|Content Type||Conference Paper|
|Title||HDPE Solves Alkylation Sewer Corrosion Problem in Refinery|
|Authors||Christine Osborne, Henkel Corporation|
|Source||CORROSION 2008, March 16 - 20, 2008 , New Orleans LA|
|Copyright||2008. NACE International|
|Keywords||acid, alkylation, anchor, anti-corrosion, concrete, caustic soda, corrosion, high-density polyethylene, HDPE, HF, H2SO4, hydrofluoric acid, hydrostatic, isobutene, junction box, lift station, liner, lining, manhole, NaOH, pit, plastic, polyolefin, precast, prefabricate, rehab, rehabilitate, rehabilitation, reline, relining, renovate, renovation, retrofit, sewer, sodium hydroxide, stud, sulfuric acid, sump, thermoplastic, vault|
Oil refineries use sulfuric acid or hydrofluoric acid as a catalyst in the alkylation of isobutene. Process wastewater streams discharging from alkylation units, where this process step takes place, are often characterized by a low pH. This low pH wastewater reacts with alkaline Portland cement in concrete wastewater collection and conveyance structures, compromising their structural integrity. This paper reviews one oil refinery?s use of high-density polyethylene liners to renovate and protect its deteriorated concrete process sewer structures downstream of its sulfuric acid alkylation unit.
The management of process wastewater collection and conveyance systems can be challenging for industrial factories that use or produce corrosive chemicals. The design criteria used to select materials of construction for these systems are sometimes difficult to define with certainty. It is hard to predict the impact of leaky flanges, valves, and pumps, spills from the occasional line break, and equipment rinse water discharges on the integrity of wastewater collection and conveyance structures. Some plant owners will choose to construct their wastewater structures out of Portland cement concrete, assuming some risk of corrosion in the unlikely event of a strong or large acid or caustic spill. Employment of diligent housekeeping and plant maintenance practices can further mitigate this risk. Others will take a more conservative approach, acknowledging that leaks are inevitable and process chemicals will discharge to the sewers unintentionally. In oil refineries, the sewers leading out of the isobutene alkylation units can be at risk of exposure to sodium hydroxide and either sulfuric acid or hydrofluoric acid. These chemicals react with the components of Portland cement based structural concrete, compromising the containment capability and structural capacity of concrete sewer system components. The Portland cement binder in structural concrete reacts with and neutralizes acids. The reaction consumes the binder, leading to deterioration of the concrete structure. In addition to neutralizing the Portland cement in structural concrete, hydrofluoric acid reacts with the silica-based aggregates. Although Portland cement concrete and sodium hydroxide share a high pH, sodium hydroxide (caustic soda) will corrode Portland cement based concrete too.
High-Density Polyethylene (HDPE) Corrosion Protection for Sewer Systems
One oil refinery in the Northeastern United States faced the challenge of renewing concrete process sewer junction boxes and piping after corrosion compromised the integrity of the structures. While some sewer pipe had been replaced using open-cut trenches, some of the piping traversed congested process areas, where trenchless (no-dig) construction methods offered some advantages. Henkel Corporation, a manufacturer of nonmetallic corrosion resistant construction materials, partnered with a sewer rehabilitation contractor specializing in no-dig sewer renewal technologies to present an integrated corrosion protection proposal to renew the sewer pipes and junction boxes. The proposal featured the use of pipe and anchored thermoplastic liners made of high-density polyethylene. High-density polyethylene has gained favor as a material of construction for chemical process sewers. It offers broad chemical resistance and lends itself to a variety of installation techniques from open cut construction to trenchless technologies, like slip-lining, pipe bursting, directional drilling, and fold-and-form relining.
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