JPH06281560A - Dip testing method for actual pipe - Google Patents

Abstract

PURPOSE:To enlarge and evaluate a stress area of a line pipe by adding a predetermined tensile stress to the inner surface of the steel pipe with the use of a turnbuckle supporting at four points. CONSTITUTION:A tensile stress is added via an interval of approximately 90 deg. to the inner surface of a steel pipe 1 with the use of a turnbuckle 2 supporting at four points. At this time, the steel pipe 1 is expanded by turning a male screw of the turnbuckle 2, and therefore there are four points where a predetermined tensile stress is attained. In order to confirm whether the predetermined tensile stress is attained, a strain gauge is attached to a measuring point and the amount of strain is converted to the stress thereby to set the predetermined stress. In this manner, when the tensile stress is impressed to the inner surface of the steel pipe 1 by the turnbuckle 2 supporting at four points, a predetermined tensile stress is obtained at four points, increased from two points in the conventional method. Therefore, a to-be-evaluated area is enlarged and the stress distribution can be detected in the state more close to the actual circumstances.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an actual pipe test method for evaluating a line pipe in a sour environment.

[0002]

2. Description of the Related Art In recent years, deterioration of materials due to corrosion has become a problem in line pipes for transporting oil and natural gas. Crude oil and natural gas flowing through the line pipe often contain moist hydrogen sulfide (H ₂ S). These H ₂ S are the atomic hydrogen (H ₂ ) generated by the corrosive action that penetrates into the steel. The crack that occurs is a problem. Hydrogen-induced cracking (HIC) and sulfide stress corrosion cracking (SS)
There are two types of C).

In HIC, atomic hydrogen generated by corrosion of iron on the surface of a steel material in a hydrogen sulfide environment penetrates into the steel, causing MnS in the steel material and oxide-based clusters.
It occurs by accumulating around inclusions having a layered spread. Moreover, since such layered inclusions are often present in the segregation zone, it is known that the HIC generated from the inclusions is promoted by the segregation zone.

On the other hand, SSC is a phenomenon that occurs particularly on the high-strength side, and since welding work is indispensable for the production and laying of line pipes, the hardness of the welded portion of the steel used for these applications It is known that SSC is generated due to atomic hydrogen that becomes high and penetrates into steel.

Test methods have been proposed to evaluate linepipes in such sour environments. This test method includes the NACETM0284 test method which mainly evaluates HIC and the NACETM0177 test method which mainly evaluates SSC.

[0006] The TM0284 test method for evaluating HIC is a standard solution (H ₂ S saturated artificial seawater) in which a coupon test piece machined from a line pipe is subjected to no stress.
It is soaked in the glass for 96 hours to evaluate whether or not HIC cracks occur.

TM0177 to evaluate another SSC
Similarly, a round bar tensile test piece machined from a line pipe was used as a standard solution (H ₂ S saturated 5% sodium chloride (NaC).
l) + 0.5% acetic acid (CH ₃ COOH)) It is a test method for evaluating whether or not it breaks by 720 hours by applying a predetermined stress.

However, the above two test methods have some differences from the actual line pipe environment. TM028
In the 4 test method, no stress is applied to the test piece, whereas in the actual environment, the internal pressure is applied to the line pipe. Further, in the TM0284 test method, hydrogen enters from all surfaces of the test piece, whereas in the actual line pipe, hydrogen enters only from the inner surface of the steel pipe. Further, the residual stress existing in the actual line pipe is not evaluated because the residual stress is removed because the test piece is processed from the line pipe.

The difference between the TM0177 test method and the actual sour environment is that the girth welding (which is welded to connect line pipes to each other) is performed in the actual environment. Therefore, stress near girth welding is simulated and evaluated. Things are very difficult. Further, similar to the TM0284 test method, there is a problem that the residual stress cannot be taken into consideration because machining is performed.

In order to solve the above problems, an actual pipe immersion test method (CAPCIS test method) has been proposed as an evaluation method of a line pipe in an actual sour environment. In this real pipe immersion test method, first, line pipes having a height of at least half the diameter are girth welded. Next, grid blasting is performed on the inner surface of the pipe. Then, the inner surface of the steel pipe is degreased with acetone. Next, as shown in FIG. 3, a predetermined tensile stress (72% minimum yield stress (SMYS)) is applied to the inner surface of the steel pipe 1 in the diametrical direction by using a turnbuckle 2 supporting two points together with a hydraulic cylinder. Then, a 5% sodium chloride + 0.5% acetic acid solution is injected into the steel pipe, and nitrogen deaeration for removing oxygen is performed. After confirming that the amount of oxygen in the solution is 150 ppm or less, H ₂ S is sealed. H ₂ S saturation (3000ppm)
After that, a 720-hour immersion test is performed, and after the test is completed, it is a test method for evaluating whether or not cracks will occur due to ultrasonic flaw detection. In the figure, 3 is a welded portion of the steel pipe, and 4 is a stress beam provided at the tip of the male screw of the turnbuckle 2.

[0011]

However, in the conventional actual pipe immersion test (CAPCIS test), the region 5 where the turnbuckle can give a predetermined tensile stress to the inner surface of the steel pipe due to the two-point support is shown in FIG. As shown in, there is a problem that there are only two regions in the direction perpendicular to the turnbuckle 2. In order to simulate the internal pressure load type stress distribution of a line pipe in an actual environment, the present invention is to expand the region where a predetermined tensile stress exists as compared with an actual pipe immersion test performed using a two-point supported turnbuckle. It is an object.

[0012]

In order to achieve the above object, in the present invention, a steel pipe is expanded to a predetermined tensile stress by using a turnbuckle with four-point support, and an actual pipe immersion test is performed. . The four-point supported turnbuckle is configured by further connecting a two-point supported turnbuckle in the vertical direction of the two-point supported turnbuckle.

[0013]

When the actual pipe immersion test is performed using the turnbuckle with four-point support as described above, the areas where a predetermined tensile stress can be applied are increased to four areas, and the evaluation target area is expanded, which is closer to the actual environment. The stress distribution of the state is obtained.

[0014]

EXAMPLES Examples will be described with reference to the drawings.
As shown in FIG. 1, tensile stress is applied to the inner surface of the steel pipe 1 at intervals of approximately 90 degrees by using a turnbuckle 2 supporting four points. At this time, the steel pipe 1 is expanded by turning the male screw of the turnbuckle 2. At this time, the stress distribution is as shown in FIG. 2, and there are four regions 5 where the predetermined tensile stress is obtained. To confirm that the stress reaches a predetermined value, a strain gauge is attached to the measurement position, and the strain amount is converted into the stress to set the predetermined stress. When tensile stress is applied to the inner surface of the steel pipe by using the turnbuckle 2 with four-point support in this way, the number of regions where the predetermined tensile stress is increased from the conventional two positions to four positions.

[0015]

Since the present invention is constructed as described above, it has the following effects. By loading a four-point supported turnbuckle on the steel pipe, the stress distribution of the line pipe in the actual environment becomes closer, and the area where the predetermined tensile stress is obtained is double that of the conventional test area, expanding the evaluation area. And the value as a test method increases.

[Brief description of drawings]

FIG. 1 is a sectional view of a steel pipe for expanding a steel pipe by using a turnbuckle supporting four points.

FIG. 2 is a stress distribution diagram when a steel pipe is expanded using a turnbuckle supporting four points.

FIG. 3 is a sectional view of a steel pipe for expanding the steel pipe by using a two-point supported turnbuckle.

FIG. 4 is a stress distribution diagram when a steel pipe is expanded using a two-point supported turnbuckle.

[Explanation of symbols]

 1 Steel pipe 2 Turnbuckle 3 Weld 4 Stress beam 5 Predetermined tensile stress area

Claims (1)

[Claims] 1. A method for immersing a real pipe in which a predetermined tensile stress is applied to an inner surface of a steel pipe by using a turnbuckle supporting four points when a line pipe is evaluated in a sour environment by a CAPCIS test. .