CARBON STEEL STACK REPLACEMENT & REPAIR

Carbon steel has low corrosion resistance by itself, which places such smokestacks particularly at risk for rusting, thinning and buckling of plate. The carbon steel stack at a CPI facility was found to be in poor condition with signs of severe deterioration. Industrial Access developed a repair strategy and performed a stack reinforcement, partial stack replacement, and a new coating installation to restore the stack’s structural integrity and improve its longevity.

A CPI plant in the Midwest was scheduled for an ASCE Class II inspection of a 60’ tall A36 carbon steel stack. Industrial Access (IA) performed a visual and ultrasonic thickness (UT) evaluation of the condition of the stack exterior and determined the structure to be in poor condition. IA crew observed multiple rust holes present in the steel plate, signs of buckling, deformities and oxidation. The top edge of the stack was found corroded and jagged. The existing steel coating appeared to have suffered from a chemical attack.

After the inspection, IA completed a report detailing the findings and providing a list of maintenance and repair recommendations to maximize potential service life of the structure. The client proceeded to contract IA to perform the urgent stack repairs, to mitigate chances of a potential failure and unscheduled shutdown.

Carbon steel is a widely used material accounting for the majority of all annual steel production worldwide. In certain applications, however, corrosive chemicals and other environmental factors can lead to severe deterioration and degradation of carbon steel. Left unchecked, carbon steel stack corrosion can have serious or even catastrophic consequences. Therefore, an effective inspection and monitoring process is imperative to prevent costly disasters.

The inspection was performed using a crane with a man basket to allow IA specialists to conduct the ultrasonic tests (UT) and assess the condition of the stack. Before the repairs were performed, a scaffolding system was installed all around the stack’s full height to provide exterior access. In addition, a 20” square access and egress opening was cut out and a door was installed at the base of the structure. This was necessary for emergency egress as well as useful for future stack inspections. IA’s expert rope access solutions were utilized for some of the work performed in the interior of the stack.

The inspection concluded that the stack’s structural integrity was compromised and thus in need of immediate intervention. The top 20’ of the structure showed the most signs of deterioration, so IA recommended for this section to be replaced. It was also critical to provide additional structural reinforcement to the rest of the stack, since the stack was experiencing buckling due to thinning steel and insufficient structural stiffener rings. Among other recommendations, IA advised for the stack to be cleaned and appropriately coated for increased protection and chemical resistance.

The client retained IA to perform the recommended repairs. Upon mobilization, the crew first installed one A36 steel stiffener ring on the lower existing section of the stack to reinforce the structure before the stack replacement work could be initiated. It was crucial to ensure that the compromised stack did not experience further failure while the repairs were in progress. Next, IA rigged, cut, and lifted the top 6’ cone section and the 14’ cylindrical section of the stack using a crane. RTV silicone was applied to the top of the remaining stack to form a gasket for the replacement installation. A newly fabricated 14’ code-compliant 3/16” A36 plate cylindrical section was lifted and erected on the stack, and splice fasteners were installed to secure it in place. The same was performed for the new 6’ conical section installation. Both of these new stack sections had been primed ahead of time.

To prevent further buckling, deformation, and damage, the remaining three stiffener rings were installed on the new cone section, in the center of the new cylindrical section, and in the center of the existing section. This was also done for ASME STS-1 code compliance. To prepare for the application of the new coating system, a washdown and tool cleaning was performed on the existing stack interior and exterior. A heat-resistant, anti-cracking, and anti-corrosion multilayer coating system was applied on the entire exterior of the stack. For the interior, the steel surface was first primed with an epoxy coat, then coated with a chemical and corrosion resistant lining system. Lastly, the team repaired the grout around the base of the stack by applying a non-shrinking precision grout.

The most severely deteriorated sections of the stack were successfully replaced, while the structure was strategically reinforced to reduce the risk of failure. The coating systems applied should increase stack’s resistance to environmental conditions and should extend the operating life of the structure. It is critical to perform regular inspections and timely maintenance on carbon steel stacks to identify signs of deterioration early and take preventive measures before extensive damage occurs. Industrial Access helps their clients maintain the safety and longevity of their smokestacks.