JP2651745B2 - Method of manufacturing supply pipe for water-based paint - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention (1) Field of Industrial Application The present invention relates to a method for manufacturing a supply pipe for water-based paint.

(2) Prior Art As a constituent pipe for this kind of supply pipe, a stainless steel pipe is used in consideration of corrosion by water.

Various pipe joints are used for joining the stainless steel pipes to each other, but when those joints cannot be used due to the restriction of the construction place, the stainless steel pipes must be welded to each other.

As a simple welding method in such a case, it is conceivable to apply a covered arc welding method, but since this welding method has some difficulties in preventing deterioration of corrosion resistance of a welded portion, conventionally,
An inert gas arc welding method that can obtain a weld having good corrosion resistance is applied.

(3) Problems to be Solved by the Invention However, in the inert gas arc welding method,
Since the equipment cost including the inert gas is high, there is a problem that the production cost of the supply pipe is high.

In view of the above, the present invention is directed to a manufacturing method in which a simple covered arc welding method is applied, and problems caused by the application can be avoided by secondary processing to reduce the manufacturing cost of a supply pipe for a water-based paint. The purpose is to provide.

B. Configuration of the Invention (1) Means for Solving the Problems The method for producing a supply pipe for water-based paint according to the present invention is to weld stainless steel pipes to each other by a coated arc welding method, and then to a welded portion of the stainless steel pipe. And a passivation treatment including a step of immersion in nitric acid.

(2) Operation As described above, when the covered arc welding method is applied, the welding device is inexpensive and its portability is good, so that workability on site is improved.

Further, the corrosion resistance of the welded portion is likely to be deteriorated under the application of the covered arc welding method, but the passivation treatment is performed on the welded portion, so that the problem of the corrosion resistance is avoided.

(3) implementation example Figure 1 shows two stainless steel pipe 2 _1, 2 ₂ of welded joints in the water-soluble paint supply line 1.

Stainless steel pipe 2 _1, 2 as the _2, austenitic stainless steel mainly excellent in corrosion resistance, for example, JIS SUS30
4. A steel pipe made of SUS316 or the like is used.

The hitting the welding of both stainless steel pipe 2 _1, 2 _2, although shielded metal arc welding method is applied, as the core of that time welding rods, it is desirable to select a close to their composition the steel pipe. For example, stainless steel pipe 2 _1, 2 ₂ of the steel species JIS SUS304
For the ones constituted from JIS D 308 as core, also when stainless steel pipe 2 _1, 2 ₂ of steels is JIS SUS316, used those composed of JIS D316 as core.

As best shown in Figure 2, in the case of performing the shielded metal arc welding butt end face mutual both stainless steel pipe 2 _1, 2 _2, the weld 4, including a weld metal 3 and the vicinity thereof, in particular the weld metal 4, On both sides slightly away from that, there are regions 5 that are easily corroded in a corrosive environment due to grain boundary precipitation of carbides.

Therefore, as a secondary treatment after welding, in particular, both regions 5
In order to improve the corrosion resistance of the weld, a passivation treatment is applied to the welded portion 4.

 The passivation process is performed in the order of the following steps.

(I) The weld 4 is immersed in a cleaning solution such as thinner or phosphoric acid to remove dirt such as oil adhering to the weld 4.

(Ii) The weld 4 is heated to room temperature or about 50 ° C.
Soak in ~ 25% nitric acid. The immersion time is 40 to 60 minutes when the nitric acid is at room temperature, and 20 when the nitric acid is heated.
Set to ~ 30 minutes respectively.

(Iii) Wash the weld 4 with water to remove nitric acid.

(Iv) The weld 4 is washed with an alkaline solution such as sodium hydroxide to neutralize residual nitric acid.

[Example I]

Outside diameter 42.7 mm, thickness two stainless steel tubes that are composed of JIS SUS304 of 1.65 mm 2 _1, 2 ₂ of the end face butt mutual, JIS
Covered arc welding was performed using a welding rod having a core wire made of D308.

Next, the weld 4 is cleaned with thinner.
Are immersed in 20% nitric acid at room temperature for 60 minutes, the weld 4 is washed with water, and the weld 4 is washed with a 1% sodium hydroxide solution at room temperature to perform passivation treatment on the weld 4. gave.

When a water-based paint (emulsion type acrylic melamine resin paint, manufactured by Kansai Paint Co., Ltd.) was supplied through the supply line 1 having such a weld 4, the weld 4 was corroded by rust and the like even after 6 months. No occurrence was observed.

(Example II)

Outside diameter 42.7 mm, thickness two stainless steel tubes that are composed of JIS SUS316 of 1.65 mm 2 _1, 2 ₂ of the end face butt mutual, JIS
Covered arc welding was performed using a welding rod having a core wire made of D316.

Next, the weld 4 is washed with a 1% phosphoric acid solution.
Immerse weld 4 in 20% nitric acid at 50 ° C for 30 minutes.
, And a passivation treatment was performed on the welded portion 4 by performing various operations such as washing with water and washing the welded portion 4 with a 1% sodium hydroxide solution at room temperature.

When the same water-based paint as in Example I was supplied through the supply pipe 1 having such a weld 4, no corrosion such as rust was observed in the weld 4 even after 6 months. Was.

(Comparative example)

Outside diameter 42.7 mm, thickness two stainless steel tubes that are composed of JIS SUS304 of 1.65 mm 2 _1, 2 ₂ of the end face butt mutual, JIS
Covered arc welding was performed using a welding rod having a core wire made of D308, and then the welded portion 4 was cleaned with thinner.

When the same water-based paint as that of Example I was supplied through the supply pipe 1 having such a weld 4, rust was observed on the weld 4 after 2 hours.

C. Effects of the Invention According to the present invention, by using a simple welding method and a simple secondary treatment method, it is possible to provide an inexpensive supply line for a water-based paint having a welded portion having excellent corrosion resistance. Can be.

[Brief description of the drawings]

FIG. 1 is a perspective view of a main part of a supply pipe for water-based paint, and FIG. 2 is a sectional view of the main part. 2 ₁ , 2 ₂ …… Stainless steel pipe, 4 …… Weld

Claims (1)

(57) [Claims] 1. A process of welding stainless steel pipes (2 ₁ , 2 ₂ ) to each other by a covered arc welding method, and then immersing the stainless steel pipes (2 ₁ , 2 ₂ ) in a welded portion (4) with nitric acid. A method for producing a supply pipe for a water-based paint, which comprises performing a passivation treatment.