Atyrau Oil & Gas
Welding «Old» and «New»: How AVC Production Modernized Coke Drums at the Atyrau Oil Refinery
A delayed coking unit (DCU) is a cornerstone of deep conversion at any refinery, with both technological and economic significance. The stability of its operation directly affects the yields of light petroleum products, the loading of downstream units, and overall refining margins.
Metal Fatigue
At the Atyrau Oil Refinery, DCU coke drums have been in service since 1980. More than forty years of operation under cyclic thermal and mechanical loads has, predictably, led to accumulated metal fatigue and defects.
In October 2024, a specialized technical organization conducted an assessment of the condition of the DCU reactors. Critical metal wear was recorded in the lower sections of the shells, in areas of maximum thermomechanical stress concentration. According to the experts’ conclusion, extending the unit’s service life was possible, but only for one year, until October 2025. After that date, operation would be prohibited unless the equipment was brought into compliance with applicable standards.
For the refinery, this meant an extremely compressed planning horizon. Full replacement of the reactors, a standard but capital-intensive and time-consuming scenario, would have required development of design and estimate documentation, fabrication of the shells, logistics planning, installation, and subsequent commissioning. Specialists estimated that implementing such a project would take two to three years.
For a refinery operating on a continuous cycle, that would mean either a prolonged unit shutdown or a forced reduction in throughput across the entire process scheme. The DCU is integrated into the refinery balance such that its shutdown affects primary processing modes and secondary units. Ultimately, this would have inevitably affected overall crude throughput and petroleum product output.
An Alternative to Full Replacement
The project’s general contractor, AVC Production, a Kazakhstan-based company, proposed an alternative approach. Instead of dismantling and replacing the entire reactor assembly, the parties opted for a targeted modernization focused on replacing the most heavily worn components. Specifically, this included the conical section, the support ring, and the two lower shell courses on each vessel.
In practical terms, the work addressed the specific zones identified by the technical assessment as having threshold residual wall thickness values and fatigue damage indicators. At the same time, the upper sections of the vessels retained an adequate strength margin and could remain in service.
Work of this complexity, involving the partial replacement of components on in-service equipment, had not previously been carried out in either the CIS or Europe. A key feature of the project was that the modernization was executed not as a major rebuild requiring an extended shutdown, but within the scope of a standard planned turnaround.
Meeting the 20-Day Window
The project was completed in 20 days, matching the unit's planned turnaround. Work proceeded around the clock, in parallel on two reactors. The first and third reactors were modernized first, followed by the second and fourth. This sequence optimized the use of heavy-lifting equipment and welding crews, minimizing downtime between stages.
Each component replaced weighed 46 tons. Removal of the old sections and installation of the new ones required two main cranes with a lifting capacity of 750 tons each, plus one auxiliary crane rated at 350 tons. Using cranes in this class was driven not only by the weight of the components, but also by the positioning-accuracy requirements within the confined space of an operating unit.
A total of 117 specialists were engaged in the project, including 83 riggers and 34 highly qualified welders. Given the 24/7 work schedule, shift teams were formed to maintain continuity across the full workflow, from dismantling and edge preparation to welding and quality control.
The Core Challenge: Welding the “Old” to the “New”
The key engineering task was welding the new sections to the existing reactor shell.
Over decades of service, the metal in the lower shell courses was exposed to cyclic thermal loading, from high temperatures during the coking cycle to cooling during coke removal. These cycles lead to gradual changes in mechanical properties, including reduced ductility, microcrack formation, and localized fatigue.
The new sections were fabricated from 28 mm-thick stainless steel. Joining metals under different conditions requires precise selection of welding consumables, calculation of preheat and subsequent cooling regimes, and control of the thermal impact on adjacent zones.
Errors at this stage could have led to residual stresses and accelerated defect growth during subsequent operations. As a result, significant attention was paid not only to the welding itself but also to non-destructive testing, including ultrasonic and radiographic inspection of the welds.
As a result of the work, a reliable joint was achieved between the existing shell and the new sections, meeting strength and tightness requirements under high operating loads.
Economics of the Solution
The unique operation developed and executed by AVC Production specialists delivered a substantial economic benefit for the refinery. A full replacement of the reactors, with a two- to three-year production shutdown, would have meant significant capital costs for the fabrication and installation of new shells, along with financial losses from the outage and lost revenue from crude oil processing.
The partial modernization completed during a scheduled turnaround enabled the refinery to avoid multi-year downtime and maintain its production balance. In addition, for the Kazakhstan market, where domestic refining is of strategic importance, solutions of this kind are directly linked to the country's energy security.
Digitalization: shift to a predictive model
Mechanical modernization was only one part of the project. The reactors were additionally equipped with a predictive analytics system. The system provides real-time monitoring of the vessel condition, records changes in metal parameters, and transmits data to operating personnel.
In effect, this is a shift from the existing "repair after a defect is found" model to forecasting future degradation. For units operating in cyclic service, this is particularly important. Analysis of temperature and strain load dynamics enables adjustment of operating modes and prevents the development of critical conditions.
With aging equipment, digital tools are no longer an add-on but a necessary element of safe operation.
Technical success in an industry context
What is the bottom line? The project to partially modernize the delayed coking unit's coke drums was completed during the scheduled turnaround and within the established 20-day timeframe.
As a result, the refinery was able to:
- extend the service life of the reactors,
- avoid a multi-year outage,
- maintain production volumes,
- implement elements of predictive analytics.
For the industry, this example matters not as a demonstration of record timing but as an illustration of an approach to managing aging infrastructure. In an environment where a significant share of process equipment in the region is approaching end-of-life, precisely targeted and engineered solutions like these can serve as an alternative to costly, time-consuming rebuilds.
The delayed coking unit modernization case at the Atyrau Oil Refinery demonstrates a rational engineering approach that is technically complex, yet execution-precise from an organizational standpoint. The success of this project was the result of systematic work by the engineering company AVC Production. Founded in 2013, the company now holds a solid position as one of the leaders in Kazakhstan’s oilfield services market, bringing together more than 1,000 specialized professionals. A broad footprint, with offices in Atyrau, Aktau, Pavlodar, and Almaty, enables the group to mobilize resources quickly at the country’s key industrial sites.
Working under a full-cycle model, AVC Production supports the entire asset life cycle, from engineering design and supply of high-technology equipment to EPC execution and service maintenance. The group’s portfolio includes more than 1,500 completed projects for strategic customers, including the Atyrau Oil Refinery, the Pavlodar Petrochemical Plant, the Shymkent Oil Refinery, and major upstream and petrochemical enterprises, Caspian Neft and Uzbekneftegaz. At a time when the industry is under pressure to raise efficiency while tightly optimizing schedules and costs, AVC Production sets new quality benchmarks, turning complex engineering challenges into a reliable foundation for stable growth of Kazakhstan’s industrial sector.