Introduction

Corrosion-resistant materials play a significant role in various industrial sectors [1 – 4]. Possessing enhanced corrosion resistance combined with the required mechanical properties [5 – 7], corrosion-resistant materials are used in aggressive environments where longevity without loss of operational characteristics is essential [8; 9]. Historically, the high cost of corrosion-resistant materials limited their use. However, over time, the understanding of the advantages of corrosion-resistant materials has led to their increasingly widespread use, particularly through the optimization of composition and properties for application in specific environments in critical components and structures [10 – 12]. At present, corrosion-resistant steels and alloys are used for more critical, expensive, and complex equipment where the potential risks, costs, or benefits outweigh the material’s cost.

For the domestic metallurgical industry, the issue of producing import-substituting grades of corrosion-resistant steels and alloys is currently pressing. Russia accounts for 0.4 % of global corrosion-resistant steel production, with the volume of products produced satisfying no more than 25 % of the total domestic consumption of steel in various industries [13 – 15]. In 2021, 120,000 tonnes of corrosion-resistant steel were produced in Russia, while 463,000 tonnes were imported from abroad. Moreover, domestic equivalents do not always meet the end user’s requirements for physical, mechanical, and corrosion properties.

A significant problem is that the domestic regulatory and technical documentation (RTD), containing requirements for the production technology and quality assessment of corrosion-resistant steels and alloys, is either outdated with minimal product requirements or entirely absent.The relevance of this study lies in the emergence of numerous requests for import substitution, selection, and comparative evaluation of the properties of stainless steels and alloys for the implementation of domestic products, equipment, and technologies. Additionally, it draws on data from open sources and the many years of experience in failure analysis by the Scientific and Technological Complex “New Technologies and materials” at Peter the Great St. Petersburg Polytechnic University. It is also important to note that discussions on the topic of failures and, moreover, their open analysis is a very contentious issue, as it leads to the search for culprits and punishment. However, in this work, the authors focused on the scientific or practical side of the issue to avoid similar problems in the future.

Review of failures

Conducting laboratory tests and research is an integral part of the justified selection of materials for specified operating conditions or their range [16 – 18]. In laboratory conditions, it is possible to carry out both standard tests according to existing methodologies (GOST, ASTM, ISO, DIN, etc.) and research work simulating aggressive environments close to real objects.

As numerous examples from open sources and the authors’ extensive practice show, the choice of a particular material depending on operating conditions can often be incorrect [19 – 22]. Additionally, factors such as installation conditions, technological impacts [23 – 25], interactions with other materials [26 – 28], changes in operating conditions, and metallurgical quality [29 – 31] may not be taken into account. All these factors lead to failures and serious economic and environmental consequences.

Tables 1 – 3 provide an overview of failures of various products made from corrosion-resistant materials in the oil and gas industry and show the causes of these failures. Analysis of the sources revealed that cases of failures can be grouped into three categories: incorrect operation of the material, low-quality material of the products, and incorrect selection of material for the operating conditions. Among the cases of incorrect operation, those where the condition of the material was compromised during installation on-site – such as during welding work in the construction of structures made from corrosion-resistant steels – were also included.

Let us examine in detail the most interesting cases of damage and the methods for resolving the problems from each category.

Incorrect operation of the material. Consider an example from open sources. The authors of [21] analyzed the causes of corrosion damage in the rectification column of a cellulose acetate production plant, made from duplex steel UNS S31803. The process fluid was an aqueous solution of 80 % acetic acid, which was separated by rectification. Due to the incomplete neutralisation of sulphuric acid in the process fluid used as a catalyst for ester hydrolysis, the column operated in a reducing environment, preventing the formation of a stable passive film on the metal surface.

To solve this problem, the authors proposed modifying the composition of the process fluid. By adding hydrogen peroxide under laboratory conditions, they created oxidizing conditions that promoted the formation of a stable passive film. Based on the results of laboratory studies, hydrogen peroxide was continuously added to the operating column. This approach proved successful in stopping corrosion processes until the next scheduled maintenance shutdown.

Low-quality material of the products. Consider a case from the authors’ practice involving intergranular corrosion, using AISI 904L steel plate as an example. Before putting the material into operation, acceptance tests for resistance to intergranular corrosion (IGC) were required. The tests were conducted according to GOST 6032 – 2017 using the weight loss method in a boiling aqueous solution of ferric sulfate (Fe2(SO4)3·9H2O) and sulphuric acid (H2SO4) in a flask with a reflux condenser. The duration of exposure in the boiling solution was 48 h. Upon completion of the tests, samples were bent at a 90° angle to assess the cracking of the base metal and the welded joint. Figs. 1, a and b show intergranular cracks in the base metal and the weld metal.

In this case, the cause of intergranular corrosion was the presence of excess phases located along the boundaries of the austenitic grains of the base metal and in the interdendritic spaces of the welded joint, as well as micro-voids that served as stress concentrators for the propagation of IGC cracks. Thus, laboratory tests established that the material of this production is prone to IGC. Introducing this plate into operation poses a high risk of subsequent cracking.

Incorrect selection of material for operating conditions. Consider the failure of heat exchanger elements in a low-temperature natural gas separation unit due to through pitting corrosion in the weld area, based on the authors’ practice (see Fig. 2). According to the approved project documentation, the material for this unit should have been steel 12Cr18Ni10T (AISI 321) with a titanium content of 0.4 to 1.0 wt. %. However, investigations revealed a substitution of the steel grade with 12Cr18Ni9 (AISI 304). In terms of pitting corrosion resistance, 12Cr18Ni10T and 12Cr18Ni9 steels are similar in their corrosion properties [32; 33]. However, in the case of welding non-stabilized steels, the corrosion resistance of the weld and the heat-affected zone can be significantly lower than that of the base metal [34]. The presence of titanium ensures the formation of favorable TiC carbides instead of undesirable Cr23C6 carbides, which reduce corrosion resistance.

Thus, the primary cause of the through defects in this case was the violation of the project documentation requirements regarding the unsanctioned change of the steel grade. This led to the incorrect selection of the welding mode, which caused activation of the metal in the heat-affected zone of the non-stabilized titanium steel, resulting in through pitting under the influence of the corrosive environment.

Results and discussion

The relatively small number of examined failures raises a broad spectrum of issues related to the production of high-quality corrosion-resistant steels and alloys, the selection of materials for operating conditions, the incompleteness of existing RTD, and the qualifications of specialists.

The issue of the quality of corrosion-resistant materials is extensive and requires the development and implementation of new RTD that describes quality requirements. This is a long-term and meticulous task; nevertheless, there are successful examples of such developments in domestic practice [35 – 38]. It is worth noting that currently, the only document in the oil and gas industry related to the selection and operation of corrosion-resistant steels is NACE MR0175, Part 3, which has not been harmonized with GOST. Moreover, this document only pertains to hydrogen sulphide-containing environments, while the evaluation of the possibility of using steels in СО2-containing environments is becoming increasingly relevant [39].

Incorrect material selection is linked to the lack of selection methodologies and proper corrosion resistance assessment techniques. Material selection guidelines are usually developed within companies and are subject to internal policies. However, the relatively new Institute of Oil and Gas Technological Initiatives (“INTI”) can gradually address such issues. The testing methodologies being developed to assess the corrosion resistance of materials should consider the reproduction of aggressive operating conditions on the sites.

At the Scientific and Technological Complex “New Technologies and materials”, there is a substantial testing base of various stands and installations, allowing materials to be tested under conditions as close to operating conditions as possible, including flow parameters. The authors’ team designed and manufactured autoclave installations of various volumes (Fig. 3, a), allowing tests to be conducted at elevated pressure and temperature in both static and dynamic conditions [40]. Tests involving supercritical fluids are also conducted in autoclaves.

The aggressiveness of the environment can manifest not only through the presence of corrosion-active agents but also through abrasive particles leading to abrasive wear. The combined influence of these two factors can significantly exacerbate the material degradation process. Their combined effect can be simulated using closed “flow-loop” stands, which also consider thermobaric parameters and fluid flow impact (Fig. 3, b).

However, conducting tests where many environmental parameters are controlled requires a lot of time and resources. Therefore, databases are created using the results of numerous tests, considering parameters determined on the stand, which are then used in a mathematical model to develop a digital twin.

The review of issues related to the justified selection of corrosion-resistant steels and alloys in the oil and gas industry highlights important aspects related to their operation in aggressive environments.

In the oil and gas industry, materials face aggressive environments, high temperatures, cyclic loads, and mechanical stresses. In practice, justified selection of corrosion-resistant materials does not always receive adequate attention, so seemingly economically advantageous solutions can turn out to be incorrect. This can lead to serious problems and additional costs for replacement or major repairs. For successful application of corrosion-resistant materials, preliminary laboratory studies must be conducted to recreate environmental factors to confirm the material’s quality and corrosion resistance under specific operating conditions. Effective solutions require close cooperation between engineers, scientists, researchers, and manufacturers.

Conclusions

A review of the causes of failures of products made from corrosion-resistant materials in the oil and gas industry has been conducted. It has been established that the causes of material failure can be incorrect operating conditions, poor-quality materials, and incorrect selection of materials for the operating conditions. Examples from open sources and the authors’ practice have been considered for each group of failure causes. The importance of conducting preliminary laboratory studies of corrosion-resistant materials and their testing with the simulation of environmental factors for a justified choice under specific operating conditions has been substantiated. The approaches used by the authors’ team for conducting physical modelling of environmental factors with the recreation of real conditions, including flow parameters, have been demonstrated.