RU2615893C1 - Pipe for transporting highly corrosive substances - Google Patents

Abstract

FIELD: machine engineering.

SUBSTANCE: pipe for transporting highly corrosive materials at temperatures up to 700°C and a pressure of 8.5 atm, which includes an outer metal shell, a working tube with a heating element on its surface, the conductor disposed therein, heat-insulating layer disposed between the working tube and the metal shell, characterized in that the working tube is made of fused silica at the ends of which are made annular grooves for placement of gaskets, with one end of the working tube is provided with a docking sleeve of fused silica for connection pipe portion of fused quartz, and the other end in place of the working tube connection portion of the metal tube, a gasket quartz material, designed as a cuff L-shaped in cross-sections.

EFFECT: corrosion reduction of the pipe material, providing mechanical strength, increase the duration of its operation.

2 cl, 2 dwg

Description

The invention relates to the field of engineering, and in particular to devices for transporting substances.

A compound is known that contains two pipes with an internal enamelled coating and a sleeve installed coaxially inside them with the formation of a cavity in the joint zone of the pipe, an annular groove is made on the outer surface of the sleeve, and radial thrust projections are made at the same time as the sleeve in the middle section of the sleeve, end sections of the sleeve are made of annular grooves in which the sealing elements are installed, and lead-in cones, between the outer surfaces of which and the inner surface of the pipes the material is placed adhesive properties with respect to said surfaces (RF patent №2080510, F16L 13/02, 1997).

A disadvantage of the known solution is the unreliability of the protection of the weld, because the sealing elements in the form of elastic rings do not provide reliable sealing of uncalibrated pipes having deviations of geometric parameters and sizes (ovality, difference, etc.) from the nominal ones, as well as permissible defects caused by the production method (minor dents, protrusions, etc. ), due to a possible jamming of the sealing elements and a violation in this regard of tightness. The installation of o-rings in such pipes is complicated by the need to center them in each installation case.

Another disadvantage is: the absence of heating elements on the surface of the pipe in the case of transportation through it of substances requiring mandatory heating, molten salts, etc. When transporting substances with high temperatures from 300 ° C and above, with a high difference in the coefficients of thermal expansion of enamel and metal, enamel will mechanically break down, which will lead to the interaction of the transported substance with the metal, corrosion and contamination of the transported substance by metal corrosion products.

The closest is a pipe for transporting petroleum products (patent RU 2453758, publ. 2012).

The pipe contains a working pipe coated with an anticorrosive and antistatic protective coating, an outer shell, a heat-insulating layer of polyurethane foam, located between the working tube and the outer shell. In the insulating layer are centralizers with supports. On the outer surface of the working pipe there is a heating element, which is made either in the form of a cable or in the form of an element of an induction-resistive skin system, which is a satellite tube made of ferromagnetic material with a conductor made of non-magnetic material placed in it. The heat-insulating layer is equipped with fire inserts along the length of the working pipe. The protective coating exceeds the length of the insulating layer. The working pipe exceeds the length of the protective coating with the formation at its ends of uninsulated end sections. The ratio of the length of one fire insert to the diameter of the working pipe is not less than 3.5: 1.

The disadvantage of this design is the impossibility of its use as an element of the pipeline for transporting chlorine-containing salt melts at temperatures up to 700 ° C due to their high corrosivity.

The present invention is the creation of a pipe through which aggressive substances can be transported, for example, chlorine-containing salt melts at temperatures up to 700 ° C, pressure up to 8.5 atm and ensuring tightness, safety, durability, simplifying the installation of pipes and their operation, as well as eliminating pollution transported substance by corrosion products.

The technical result of the claimed invention is to reduce the corrosion of the pipe material, providing mechanical strength, increasing the duration of its operation.

The technical result is achieved in the design of the pipe for transporting highly corrosive substances, including an external metal shell, a working pipe with a heating element on its surface, a heat-insulating layer located between the working pipe and the metal shell, and the working pipe is made of fused silica, at the ends of which ring grooves are made for placement of gaskets made of quartz material, while at one end the working pipe is equipped with a fused quartz coupling for connection with a closed pipe made of fused quartz, and at the other end, at the junction of the working pipe with the section of the metal pipe, a gasket is installed made in the form of an L-shaped cuff in cross section, the minimum thickness of which is determined by the formula

β≥L ^m ₀ × T × α _m + L ^q ₀ × T × α _q ,

where β is the thickness of the strip, mm;

L ^m ₀ - the initial length of the metal pipe, mm;

T is the temperature of the transported substance, ° C;

;α _m - coefficient of thermal linear expansion of the material of the metal pipe,

;

L ^kv ₀ - the initial length of the working tube of fused silica, mm;

α _kv - coefficient of thermal expansion of quartz,

The thermal insulation layer consists of a quartz material, for example a mixture of silicic acid gel with silica glass powder with a grain diameter of 0.1-0.8 mm.

In FIG. 1 shows a section through a pipe.

In FIG. 2 - construction of the working pipe in the outer metal shell.

The pipe for transporting molten salts and other highly corrosive substances includes (Fig. 1) an outer metal shell 1, a working tube 2 of fused silica, GOST 8894-77, at the ends of which annular grooves 8 are made to accommodate gaskets 7 of quartz material, at one end, the fused silica working tube 2 is provided with a fused silica sleeve 3 for connection to a portion of fused silica pipe 2, and at the other end, at the junction of the working tube 2 with a portion of a metal pipe 9, for example, nickel and of nickel alloys, a gasket 7 made of quartz material is installed, made in the form of an L-shaped cuff in cross section.

In the space between the outer metal shell 1 and the fused silica working tube 2, there is a heat-insulating layer 4 to reduce heat loss, which consists of a quartz material, for example, a mixture of silicic acid gel with silica glass powder with a grain diameter of 0.1-0.8 mm.

To ensure the mechanical strength of the outer metal shell 1 during its thermal expansion, a compensator 5 is provided. To maintain the temperature of the melt, a heating element 6 is wound on fused silica working pipe 2, which is led out through ceramic tubes 10 (Fig. 2). The tight connection of the working pipe with a section of the metal pipe is carried out using the flange 11.

The assembly of the pipe connection is carried out as follows: at the ends of the working pipe, gaskets 7 of quartz material are installed in the annular grooves 8. A sleeve of quartz material is put on one end of the working tube 2 and a portion of the fused silica working tube is inserted into it.

The assembly of the connection of the working pipe 2 from fused quartz and the section of the metal pipe 9 is carried out by installing on the end of the section of the metal pipe 9 a gasket 7 made of quartz material made in the form of an L-shaped cuff in cross section, while the working pipe 2 from fused quartz and the section metal pipes 9 mate with each other using the flange 11. Thus, a reliable and tight connection of the mating parts with each other is achieved.

In the pipe there should be no direct contact of the fused silica working pipe with a section of the metal pipe. Due to the difference in thermal expansion coefficients (CTE) of silica glass and metal, the destruction of the silica tube is possible. To exclude its mechanical destruction, gaskets made of quartz material are installed at the junction of the working tube of fused quartz with a section of the metal pipe.

The main problems of using quartz pipes in combination with metal pipes is the big difference in the thermal expansion coefficients of metal and quartz, as well as the melt pressure in the pipe up to 8.5 atm and temperature up to 700 ° C.

Based on the foregoing, laboratory studies were conducted to determine the mechanical stability of quartz-metal assemblies of various configurations and compounds at temperatures up to 700 ° C and pressures up to 8.5 atm.

Methodology

Investigations were carried out both to determine the corrosion resistance of a fused silica pipe in a chlorine-containing salt melt, and to determine the gap value taking into account the coefficients of the gap value taking into account the linear thermal expansion coefficients (CTE) between the quartz tube and the metal. In this case, the gap value was determined as the sum of the CTE of the metal, quartz, and the required thickness of the quartz material gaskets, preventing mechanical destruction of the quartz tube. In addition, the gaskets were also used to seal the assemblies.

experimental part

Investigations were made of assemblies in which the thickness of the gaskets was determined by calculation as the sum of the calculated values of the CTE of the metal, quartz, at the highest temperature of the experiments and the required thickness of the gaskets to achieve tightness of the assemblies at all values of the studied pressures; from 2.0 to 8.5 atm. Then experimentally determined the correctness of the calculations.

The coefficient of thermal linear expansion is:

- for nickel - 13.4 × 10-7 1 / deg,

- for quartz - 5.7 × 10-7 1 / deg.

The value of thermal linear expansion is determined by the formula

L = L ₀ + (l + αt),

where L is the length of the sample after heating, mm;

L ₀ is the length of the sample before heating, mm;

α is the coefficient of thermal linear expansion of the sample material, 1 / deg;

t is the temperature of the samples, equal to the temperature of the transported substance, ° C.

The estimated linear expansion at 700 ° C was:

- for nickel - 0.675 mm,

- for quartz - 0.0347 mm.

Thus, the thickness of the gaskets should be at least - 0.675 + 0.0347 = 0.7097≈0.71 mm.

To guarantee the shrinkage of the gasket during assembly of the samples, the thickness of the gasket was increased by 1 mm, and the total thickness of the gasket was 1.71 mm.

To determine the correctness of the selected values of the gaps and the thickness of the gaskets in the assemblies, taking into account the KLTR, the samples of the assemblies were placed in a shaft electric furnace with program control, grade SCHOL-2/12-I2, maintaining the temperature in automatic mode. Samples were tested at 350 and 700 ° C in potassium chloraluminate.

The furnace with samples was heated to a predetermined temperature regime and kept at a given temperature for 4 hours. All assembly samples were not destroyed, which confirmed the correctness of our calculations.

Then, studies were conducted to determine the mechanical strength of samples of quartz assemblies at pressures of up to 8.5 atm in a hydraulic press.

Samples were tested at a water pressure of 2, 4, 6, 8, 5 atm. At all investigated pressures, assembly samples showed tightness and mechanical strength - they did not collapse.

- Samples of transparent quartz glass products in the melt used in the separation unit of zirconium and hafnium chlorides in ChMZ JSC are corrosion-resistant both in sealed conditions and in conditions simulating equipment depressurization;

- on the scale of corrosion resistance of metals, the calculated group of resistance of the investigated samples of quartz corresponds to the characteristics of a very resistant material;

- samples of quartz products with a wall thickness of 1.6 mm, tested at a water pressure of 2, 4, 6, 8.5 atm showed tightness and mechanical strength.

Thus, the corrosion of the pipe material is reduced, mechanical strength is ensured, and the duration of its operation is increased.

Claims (9)

1. A pipe for transporting highly corrosive substances, including an external metal shell, a working pipe with a heating element on its surface, a heat-insulating layer located between the working pipe and a metal shell, characterized in that the working pipe is made of fused silica, at the ends of which ring grooves are made for placement of gaskets made of quartz material, while at one end the working pipe is equipped with a fused silica sleeve for connection with a portion of the fused silica pipe, at the other end, at the connection portion of the working tube with the metal tube, a gasket, designed as a cuff T-shaped in cross section, the minimum thickness is determined by the formula β≥L ^m ₀ × t × α _m + L ^q ₀ × t × α _q , where β is the thickness of the strip, mm; L ^m ₀ - the initial length of the metal pipe, mm; t is the temperature of the transported substance, ° C; α _m - coefficient of thermal linear expansion of the material of the metal pipe,

L ^kv ₀ - the initial length of the working tube of fused silica, mm; α _kv - coefficient of thermal expansion of quartz,

2. The pipe according to claim 1, characterized in that the heat-insulating layer consists of quartz material, for example a mixture of silicic acid gel with silica glass powder with a grain diameter of 0.1-0.8 mm.

Images