JPS60592B2 - Method for preventing groove-like corrosion of ERW steel pipes in circulating water piping systems - Google Patents

Description

[Detailed Description of the Invention] This invention prevents groove corrosion (hereinafter referred to as groove corrosion) that occurs locally in the welded parts of electric steel pipes that constitute piping systems in which industrial water, tap water, etc. circulate. Regarding the method.

In general, it was thought that sufficient durability could be ensured by using inexpensive carbon steel electric resistance welded pipes for piping systems for industrial water, tap water, etc., which are relatively less corrosive.

However, in recent years, it has become clear that even under such usage conditions, the welded portions of ERW pipes are subject to early groove corrosion, which eventually leads to water leakage accidents. Conventionally, as a method to prevent this groove corrosion, the entire bolt welded tube is normalized after welding (for example, 950
A method in which the quenched structure of the weld zone, which consists of bainite and martensite, is changed to the same ferrite and pearlite structure as the base metal by holding the weld at a temperature of about 100°F for at least 1 minute and then cooling it in air, thereby eliminating the unevenness of the structure. There is.

However, it is not preferable to add such a normalizing step to the manufacturing process of the woven pipe from the viewpoint of productivity. In addition to this method, there is a method to prevent groove corrosion in welded parts by adding Cu and alloying elements such as Ti and Sb to copper as a pipe material to make the steel itself higher quality. In this case, a rise in cost cannot be avoided, and the inherent advantages of the open seam pipe are diminished.

SUMMARY OF THE INVENTION The present invention aims to provide a method for avoiding a decrease in productivity and an increase in cost of open pipes as much as possible, and effectively preventing groove corrosion of seam pipes in a circulating water piping system.

Conventionally, for example, in cooling water piping for air conditioners that uses industrial water or tap water as circulating water, corrosion inhibitors (hereinafter referred to as inhibitors) such as polymeric phosphates, organic substances, or silicate are added to the circulating water. It has generally been done to suppress corrosion of pipes by mixing them with other substances.

Inhibitors are originally used for the purpose of suppressing general corrosion of piping, and it is well known that they have no appreciable effect on groove corrosion. However, according to the experiments and research conducted by the present inventors, under the conditions in which this inhibitor is used, simply adding Cu alone to carbon steel, which is the material of the Kasumi pipe, effectively suppresses groove corrosion due to the synergistic effect with the inhibitor. It was found that this could be prevented and was issued.

That is, the present invention provides ~ carbon steel with Cuo. 10-0.80%
The piping system is made of silk-woven pipe made of steel with addition of ``inhibitor'' mixed into the circulating water of the piping system.

In addition, carbon steel is CO. 3% or less "Sio. 30% or less, Mno. 25 to 1.00%, PO. 040% or less, S
O. 0.050% or less, with the remainder essentially consisting of Fe.

Using an inhibitor alone or simply adding Cu to steel as a material has little effect on preventing groove corrosion in open seam pipes that make up piping, but when both are used together, They act synergistically and exhibit excellent effects in preventing groove corrosion.

Moreover, this method does not require any special process to be added to the manufacturing stage of the welded pipe, so there is no drop in productivity, and carbon steel to which only Cu is added can be used as the pipe material steel. , it is also advantageous in terms of cost. The reason why the amount of Cu added in the present invention is set to 0.10 to 0.80% is that if it is less than 0.1%, a synergistic effect cannot be expected when using an inhibitor, and if it exceeds 0.8%, it cannot be used during hot processing. This is because the quality deteriorates.

As for the inhibitor, currently available commercially available polymeric phosphate, organic or silicate inhibitors as mentioned above can be used, and their concentration is ineffective at less than ippm, and is ineffective at concentrations exceeding 1000 ppm. Even if added, there is no noticeable improvement in the effect and it is uneconomical, so 1 to 1
It is preferable to set it to about 000 pp■.

Next, the effects of the present invention will be explained using examples.

According to the method of the present invention, a circulating water piping system is constructed with open seam pipes made of steel-containing carbon steel with the components shown in Table 1.
．． 0, temperature 50oo, flow rate 1. (h/sec) for 80 days.

The groove corrosion status of this electric pipe is shown in the same table.

For comparison, carbon steel open seam pipes without Cu added or Cu in a range that is not compatible with the method of the present invention are shown.
The table also shows the results of investigating the groove corrosion of carbon steel hexagonal pipes with added carbon steel under the same conditions as above or without using an inhibitor.

The evaluation of the groove erosion status is: 0: almost no occurrence (groove erosion depth 20 peaks or less), △: considerable occurrence (20 to 150 peaks)
, ×: Significantly occurring (more than 150 cases). Table 1 *A: Polymerized phosphate type B: Polymer type 0: Silicic acid.

Active addition of Cu to steel pipe material as shown in the table above
In most cases, significant groove erosion occurs, not only in the case 7) when ``■'' and ``■'' are not added at all to the circulating water, but also in cases 8), 9), 10), and 14) when ``■'' and ``■'' are performed independently. The occurrence of C was observed, and even when ■ and ■ were used together,
No noticeable effect was seen in cases 15) and 16) when u was added outside the range of the present invention, whereas cases 1) to 6) in which the method of the present invention was carried out all showed extremely good results. There is. As shown above, the method of the present invention exhibits an excellent effect as a measure to prevent groove corrosion of the turtle governor that constitutes the circulating water piping system without impeding the original economic efficiency and productivity of the military general management, and at the same time Since it uses -, it has the rationality of suppressing general corrosion, and can be said to be an extremely useful invention for improving the durability of circulating water piping systems.

Claims (1)

[Claims] 1 The piping system is constructed with an electric resistance welded pipe made of steel with 0.10 to 0.80% Cu added to carbon copper, and the circulating water of the piping system contains polymerized phosphates, organic substances, and silicates. 1. A method for preventing groove-like corrosion of electric resistance welded steel pipes in a circulating water piping system, which is characterized by using a corrosion inhibitor mixed therein.