PRODUCTION • PROCESSING • HANDLING
REINFORCING FRACTIONATING COLUMNS Sulzer’s expert team performed an in-depth visual inspection. To do so, the bonded plate was removed to expose the carbon steel shell. Tis examination revealed that the extent of column shell corrosion was almost double that of the initial estimate, covering approximately 110m2
.
In these situations, refineries are often faced with the choice between replacing the entire column or part of it, which is costly and time consuming, or applying thermal- spray coatings that can prevent column corrosion only for a limited time. Sulzer offered a third, more time- efficient, economical and long-lasting option: weld overlay. By using this in situ process, it is possible to cover large column surfaces with corrosion-resistant alloys. Te company is highly experienced in this technique and has developed an advanced, fully automated weld overlay equipment to support its operations.
Tis machine consists of a carriage
travelling along a laser-levelled track system fixed to the column shell wall. On the carriage, a robotic index arm moves the welding torch and the oscillator in order to create weld beads. All the relevant process parameters, such as carriage speed or bead thickness, are controlled by a programmable logic controller (PLC), with which human operators can communicate by means of human-machine interfaces (HMIs). One single PLC can monitor multiple welding machines following the same instructions. Te automated process can quickly
perform welding with high accuracy. As a result, customers can benefit from a high- quality and consistent process as well as
short downtime. In this case, Sulzer could complete the overlay of the 110m2
VDU
corroded surface in the time allocated to 65m2
. To reduce the likelihood of future
corrosion, the VDU column shell was overlaid with layers of austenitic stainless steel type 316 alloy, which is widely used in welding processes to avoid carbide precipitation. In addition, the presence of molybdenum and nickel makes the alloy suitable for applications in harsh conditions.
COMPREHENSIVE MAINTENANCE AND REVAMP SERVICES In addition to repairing the VDU column
shell, Sulzer also performed weld overlay on the corroded surfaces of the other two towers, namely the ADU and the third fractionator. Also, column internals, such as trays and packings, were replaced to further improve the performance of the entire oil distillation system. Te weld overlay process was performed
in two weeks, while the entire revamp was concluded in 25 days, without any delays despite of the discovery of larger corroded areas within the VDU, increasing the required weld overlay to almost double of the originally estimated area. Since the revamp, the refinery has operated smoothly at full capacity and the solution from Sulzer could also support the shift towards different crudes without affecting the columns’ corrosion resistance. Te customer was so pleased with the work that it offered to provide positive reference to any potential customers of Sulzer.
Andrew Petticrew at Sulzer Tower Field
The weld overlay process was performed in less than two weeks
38
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Services, comments: “Te ability of our experts to resolve unexpected issues, coupled with our automated weld overlay capabilities, were crucial to ensure the timely repair of the corroded column shells. In addition, the customer could benefit from a one-stop-shop for the revamp project, as we took care of dismantling the existing column internals, as well as the manufacture and installation of new ones.”
Refineries are often faced with the choice between replacing the entire column or applying coatings that can prevent corrosion only for a limited time
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