JPH0515545B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to flexible fluid transport pipes used to transport fluids such as gas, oil, and water.

[Prior Art] In recent years, as gas and crude oil wells have become deeper, sour environments containing hydrogen sulfide (wet hydrogen sulfide environments) have become more common.

In a flexible fluid transport pipe that has a metal reinforcing layer on the plastic inner tube, the metal reinforcing layer does not come into direct contact with the sour fluid inside, but the water and hydrogen sulfide that permeate through the plastic inner tube are ,
It stays between the reinforcing layers and causes hydrogen-induced cracking (HIC), sulfide stress corrosion cracking (SSCC), etc. in metal-reinforced steel materials.

Regarding sulfide stress corrosion cracking, the hardness of carbon steel is generally determined by HRC22 (Rockwell C hardness).
22) You can prevent this from occurring by doing the following:
For this reason, conventionally, flexible fluid transport pipes used in sour environments are made by drawing low-carbon steel wire rods with C0.2% or less as metal reinforcement, and then drawing them into different shapes, roller die processing, rolling, etc. Deformed steel wires with a predetermined cross-sectional shape were used, either as they were, or by low-temperature annealing at 500°C or lower to have a tensile strength of 80 kg/mm ² or less (tensile strength 80 kg/mm ²
approximately equal to HRC22).

However, it has become clear that hydrogen-induced cracking occurs in rolled low-carbon steel materials as the hydrogen sulfide partial pressure in the usage environment increases.

Furthermore, with conventional low carbon steel reinforcements, the strength of the connected (welded) portions is significantly reduced, making it impossible to increase the design stress.

[Problems to be Solved by the Invention] An object of the present invention is to provide a flexible sour fluid having a reinforcing layer made of high-strength steel that has excellent hydrogen-induced cracking resistance and sulfide corrosion cracking resistance, and has little strength loss at welded parts. The purpose is to provide transportation pipes.

[Means to solve the problem] C0.40-0.70%, Si0.1-1%, as pressure reinforcement material,
Contains Mn0.2-1%, P0.025% or less, S0.010% or less, and optionally contains Al0.008-0.050%,
The remainder is the composition of Fe and unavoidable impurities,
It has a spheroidal structure and has a tensile strength of 50Kg/mm ² to 80Kg/
mm ² and has excellent hydrogen-induced cracking resistance, etc. (in the present invention, high-strength steel wire and high-strength steel strip are abbreviated as high-strength steel strip). use.

[Function] The reason for limiting the components of the reinforcing material of the present invention will be explained below.

If C is less than 0.40%, the target strength cannot be obtained due to spheroidizing annealing, and the strength of the welded area will be greatly reduced, so 0.40% was set as the lower limit. Also
If C exceeds 0.70%, strong cold working becomes difficult, and fine cracks occur inside the steel wire or steel strip during processing, which not only deteriorates the HIC properties but also causes cracks to occur on the end face. The upper limit was set at 0.70%.

As a deoxidizing agent, Si is required to be at least 0.10% or more, and as the amount increases, the strength improves.
However, if it exceeds 1%, decarburization in the slab and billet heating furnace becomes severe, and this remains in the steel wire or strip, which is not preferable because it causes frequent cracks during cold working.

Mn is required at 0.2% or more to prevent hot brittleness. Furthermore, since Mn is an element that is inexpensive and improves strength, the larger the amount, the more preferable. but
Mn is an element that tends to segregate together with P, and in particular, in the present invention, the frequency of HIC caused by center segregation increases, so the upper limit was set at 1%.

P tends to segregate at grain boundaries, resulting in decreased workability and
Since it is easy to induce HIC cracking, the smaller the amount, the better. However, when manufacturing by continuous casting,
Since re-P occurs due to the high melting temperature, only the upper limit was set at 0.025%.

In addition to the same disadvantages as P, a small amount of S is preferable in terms of corrosion resistance, but 0.010 S is currently economically producible.
% or less. Note that industrial production of S up to 0.001% is possible.

Al is used in some cases to refine the crystal grains and as a deoxidizing agent, while in other cases Al is not added to designate coarse-grained steel and to prevent nonmetallic inclusions in the steel due to Al. In the case of Al addition, for example, the minimum amount of SolAl required for grain refinement is 0.006% or more, but since the distribution (ratio) of SolAl and Insol in the total amount of Al is 8:2, the lower limit is set to 0.008%. %
And so.

When Al exceeds 0.050%, nonmetallic inclusions in the steel increase, resulting in a decrease in product quality and yield.

Considering the melting yield and variation, it is usually preferable to add Al in an amount of 0.015 to 0.035%.

On the other hand, the amount of Al in steel without Al addition shows a value of less than 0.008%.

Al may be used as necessary depending on the purpose described above.

Steel materials with the above compositions are processed to make reinforcing steel wires (shaped steel wires) and reinforcing steel strips, but if the processed steel wires and steel strips are used as they are, the internal strain of the steel wires and steel strips will be relatively low. Since hydrogen-induced cracking occurs in concentrated areas, it is necessary to remove the strain by annealing.

Here, the tensile strength after annealing must be 50Kg/mm2 or more in order to increase the design stress and reduce the weight of the flexible tube, and 80Kg/mm2 or ^more to prevent sulfide stress corrosion cracking. It is required to be less than mm ² .

In order to obtain a preferable tensile strength with the component system of the reinforcing material according to the present invention, spheroidizing annealing is performed at a temperature of around 600°C to remove processing strain and to create a pearlite structure with fine spherical cementite in the ferrite matrix. It is necessary to form a dispersed structure, that is, a spheroidized structure. The degree of the spheroidized structure mentioned above is determined by the classification shown in the spheroidized structure photograph of JIS G 3539, for example.
Among No. 1 to No. 6, No. 1 to No. 3 are preferred. That is, No.
If it is 4 or more, the degree of spheroidization is small and hydrogen-induced cracking is likely to occur, which is not preferable.

[Example] FIG. 1 shows an example of a longitudinal cross-sectional view of a flexible sour fluid transport pipe according to the present invention. Reference numeral 1 denotes a plastic inner tube, on which an internally reinforcing steel wire 2 (channel steel wire) with excellent resistance to hydrogen-induced cracking is placed on an upper layer 2-1 and a lower layer 2-.
2 are spirally wound so as to mesh with each other, and furthermore, an external reinforcing layer 3 (steel strip) made of the same material is further spirally wound in opposite directions with a pitch larger than that of the internal reinforcing layer 2. The metal reinforcing layer may be formed of either the inner or outer reinforcing layer (either 2 or 3). The outermost layer 4 is a plastic jacket;
The metal reinforcing layer is protected from damage from the external environment.

Table 1 shows examples of the characteristics of the metal reinforcing layer in comparison with conventional materials.

In the reinforcing material according to the present invention, hydrogen-induced cracking does not occur, and the tensile strength of the steady portion and welded portion is higher than that of conventional products.

[Effects of the Invention] According to the present invention, harmful damage such as hydrogen-induced cracking and sulfide stress corrosion cracking does not occur in the metal reinforcing layer of the flexible pipe for transporting sour fluid, and furthermore, the steady state of the reinforcing layer The strength of the parts and welded parts is high, making it possible to have a high design stress, and making it possible to reduce the weight of the flexible tube.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of an example of a flexible sour fluid transport tube according to the present invention. 1...Plastic inner tube, 2 (2-1, 2-2)
...Internal reinforcing layer, 3... External reinforcing layer, 4... Plastic jacket.

【table】

Claims (1)

[Claims] 1. A flexible fluid transport comprising a rubber or plastic inner tube, a metal reinforcing layer provided on the inner tube, and a plastic outer jacket provided on the metal reinforcing layer. In the pipe, the metal reinforcing layer contains 0.40 to 0.70% C, 0.1 to 1% Si, 0.2 to 1% Mn, 0.025% or less of P, and 0.010% or less of S, and if necessary, Al0. Contains .008 to 0.050%, the remainder is Fe and unavoidable impurities,
Tensile strength with spheroidized structure 50Kg/mm ² ~ 80Kg/mm ²
A flexible sour fluid transport pipe characterized in that it is made of high strength steel strip.