Atlac Resins Resist Corrosion at Saudi Petrochemical Plant

Composite materials are well known for their resistance to highly corrosive environments but for optimal performance it’s essential to select the right resin for each application. For a demanding project at a petrochemicals plant in Saudi Arabia, Ollearis turned to AOC’s Atlac resins, which have a proven track record in challenging industrial processes.

Cost-effective solution

Corrosion-resistant piping and vessels were required for a combustion unit at the SABIC subsidiary Petrokemya (formerly SADAF) petrochemical complex in Jubail (Saudi Arabia). The exhaust gas from the combustion unit contains Hydrochloric Acid which must be neu-tralized using a wet scrubber system. Fiber reinforced polymer composites provided the ability to withstand the highly corrosive chemicals involved in this process and offered a more cost- effective solution than specialized corrosion-resistant metal alloys.

Ollearis, an experienced manufacturer of corrosion-resistant pipes, tanks and process equipment, collaborated with the project’s EPC contractor, China Tianchen Engineering Corporation (TCC), and the engineering firm responsible for the combustion package, John Zink Hamworthy Combustion, to design and manufacture the composite vessels and piping required for the quench tank, scrubber and exhaust stack. Ollearis selected three different Atlac resins in order to provide the most economic solution satisfying the performance requirements of each component.

The right resin for the job

Ollearis selected AOC’s Atlac 590 Epoxy Novolac Vinyl Ester resin for the first phase of the gas cleaning process, the quench tank, which is 11.8 m high and has an internal diameter (ID) of 3 m. This is a highly demanding application since the exhaust gas from the com-bustion unit enters the tank at a temperature of approximately 300 °C and is cooled extremely quickly by water sprayed from nozzles located near the gas inlet. The high per-formance Atlac 590 resin provides both the resistance to the aggressive Hydrochloric Acid solution and the retention of strength at elevated temperatures necessary for this vessel.

Atlac 430, a versatile, standard Bisphenol A Epoxy Vinyl Ester resin, was chosen to match the less challenging conditions found in the 1.8 m ID, 1.45 m long duct connecting the quench tank to the scrubber, the scrubber itself, and the exhaust stack from which the cleaned gas is released. The 14.10 m high scrubber has a 3.5 m ID and a design temperature of 85 °C. It is exposed to the Hydrochloric Acid solution entering from the quench tank as well as the Sodium Hydroxide solution present in the scrubbing water which is used to neutralize the acid. The 39.70 m high stack has a 1.3 m ID and is exposed to air containing a small amount of Hydrochloric Acid and wet Chlorine. It has a design tempera-ture of 85 °C.

Finally, Atlac 382 Unsaturated Bisphenol A Polyester resin was selected for a section of the piping system installed around scrubber and quench tank. This resin delivers good chemical resistance against both acid and caustic fluids at a lower cost than standard Vinyl Ester resins. Ollearis manufactured the quench tank, scrubber and cylindrical parts of the stack using the filament winding process.

Unlike a typical filament winding process using glass fiber direct rovings, for this project Ollearis interspersed layers of woven roving with the direct roving layers, producing a structure with better mechanical properties in both hoop and axial directions. The higher resin content of the woven roving structural layer also results in a higher chemical re-sistance, which is an advantage if the corrosion barrier fails.

All the other components were produced in a hand lay-up procedure.

Specific challenges

Ollearis faced several challenges when designing the equipment for this project. The first concerned the risk of crazing on the resin-rich layer (corrosion barrier) on the inner sur-face of the quench tank as a result of thermal shock. To improve resistance to thermal shock, a carbon fiber surfacing veil was used to reinforce the corrosion barrier and increase its resistance to cracking.

The second challenge involved finding a way to support the weight of the packing inside the scrubber. Ollearis solved this issue by installing a composite grating below the packing, which is supported by a composite ledge and two composite beams. The ledge and beams have a hollow rectangular cross section, and the ledge profile is filled with a polyurethane foam.

Ollearis decided not to bond the ledge directly to the scrubber since the peel strength on bonded laminates is relatively low and the shear and peel loads on the laminate generated by the packing weight could risk the ledge debonding. The ledge was therefore inte-grated into the cylindrical scrubber shell during its manufacture. The beams are supported on specially-designed composite nozzles, bonded to the scrubber shell, that provide a ‘chair’ in which the ends of the beams sit.

The bottoms of the quench tank and scrubber are flat and both vessels operate under vacuum. This presented a further challenge for Ollearis since flat composite panels have poor resistance to pressure and vacuum and usually need to be very thick to withstand such loads, making them expensive to manufacture. Ollearis developed a less costly solution by using a sandwich construction comprising a core of resin-impregnated 3D glass fiber fabric faced with composite skin layers. This reduced both the cost and weight of the parts.

Ollearis’ composite vessels and piping were installed at the plant in 2017. Installation proceeded smoothly and EPC contractor TCC was very pleased with the way that the piping and vessels connected together easily on site.

Years of experience

Ollearis relies on AOC’s chemical resistance expertise to select the best resin for the specif-ic chemical environment of each application. This resource builds on years of chemical resistance testing on AOC’s resins, combined with the experience gained in many projects around the world.

“We select the resin types using the AOC Chemical Resistance Guide as well as the exper-tise from AOC’s Technical Service team, considering the fluids handled and the design temperatures detailed by the client,” said Adriano Ureña, technical manager at Ollearis. “For this project, the fluids and design conditions were very typical, so it was only necessary to make sure that the resins proposed would perform well under these conditions. For technical support regarding non-standard combinations of fluids/ design tempera-tures, as well as special requirements such as flame resistance, food contact approval and electrical conductivity, we collaborate closely with AOC’s corrosion specialists to find the best solution.”