Method for inspecting corrosion under insulation

Abstract

A method for inspecting corrosion under insulation simply and precisely at a low cost is provided. The method for inspecting CUI is characterized by obtaining signals from a fiber optical Doppler sensor attached to equipment and counting a waveform for a predetermined time before and after a point where an amplitude is over a threshold value as one acoustic emission (AE) signal, recording the AE signals and the maximum amplitudes thereof, subjecting the AE signals to a filtering process to remove noise signals, determining a frequency distribution of the AE signal hits relative to various maximum amplitude values, determining a regression line of the number of the AE hits relative to the maximum amplitudes from a scattering diagram which is obtained by double logarithmic expression of the frequency distribution, and judging existence or nonexistence of the corrosion based on a gradient of the regression line.

Description

technical field

[0001] The invention relates to a method for inspecting corrosion under insulation in equipment. In particular, the present invention relates to a method for under-insulation inspection that enables simple and precise inspection of said corrosion in insulation-covered equipment at relatively low cost. Background technique

[0002] Since corrosion under insulation is a major cause of leakage failures in equipment made of carbon steel or low alloy steel, corrosion under insulation is one of the severe degradation phenomena monitored in chemical plants that have been in operation for many years.

[0003] Typically, in chemical plants and the like, many pieces of equipment such as towers and vessels, valves and plugs, and heat exchangers are covered with insulation.

[0004] The insulation needs to be removed in order to visually inspect corrosion under insulation (hereinafter referred to as "CUI"). Furthermore, when scaffolding is erected in order to dismantle...

Examples

example 1

[0092] The insulating layer was removed from the air oxidation reactor (3.8 m in inner diameter) in which the liquid moved, and 4 FOD sensors (ch1 to ch4) were attached at intervals of 90° in the circumferential direction. The coating on the outer surface was removed with sandpaper, the FOD sensor was attached to the outer surface using a heat resistant epoxy based adhesive, and the FOD sensor was secured with aluminum tape attached to the FOD sensor.

[0093] Corrosion with an area of ​​about 320 mm x about 90 mm and a depth of about 0.3 mm to about 0.5 mm was found at about 2.5 m above the FOD sensor ch1. No corrosion was found within 4m from the FOD sensor ch2. Corrosion with an area of ​​about 350 mm x about 65 mm and a depth of about 0.3 mm to about 1.0 mm was found at about 2.5 m above the FOD sensor ch3, and at a position about 2 m from the lower right of the FOD sensor ch3 with an area of Corrosion of about 720mm by about 110mm, with a depth of about 0.3mm to 0.6mm. ...

example 2

[0108] Such as Figure 9 A model piping system was prepared as shown.

[0109] An insulating layer 13 was attached to a carbon steel pipe 10 having a total length of 5 m, and silicon oil heated by a heater 12 was circulated in the pipe 10 . In addition, corrosion is artificially accelerated in order to efficiently produce CUI. Specifically, pure water is continuously dripped from the dripping device 11 to the surface of the pipe 10, and the amount of the dripping liquid is finely adjusted to alternately produce a wet state and a dry state. Besides, common salt is coated on the surface of the pipe 10 . In addition, the silicone oil circulating through the pipe 10 is heated to a temperature in the range of 60°C to 70°C, thereby artificially accelerating corrosion.

[0110] About one month after the start of the artificially accelerated corrosion, the FOD sensor 14 was fixed by using U-bolts.

[0111] The silicone oil was heated for 3 hours after starting to determine AE, all...

technical field

[0001] The invention relates to a method for inspecting corrosion under insulation in equipment. In particular, the present invention relates to a method for under-insulation inspection that enables simple and precise inspection of said corrosion in insulation-covered equipment at relatively low cost. Background technique

[0002] Since corrosion under insulation is a major cause of leakage failures in equipment made of carbon steel or low alloy steel, corrosion under insulation is one of the severe degradation phenomena monitored in chemical plants that have been in operation for many years.

[0003] Typically, in chemical plants and the like, many pieces of equipment such as towers and vessels, valves and plugs, and heat exchangers are covered with insulation.

[0004] The insulation needs to be removed in order to visually inspect corrosion under insulation (hereinafter referred to as "CUI"). Furthermore, when scaffolding is erected in order to dismantle...

Examples

example 1

[0092] The insulating layer was removed from the air oxidation reactor (3.8 m in inner diameter) in which the liquid moved, and 4 FOD sensors (ch1 to ch4) were attached at intervals of 90° in the circumferential direction. The coating on the outer surface was removed with sandpaper, the FOD sensor was attached to the outer surface using a heat resistant epoxy based adhesive, and the FOD sensor was secured with aluminum tape attached to the FOD sensor.

[0093] Corrosion with an area of ​​about 320 mm x about 90 mm and a depth of about 0.3 mm to about 0.5 mm was found at about 2.5 m above the FOD sensor ch1. No corrosion was found within 4m from the FOD sensor ch2. Corrosion with an area of ​​about 350 mm x about 65 mm and a depth of about 0.3 mm to about 1.0 mm was found at about 2.5 m above the FOD sensor ch3, and at a position about 2 m from the lower right of the FOD sensor ch3 with an area of Corrosion of about 720mm by about 110mm, with a depth of about 0.3mm to 0.6mm. ...

example 2

[0108] Such as Figure 9 A model piping system was prepared as shown.

[0109] An insulating layer 13 was attached to a carbon steel pipe 10 having a total length of 5 m, and silicon oil heated by a heater 12 was circulated in the pipe 10 . In addition, corrosion is artificially accelerated in order to efficiently produce CUI. Specifically, pure water is continuously dripped from the dripping device 11 to the surface of the pipe 10, and the amount of the dripping liquid is finely adjusted to alternately produce a wet state and a dry state. Besides, common salt is coated on the surface of the pipe 10 . In addition, the silicone oil circulating through the pipe 10 is heated to a temperature in the range of 60°C to 70°C, thereby artificially accelerating corrosion.

[0110] About one month after the start of the artificially accelerated corrosion, the FOD sensor 14 was fixed by using U-bolts.

[0111] The silicone oil was heated for 3 hours after starting to determine AE, all...

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