The industry choice for weld metal overlay

Digester vessels are typically manufactured from carbon steel. Because of increased production expectations and environmentally driven process changes, these vessels suffer severe corrosion attack by cooking liquor. The Unifuse^® vessel weld overlay technology was originally developed for the field installation of a fully fused, low dilution, corrosion-resistant cladding to mitigate this degradation process.

In continuous digesters, corrosion zones are easily identified with a periodic thickness mapping program. As critical wastage zones are identified, the Unifuse vessel overlay process is used to deposit a 309 or 312 stainless steel deposit. Because of the large size and short turnaround windows required for continuous digester plant maintenance, the industry-leading application production rates that are achieved using the WSI process offers our clients the best possible solution.

Because of their more aggressive corrosion environment, batch digesters typically require the use of 312 stainless steel as a protective deposit. One major difference between the WSI Unifuse process and other welded approaches offered in the industry is our patented duplex stainless welding technology, which eliminates the solidification cracking found in conventional 312 weld deposits.

Due to technical success and unparalleled return on investment, the industry chooses WSI Unifuse solution above all others. This has resulted in the largest installed base of weld metal overlay in the industry, and a solid reputation for safety, quality, and overall value.

A unique cost-effective solution

Upper furnace components in boilers experience some of the most challenging erosive/corrosive environments in any industry. Being exposed to flue gas corrosion products, their operating temperature is typically higher than other components, such as waterwalls. In addition, these critical components are also exposed to flue gas particulates traveling at high velocities because of the area reduction typically designed into the units.

WSI has over 30-year’s experience in the protection of upper furnace components using the patented Unifuse360^® technology. This unique product features a fully fused welded bond between the corrosion resistant overlay material and the tube base material. The patented welding process utilized provides a fully tempered heat affected zone that allows the tube to be bent to final product configuration after the application of the coating. The bond quality of these tubes is significantly better than other approaches, such as coextruded tubes and tubes that have been heat treated after overlay is applied.

Unifuse360 can be manufactured in small batches using corrosion resistant alloys that are tailored specifically for the corrosive environment of your boiler. With the largest installed base in the industry, the reliability of the technology has been time tested and has offered successful protection for hundreds of boilers throughout the world.

Watch our Europe facility as they perform panel overlay process:

The industry standard in fireside erosion/corrosion control

Fireside corrosion of the waterwall panel is among the most expensive repair/replacement for a boiler operator. WSI developed Unifuse180^® technology for mitigation, and over the years, this process has become the industry standard in fireside erosion/corrosion control.

In coal-fired boilers, the primary damage mechanism is sulphidation attack. Although fireside corrosion is found in all boilers, the accelerated thinning of coal-fired boiler waterwalls became a critical issue when the combustion chemistry of boilers was changed to address the formation of Nitrous Oxides (NOx) during combustion. By installing LoNOx burners, which change the combustion atmosphere in the furnace box to a reducing atmosphere, NOx compounds were reduced. But this change significantly accelerated the waterwall wastage caused by corrosion.

WSI Unifuse180 has the largest installed base in the world for the mitigation of fireside corrosion in critical as well as sub-critical, coal-fired units. The product can be field applied when existing waterwall panels need protection, or can be shop applied for new construction or waterwall change-outs when the existing base material is beyond repair.

In Waste to Energy Boilers (WTE) the primary damage mechanism is caused by heavy metals that react with chlorine to form low melting point chlorides.  In 1985 WSI developed a weld metal overlay process utilizing alloy 625 that provided a revolutionary technology for the mitigation of fireside corrosion in these boilers.   With a true welded bond, the coating cannot disbond from the boiler base material so it can withstand the thermal cycling caused by changes in operating load and other contributors such as soot blowers.

The field applied corrosion-resistant weld metal overlay (Unifuse180) originally developed by WSI for waste to energy boilers has proven to be the most reliable method for the mitigation of fireside thinning. With a true welded bond, the coating cannot disbond from the boiler base material, so it can withstand the thermal cycling caused by changes in operating load and other contributors, such as soot blowers. As a welded coating, the protective barrier does not have any porosity or other imperfections that would allow the corrosive environment to penetrate the barrier and create base metal damage.

Shop production services

As a global organization, WSI maintains two production facilities (USA and Europe) for the application of Unifuse180 weld metal overlay. Our resources and expertise enable us to handle the largest and most complex panel configurations in the world for customers who are individual plant operators as well as boiler original equipment manufacturers. WSI offers an unrivaled fabrication resource. We can handle large panels up to 18 m long and 2 m wide, giving you a lower cost per panel. Plus, we can apply an overlay thickness of 1.2–3 mm, or even more, to suit your specific requirements.

Field production services

Field applied waterwall overlay is performed by WSI’s field application specialists. WSI is the world’s largest provider of weld metal overlay with global application resources. With the largest fleet of equipment and trained personnel in the industry, no application project is too big to handle.

Industry-leading engineered repair and upgrade solutions

Delayed coking has been in use since before the 1950s. Because delayed coking is a batch process, the components involved see significant temperature and pressure fluctuations during operation that are not common in other refinery assets. These cyclic changes cause low cycle fatigue failure mechanisms in the coker drums of the system. Since these drums are extremely costly to replace and are a critical asset, solutions that extend life, shorten turnaround cycles, and improve operational reliability and safety are of prime importance.

WSI has provided advanced repair options to address the more prevalent coke drum failures for decades. This includes bulging and cracking of the pressure boundary shell, cracking of the support skirt to shell interface weld area, and cladding damage of the lower cone. Today, WSI is the largest provider in the industry of structural repairs for coke drums.

Our unique process consists of installing a highly engineered weld metal overlay to the existing vessel to modify the structure of the vessel to mitigate bulging and cracking caused by the low cycle fatigue mechanisms to which the vessels are exposed.

Because the welding parameters are tightly controlled by the use of closed-loop automated welding systems, controlled deposition techniques (temperbead) are implemented to eliminate the need to perform post-weld heat treatment of the deposit. This approach has been implemented in over 100 coke drums throughout the world with flawless performance.

For support skirt crack repairs, WSI utilizes proprietary welding processes to replace the critical welds and, in some cases, install new sections of skirt, also without requirement for post-weld heat treatment. With dozens of skirt repairs installed throughout the industry without subsequent cracking, this approach has been demonstrated to be superior to conventional methods of repair.

Our long history in the development and implementation of specialty coke drum life extension and repair processes positions us to be your primary source for coke drum reliability.

WSI engineered solutions for coke drums

• Bulge repair and structural shell reinforcement
• Lower cone replacement welds utilizing the HotPulse^® critical weld process
• Shell and support skirt crack repair
• ID cladding damage and defect repair

Specialty machine welding solutions specifically configured to address difficult welds

Product heaters and furnaces are some of the most common components in any refinery. Many refiners are in the process of upgrading the metallurgy of these components to reduce degradation and maintenance costs. Since these replacements involve a large number of orbital welds and these welds are performed in-situ, the high preheat requirements and difficult geometry often cause significant weld failures. Advanced materials are not very forgiving to multiple repairs, which creates a difficult challenge in meeting quality and schedule requirements. WSI has developed HotPulse^®-enabled specialty machine welding systems specifically configured to make these difficult U-Bend welds. The equipment safely places the operator away from the discomfort of the high preheat and, because of the HotPulse technology, provides an extremely high-quality GTAW weld at high production rates. When high alloy base materials such as 9CrV are used, the mechanical and chemical properties of the welds are also significantly improved over conventional welding.

Watch our U-Bend welding video to learn more about our welding solutions.