Roy Johnsen

Cathodic Properties of Different Stainless Steels in Natural Seawater

Abstract The cathodic properties of a number of stainless steels, which were exposed to natural seawater flowing at 0 to 2.5 m/s and polarized to potentials from −300 to −950 mV SCE, have been stud...

Prediction of Galvanic Corrosion Rates and Distribution by Means of Calculation and Experimental Models

Abstract For numerical calculation of galvanic and total corrosion current densities on galvanic elements, the boundary element method has been used. Polarization curves have been determined experi...

A Combined Approach for High-Resolution Corrosion Monitoring and Temperature Compensation Using Ultrasound

A novel approach for combined corrosion monitoring and temperature compensation (CMTC) using permanently installed immersion ultrasound probes with a well-defined standoff is presented. Combining subsample delay estimation with knowledge of how the sound speed in the immersion fluid and the steel varies with temperature enables us to simultaneously estimate the temperature variations and the changes in wall thickness using a linearized maximum-likelihood estimator (MLE). The results show that submicrometer changes in the wall thickness are detected and that the corrosion rates are predicted in good accordance with theory, also in the presence of temperature variations.

Significance of Hydrogen Evolution during Cathodic Protection of Carbon Steel in Seawater

Abstract Current requirement and calcareous scale properties on carbon steel were investigated as a function of applied potential, flow rate, and time in natural seawater. The current requirement w...

EFFECTS OF FLOW ON THE CATHODIC PROTECTION OF A STEEL CYLINDER IN SEAWATER

Abstract The electric current density distribution around the circumference of a cathodically protected steel cylinder has been investigated. The water flow was perpendicular to the cylinder axis w...

Materials and corrosion trends in offshore and subsea oil and gas production

The ever-growing energy demand requires the exploration and the safe, profitable exploitation of unconventional reserves. The extreme environments of some of these unique prospects challenge the boundaries of traditional engineering alloys, as well as our understanding of the underlying degradation mechanisms that could lead to a failure. Despite their complexity, high-pressure and high-temperature, deep and ultra-deep, pre-salt, and Arctic reservoirs represent the most important source of innovation regarding materials technology, design methodologies, and corrosion control strategies. This paper provides an overview of trends in materials and corrosion research and development, with focus on subsea production but applicable to the entire industry. Emphasis is given to environmentally assisted cracking of high strength alloys and advanced characterization techniques based on in situ electrochemical nanoindentation and cantilever bending testing for the study of microstructure-environment interactions.

Hydraulic Cylinders for Offshore Splash Zone Operation: A Review of Piston Rod Failure Cases and Alternative Concepts

Hydraulic cylinders are used for many vital applications on offshore installations. For the long stroke cylinders used in the direct acting riser tensioning application the piston rod surface is exposed to severe degradation; combining corrosion, wear and mechanical stress. Direct acting riser tensioning systems are often used during ultra-deepwater offshore drilling, when exploring for oil and gas. These direct acting riser tensioning systems usually consist of 6 long stroke hydraulic cylinders located at the splash zone level. These cylinders ensure constant tensioning of the drilling riser as the drilling vessel is operated in ultra deep waters up to 3000 meters compensating for heave due to sea waves and tide. The direct acting tensioning systems have been in operation since the late 1990’s, but the system integrity and service life has so far not been acceptable. Operational experience shows that the thermal sprayed coatings applied on these piston rods have dramatically shorter life than predicted by qualification tests programs. The consequence of the failing rod surface is sudden coating damage such as pits and flaking which further damages the seals in the packing flange. As a result hydraulic oil leakages occurs, thus polluting the environment and in the worst case leads to loss of the tensioning in the riser causing subsequent drilling down time and eventual riser breakage and blowout. This paper will provide a generic summary of operational experience, development and degradation issues of direct-acting riser tensioning cylinder piston rod surfaces. Several case histories are included to highlight piston rod failures and an evaluation of alternative concepts to improve service life of piston rods is given.Copyright

Hydrogen Induced Stress Cracking (HISC) of Stainless Steels Under Cathodic Protection in Seawater: Presentation of a New Test Method

There has been an increasing trend in the use of stainless steel alloys instead of carbon steel for subsea flowlines and production systems during the last 15 years in the oil industry. Even if this normally is a more robust solution compared to the use of carbon steel insofar as internal corrosion problems are concerned, the use of stainless steels has led to leakage, production shutdown and expensive repair work. The reported failures were associated with hydrogen entrapment resulting from welding and/or external cathodic protection (CP), combined with a certain stress/strain level. Atomic hydrogen entering the alloy can weaken the mechanical strength of the alloy, cause cracks and destroy the integrity of equipment or a system. Such failures attributed to hydrogen induced stress cracking (HISC) are clearly not acceptable from the perspective of safety, environmental hazard and cost. Leading oil and engineering companies and supplier industry have pointed out HISC as one of the major obstacles against safe operation of stainless steel subsea pipelines and production systems. It is important for the oil industry to have design guidelines and reliable test method(s) for qualification and safe utilization of subsea pipelines and components made from the actual stainless steels. This paper describes a test method that has been developed through a Joint Industry Project (JIP) executed by SINTEF and Det Norske Veritas (DNV) with support from leading oil companies and material suppliers. The method has been qualified for use on 13% Cr super martensitic (SMSS) and 22% Cr / 25% Cr duplex stainless steels (DSS/SDSS). The link to DNV-RP-F112 [1] will also be described.Copyright

Hydrogen Effect on Nanomechanical Properties of the Nitrided Steel

In situ electrochemical nanoindentation is used to examine the effect of electrochemically charged hydrogen on mechanical properties of the nitride layer on low-alloy 2.25Cr-1Mo martensitic structural steel. By application of this method, we were able to trace the changes in the mechanical properties due to the absorption of atomic hydrogen to different depths within the compound and diffusion layers. The results clearly show that the hydrogen charging of the nitriding layer can soften the layer and reduce the hardness within both the compound and the diffusion layers. The effect is completely reversible and by removal of the hydrogen, the hardness recovers to its original value. The reduction in hardness of the nitride layer does not correlate to the nitrogen concentration, but it seems to be influenced by the microstructure and residual stress within the compound and diffusion layers. Findings show that nitriding can be a promising way to control the hydrogen embrittlement of the tempered martensitic steels.

Using a multi-layered transducer model to estimate the properties of paraffin wax deposited on steel.

When using ultrasound for detecting low impedance materials on the surface of high impedance materials, a major challenge is the contrast difference between the strong reverberations from the high impedance material and the weak echoes received from the low impedance material. The purpose of this work is to present the theoretical and experimental validation of an ultrasonic methodology for estimating the acoustical properties of paraffin wax on the surface of steel. The method is based on modeling and inversion of the complete electro-acoustic channel from the transmitted voltage over the active piezoelectric element, to the received voltage resulting from the acoustic reverberations in the multilayered structure. In the current work, two conceptually different models of the same multi-layer transducer structure attached to steel is developed and compared with measurements. A method is then suggested for suppressing the strong reverberations in steel, hence isolating the wax signals. This contrast enhancement method is fitted to the model of the structure, facilitating parameter inversion from the wax layer. The results show that the models agree well with measurements and that up to three parameters (travel time, impedance and attenuation) can be inverted from the wax simultaneously. Hence, given one of the three parameters, density, sound speed or thickness, the other two can be estimated in addition to the attenuation.