Sour Media Research Articles

Evaluation of corrosion behaviour and susceptibility to hydrogen-induced cracking in high-strength low-alloy X70 steels under sour gas conditions

High-strength low-alloy (HSLA) steels find extensive usage in the oil industry for manufacturing pipes due to their requirement for materials with high mechanical and corrosion resistance. Among these steels, the HSLA X70 steels are particularly of great interest to the petroleum industry because of its high mechanical resistance, ductility and weldability. In this study, it was aimed to assess the corrosion behaviour of HSLA API X70 pipelines using electrochemical impedance spectroscopy (EIS) technique and evaluate its resistance to hydrogen-induced cracking (HIC). The analyses were conducted in non-sour and sour media, as per NACE TM0284 standard. Microstructural characterisations of polished and corroded samples were also conducted using scanning electron microscopy (SEM) and optical microscopy (OM). The results indicate that the resistance to HIC in API 5L X70 steel is compromised when exposed to surface corrosion in sour gas media. This susceptibility may be attributed to the presence of microconstituents MnS and M/A along the grain boundaries, which were found in the crack trajectory. The identified microstructural features are deemed to exert a significant influence on the propagation of cracks and the consequent susceptibility to HIC. Moreover, the EIS tests revealed the lowest corrosion resistance when exposed to H2S media, as MnS inclusions accelerate the active regions in the matrix, consequently leading to the formation of a plethora of corrosion products and the dissolution of iron.

Effects of Mn and Microalloying Composition on Corrosion and Hydrogen-Induced Cracking of API 5L X65 Steels

The corrosion and hydrogen-induced cracking (HIC) resistance as well as hydrogen permeation behavior of two API 5L X65 steels with different amounts of Mn and microalloying elements were compared. The corrosion behavior of both steels, evaluated using electrochemical impedance spectroscopy and polarization curves in solution A of NACE TM0284-16 standard with and without H2S saturation (sour medium), showed no relevant differences in each medium, which can be ascribed to their similar microstructures; however, the corrosion resistance of both steels was lower in the sour medium. The investigation of resistance to hydrogen-induced failures disclosed better performance for the low Mn steel. This was confirmed using a harsher HIC test performed in an HCl acidified sour medium and was ascribed to the presence of Nb carbides nanoprecipitates, as revealed by the scanning transmission electron microsccopy analysis.

Corrosion characterization of new low manganese microalloyed X65 steels in sour and NON-SOUR synthetic seawater

API 5L X65 microalloyed steels are extensively used for oil and gas transportation. In many cases, reserves of such resources contain H2S, constituting what is called a sour medium, at which hydrogen-induced failures are critical. Even though essential for improving mechanical resistance, the addition of high contents of manganese (Mn) may increase the tendency for segregation and the precipitation of MnS inclusions, increasing the susceptibility to hydrogen-induced failures. In this study, electrochemical techniques were employed to compare the corrosion resistance in the B solution of ASTM D1141−98 (synthetic seawater) of three API 5L X65 microalloyed steels with low Mn content, designed for severe sour service applications. Experiments were performed in naturally aerated (pH 8.0), deaerated (pH 8.0 and 5.0), and H2S-saturated (sour pH 5.0) media. Although the steels exhibit very similar chemical compositions and mechanical properties, it was possible to rank their corrosion resistance. Microstructural characterization allowed associating corrosion susceptibility with the presence of pearlite grains in a ferritic matrix. The results also demonstrated the superior aggressiveness of the sour medium, and that the precipitation of a poorly adherent layer of Mackinawite slightly increases the corrosion resistance with immersion time.

Investigations of polyethylene of raised temperature resistance service performance using autoclave test under sour medium conditions

Abstract The chapter deals with the performance evaluation of the polyethylene of raised temperature resistance (PE-RT) and polyethylene (PE) using autoclave test under sour oil and gas medium conditions. The analyses of performance changes showed that PE-RT has good media resistance at 60°C. As the temperature increases, its mechanical properties decrease, accompanied by an increase in weight. Comparative analyses showed that no matter what temperature conditions are, PE-RT media resistance is better than PE80. The better media resistance of PE-RT depends on its higher degree of branching. Short branches are distributed between the crystals to form a connection between the crystals, thereby improving its heat resistance and stress under high-temperature conditions. PE-RT forms an excellent three-dimensional network structure through copolymerization, ensuring that it has better media resistance than PE80. However, the mechanical performance will be attenuated due to the high service temperature.

A Comparative Investigation of the Corrosion Resistance and HIC Suceptibility of API 5L X65 and API 5L X80 Steels

High strength low alloy (HSLA) steels are used for the construction of pipelines for oil and natural gas transportation. For such applications pipelines must exhibit mechanical resistance and resistance to corrosion and hydrogen induced cracking (HIC). API 5L X65 steels are the main materials used for this purpose. However, for economic reasons, the use of steels of superior grades would be of interest. This work presents a comparative study of the corrosion and HIC resistances of an API 5L X65 and an API 5L X80 steel in deaerated solution A of NACE TM0284 standard. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization experiments were performed in non-sour and sour (H2S-saturated) media, and HIC resistance tests were carried out in the sour medium. Scanning electron microscopy (SEM) and optical microscopy (OM) characterizations of polished and corroded samples were also done. Electrochemical tests showed that the API 5L X80 steel is slightly more susceptible to surface corrosion, which can be probably linked to its higher inclusion content and smaller grain sizes, it was also susceptible to HIC. Mn and S-rich inclusions found in the crack path indicate that this microstructural feature may play a key role in crack propagation and HIC susceptibility

Understanding the Scales Formation Inhibition Mechanism on C-Steel in a Sour media

Corrosion control in sour environments is a serious challenge for oil and gas industry. One of the approaches to mitigate such problem is to use corrosion inhibitors (CI). The selection of a single or a mixture of CIs for a particular oil or gas production, transportation or storage facility depends on different parameters e.g. the ratio between carbon dioxide and hydrogen sulfide, pH, pressure, temperature, and brine chemistry where different kinds of iron sulfide and/or iron carbonate layers can be formed. To select the right corrosion inhibitor/s, it is highly crucial to understand the mechanism of corrosion of C-steel and its inhibition in H2S systems in absence and presence of CIs [1,2]. In this work, the electrochemical behavior of C-steel in (i) deionized water (DIW) and (ii) different NaCl solutions were examined in an H2S system. A series of experiments were conducted at different temperatures and two concentrations of inhibitors (A and B). The corrosion behavior of C-steel was investigated by measuring the open circuit potential (OCP), linear polarization resistance (LPR), and potentiodynamic polarization (PDP) in addition to scanning electron microscopy (SEM) coupled with an energy dispersive X-ray (EDX) besides Raman spectroscopy (RS). The results have shown that the corrosion rate of C-steel gradually decreased then stabilized with time in the inhibited solutions. The inhibition efficiency was found to increase in the presence of both types of inhibitors with temperatures. Surface analysis shows that no film of corrosion products existed. In fact, CIs controlled the corrosion process and prevented passive film formation (iron sulfide), even in the presence of H2S in all tests. 2.5.0.0 2.5.0.0

Detailed mechanism of surface blistering in sour media

The known occurrence or absence of surface blistering (SB) are reminded, either in field failures or in HIC testing in the laboratory, i.e. in sophisticated fitness for purpose tests at low pH or in simplified acceptance tests at conventional pH values (NACE TM 0284). A previous analysis of charging severity is also reminded, together with the presence of temporary degassing barriers. Then, through an accurate modelling of charging transients, significant overshots of the hydrogen content close to surface are shown to be present soon after immersion when looking for the most resistant steels in HIC testing on full thickness samples, so that SB can be met alone in such tests. On commissioning in the field, their magnitude is necessarily much lower, so that in field failures, SB is always met together with SWC in the bulk. Conversely, overshots are totally unlikely with small specimens, short durations and medium severity, and SB is never reported in TM 0284 tests. They are also made impossible in the field by a progressive commissioning, and SWC is often reported alone in field failures. Such agreement in a very complex situation is indeed one more indirect proof of the protonic nature of dissolved hydrogen in steel.

Sulfide Scaling and Corrosion of Carbon Steel in a Sour Medium

The damage caused by the building up of scale inside wellbores and pipelines costs millions of pounds each year. A better understanding of scale formation and the kinetic nature of the process is essential, for asset management in general and the development of new protection approaches. Surface scale formation is one of the important factors related to the corrosion rate. The internal corrosion of carbon steel in the presence of hydrogen sulfide represents a significant problem for both oil refineries and gas treatment facilities/pipelines. Many studies have revealed that the system is complex since more than one iron sulfide compound may form. However, the kinetics of scale formation, such as the nucleation and growth processes of the scale are not at all well-understood and how corrosion inhibitors interact with scales. The kinetics of the scale formation will be investigated by using a variety of methods, some more successful than others. The methods employed include SEM, TEM, EDX, and Raman analysis, and this was done with the aim of obtaining the physical structure, the chemical composition and the crystal structure of the iron sulfide scale formed at different time scales.

Electrochemical impedance spectroscopy (EIS) modelling of different behaviours of Ni and Ni oxide thin films for corrosion prevention in sour media

PurposeThe purpose of this paper is a theoretical modeling use of electrochemical impedance spectroscopy (EIS) technique for different cases that could describe the possible electrochemical behaviour on steel coated with metallic and oxide thin films (of nickel) deposited by magnetron sputtering, and compare them to know if the theoretical analysis resembles the real case. It is extremely important to clarify that such simulations do not consider the use of the constant phase element (CPE) for the analysis. Therefore, the goal for the theoretical models should be to gain acceptance in electrochemical research.Design/methodology/approachIn order to obtain the equivalent circuits to explain the different possible behaviours of the films and their protective properties in sour media, EIS experimental data were correlated with data from the simulation software. The different nickel and nickel oxide thin films were tested after their deposition by magnetron sputtering on low‐carbon steel and after they had then been exposed to the sour media electrolyte of NaCl 3 wt% + H2S (saturated).FindingsThe EIS simulation starts from the laboratory evaluation of nickel and nickel oxide thin films as anticorrosive protection for low‐carbon steel exposed to sour media. From these results, it is found that the nickel and nickel oxide films could adopt seven different behaviours, and all are possible to occur.Practical implicationsThe equivalent circuits proposed will give an insight into the corrosion phenomena for different metals coated with thin films and exposed to sour media, because all of the simulations are made on the basis of real EIS results.Originality/valueThe electrical analysis in the simulation diagram did not consider the use of the CPE to adjust the plots. In consequence, the values of all parameters for the seven different adjustments obtained through the simulations establish a reference for the explanation of the corrosion phenomena. They are also a tool with which to predict the possible behaviour of a thin film deposited on metal and exposed to electrolytes that are as aggressive as sour media.

Wet hydrogen sulfide cracking of steel monitoring by acoustic emission: discrimination of AE sources

In the petroleum industry, it is known that equipments which operate in wet hydrogen sulfide (H2S) media can be subjected to damages like Hydrogen Induced Cracking (HIC) and Sulfide Stress Cracking (SSC). In this study, Acoustic Emission (AE) technique is used to monitor the cracking of steels immersed in sour media. The aim is to establish a methodology for HIC and SSC detection by AE and therefore to get more detailed information on the cracking mechanisms in steels during standard tests. The main focus of this article is the preliminary identification of the different AE sources involved during the tests performed in sour media. The methodology of identification of the different AE signals and the monitoring of HIC and SSC tests performed on different steel grades are described. The results indicate that AE can provide an early detection of cracking (HIC and SSC) when the various AE sources are identified.

Behaviour of Ni and Ni oxide thin films obtained by different techniques for the prevention of corrosion in sour media

Purpose – The purpose of this paper is to evaluate the use of nickel and nickel oxide thin films as anticorrosive protection for low‐carbon steel when expose to sour media. The purpose of this paper is also the study of a superior oxide nickel thin film over the nickel thin film.Design/methodology/approach – Nickel thin films are applied on steel AISI 1018 (UNS G 10180) by magnetron sputtering and electrolytic techniques. The films are tested after deposition on low‐carbon steel. A massive nickel electrode also is evaluated as a reference. In order to evaluate the protective properties of films in sour media, electrochemical techniques are employed, but also scanning electron microscopy in order to identify the difference in porosity and surface of the films coated by both techniques.Findings – Micrographs of thin films deposited by magnetron sputtering reveal a homogeneous surface whereas the electrolytic films show many micro‐crevices and expose the substrate even on the oxide films. These results indic...

The Relationship between the Surface Composition and Electrical Properties of Corrosion Films Formed on Carbon Steel in Alkaline Sour Medium: An XPS and EIS Study

This work studies the evolution of 1018 carbon steel surfaces during 3-15 day immersion in alkaline sour medium 0.1 M (NH4)2S and 10 ppm CN(-) as (NaCN). During this period of time, surfaces were jointly characterized by electrochemical techniques in situ (electrochemical impedance spectroscopy, EIS) and spectroscopic techniques ex situ (X-ray photoelectron spectroscopy, XPS). The results obtained by these techniques allowed for a description of electrical and chemical properties of the films of corrosion products formed at the 1018 steel surface. There is an interconversion cycle of chemical species that form films of corrosion products whose conversion reactions favor two different types of diffusions inside the films: a chemical diffusion of iron cations and a typical diffusion of atomic hydrogen. These phenomena jointly control the passivity of the interface attacked by the corrosive medium.

The impedance characteristics of protective corrosion films on carbon steel in an alkaline sour medium

A physical model describing the impedance response of iron deficient (Fe 1− x S) iron sulfide films in alkaline sour solutions has been developed. It assumes that the faradaic impedance of the anodic reaction was dominated by the transport of cation vacancies, which are created at the film/solution interface and annihilated at the metal/film interface. Simulations showed that the model is sensitive, in the typical frequency range used in EIS measurements, to variations in the values of the diffusion coefficient of cation vacancies and the rate constants of the reaction at the metal/film interface. A typical impedance diagram for Fe x S y films in a 0.1 M (NH 4) 2S, 10 ppm CN − solutions was compared to a calculated diagram using the model equations. Qualitatively, there is a good agreement between the model and experimental data, and the parameters make physical sense.

Modification of 1018 carbon steel corrosion process in alkaline sour medium with a formulation of chemical corrosion inhibitors

This work is focused on researching corrosion mechanism modifications of 1018 carbon steel in alkaline sour medium (0.1 M (NH 4) 2S and 10 ppm CN −) using inhibitor formulation (IHF) composed of hydroxyoleic imidazoline (C 12H 42ON 2), HI, and aminoether (C 20H 28O 3N 2), AE. The accelerated formation of corrosion products was thereby carried out in the presence of the formulation alone and of each of its components separately; these films were subsequently characterized by electrochemical impedance spectroscopy and scanning electron microscopy. The study in the presence of the IHF components revealed that the films formed have different nature, because their physical and chemical properties such as thickness, porosity and (electronic and ionic) conductivity are determined by the media where they are grown. The film formed in the presence of HI has a homogeneous, non-porous topography that impairs the diffusion process of H 0, in addition, its electronic conductivity is above that observed in the film formed with AE. Then, it was determined that the film formed with IHF presents some distinctive component characteristics which interact in a complementary way improving film passivity.

Electrochemically grown passive films on carbon steel (SAE 1018) in alkaline sour medium

Corrosion films were prepared by applying cyclic potential pulses to the 1018 carbon steel–sour medium interface (1 M (NH 4) 2S, 500 ppm CN −) for 1 min. Electrochemical behavior and surface morphology of these films were determined using electrochemical impedance spectroscopy (EIS), scanning electron microscopy, and scanning photoelectrochemical microscopy (SPECM). EIS diagrams and SPECM images show the passive properties and homogeneity of the films. Furthermore, X-ray photoelectron spectroscopy (XPS) was used to characterize their chemical nature and structure. XPS results show that different oxide and sulfur structures were developed during the electrochemical oxidation of carbon steel in concentrated sour media. The analysis of O 1s data indicated that, during film growth, H 2O and/or hydroxyl groups are incorporated into the film structure. The XPS spectra of Fe 2p show iron bonds with S as iron sulfide (FeS 2 and FeS) and the corresponding peak of O 1s shows those bonds with oxygen as Fe 2O 3 and/or FeO. XPS depth profile analyses for the film showed that the ratio of FeS and FeO increases from film surface to film–carbon steel interface. This corroborates the diffusion of iron ions through the film during its electrochemical growth. The chemical shift through the film for the peak associated with Fe 2p signal proves that transport mechanism of iron ions through the film is carried out by chemical diffusion.

Electrochemical study on carbon steel corrosion process in alkaline sour media

Electrochemical impedance diagrams were obtained for the carbon steel/sour refinery medium interface to evaluate how the corrosion process depends on the immersion times. A corrosion product film was formed during the initial time and the corrosion velocity was high. During the first 7 h, the film thickness increases and then diminishes, after 50 h of immersion, growth and dissolution reach equilibrium. Moreover, different carbon steel damaged surfaces were prepared using the cyclic voltammetry, using as damaging parameter the inversion potential ( E λ+). Comparing the impedance diagrams for the interfaces above mentioned we established that the carbon steel surfaces prepared by cyclic voltammetry and those prepared by immersion time were equivalent. Additionally, Scanning Electron Microscopy was used to identify that at E λ+=−0.7 and −0.6 V versus SSE, appears the first corrosion product over the carbon steel surface and its characteristics show a very compact (0.047 μm) and passive film. It was also determined that this corrosion film is the same obtained for 0 h of immersion time. A second corrosion product was formed with the cyclic voltammetry technique at more anodic potentials ( E λ+>−0.5 V vs. SSE). This new film had a greater thickness (0.4 μm) and an important electrochemical activity that leads to assume a porous layer, these properties are similar to those obtained when the carbon steel was immersed in a sour medium for times longer than 50 h. Concerning the impedance spectra analysis for the different carbon steel surfaces formed by the described strategies, we used the same equivalent circuit, assuming that the same steps were involved: charge transfer between the carbon steel/corrosion products interface, diffusion of Fe 2+ from the interface to the corrosion products film (associated to the vacancies in the pyrrotite crystalline structure) and atomic hydrogen diffusion from the sour medium/corrosion products interface to the corrosion products film. The last one was supposed to be the most important step in the corrosion process of the carbon steel in the sour medium because it induces the blistering corrosion.

The influence of different surface conditions in the corrosion process of carbon steel in alkaline sour media

Different electrochemical methodologies were established to induce general corrosion and blistering on homogeneous and heterogeneous carbon steel surfaces similar to the corrosion damage in a catalytic oil refinery plant. In one case, the film porosity and the iron sulphide stoichiometry were modified and in other case, the surface conditions were changed with sulphur films and microblisters. Additionally, we studied the influence of 1018 carbon steel surface conditions on the corrosion process in a medium simulating the average composition of sour waters in catalytic plants of PEMEX Mexico (0.1 M (NH 4 ) 2 S, 10 ppm CN - as NaCN, pH 8.8). Using the impedance spectra, from 10 kHz to 0.01 Hz, it was possible to qualitatively identify the carbon steel surface condition in an alkaline sour environment and to suggest the same corrosion process steps for this system, despite different surface conditions: charge transfer resistance of steel oxidation in the metal/corrosion product film interface and Fe 2+ ion and H° diffusion through the corrosion product film. Finally, scanning electron microscopy of a freshly polished surface showed the formation of a homogeneous film immediately after introducing the carbon steel into the sour media. The other surface changes depended on the induced corrosion process and corroborated the electrochemical impedance predictions.

Electrochemical characterization of the different surface states formed in the corrosion of carbon steel in alkaline sour medium

In this study the different surface states that manifest in the corrosion process of 1018 carbon steel in alkaline sour environment, solution prepared specifically to mimic the sour waters occurring in the catalytic oil refinery plants of the Mexican Oil Company (PEMEX) (0.1 M (NH 4) 2S and 10 ppm NaCN at pH 9.2) were prepared and characterized. The surface states of the carbon steel were formed by treating the surface with cyclic voltammetry at different switching potentials ( E λ+ ), commencing at the corrosion potential ( E corr=−0.890 V vs sulfate saturated electrode, SSE). The surface states thus obtained were characterized using electrochemical impedance spectroscopy and scanning electron microscopy techniques. It was found that for E λ+ =−0.7 and −0.6 V vs SSE a first product of corrosion formed, characterized by a high passivity. Moreover, it was very compact (with a thickness of 0.047 μm). However, at more anodic potentials ( E λ+ >−0.5 V vs SSE) a second corrosion product with non-protective properties (porous with a thickness of 0.4 μm and very active) was observed. The diffusion of atomic hydrogen (H 0) was identified as the slowest step in the carbon steel corrosion process in the alkaline sour media. The H 0 diffusion coefficients in the first and second products that formed at the carbon steel–sour medium interface were of the order of 10 −15 and 10 −12 cm 2/s respectively.

Characterisation of organic coatings in sour media and influence of polymer structure on corrosion performance

Epoxy coatings were evaluated in hydrogen sulphide containing sour media. Coatings exhibit no change in electrochemical impedance spectroscopy (EIS) spectra, though under-film corrosion occurs. In fact, hydrogen sulphide and water permeate through the polymer and provoke corrosion without causing film damage. EIS was also used to associate polymer structure and the corrosion protection performance. The effects of stoichiometric composition, average weight between cross-links and temperature changes as interpreted by glass transition effect were investigated.

Selection of Corrosion Inhibitors for Use in Sour Media

Abstract Extended Huckel molecular orbital (EHMO) calculations were performed on some substituted aliphatic amines and some substituted pyridine derivatives that are used as corrosion inhibitors in...