 0.94 V vs RHE. Koutecky-Levich analysis showed that the electrons transfer mainly followed the four-electron pathway, and the electrocatalyst showed good stability during a 15-h stability test.

2020 International Conference on Unmanned Aircraft Systems (ICUAS), 2020

Industrial use of multirotor drones is gaining traction, and fuel cell based power sources have b... more Industrial use of multirotor drones is gaining traction, and fuel cell based power sources have been identified as a way of improving the flight endurance from what is possible to achieve with current lithium-based battery options. The state-of-technology and barriers for further adoption are presented. It is found that there are lightweight options commercially available and that the viability of powering multirotor drones for long-range and high endurance missions is demonstrated. The barriers mainly relate to the future required level of certification, technical improvements, and operational aspects. For advancing the state-of-technology, liquid-cooled fuel cells are identified as an attractive alternative that can expand the environmental flight envelope. However, a high system mass of these fuel cells remains a constraint. Hydrogen storage is a central challenge, and storage alternatives are investigated. To further improve the adoption of fuel cell based power sources for multirotor drones, operational and financial rewards must be well proven for realistic operations and relevant operating conditions.

Volume 5: Ocean Space Utilization, 2021

A novel subsea shuttle tanker (SST) concept was recently proposed as a cost-effective alternative... more A novel subsea shuttle tanker (SST) concept was recently proposed as a cost-effective alternative to subsea pipelines and tanker ships for liquid CO2 transportation between a source facility and a subsea well. It is envisioned that the SST will be deployed to transport CO2 to marginal subsea fields with an annual CO2 storage capacity less than 1 million metric tons; volumes that do not justify a full subsea field development. The SST is designed to be a fully autonomous underwater vessel with a cargo capacity of over 17,000 metric tons. It is 155 m long and it has a 17 m diameter hull. The vessel may operate at a water depth of between 50 to 200 m in a weather-independent environment. Furthermore, it travels at a slow speed for minimal energy consumption and maximal range. During the offloading process, the SST will approach the subsea well and land on the seabed just outside the safety radius of the well. After that, a remotely operated vehicle (ROV) will mate the offloading flowli...

Ocean Engineering, 2021

This paper presents the baseline design of a 34,000-tonne subsea shuttle tanker (SST). The SST is... more This paper presents the baseline design of a 34,000-tonne subsea shuttle tanker (SST). The SST is proposed as an alternative to subsea pipelines and surface tankers for the transportation of liquid carbon dioxide (CO 2) from existing offshore/land facilities to marginal subsea fields. In contrast to highly weather-dependent surface tanker operations, the SST can operate in any condition underwater. The SST is an electric-powered autonomous underwater vehicle with a length and beam of 164 m and 17 m, respectively. It has a cargo carrying capacity of 16,362 m 3. This capacity is sufficient to allow the SST to fulfil the annual storage demands of ongoing carbon capture and storage (CCS) projects in Norway. It travels with a slow speed of 6 knots at 70 m constant water depth for maximum energy efficiency and offloads CO 2 via a connected coupling to the subsea well where CO 2 is directly injected. To be economically attractive, the SST has a high payload of 50% displacement which makes a low structural weight design extremely crucial. This is achieved by employing a double hull design for the SST with active pressure compensating systems to cope with the large collapse pressure loads underwater.

Fatigue & Fracture of Engineering Materials & Structures, 2019

A formula is proposed to predict fatigue strength of corroded members and joints of steel structu... more A formula is proposed to predict fatigue strength of corroded members and joints of steel structures. The concept of the formula is first studied from recently identified mechanism of corrosion fatigue. Hence, the corresponding fatigue strength curve (i.e. S-N curve) of corroded steel is presented. It is further improved to derive linear, bilinear or trilinear S-N curve for corroded constructional details of steel structures. The parameters of the corroded steel S-N curve are determined based on the corrosion fatigue testing results of different types of steel specimens in air, fresh water and seawater. Hence, the parameters for the derived S-N curve of corroded constructional details are predicted based on the above parameters and tabulated for the detail categories given in the Eurocode and DNVGL code. The proposed S-N curve formula is compared with full-scale fatigue test results of several constructional details, and the validity of the formula is confirmed. KEYWORDS corrosion fatigue, joints and connections, S-N curve, steel structures 1 | INTRODUCTION Corrosion is one of the main structural degradation processes that affect integrity. Fractures due to cyclic stress in corrosive media are designated as corrosion fatigue (CF) which is a type of environmental assisted cracking. The forty percent failures in oil and gas pipelines and 8% of failures in offshore steel structures are reported to be caused degradation/deterioration due to corrosion. Corrosion commonly takes place in the splash zone area of offshore structures as the coating in this area disappears a few years after installation. 1 Recent collapses of steel bridges due to corrosion are reported and some examples are the Silver Bridge in 1967, the Mianus River Bridge in 1990 and the Minnesota Bridge in 2007. 2-4 Though many bridges are located onshore, de-icing salt may simulate marine environment to the bridges in snowy regions. 2 These failures emphasize the importance of more accurate simulation of CF strength of structural joints and connections (i.e. constructional details) in different corrosive environments. 3,5,6 Corrosion pit induced stress concentration models and fatigue notch factor are commonly used to determine structures integrity. 7-10 Fatigue crack initiation life is determined when micro-cracks propagate to certain critical length. Fatigue crack propagation life is determined by fracture mechanics approach. Accurate determination of modified corrosion-fatigue stress intensity threshold and the critical length has been reported as challenging and difficult. 2-4 Therefore, limited amount of published

International Arctic Petroleum Cooperation, 2015