CRITICAL DEFECTS THAT CAN BE ENCOUNTERED IN OIL PIPELINES

ABSTRACT

Currently, the number of accidents and incidents in oil pipelines is constantly increasing, which is due to the aging of the pipelines and the lack of funds for major repairs of enterprises. The main problems during oil pipeline accidents are the implementation of measures to eliminate accidental oil spills, the recultivation of oil-contaminated lands and soil pits, and the release of natural gas during gas pipeline accidents. As a result, emergency situations cause not only economic losses of enterprises, but also environmental pollution.

АННОТАЦИЯ

В настоящее время количество аварий и происшествий на нефтепроводах постоянно увеличивается, что связано с старением трубопроводов и отсутствием средств на капитальный ремонт предприятий. Основными проблемами при авариях на нефтепроводах являются проведение мероприятий по ликвидации аварийных разливов нефти, рекультивация нефтезагрязненных земель и грунтовых котлованов, выбросы природного газа при авариях на газопроводах. В результате чрезвычайные ситуации вызывают не только экономические потери предприятий, но и загрязнение окружающей среды.

Keywords: oil pipeline, internal defectoscopy, external defectoscopy, critical defects, structural scheme.

Ключевые слова: нефтепровод, внутренняя дефектоскопия, внешняя дефектоскопия, критические дефекты, структурная схема.

Main part

The oil and gas industry is the world's leading energy producer, producing over half of US energy in 2016. As energy demand increases, energy production infrastructure expands, including subsea operations. These complex operations require various structures and systems to extract oil from underground formations and transport it to the surface. Oil pipelines (PIPs) are crucial for transporting products from oil wells to processing facilities and converting oil into commodity properties. However, they are exposed to harmful impurities, leading to corrosion and increased risk of emergency situations. To ensure operational reliability and efficiency, technical defectoscopy is used to identify defects, determine trouble-free operation times, and assess the technical condition. Development directions include studying internal and external defectoscopy, comparative analysis of modern methods, developing a primary information converter, and constructing a structural scheme for new facilities.

It follows from the above that the task of assessing the strength and service life of oil pipeline systems in the presence of defects is currently relevant.

To achieve this goal, it is necessary to perform the following tasks:

1. Analysis of existing defectoscopy methods and technological schemes for the evaluation of the current technical situation;

2. Selection of methods and technologies for complex defectoscopy of the technical condition of oil pipelines;

3. Development of the initial information converter capable of detecting defects of oil pipes and construction of the structural scheme of the device.

A primary information transducer based on the galvano-magnetic principle is used to detect defects such as internal and external microcracks, bends, internal cavities, and corrosion of oil pipelines.

Thus, the value of the magnetic field induction, which depends on the presence of the defect and its geometrical size, changes. This situation causes the value of the Hall sensor to change. As a result, it is possible to determine the presence and geometric dimensions of the defect on the display (screen) of the built defectoscopy device.

Main part

Pipe geometry defects involve changes in the shape of the pipe, such as surface crush injury, shrinkage damage to the pipe wall, and narrowing (ovality). Surface crush injury occurs when a pit decreases the flow field without a break in the axis of the oil pipeline. Shrinkage damage reduces the flow area of the pipe, accompanied by transverse bulges and voids. Narrowing reduces the flow area of the pipe, and the actual center of the constriction may be offset from the nominal diameter pipe. Pipe wall defects include corrosion of metal, cracks, and crack-like corrosion, which are determined by the action of stresses such as pressure, corrosion cracking, and corrosive environment on the metal.

Photo 1. Defects of the main oil pipeline detected during additional defectoscopic control in the locations of hazardous acoustic emission sources

a - abnormal welding joints; b - areas with local corrosion defects; v - to repair internal damaged structures; q-areas of general and pitted corrosion with metal loss.

Now let's take a look at the overview of malfunctions in oil pipelines in some scientific literature.

Failure of pump-compressor pipes (pipes) in contact with various elements contained in the oil at a pressure of up to 20 MPa is shown in Photo 2. On the outer surface of the pipe there are traces of the key used during installation, the depth of the Marks is 0.2-0.7 mm (Photo 2 a). Also, in the place where the key is held, there is a hole 2 mm deep and 41 mm long along the forming tube. The length of the crack along the surface of the pipe is up to 0.1 mm, with a maximum opening in the welding area of 79 mm. The cause of damage to pipes when working under the influence of repeated static loads and the risks of exposure to the impact environment of the elements contained in the oil are the reasons for failure. As a result of these causes, microcracks are formed, like pressure concentrators, merging with the main crack at length L [2].

Photo 2. Cracks in the oil pipeline (A) and pipe coupling (B)

Taking into account the nature of the failure of the coupling and the presence of visually noticeable defective areas of the threaded part of the pipeline (Figure 2 b), it was established that the cause of the destruction of the coupling was the misalignment of the threaded grooves [3].

The reason for the failure of the block-shaped detail made of uranium 50 steel (06Х20Н8М3Д2Г2) occurred after 24 years of operation when it was exposed to a gas mixture containing up to 6% hydrogen sulfide (Photo 3 a). When checking the block-shaped deal, two diametrically opposite cracks with a maximum opening of up to 1 mm were found in the cross-sectional areas of the surfaces of two mutually perpendicular holes on the surface of the holes along the working surface (Photo 3 b). The microstructure of the cast metal of the detail is approximately dendritic, austenitic-ferritic in the presence of secondary austenite (Photo 3 c, d) [1-3].

Visual inspection of the failed part should include identifying the source from which the crack or corrosion began. The source may appear as a bulge, for example, as a result of overload or at the place of stress concentration, for example, in the form of sharp edges and welding. For example, Photo 3 shows the site of the break that occurs in an 18-inch (457 mm) gas pipeline, where the break site is in the form of a bulge; a nose-like shape (bulge) shows an overload event. After all, during visual inspection, crash analysts can use failure morphology to brainstorm and present anticipated scenarios for the causes of failures.

Photo 3. It shows the origin (bulge) of the fast-flowing plastic rupture of the 18-inch (457 mm) oil pipeline

Corrosion and defects in pipeline materials are common breakdowns, leading to liquid hydrocarbon collapse. This poses severe environmental and economic risks due to the high toxicity of oil and its products. Designing oil pipeline transport systems is crucial for efficient delivery of raw materials. Identifying accident scales and spill volumes is essential for assessing environmental and economic damage.

The main characteristics of the oil line necessary to calculate the dispersion of petroleum products are presented in Table 1.

Table 1.

Main characteristics of the main oil pipeline

In accordance with the methodology for determining damage in accidents [1-3], the volume of dispersed oil is determined:

V_max=V₁+V₂

where,

V₁ - the volume of injection of hydrocarbon raw materials in 6 hours, m³;

V₂-the volume of oil inside the emergency section of the oil line, m³

The pump volume (V₁) will be calculated as follows:

V₁=0,25Q_px6=1,5Q_p

Then (2) the volume of the pump according to the formula:

V₁=1,5x2686=4029m³

The amount of petroleum products in the emergency zone:

V₂=0,785L²

where D_н-the outer diameter of the oil line, m;

L-length of the breakdown section, m;

δ-pipe wall thickness, m.

V₂=5502,29 m³

Thus, in the event of an accident on a 5000 m long section of the oil pipeline, the maximum spill volume will be as follows:

V_max=4029+5502,29=9531,29m³=8101,6 ton

CONCLUSION

As a result of the literature analysis conducted in accordance with the scientific research work, the following ideas can be said:

1. Today, oil pipeline accidents are quite common. The most common causes of failure of linear sections of oil pipelines can be metal corrosion, as well as technical defects during manufacturing or installation.

2. In the event of an accident in the linear part of oil pipelines with a length of 5000 m, a volume of 9531.29 m³ equal to 8101.6 tons will be spilled.

3. From the ecological and economic point of view, oil spills can affect absolutely every component of the ecosystem, so a complex of measures should be implemented to localize the emergency situation.

Reference:

1. «ЭМА преобразователи для ультразвуковых измерений» // А.А. Самокрутов, В.Г. Шевалдыкин, В.Т. Бобров, С.Г. Алехин, В.Н. Козлов №2 (40) июнь 2008. https://www.ntcexpert.ru/562.
2. Васин Е.С. Методология обеспечения несущей способности стальной оболочки магистральных нефтепроводов на основе результатов внутритрубной дефектоскопии. – Дис. ... д-ра техн. наук: 25.00.19 – М., 2003. -321 с.
3. Внутритрубная диагностика методом ЭМАП. Научно-технический центр «НефтеГазДиагностика». [Электронный ресурс]. – режим доступа к стр.: http://ntcngd.com/uslugi/article_post/vnutritrubnaya-diagnostika-metodom-emap-emat (дата обращения: 10.05.18).