RU2760782C1 - Protective coating of steel pipeline against underground corrosion - Google Patents

Abstract

FIELD: metal protection.

SUBSTANCE: invention relates to the field of protection of metals against corrosion and can be used to protect pipelines from underground corrosion. It is proposed to use an emulsifier containing cubic residues of the production of aliphatic amines C10 - C15, C16 - C20 as a protective coating of a steel pipeline from underground corrosion.

EFFECT: emulsifier forms a solid coating, it is hydrophobic, non-flammable, is an inhibitor of anodic action in relation to underground corrosion of steel, while there is a inhibition of the anodic partial electrode reaction of steel by more than 90-95%.

1 cl, 4 tbl

Description

The length of underground structures and structures in the Gazprom system alone reaches more than 170 thousand kilometers [Methods and technologies of anti-corrosion protection, new materials and equipment for the protection of gas pipelines from various types of corrosion. / Materials of the industry meeting. Saratov, May 2003. //. M .: IRTs "Gazprom". 2004. 192 s.]. Their service life depends on their corrosion resistance. Accidents on oil and gas pipelines cause significant economic and environmental damage to the national economy. Predicting the danger of underground corrosion and improving the anticorrosive protection of pipelines are priority areas at the facilities of the fuel and energy complex [Budzulyak BV, Tychkin IA, Remizov VV, Tukhbatulin FG, Petrov NA / Effective protection of objects from corrosion. // M .: Gazoil press. Gas industry. 2002. No. 1. S.66-69.].

The main structural material for pipelines is steel. It has good strength properties, but low corrosion resistance in soil or ground conditions. Ground waters (soil electrolyte) play a significant role in the development of corrosion processes, which actualizes the use of inhibitors to protect steel.

Underground structures are exposed to a huge amount of constantly changing chemical, physical and biological factors that determine the intensity of metal corrosion [Goroshevsky A.V. The interaction of soil and underground pipelines: abstract of dis. Cand. biol. Sciences: 03.00.27, Moscow State University im. M.V. Lomonosov. - Moscow, 2005 .-- 25 p., Kamaeva Svetlana Sergeevna. Biogenic sulfate reduction as a factor of biocorrosion of underground pipelines: abstract of thesis .... Cand. tech. Sciences: 05.17.03. - Moscow, 2003 .-- 28 p., Harris N.A., Askarov G.R. The reason for the corrosiveness of soils around large-diameter gas pipelines. // Materials of Novoselovsky readings: Sat. scientific. tr. Issue 2. - Ufa: Publishing house of USPTU, 2004. - pp. 167-173., Ismagilov I.G. Features of thermal interaction of a large-diameter main gas pipeline with soil: abstract of thesis. tech. Sciences - Ufa, 2010. - 191 p., Maleeva M.A., Petrunin M.A., Maksaeva L.B., Yurasova T.Α., Marshakov A.I. Local corrosive dissolution of steel in solutions simulating soil electrolyte. // Corrosion: materials and protection, 2014. No. 11. P. 1-7.].

Studies of soil corrosion of main pipelines [Brylov I.F. Method of control of corrosion processes on main pipelines and development of protective electrolytic coatings based on zinc: abstract of dissertation…. Cand. tech. Sciences 05.17.03 - Technology of electrochemical processes and corrosion protection. - Novocherkassk, 2013. - 17 pp.] Showed that the effect of the concentration of hydrogen ions in a corrosive environment on the corrosion rate of metals is determined by their participation in the electrode process, the ability to influence the solubility of corrosion products, the ability to form protective oxide films when the pH of the solution changes. The predicted corrosion rate of main pipelines was calculated on the basis of studies carried out on the effect of the type of soil, pH of soil electrolyte, humidity, temperature, porosity, electrical resistivity and duration of operation on the corrosion rate of main pipelines. This makes it possible to identify sections of underground pipelines with varying degrees of danger.

When studying the electrochemical kinetics of partial electrode reactions occurring during corrosion of pipe steel in environments simulating a ground (sub-film) electrolyte, the types of organic compounds that effectively inhibit the processes of anodic dissolution of iron, cathodic release and the introduction of hydrogen into the metal have been established. It has been shown that inhibitors IFKHAN-29-ACh, IFKHAN-P-3, IFKHAN-AKN and IFKHAN-KAB have the best inhibiting and adhesive properties [Maleeva MA, Redkina GV, Bogdanov RI, Ryakhovskikh I V.V., Ignatenko V.E. and others. Development of inhibited polymer compositions in order to prevent the risk of SCC on main gas pipelines. // Inhibitors. 2 (31) 2015. pp. 24-30.].

One of the ways to protect pipelines from soil corrosion [Mustafin F.M. The use of hydrophobized soils in the construction and repair of pipeline transport facilities: thesis abstract…. doct. tech. Sciences: 25.00.19. - Ufa, 2003. - 47 p.] Is the use of hydrophobic soils to reduce the aggressive mechanical and physicochemical effects of the environment on the coating. Binders for main pipelines produced according to TU 0258-001-02080196-2000 “Summer oil binder VMT-L” and TU 0258-002-02080196-2003 “Winter oil binder VMT-3” were used as a binder for soil hydrophobization.

Authors [Semenova I.V., Florianovich G.M., Khoroshilov A.V. Corrosion and corrosion protection. / Ed. I.V. Semenova. - M .: FIZMALIT, 2002. - 336 p.] Offer bituminous coatings for isolation of structures from the electrolytic environment, used both independently and in combination with electrical methods. The average service life of multilayer bituminous coatings is 7 ... 10 years, and in saline soils no more than 2 ... 4 years. They are used for corrosion protection of cast iron sewer pipes in accordance with GOST 6942.3-80 at Svobodny Sokol OJSC (Lipetsk), at the Khabarovsk Heating Equipment Plant, Nizhniy Tagil Boiler and Radiator, Lipetsk Pipe, Duminichi, Makeevka Pipe Foundry. Petroleum bitumen of the BNI-1U-3 grade (GOST 9812-74), construction bitumen of the BN 70/30, BN 90/10 grades (GOST 6617-76), and road bitumen of the BN 90/130 grades are used as an anti-corrosion coating. BN 60/90 (GOST 22245-90). Bitumen preparation consists of dehydration and oxidation stages in an oxidizing plant. Before bitumenation, the pipes are heated in a continuous furnace to 200 ... 250 ° C for 10 minutes, then they are immersed in a bath with bitumen. The bitumen temperature in the bath should be 180… 200 ° С. From the tub, the pipes go to the tilting table, which lifts them in an inclined position to drain the residual bitumen from the pipe surface. The quality of the coating must meet the requirements of GOST 9583-75 and TU 14-3-259-74. The main disadvantage of this technology is fire hazard, since petroleum bitumen is a combustible substance with a flash point of 220 ... 300 ° C and a minimum autoignition temperature of 368 ° C. In the practice of bituminizing cast iron pipes, there are cases of bitumen burning in baths. In addition, bitumen is classified as a carcinogenic substance, which should also restrain its use as an anticorrosive material [https://truba24.ru/library/articles/ (date of treatment 12/2/2020)].

An oil bitumen coating obtained from bitumen after the stages of dehydration and oxidation in an oxidizing plant was chosen as a prototype. Such features of the prototype as a finished form that does not require mixing of components or mixing of the composition before application, hydrophobicity, the presence of oxygen atoms in the composition capable of adsorption on the active centers of the protected metal surface, the need for preheating before being applied to the steel surface, coincide with the essential features of the claimed way.

The technical task is to develop a method for protecting pipelines from underground corrosion by applying coatings of emulsin to their surface. Emulgin is a distillation residue from the production of aliphatic amines C10-C16, C15-C20, belongs to the second class of hazard. Emulgin is non-flammable.

This technical problem is solved by evaluating the protective effect of emulsin coatings on the surface of carbon steel St3, calculated based on the results of corrosion tests and electrochemical measurements on St3 in aqueous soil extracts in the presence and absence of emulsin coating on the metal surface. As a corrosive medium, we used water extracts from the most common types and subtypes of soils in the Central Federal District of the Russian Federation and, for comparison, 0.5 Μ sodium chloride solution.

The essence of the method lies in the fact that non-fire hazardous, solid at room temperature, hydrophobic, containing polar groups with nitrogen atoms, emulgin is capable of inhibiting the anodic electrode reaction of carbon steel due to the adsorption of the polar group of amines on the active centers of the metal surface.

Emulgin - distillation residues of the production of higher aliphatic amines at JSC "Azot", Bereznyaki. Emulgin includes fractions of higher aliphatic amines of unidirectional action C10-C15 (57.6%) and C16-C20 (42.4%), taking into account the additive interaction. Higher aliphatic amines - substances of the 2nd hazard class. The maximum permissible concentration of emulsin in the air of the working area MPC _r.z. = 1 mg / m ³ [Inventor's certificate No. 1385607. C10M 133/06 // (C10M 133/06, 127: 02) C10N 30:12. "Anticorrosive additive" Emulgin "for oils, registered on 01.12.1987].

Emulgin, which contains amino groups with nitrogen atoms capable of being adsorbed on the active centers of the protected surface, effectively suppresses electrochemical corrosion of steel, can solubilize water [Shubina A.G. Higher aliphatic amines as multifunctional components of oil-based anticorrosive preservation materials. Abstract dissertation. Cand. sciences. Tambov. 2001.23 p., Pozdnyakov A.P. Investigation of the polyfunctional properties of emulsin as a component of oil-based anticorrosive compounds. Abstract dissertation ... cand. chemical sciences. Tambov. 1999. 23 S.], has a significant viscosity and a tendency to structure in mineral oils.

To assess the protective efficiency of emulgine coatings, corrosion and electrochemical studies were carried out in soil water extracts of St3 steel in the presence and absence of these coatings on the metal surface. To obtain aqueous soil extracts, a 200 g sample of soil was placed in 800 g distilled water and stirred continuously for 30 minutes. Then the suspension was left for a day and subsequently the liquid was used in corrosion and electrochemical studies [GOST 26483-85]. Corrosion tests in soil extracts and 0.5 Μ sodium chloride solution (reference solution) were carried out on St3 steel samples (three samples per point) for 15 days at room temperature. Samples St3 were processed according to the 6th grade of purity, defatted with ethanol, and weighed on an analytical balance (m ₀ ). Using a vernier caliper, the dimensions of the samples were determined and the surface area (S) was calculated.

Emulgin was heated in a water bath and applied by dipping onto previously prepared samples. Then the thickness of the coating was determined gravimetrically, which on average reached 250 ... 270 µm.

The corrosion rate was calculated using the formula:

K = ([(m ₀ -m ₁ ) / (S⋅τ)] - N) ⋅10 ⁴ ,

where τ is time, h; m ₁ is the mass of the sample after 15 days of exposure in an aqueous soil extract or 0.5 Μ sodium chloride solution after removing the coating of emulgin and corrosion products (pickling solution); N is the rate of corrosion of the sample during over-etching of pure metal.

The value of the protective effect of the emulsin coating Ζ was calculated by the expression:

Ζ = [(K ₀ -K ₁ ) / K ₀ ] 100%,

where K ₀ and K ₁ are, respectively, the corrosion rate in the absence and in the presence of a protective coating.

Stationary potentiostatic polarization measurements were carried out with a potential step of 20 mV (room temperature, natural aeration) (IPC-Pro potentiostat) in a three-electrode Pyrex glass cell with a separated anode and cathode space in contact through the microsection. The potentials were measured relative to a saturated silver chloride reference electrode and recalculated according to n.v.sh. A working electrode made of steel St3 with a horizontal working surface of 0.5 cm ^{2 was} reinforced in a mandrel made of ED-5 epoxy resin with a polyethylene polyamine hardener, polished without the use of pastes, degreased with acetone and dried with filter paper. A protective film of the test composition with a fixed thickness was formed within 15 minutes, followed by gravimetric evaluation. As an electrolyte - 0.5 Μ sodium chloride solution (reference solution) or aqueous soil extract. Exposure 15 minutes. The protective efficiency in relation to the overall corrosion rate of steel was determined by the formula:

Z = [(i ₀ -i ₁ ) / i ₀ ] 100%,

where Ζ - protective effect,%; i ₀ and i ₁ - corrosion current obtained from the polarization curves, respectively, in the absence of a protective coating. To calculate the degree of inhibition of the anodic process Z _a , the values of the anode currents were substituted into the formula in the presence and in the absence of a coating at a potential of -0.20 V (n.v.sh.).

To prepare water extracts, we used soil samples from districts of the Tambov region (Table 1) and samples of the most common soil types and subtypes in the Central Federal District of the Central Federal District (Table 2).

The corrosion rate of steel 3 in a 0.5 Μ NaCl solution selected as a reference solution is slightly lower than in any of the aqueous extracts from soils in the absence of a coating, and the protective effect of the emulsin coating on St3 in the same media is higher than that in a 0.5 Μ solution NaCl (tables 3 and 4). This is apparently due to the presence of nitrogen and phosphorus compounds in aqueous extracts. Although the solubility of phosphorus compounds in water is reduced due to the presence of calcium ions in the extracts (Tables 1 and 2). The nitrogen and phosphorus compounds present in the soil can act as synergists with respect to the emulsin components (aliphatic amines), which can suppress the corrosion of carbon steel in the soil electrolyte.

In the presence Emulgin coatings on steel 3 in aqueous extracts of soil corrosion potential shift occurs steel E _armature into the anode region as compared with that of the unprotected St3 ceteris paribus. This indicates that the emulgin behaves as an inhibitor of anodic action.

The protective effect, calculated at a fixed anode potential (-0.2 V), is significantly higher than that at a corrosion potential (40 ... 90%). The protective effect, calculated at a fixed anodic potential (-0.2 V), in some cases approaches 100% and practically does not depend on the composition of the soil from which the water extract is prepared. This once again indicates that the components of the emulsin act as inhibitors of the anodic action. Quantitatively, the values of the protective action from the data of corrosion tests are close to those calculated from electrochemical measurements on steel under a protective coating of emulgin at a fixed anodic potential.

The proposed method of protecting pipelines from underground corrosion by applying coatings of emulsin to their surface is expedient, since emulgin is an effective inhibitor of anodic action in relation to underground corrosion of steel, is hydrophobic, forms a hard coating and is not fire hazardous.

Claims (1)

The use of emulsin containing distillation residues from the production of aliphatic amines C10 - C15, C16 - C20, as a protective coating of a steel pipeline against underground corrosion.