How And Why Does Scale Stick—Can the Surface Be Engineered To Decrease Scale Formation and Adhesion?

A subsurface safety valve is used to shut in a well automatically, if the wellhead equipment or other surface production equipment fails. It is almost always installed as a vital component on the completion. In many industrial systems, scale formation causes significant problems, not when it precipitates in bulk solution but when it deposits on the surface. Surface scaling is a complex phenomenon where several processes such as heterogeneous crystallization or particle adhesion are inextricably linked and occur simultaneously. The sub-surface safety valve can accumulate carbonate, sulphate and sulphide scale. Even a thin layer of scale can impede the smooth operation of the valve and pose serious regulatory and safety risks. In this study twenty coatings from seven different natures have been tested. These coatings are Fluoropolymers, Composite (fluotopolymer matrix), Sol-gelnano-coating, Textured hydrophobic paint, Diamond Like Carbon (DLC), Polished Inconel and Nitro carburated Inconel. Whilst the anti-scaling capability of the coating is the key functional element, it is extremely important that the coating presents other important parameters such as hydrophobicity property, surface roughness, coatingthickness and hardness, resistance to erosion, corrosion and temperature as well as coating adhesion. In this paper the controlling factors of anti-scaling coatings are discussed. Promising coatings with anti-scaling properties have been identified. Introduction The spring cavities and the inner wall of the sub-surface safety valve can accumulate deposits of carbonate, sulphate and sulphide scale. The precipitated scale can impede the smooth operation of the valve and pose serious regulatory and safety risks such as the malfunctioning during well blow-out. There are several techniques used to remove scale; these include the use of chemical inhibitors, chemical scale removers and mechanical methods. Scale control at surfaces may be addressed by anti-scaling coatings and surface engineering options. In the desalination units and heat exchangers, there have been a few attempts at using surface engineering to control scale deposition (Cheong et al., 2008). Surface deposition and precipitation are interlinked but it has been shown that they have very different kinetics and that controlling bulk precipitation does not by default control surface scaling. In order to fully understand a scaling system both an appreciation of the bulk precipitation and surface deposition characteristics must be obtained (Chen et al., 2003). In surface deposition the important steps are (i) nucleation of crystals, (ii) the growth of these crystals at the surface site and (iii) the adhesion of crystals to create a scale layer. Application of 'non stick' materials is considered as a promising method to alleviate scale deposition (Wang and Neville, 2005).

Scale-resistant surfaces: Fundamental studies of the effect of surface energy on reducing scale formation

Super duplex stainless steel UNS S32750 is widely used in marine industries, pulp and paper industries, and the offshore oil and gas industry. Welding manufacturing is one of the main manufacturing processes to make material into products in the above fields. It is of great importance to obtain high-quality welded UNS S32750 joints. The austenite content and ferrite content in UNS S32750 play an important role in determining UNS S32750 properties such as mechanical properties and corrosion resistance. However, the phase proportion between the ferrite phase and austenite phase in the welded joint will be changed during welding. Lots of research has been done on how to weld UNS S32750 and how to obtain welded joints with good quality. In this work, the recent studies on welding UNS S32750 are categorized based on the welding process. The welding process for UNS S32750 will be classified as gas tungsten arc welding, submerged arc welding, plasma arc welding, laser beam welding, electron beam welding, friction stir welding, and laser-MIG hybrid welding, and each will be reviewed in turn. The microstructure and properties of the joints welded using different welding processes will also be discussed. The critical challenge of balancing the two phases of austenite and ferrite in UNS S32750 welded joints will be discussed. This review about the welding process for UNS S32750 will provide people in the welding field with some advice on welding UNS S32750 super duplex stainless steel.

The sea water resistance of members of the duplex family of UNS S32304, S31803 and S32750 is very different. UNS S2304 should not be used in sea water and UNS S31803 has roughly the same corrosion resistance as AISI904L. Finally, there is the superduplex stainless steel UNS S32750, with a similar resistance to austenitic 6Mo-steels. A 'super' stainless steel here refers to a high alloy stainless steel with a PRE (PRE = Cr + 3.3Mo + 16N) of more than 40. The superduplex UNS S32750, 25Cr-7Ni-4Mo, has a PRE of minimum 41. It has now been in service for more than 10 years. Extensive experience of using SAF 2507 in different environments has been gained. Experiences of the use in sea water of the three duplex stainless steels UNS S32304, S31803 and S32750 are summarised in this paper and instructions for good practice are given. Results are also given from an exposure of butt-welded tubes exposed in natural sea water. No significant corrosion was found on the samples included in this test.

Inorganic scale (salt) deposition in the oil and gas industry is a serious and widespread problem that requires timely measures for effective control and management. The process of formation and deposition of mineral salts depends on a large number of changing factors, which creates additional difficulties for predicting and controlling scale formation processes. The fields of Eastern Siberia, the formation waters of which belong to the category of brines with a mineralization of 250 g/l and more (in some cases more than 600 g/l), are characterized by the scale formation of complex composition (sulfate, carbonate and chloride salts). Scale deposits can occur in the near-wellbore zone of the formation, which can lead to a significant decrease in the productivity of production wells. Many fields in Eastern Siberia have a number of features that complicate their operation. Among them are low reservoir temperature (10–14 °C), reservoir pressure close to the saturation pressure and salinity (halitization) of the reservoir. In the practice of the global oil and gas industry, it has been repeatedly proven that the implementation of technologies to prevent scale deposits is much more technologically and economically efficient than removing already formed sediments. In this regard, the use of scale inhibitors (SI) is one of the key methods to combat the formation of salts. When scale deposits lead to disruption of the operation of submersible well equipment, technologies for continuous or periodic dosing of SI into the annulus of the well can be effective. To protect the bottomhole zone of the formation from scale deposits, the priority technology should be the injection of scale inhibitors or squeeze treatment into the formation under pressure.In this work, based on a set of laboratory filtration experiments, a module has been developed that allows calculating the volumes of scale inhibitor and process fluids required for SI squeeze into the reservoir. The successful results of two operations of SI squeeze into the formation of horizontal wells for protection against deposits of sulfate salts are shown.

Laser surface modification of UNS S31603 stainless steel using NiCrSiB alloy for enhancing cavitation erosion resistance

The formation of mineral scaling on engineering components can occur as a result of cathodic protection (CP). The consequences of such scale formation have been generally considered to be beneficial owing to the reduced current requirement and hence reduced costs of CP. This paper reports results of a study focusing on the type of scale compound precipitated during CP, its relation to applied potential and current levels, and the effect of scale formation on the subsequent corrosion resistance of stainless steel and carbon steel. Using dc electrochemical accelerated polarisation tests, the corrosion behaviour of UNS S31603 stainless steel and BS 4360 carbon-manganese steel was studied. Results have shown that scale formation can result in a significant decrease in the resistance of the passive stainless steel alloy to localised corrosion attack. The practical implications of these findings are discussed.

The nose temperature for σ-phase precipitation in super-duplex stainless steel (SDSS) UNS S32750 was evaluated by hardness method. Color-optical microscopy, scanning electron microscopy, energy spectrum analysis, impact and corrosion testing were carried out to investigate characteristics of microstructure and properties of the SDSS aged at the nose temperature. The experimental results indicate that the nose temperature of precipitation is 920 °C and aging at this temperature tiny σ phases can precipitate at phase interfaces or ferrite grain boundaries within 2 min. Prolonging aging duration the amount of σ-phase increases and a dual structure with σ and γ is obtained when aging for 120 min. The precipitation of σ-phase leads to severe deterioration in impact toughness (longitudinal/transverse direction) and corrosion resistance of SDSS.

Scale formation is a serious and costly problem encountered in the oil and gas industry. Polyphosphinocarboxylic acid (PPCA) is a common commercial organic scale inhibitor used in the oil and gas industry which is normally referred to a nucleation inhibitor. In this paper, the effect of PPCA on calcium carbonate scale is studied systematically and some new insights into the mechanisms of PPCA inhibition are given. Traditionally, the studies of scale formation and inhibition have focused on bulk precipitation or surface deposition. Few studies have focused on the difference between surface deposition and bulk precipitation processes. In this paper, the effect of PPCA inhibitor on calcium carbonate scale formation is studied both in the bulk solution and on the metal surface in supersaturated scale formation solutions which represent typical waters encountered in oil and gas production. It is clear that PPCA inhibits both bulk precipitation and surface deposition but to a different degree. At 4 ppm...

Currently the use of sour service metallic materials is guided by ISO 15156/NACE MR0175 standard and guideline documents such EFC N°16 and 17. Carbon and low alloy steels are used according to the sulfide stress cracking (SSC) severity diagram in ISO 15156-2. However, there is a zone in the lower left hand corner which is undefined so far. Hence, the severity is unknown and qualification may need to be specifically carried out for using steels under these conditions. Work has been undertaken to test several steels of known sour service resistance to better assess the severity in this area of the diagram. For corrosion resistant alloys such as stainless steels the limits of use are still under investigation and so far only limited data is available in the open literature. The work reported here has been carried out to test the resistance of UNS S31603 (AISI 316L) stainless steel in a number of sour service media. The data obtained has been compared with published data to better assess the limits of use of this alloy and extend its use in upstream sour service. The first part of the paper deals with the resistance of carbon and low alloy steels and the limits of use of UNS S31603 stainless steel are addressed in the second part. Both topics are important to optimise the use of these steels in sour service conditions.

A comparative parametric investigation of thin diamond-like and polymer-like carbon coatings to explore carbonate anti-scaling performance

Chloride induced stress corrosion cracking of candidate canister materials for dry storage of spent fuel

ISO15156 / NACE MR0175 1 Part 3 table A.2 allows pH2S = 1bar up to 60°C with “any” chloride concentration and pH for the use of UNS S31603. Hence, it was recommended to evaluate UNS S31603 for the flow lines, trunk lines and equipment in one of the projects in the Middle East. A detailed program of laboratory testing was designed which consisted of duplicate Cyclic Slow Strain Rate Tests (CSSRT) to verify the ISO15156 / NACE MR0175 1 limits for sour service cracking resistance of UNS S31603. It included representative environmental conditions for the application. Testing was planned to be carried out first on UNS S31603 plate produced according to ASTM A240 2 specification and later during the detailed design project phase on specimens containing a weld. The testing program started with the validation of the ISO limit for UNS S31603 and continued with application specific conditions. Cyclic Slow Strain Rate Tests (also known as Ripple Strain Rate Tests, RSRT) were conducted at a third party laboratory as per NACE Corrosion/97 paper P97058 3. The test matrix included nine (9) sour environments and the testing sequence was determined by the test results. This resulted in only three (3) environments being tested. It was concluded that accepting “any chloride concentration” for UNS S31603 as per ISO15156 / NACE MR0175 Part 3 table A.2 is too optimistic since testing at 1 bar H2S at 60 °C with 230,000 mg/kg NaCl gave a fail result. Lowering the concentration to 132,000 mg/kg NaCl gave a pass, showing this concentration to be acceptable. To arrive at a less conservative limit than this concentration testing at intermediate chloride levels is required. The current testing program concluded that UNS S31603 stainless steel cannot be used under at least some of the expected operating conditions (represented by cases 1-6 in Table 2).

Stainless steels are widely used in the Oil & Gas and chemical process industry. This group of materials is today available in a large variety of alloy compositions, and practically all product forms needed for a construction are available. A historical view and application examples are given on the stainless steel evolution, from the standard grades used in chemical processes to todays most advanced applications in the chemical and oil & gas industry, where demands on reliable and long lasting solutions are necessary. The influence of alloying elements on the properties and manufacturability is described. The chemical industry is a very wide definition of a large group of industries with very different products, from plastics and organic acids to fertilizers, drugs and pesticides. Applications of stainless steels within the chemical industry are described. The first example is organic acids, where the use of high alloyed duplex stainless steels such as UNS S32205 and UNS S32750 have been successful. Another example is phosphoric acid applications, where the aggressiveness of the process solution depends very much on the fluoride and chloride content of the rock phosphate. In sulfuric acid, the material of construction is very much dependent on the acid concentration and temperature. Nitric acid is another common fertilizer acid which is highly oxidizing, and thereby demands stainless steels with high chromium content but with low molybdenum contents. The Oil & Gas industry uses very high quantities of carbon steel and stainless steel in their constructions. The oil wells are defined as sweet when the well contains carbon dioxide and no substantial amounts of hydrogen sulfide, when there is hydrogen sulfide present in the well, the wells are defined as sour. An overview on materials depending on the application is given. In subsea applications, hydraulic control lines (umbilicals) are used for control of valves and for methanol injection in subsea platforms. UNS S32750 is a high strength duplex stainless steel which today is the first choice for umbilicals and has been chosen for a very large amount of umbilical projects worldwide. The newly developed hyper duplex stainless steels with a combination of even higher corrosion resistance and strength are introduced for applications in oil-gas industry. The possibilities with stainless steels are endless, and new alloys are constantly being developed to meet industrial challenges of today and in the future. By choosing the right stainless steel grade, it is possible to find a solution to almost all challenges in the Oil & Gas and Process industry.

The purpose of this study was to investigate the difference between tungsten inert gas (TIG) welding of austenitic stainless steel assisted by microparticle oxides and that assisted by nanoparticle oxides. SiO2 and Al2O3 were used to investigate the effects of the thermal stability and the particle size of the activated compounds on the surface appearance, geometric shape, angular distortion, delta ferrite content and Vickers hardness of the UNS S31603 stainless steel TIG weld. The results show that the use of SiO2 leads to a satisfactory surface appearance compared to that of the TIG weld made with Al2O3. The surface appearance of the TIG weld made with nanoparticle oxide has less flux slag compared with the one made with microparticle oxide of the same type. Compared with microparticle SiO2, the TIG welding with nanoparticle SiO2 has the potential benefits of high joint penetration and less angular distortion in the resulting weldment. The TIG welding with nanoparticle Al2O3 does not result in a significant increase in the penetration or reduction of distortion. The TIG welding with microparticle or nanoparticle SiO2 uses a heat source with higher power density, resulting in a higher ferrite content and hardness of the stainless steel weld metal. In contrast, microparticle or nanoparticle Al2O3 results in no significant difference in metallurgical properties compared to that of the C-TIG weld metal. Compared with oxide particle size, the thermal stability of the oxide plays a significant role in enhancing the joint penetration capability of the weld, for the UNS S31603 stainless steel TIG welds made with activated oxides.