## 1 Introduction  
High-strength low-alloy (HSLA) steels are used in many types of structure. In comparison to conventional low-carbon steels, HSLA steels are characterized by favorable strength-to-weight ratio. That results in a lower cost of structures [1]. The usage of these materials has been changing in recent years. Earlier, they have been used only in the air. Now, they are the most common materials used for marine structures, which are characterized by direct contact with water [2]. The following application may be classified as an example of marine and offshore structures:* bridges [3];
* pipelines [4,5];
* wind turbines [6];
* ships [7];
* wharfs [8]. Defects could occur in marine and offshore structures, so it is important to find the proper strengthening technique [9]. The technique could be applied during preparation of the structures. The laying of the coating is widely used to improve the surface and properties of the substrate. Coatings are widely deposited by pad welding [10] and arc spraying [11]. The other method of improving the properties of the material surfaces could be the use of the ceramic brush tools to change the roughness. High roughness can generate the notch effect, which can cause a cracking effect [12]. Also, welding imperfections may occur in offshore constructions. During preparation of the structure, numerical analysis can be used for prediction the potential location of the failure [13,14]. Welding of HSLA steels in the air is a well-known process. There is a lot of literature addressing concerns about joining of these group of materials by different welding methods. To improve the quality of welded joints, the modeling of temperature field during multi-pass gas metal arc welding (GMAW) surfacing or rebuilding of steel elements taking into account that the heat of the deposit metal could be applied [15]. The cooling time between temperatures 800 \({}^{\circ}\)C and 500 \({}^{\circ}\)C (t8/5) is a factor with high influence on the quality of the joint [16]. This factor is responsible for microstructural transformations in a welded joint. There are HSLA steels in which the preheating process generates positive effects and provides increasing t8/5, which is responsible for decreasing the occurrence of the welding imperfections [17]. During joining in the air, the quality of a welded joint also depends on welding parameters [18] and filler material storage conditions [19]. However, offshore structures may undergo failures. Damaged areas can be located under the water surface, which determines the necessity of repairs in water conditions. There are three methods of underwater welding [20, 21, 22, 23]:  
* dry welding (hyperbaric and isobaric)--the welding area and welder are isolated from the environment by a special chamber;
* local dry cavity welding--the welding area is in situ isolated from environment, the steel plates and welder are in direct contact with environment;
* wet welding--the welding area and welder are in direct contact with the water environment. The method of underwater welding used most often is wet welding. The most common methods of wet welding are flux-cored arc welding (FCAW) [24] and manual metal arc welding (MMA) [25,26]. The water, as a welding environment, generates problems, which have a negative influence on the quality of the joint. The biggest negative phenomenon during wet welding is presence of high diffusible hydrogen content in deposited metal. The results of the measurements of diffusible hydrogen in deposited metal ranged from 32.61 to 39.95 mL/100 g for specimens welded in air and from 51.50 to 61.34 mL/100 g for specimens made in the water [27]. This chemical element is a factor with significant impact on the properties of welded joints. A phenomenon of hydrogen embrittlement is characteristic for low-carbon structural steel also in the air [28,29]. This type of embrittlement can occur even with the cathodic protection conditions [30].