JPH04290692A - Coated inner surface steel pipe for resisting sour - Google Patents

Abstract

PURPOSE:To provide a coated inner surface steel pipe having the superior durability by using the coating which is inert for hydrogen sulfide and a stainless steel coupling, for the environment where the erosion due to hydrogen sulfide is violent, as transport pipe, gathering pipe, etc., for natural gas. CONSTITUTION:A stainless pipe is welding-joined at both the edges of a carbon steel pipe, and after the inner surface of the steel pipe is blasting-treated, the steel pipe which is coated to a part of the stainless steel including the welding joint part is welding-joined.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to natural gas containing hydrogen sulfide, internally coated steel pipes such as gathering pipes, and in particular to internally coated steel pipes used in harsh environments containing corrosive substances such as hydrogen sulfide and salt compounds. This relates to painted steel pipes.

0002

[Prior Art] Pipelines that are normally buried underground, such as pipelines for the purpose of transporting natural gas, etc., are difficult to maintain once they are buried, and hydrogen sulfide, such as gathering pipes, etc. For products used in highly corrosive environments containing high salt content, long-term durability is required because pipes must be replaced frequently and are expensive. Therefore, various methods are used to deal with corrosion, which particularly affects the service life of pipes. The most common method is coating, and it is required to coat not only the outer surface of the pipe but also the inner surface. However, in the case of welded joints of steel pipes, in order to prevent damage to the coating film due to welding heat, the pipe ends are left unpainted in advance and painted after welding. In this case, it is relatively easy to paint the welded joints of large-diameter steel pipes that workers can fit inside the pipe, but for relatively small-diameter steel pipes that workers cannot fit into the pipes, Painting welded joints is extremely difficult. As a coating method for welded joints on the inner surface of small diameter pipes, Japanese Patent Publication No. 48-38460 and Japanese Patent Publication No. 49
-27410, Utility Model Publication No. 51-15829, etc., but in both cases, the groundwork of the welded joint cannot be completely prepared, so the corrosion resistance is extremely inferior to that of the non-welded part, and long-term durability cannot be expected. In addition, conventionally, the inner surface of steel pipes has been mainly coated with paints such as tar epoxy and pure epoxy. However, these paints do not have sufficient corrosion resistance in severe corrosive environments containing hydrogen sulfide and high salt content, and when applied to stainless steel joints, their adhesion to stainless steel is inferior to that of carbon steel. Corrosion protection of the joint cannot be ensured.

0003

[Problems to be Solved by the Invention] The object of the present invention is to improve the adhesion of the paint film to stainless steel in particular by using a paint and stainless steel joint that is inert to hydrogen sulfide and high salt and has excellent adhesion to stainless steel. The objective is to provide inner-coated steel pipes with excellent durability.

0004

[Means for Solving the Problems] That is, the present invention provides a steel pipe in which a stainless steel pipe is welded to both ends of a carbon steel pipe, the inner surface of the steel pipe is blasted, and then the inner surface of a portion of the stainless steel including the welded joint is painted. In sour-resistant internally coated steel pipes that are welded together, the paint used for the internal coating has an epoxy equivalent of 4 and has 1 to 2 oxirane rings per molecule.
00 to 2500 bisphenol type epoxy resin as the main resin, and the epoxy equivalent is 180 to 140 with respect to 2 to 4 moles of polyamide amine consisting of aliphatic diamine and dimer acid.
Using a polyamide amine adduct obtained by reacting 1 mole of a bisphenol type epoxy resin of 0.0 as a curing agent, the ratio of the epoxy resin to the polyamide amine adduct is 0.0 in terms of reaction equivalent.
A total of 50 to 200 parts by weight of fillers of titanium oxide and talc and 3 parts of zinc chromate ZTO type as a rust preventive pigment were added to 100 parts by weight of vehicle of 8/1 to 1.4/1.
This is a sour-resistant inner-coated steel pipe characterized by containing ~40 parts by weight of the main agent and/or hardening agent, which enables long-term durability in corrosive environments containing hydrogen sulfide, high salt content, etc. be.

The present invention will be explained in detail below. The stainless steel pipe used at both ends of the carbon steel pipe of the present invention is, for example, J
IS G-3459 SUS304, SUS316 austenitic stainless steel, JIS G-430
3-4307 standard SUS329J1, ASTM A
329 of 240 standard, X8C of DIN1.4462 standard
rNiMo275, OX21H of GOST5632 standard
5T, Nippon Steel standard YUS-DX1, YUS-31
There are duplex stainless steels such as 7LN, but among them, the Cr equivalent in the stainless steel is 22 to 24% and the Ni equivalent is 6 to 6%.
Duplex stainless steel containing a ferrite content of 7% and a ferrite content of 40 to 60% is preferred. For example, YUS
- In the case of DX1, a matching welding material is used for submerged arc welding, shielded arc welding, and TIG welding. In addition, the paint used in the present invention includes, as a vehicle, an epoxy resin having an epoxy equivalent of 400 to 1400 obtained by the addition reaction of bisphenol A having 1 to 2 oxirane rings per molecule and epihalohydrin, and an aliphatic diamine. and polyamide amine consisting of dimer acid and bisphenol type epoxy resin from 2/1 to 4/
It consists of a compound obtained by reacting at a reaction molar ratio of 1 (so-called polyamide amine adduct). This resin is
It is called diglycidyl ether of bisphenol A. Specifically, those commercially available under brands such as Epicote (Yuka Shell Epoxy Co., Ltd.), Epotote (Toto Kasei Co., Ltd.), Araldite (Ciba Geigy), and Epiclon (Dainippon Ink & Chemicals Co., Ltd.). and the epoxy equivalent is 400-2500 and the molecular weight is 800-30.
00 epoxy resin is suitable. When the epoxy equivalent is less than 400, the reactivity becomes high, the pot life becomes short, and the workability deteriorates. Moreover, in this case, the cured product becomes brittle and does not pass the API standard bending test. Furthermore, if the epoxy equivalent exceeds 2500, the reaction at room temperature becomes extremely slow and the viscosity becomes too high, making coating difficult. The polyamide amine used as one of the curing agents contains 2 to 4 moles of polyamide amine obtained from an aliphatic diamine and a dimer acid, and an epoxy equivalent of 180 to 1,400.
It is obtained by reacting 1 mole of bisphenol type epoxy resin. Dimer acid, which is one component of this polyamide amine adduct, can be obtained by heating and polymerizing unsaturated fatty acids in natural oils and fats. A specific example is Versadime (Henkel Japan Ltd.). Aliphatic diamines, which are the second component of polyamide amine adduct, include xylene diamine, ethylene diamine, hexamethylene diamine,
Bisaminopropyl-tetraoxaspiroundecane and the like can be used. The bisphenol type epoxy resin which is the third component of the polyamide amine adduct needs to have an epoxy equivalent of 180 to 1400, preferably 180 to 500. The epoxy equivalent of the epoxy resin is 140
If it exceeds 0, adduct reaction becomes difficult. Furthermore, if the epoxy equivalent is less than 180, the number of epoxy groups per molecule will decrease, making it impossible to obtain the desired hardness and flexibility of the coating film. Dimer acid, which is a raw material for polyamide amine adduct, which is one of the vehicle components of the paint in the present invention, overcomes the hard and brittle properties of general epoxy resin amine cured products, and is particularly effective when used with aliphatic diamine, another raw material. This reaction provides a cured resin with properties similar to that of an elastic body, which is hard and flexible. The blending ratio of this epoxy resin and polyamide amine adduct is 0.8/1 to 1.4/1 in terms of equivalent ratio, preferably 0.8/1.
~1.2/1. If this ratio is less than 0.8/1,
The paint film will become too soft and its anti-corrosion properties such as water resistance will deteriorate. On the other hand, if the blending ratio exceeds 1.4/1, the coating film will become hard and brittle, and the anticorrosion performance such as water resistance will also deteriorate. Next, fillers and anti-rust pigments for the paint in the present invention are selected from those that are inert to hydrogen sulfide and have a small water-soluble content, thereby creating a coating film that is stable against hydrogen sulfide. did. That is, titanium oxide and talc were selected as the filler, and zinc chromate ZTO type was selected as the anticorrosive pigment after conducting salt spray resistance, water resistance, salt water resistance, and hydrogen sulfide saturated water immersion tests.

[0006] The blending amounts of these materials are, on a weight basis, 50 to 200 parts by weight of the filler and 3 to 40 parts by weight of the rust preventive pigment to 100 parts by weight of the binder component. The amount of filler is 50
If the amount is less than 1 part by weight, the strength of the coating film will be low, resulting in poor impact and bending properties. Additionally, if the amount of filler exceeds 200 parts by weight, the binder will be insufficient and a uniform coating will not be formed.
This is not preferable because it causes defects such as pinholes and deteriorates physical properties. Next, if the amount of the rust preventive pigment is less than 3 parts by weight, the anticorrosive performance will be insufficient, and if it exceeds 40 parts by weight, the absolute amount of the rust preventive pigment will dissolve in water even if a pigment with a reduced water-soluble content is used. This is undesirable because it increases the amount of corrosion and deteriorates the anticorrosion performance. In addition to the above-mentioned essential components, the paint according to the present invention can contain appropriate additives such as anti-cissing agents, anti-sagging agents, and spreading agents. Further, in order to improve painting workability, solvents can be added as necessary. Hereinafter, the present invention will be explained in more detail according to Examples.

[0007]

[Example] (Example and Comparative Example) ■ The test steel pipe is 8
100m on both ends of 00mm long SGP steel pipe (200A)
After welding a m-long YUS-317LN steel pipe, it is blasted with alumina grit, and a paint with the composition shown in Table 1 is applied to the area up to about 50 mm from the end of the pipe to a dry film thickness of 200 to 250 mm.
It was coated with μm coating and dried at 100°C for 90 minutes. Furthermore, after joining the two painted steel pipes by TIG welding, stainless steel flanges were attached to both ends, and the pipes were attached to an existing gathering pipe, and an exposure test was conducted for two years under the corrosive environment shown in Table 2. ■ The test steel pipe is an 800mm long SGP steel pipe (200mm long).
After welding a 100 mm long SUS-304 steel pipe to both ends of A), it was blasted with alumina grit, and a paint with the composition shown in Table 1 was applied to about 50 mm from the pipe end to a dry film thickness of 200 to 250 μm. It was dried for 90 minutes at ℃. Furthermore, after joining the two painted steel pipes by TIG welding, stainless steel flanges were attached to both ends, and the pipes were attached to an existing gathering pipe, and an exposure test was conducted for two years under the corrosive environment shown in Table 2.

[0008] ■ The test steel pipe is SGP with a length of 800 mm.
100mm long SUS-31 on both ends of steel pipe (200A)
6 After welding the steel pipes, they were blasted with alumina grit, and a paint with the composition shown in Table 1 was applied to a dry film thickness of 200 to 250 μm from the pipe end to about 50 mm, and heated at 100°C.
It was dried for 90 minutes. Furthermore, the two painted steel pipes mentioned above were treated with TI.
After joining by G welding, stainless steel flanges were attached to both ends, attached to an existing gathering pipe, and an exposure test was conducted for 2 years under the corrosive environment shown in Table 2.

[0009]■ The test steel pipe is SG with a length of 1000 mm.
A P steel pipe (200A) was blasted with alumina grit, and a paint with the composition shown in Table 1 was applied to a dry film thickness of 200 to 250 μm from the end of the pipe to about 50 mm.
It was dried for 90 minutes at ℃. Furthermore, after joining the above two painted steel pipes by TIG welding, carbon steel flanges were attached to both ends, attached to an existing gathering pipe, and an exposure test was conducted for two years under the corrosive environment shown in Table 2. .

0010

[Table 1]

[0011]

[Table 2]

0012

[Table 3]

After 2 years of exposure, the joint and base metal parts were cut out, and the paint film adhesion, pitting corrosion, and stress corrosion cracking on the stainless steel parts were evaluated, and the appearance of the paint film on the base metal parts, pinholes, and paint film adhesion were evaluated. The strength and insulation resistance were evaluated. The results are shown in Table 3.

[0014]

[Table 4]

[0015]

[Table 5]

[0016]

[Effects of the Invention] According to the present invention, there is no pitting corrosion or stress corrosion cracking of the stainless steel in the joint, and the adhesion between the stainless steel and the paint film is good because the peeling state is due to cohesive failure of the paint film. Ta. In addition, there is no discoloration or pinholes in the paint film on the base material, and the initial quality of both paint film adhesion and insulation resistance is maintained, and it has excellent durability against harsh corrosive environments such as hydrogen sulfide and high salt content. demonstrate.

Claims (1)

[Claims] Claim 1: A sour-resistant inner surface coating in which a stainless steel pipe is welded to both ends of a carbon steel pipe, the inner surface of the steel pipe is blasted, and then a part of the stainless steel including the welded joint is welded and joined. In steel pipes, the paint used for the internal surface coating is based on a bisphenol type epoxy resin having 1 to 2 oxirane rings per molecule and having an epoxy equivalent of 400 to 2,500, and contains 2 to 4 moles of polyamide amine consisting of an aliphatic diamine and a dimer acid. Using a polyamide amine adduct obtained by reacting 1 mol of bisphenol type epoxy resin with an epoxy equivalent of 180 to 1400 as a curing agent, the ratio of the epoxy resin to the polyamide amine adduct is 0.8/1 to 1.4/ in terms of reaction equivalent. 1 vehicle 1
00 parts by weight, a total of 50 to 200 parts by weight of titanium oxide and talc fillers and 3 to 40 parts by weight of zinc chromate ZTO type as a rust preventive pigment are contained in the main ingredient and/or curing agent. Internally coated steel pipe for sour resistance.