JP6344839B2 - Lining - Google Patents

Description

The present invention also relates to the lining.

  For example, in a nuclear power plant or the like, seawater is used as a cooling medium. Metal pipes are used for the distribution pipes through which the seawater circulates on the premise of long-term use, but carbon steel is often used from the viewpoint of cost. Carbon steel may cause corrosion of piping due to seawater. In order to prevent such corrosion, the entire inner surface of the piping is covered with a lining (lining layer).

  The lining described above is formed by a lining composition, and examples of the lining composition include rubber and polyolefin. In particular, among polyolefins, polyethylene is known to be effective in preventing corrosion of the inner surface of a pipe made of carbon steel or the like because it is a polymer material that has a low moisture permeability and is chemically stable.

  Among polyethylenes, in particular, linear low density polyethylene (LLDPE) has a molecular structure with few branched chains, and molecules are packed relatively densely. For this reason, the gap between molecules is small, and the moisture permeability is further smaller than that of low density polyethylene (LDPE). Therefore, in recent years, this linear low density polyethylene is often applied to the lining composition.

  By the way, a valve for adjusting the flow rate of the seawater may be provided in the pipe in which the lining as described above is formed. On the downstream side of such a valve, cavitation may occur in the pipe (in the water). Further, there is a problem that the lining is damaged by erosion (cavitation erosion) caused by a shock wave when the cavitation collapses.

Here, Patent Document 1 discloses polyethylene having excellent mechanical properties such as tensile strength. This polyethylene is synthesized using a metallocene catalyst, and compared with the one synthesized using a conventional Ziegler catalyst, the molecular weight distribution of polyethylene falls within a narrow range, resulting in a sharp distribution, resulting in a molded product (lining). It is possible to improve the mechanical properties.
Patent Document 2 discloses that in a styrene-based thermoplastic elastomer constituting a resin composition, wear resistance is improved by defining a peak temperature of a dynamic loss coefficient measured by a viscoelasticity measuring device. Has been.

Non-patent document 1 refers to the relationship between the physical properties of plastic and the cavitation erosion characteristics. Non-Patent Document 1 shows that the resistance to cavitation erosion (cavitation erosion resistance) is higher when σ _B ² / (2E) or σ _B is larger. Here, σ _B is the compressive strength, and E is the compressive elastic modulus.

Japanese Patent No. 3525818 JP 2009-173734 A

2000, Japan Oil and Pneumatic Society Proceedings (A), Vol. 31, No. 7, p. 177-182

  By the way, in Patent Document 1, although the above-described polyethylene is used as a lining to improve the mechanical characteristics and improve the lining performance, there is no mention of cavitation erosion resistance.

Further, in Patent Document 1, mechanical properties such as tensile strength are measured, and in Non-Patent Document 1, compressive strength (σ _B ) is measured, and these physical property values indicate static viscoelastic properties. I'm just evaluating. High-frequency pressure fluctuations due to cavitation erosion (cavity collapse) are repeated in units of time of 1 millisecond or less, so physical properties such as static viscoelastic properties such as tensile strength, compressive strength (σ _B ), and compressive elastic modulus There was a limit to evaluating cavitation erosion resistance by value.

  Further, in Patent Document 2, dynamic viscoelasticity is measured, but there is no mention of frequency characteristics, and there is no mention of cavitation erosion. The cavitation erosion resistance is only evaluated by evaluating the dynamic loss coefficient. It was difficult to accurately evaluate.

  As described above, there is currently no established method for accurately evaluating the correlation between the physical properties of plastics and cavitation erosion resistance, and it has been difficult to reliably prevent lining damage due to cavitation erosion. .

The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a lining having moisture barrier properties and chemical stability and good cavitation erosion resistance.

As a result of studying to solve the above-mentioned problems, the present inventors have clarified viscoelastic characteristics in a frequency region corresponding to the time change of pressure accompanying cavity collapse in lining , and the storage elastic modulus and the amount of erosion caused by cavitation We found that there is a correlation between That is, it has been found that the cavitation erosion resistance can be improved by controlling the storage elastic modulus at 1 kHz to 50 kHz within a predetermined range.
The present invention has been completed based on the above findings, and the gist thereof is as follows.

That is, the lining of the present invention is formed using a metallocene linear low density polyethylene having a density of 0.940 g / m ³ and has a storage elastic modulus in the range of 1 kHz to 50 kHz of 650 MPa to 740 MPa. It is said.

According to the lining of the present invention, since the density includes 0.940 g / m ³ metallocene linear low density polyethylene and the storage elastic modulus in the range of 1 kHz to 50 kHz is 650 MPa to 740 MPa, cavitation resistance Good erosion. In addition, since it contains linear low density polyethylene, it has good moisture barrier properties and chemical stability.
Here, 1 kHz corresponds to an impact load time of 1 millisecond, and 50 kHz corresponds to an impact load time of 0.02 millisecond. That is, 1 kHz to 50 kHz is a frequency region corresponding to the time change of pressure accompanying cavity collapse. In the lining of the present invention, the storage elastic modulus in this frequency region is 650 MPa or more and 740 MPa or less , thereby causing erosion due to cavitation. Is suppressed.
The storage elastic modulus is a physical quantity obtained by measuring dynamic viscoelasticity.
Furthermore, since the linear low density polyethylene is synthesized by the metallocene catalyst, the molecular weight distribution is in a narrower range as compared with the case where it is synthesized using another catalyst. That is, the molecular sizes are more uniform. As a result, the storage elastic modulus can be made relatively high, and the cavitation erosion resistance can be improved.

The lining of the present invention may further contain a polymer antioxidant.
Such an additive makes it possible to prevent the oxidation of the linear low-density polyethylene, and in addition to improving the resistance to cavitation erosion, the durability against oxidative deterioration can be improved.

In the lining of the present invention, the linear low density polyethylene is preferably cross-linked.
By generating a cross-linking reaction and cross-linking the molecules of the linear low density polyethylene, the molecular structure becomes a three-dimensional network structure. As a result, cavitation erosion resistance can be further improved.

According to the present invention, it is possible to provide a lining having moisture barrier properties and chemical stability and having good cavitation erosion resistance.

It is explanatory drawing of the lining which concerns on one Embodiment of this invention. It is a figure which shows an example of the measurement result of a storage elastic modulus. It is a figure which shows the relationship between the storage elastic modulus and frequency which concern on an Example and a comparative example. It is a figure which shows the relationship between the storage elastic modulus in case of 1 kHz, and the erosion depth. It is a figure which shows the relationship between the storage elastic modulus in case of 20 kHz, and erosion depth. It is a figure which shows the relationship between the storage elastic modulus in case of 50 kHz, and erosion depth.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
As shown in FIG. 1, the lining pipe 10 in one embodiment of the present invention includes a pipe 11 and a lining 12 (lining layer) formed on the inner surface of the pipe 11.
The pipe 11 is a cylindrical steel pipe made of carbon steel, for example. Since the inside of the pipe 11 may corrode due to a medium flowing inside, a lining 12 for preventing this corrosion is formed on the inner surface.

The lining 12 is formed by a lining composition. The lining 12 is applied to the pipe 11 by powder molding using powder of the lining composition or by inserting a lining composition previously formed into a cylindrical shape into the inner surface of the pipe 11.
In addition, the lining 12 is not limited to what is formed in the inner surface of the piping 11, It is also possible to apply to the structural member of another shape.

The lining composition (lining 12) according to this embodiment contains linear low-density polyethylene (hereinafter sometimes referred to as LLDPE), and has a storage elastic modulus in the range of 1 kHz to 50 kHz of 200 MPa or more. ing.
The storage elastic modulus is a physical quantity obtained by measuring dynamic viscoelasticity.

LLDPE is a polymer compound obtained by copolymerizing ethylene and α-olefin using a polymerization catalyst.
Here, LLDPE is preferably synthesized using a metallocene catalyst which is a kind of polymerization catalyst (hereinafter referred to as metallocene LLDPE). The metallocene catalyst is a combination of zirconocene and methylaluminoxane, and exhibits high polymerization activity with respect to ethylene.
That is, in metallocene LLDPE, the molecular weight distribution falls within a narrow range. Therefore, for example, LLDPE having a high storage elastic modulus can be synthesized as compared with the case where LLDPE is synthesized using another catalyst such as a Ziegler catalyst.

Metallocene LLDPE is an ethylene-α-olefin copolymer, which is a polymer obtained by copolymerizing ethylene and an α-olefin having 3 to 30 carbon atoms, preferably 3 to 8 carbon atoms, in the presence of a monosite catalyst. is there.
Examples of α-olefins having 3 to 30 carbon atoms as comonomer include propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3- Methyl-1-pentene, 1-octene, 1-decene, 1-docosene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-icosene [sic], 1-docosene [sic], 1-tetracosene [sic] 1-hexacosene [sic], 1-octacosene [sic] and 1-triacontacene. These α-olefins may be used alone or in combination of two or more.
Moreover, a commercial item can be used for metallocene LLDPE.

The lining composition preferably has a storage elastic modulus of 400 MPa or more in the range of 1 kHz to 50 kHz.
Further, the lining composition preferably has a storage elastic modulus in the range of 1 kHz to 50 kHz of 500 MPa or more.
The upper limit of the storage elastic modulus is not particularly limited, but is practically 1000 MPa or less.

Further, the lining composition may contain a polymer antioxidant in addition to LLDPE.
Here, examples of the polymeric antioxidant (additive having an antioxidant function) include, for example, hindered phenol compounds, semi-hindered phenol compounds, resindered phenol compounds, and hindered amine compounds generally abbreviated as HALS. Compounds. In order to improve the antioxidant function of the polymer antioxidant, a sulfur-based antioxidant or a phosphorus-based antioxidant may be used. Furthermore, a phenolic compound in which features of both a phenolic compound and a phosphorus compound are combined can also be used.
In addition, it is not limited to said polymeric antioxidant. Moreover, said polymeric antioxidant may be individual and may use 2 or more types together.

It is preferable that the compounding quantity of a polymeric antioxidant is 0.005 weight part or more and 1.0 weight part or less with respect to 100 weight part of LLDPE (or metallocene LLDPE).
When the blending amount of the polymeric antioxidant is less than 0.005 parts by weight, the blending amount is too small, so that the antioxidant effect may not be sufficiently obtained. Moreover, when it exceeds 1.0 weight part, it becomes the upper limit of compatibility with LLDPE in many cases, and the phenomenon that the added polymeric antioxidant precipitates on the polyethylene surface in a short time appears. The effect of adding 0 part by weight or more cannot be expected. For these reasons, the preferred blending amount of the polymeric antioxidant is within the above range.

Moreover, the lining 12 (lining composition) may contain crosslinked LLDPE.
Here, crosslinking is a reaction that links molecules to form a three-dimensional network structure in the molecular structure. For example, crosslinking using an organic peroxide as a crosslinking agent, electron beam crosslinking, water crosslinking, etc. It has been known.

  Examples of organic peroxides that are crosslinking agents include dicumyl peroxide (DCP), di-t-butyl peroxide (DBP), and 2,5-bis (t-butylperoxy) -2,5-dimethylhexyne. -3 (25YB), di-t-amyl peroxide (DAM) and the like, but are not limited thereto.

Moreover, it is preferable that the compounding quantity of a crosslinking agent is 0.5 to 10 weight part normally with respect to 100 weight part of LLDPE (or metallocene LLDPE).
If the blending amount of the cross-linking agent is less than 0.5 parts by weight, the degree of cross-linking is so small that it may be difficult to obtain the effect of blending the cross-linking agent. Since the stretchability is lowered and the lining 12 may become brittle, the above range is adopted.

In the construction of the lining 12, after forming a lining layer (lining 12) using a powder molding method using a powder of the lining composition, a polymerization inhibitor is added so as to promote the crosslinking reaction. You may set the induction period.
Such a polymerization inhibitor is preferably a phenol compound or a compound having a polycyclic aromatic structure, but is not limited thereto.
Examples of phenolic compounds include hydroquinone, methylhydroquinone, 4-tert-butylcatechol, 4-methoxyphenol, and the like.
Examples of the compound having a polycyclic aromatic structure include 4-methoxy-1-naphthol, “Kinopower (registered trademark) LSN, and ATR” (Kawasaki Chemical Industry Co., Ltd.), and the like.
The induction period is preferably set to a time until the lining composition powder is melted by heat and the lining layer becomes substantially smooth.

  Electron beam crosslinking is a technique in which a lining layer is formed on the inner surface of the pipe 11 serving as a base material by using a powder molding method, followed by irradiation with an electron beam for crosslinking.

  Water cross-linking is a technique in which an organic silane compound is mixed with LLDPE or a lining layer is formed using LLDPE knitted with an organic silane compound, and then water or water vapor is permeated in the presence of a catalyst to cross-link. is there.

The lining 12 is preferably applied to the pipe 11 using a powder molding method in which the lining 12 is applied to the pipe 11 using the powder of the lining composition described above.
The construction temperature for forming the uniform lining 12 on the inner surface of the pipe 11 using the powder molding method is set to 150 to 280 ° C, preferably 160 to 250 ° C. When the pipe 11 is heated in the heating furnace and then taken out from the heating furnace and allowed to cool, the temperature of the pipe 11 immediately before the construction is preferably 250 to 320 ° C.

  When the temperature exceeds the above range, problems such as bubbles may occur at the interface between the LLDPE and the pipe 11 (base material). Also, if the temperature is below the above range, the LLDPE powder is insufficiently melted and part of the powder remains in the lining layer in the powder state, or bubbles contained in the powder are not defoamed. There is a possibility that the uniform lining 12 cannot be formed on the entire surface of the pipe 11 due to remaining in the layer. For these reasons, the construction temperature range is set to the above range.

  According to the lining composition according to this embodiment having the above-described configuration, it contains linear low-density polyethylene and has a storage elastic modulus of 200 MPa or more in the range of 1 kHz to 50 kHz. Good cavitation erosion. Moreover, since the linear low density polyethylene is included, the moisture barrier property and chemical stability are also good.

In the lining 12, cavitation erosion (erosion) occurs as the cavity collapses. The frequency corresponding to the time change of the pressure accompanying the cavity collapse is 1 kHz (1 millisecond) or more and 50 kHz (0.2 milliseconds) or less. In this embodiment, the cavitation erosion resistance is improved by setting the storage elastic modulus at 1 kHz or more and 50 kHz or less to 200 MPa or more in the lining resin (lining 12).
Therefore, when the lining 12 is formed of the lining composition as described above, the cavitation resistance is improved, and the reliability and durability of the lining 12 can be improved.

  Moreover, in the lining composition (lining 12) of this embodiment, since the storage elastic modulus is preferably 400 MPa or more, cavitation erosion resistance can be further improved.

  Moreover, when the linear low density polyethylene contained in the lining composition (lining 12) is synthesized by a metallocene catalyst, the storage elastic modulus can be made relatively high, and further the cavitation erosion resistance can be improved. Can do.

  In addition, when the lining composition further contains a polymer antioxidant, it becomes possible to prevent the oxidation of the linear low density polyethylene, and in addition to improving the cavitation erosion resistance, the durability can be improved. Can be planned.

  Further, when the linear low density polyethylene is crosslinked after the lining is formed, the molecular structure becomes a three-dimensional network structure, and the cavitation erosion resistance of the lining 12 is further improved.

  The lining resin and the lining according to an embodiment of the present invention have been described above. However, the present invention is not limited thereto, and can be appropriately changed without departing from the technical idea of the present invention. It is.

  In addition, as polyethylene having a higher storage elastic modulus than LLDPE, there is ultrahigh molecular weight polyethylene, etc., but the storage elastic modulus is increased and the melting point may be increased. It is possible to become.

Below, the confirmation experiment performed in order to confirm the effect of this invention is demonstrated.
Sheets of Examples 1 to 3 were formed by compression molding at a temperature of 165 ° C. using the powder of the lining composition described in Table 1.
Comparative Example 1 was a vulcanized chloroprene rubber sheet.
Using these sheets as test pieces, the storage elastic modulus and the erosion depth (erosion amount) due to cavitation erosion were measured. The storage elastic modulus and the erosion depth by cavitation erosion were evaluated as follows.

(Evaluation method of storage modulus)
For example, as shown in FIG. 2, the storage elastic modulus in the temperature range: −135 ° C. to 20 ° C. and the frequency (vibration frequency) range: 0.1 Hz to 10 Hz was measured for the sheet of Example 1.
Here, a test piece having a thickness of 2 mm was used.

From the relationship between the frequency and the storage elastic modulus shown in FIG. 2, the horizontal axis is shifted so that the data in FIG. 2 becomes one curve based on the time-temperature conversion rule, and the vertical temperature is set so that the reference temperature becomes 20 ° C. By shifting the axis, a master curve of the storage elastic modulus of the sheet of Example 1 was obtained as shown in FIG.
Here, the master curve means a curve showing a storage elastic modulus at a temperature of 20 ° C. and in a frequency range of 1 kHz to 50 kHz.
Next, in the same manner as in Example 1, the storage elastic modulus master curve was obtained for the sheets of Example 2, Example 3, and Comparative Example 1. FIG. 3 shows the master curves of the storage elastic modulus of the sheets of Example 2, Example 3, and Comparative Example 1, together with the master curve of the sheet of Example 1.

The storage elastic modulus at frequencies of 1 kHz, 20 kHz, and 50 kHz was estimated from the master curve obtained as described above. The results are shown in Table 2.
In this embodiment, the storage elastic modulus at a frequency of 1 kHz to 50 kHz is calculated using a time-temperature conversion rule, but may be measured.

(Evaluation method of erosion depth by cavitation erosion)
A cavitation erosion test was performed according to ASTM G134-95 using the sheets of Examples 1 to 3 and Comparative Example 1 as test pieces. The exposure time for the cavitation erosion test was 24 hours, and the test was performed under the conditions of a cavitation number of 0.025 and a flow rate of 150 m / sec.
Here, the thickness of the test piece was set to 5 mm, and each test piece was heat-sealed to a metal jig using a test piece of φ = 12 mm, and the test was performed.

Table 3 shows the evaluation results of the erosion depth by cavitation erosion.
4 to 6 are graphs illustrating the storage elastic modulus in Table 2 as the vertical axis and the horizontal axis as the erosion depth. Specifically, FIG. 4 shows the relationship between the storage elastic modulus and the erosion depth at 1 kHz, FIG. 5 at 20 kHz, and FIG. 6 at 50 kHz.

(Evaluation results)
As shown in Table 2, in Examples 1 to 3, the storage elastic modulus of 1 kHz to 50 kHz was 200 MPa or more, and the storage elastic modulus was sufficiently high.
On the other hand, the comparative example 1 showed the low value compared with Examples 1-3 in the storage elastic modulus.
In addition, when a frequency exceeds 50 kHz, compared with the storage elastic modulus of Examples 1-3, the increase width of the storage elastic modulus of the comparative example 1 becomes large. That is, compared with the area | region below 50 kHz, in the area | region exceeding 50 kHz, the storage elastic modulus of the comparative example 1 becomes a value close | similar to the storage elastic modulus of Examples 1-3.

Moreover, as shown in Table 3, Examples 1-3 have a small erosion depth, and it was confirmed that this Example has favorable cavitation erosion resistance. In addition, it was confirmed that Example 1 has a smaller erosion depth than Example 3 and has better cavitation erosion resistance. In Example 2, it was confirmed that the erosion depth was smaller than that in Example 1 and the cavitation erosion resistance was excellent. That is, it was confirmed that Example 2 having the highest density of LLDPE has particularly excellent cavitation resistance.
On the other hand, the erosion depth of Comparative Example 1 was larger than that of Examples 1 to 3, and the cavitation erosion resistance was poor.

  As shown in FIGS. 4 to 6, it was confirmed that the erosion depth has a correlation with the storage elastic modulus at 1 kHz to 50 kHz. That is, it was confirmed that Examples 1 to 3 having a storage elastic modulus of 200 MPa or more have a small erosion depth and good cavitation erosion resistance.

12 Lining (lining layer)

Claims (3)

Formed using a metallocene linear low density polyethylene having a density of 0.940 g / m ³ ,
A lining having a storage elastic modulus in a range of 1 kHz to 50 kHz in a range of 650 MPa to 740 MPa. The lining according to claim 1 , further comprising a polymeric antioxidant. The lining according to claim 1 or 2 , wherein the metallocene linear low density polyethylene is crosslinked.

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