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44 OCTOBER 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 10 CHEMICAL TREATMENT A This article summarizes the results of an investigation into the source of organochloride compounds in a naphtha hydrotreater unit. The con- taminated naphtha feed was traced back to a single crude and slop source that had dumped organochloride- containing hydrocarbon waste and/or organochloride chemicals used within the refinery processes. A naphtha sample was collected during a high- chloride excursion and used as a ref- erence sample. The investigation results showed that two organochlo- ride compounds were present in the analyzed sample; namely, tetrachloro- ethylene (perchloroethylene) and tri- chloroethylene. A Middle East refinery suddenly began to exp eri enc e low pH in th e naphtha hydrotreater (NHT) unit of the spent wash water from the separator water boot and stripper receiver that contributed to a leak in the air -cooled carbon steel product condenser tub es. Th e leak result ed in shutting down the NHT unit, and inspec- tion of th e condenser re vealed se vere corrosion attack of several tubes, requiring a complete retubing. Some of these tubes in the air-cooled product condenser corroded severely, and the measured metal loss was 60 to 80%. The immediate cause of the tube corrosion attack was attributed to the presence of high organochloride concen- tration in the naphtha feed to the NHT unit. However, the source of the chlorides in the naphtha feed was not identified. Figure 1 shows a diagram of the NHT process illus- trating the corrosion incident. Numerous references in industry can be found that describe the experience of cor- rosion in NHT unit effluent systems associ- ated with excess organic chloride in the NHT feed. 1-7 Two types of organic chloride are typically identified at NHT inlets: 1) nondesaltable organic chloride such as light chlorinated solvents, and 2) water- s o l u b l e a m i n e - h y d r o c h l o r i d e s a l t s entrained with water in the naphtha from the overhead accumulators of the crude di sti l l ation unit (C DU). Three ppm of organic chloride in the naphtha feed is typi- cally considered a maximum value to avoid problems. 1 Organochloride compounds are organic substances containing at least one cova- lently bonded atom of chloride (in this case, C-Cl). For example, chloroform (CHCl 3 ) and dichloromethane (CH 2 Cl 2 ) are representa- tives. They are effective solvents for clean- ing and removing paraffin and other depos- its or in other degreasing operations. The crude oil can be contaminated by th e organochloride compounds from different processes, whether upstream processes or w ith i n th e re f i n e r y p r o c e ss e s . Th e s e organochloride compounds are not simple to detect. They can be hydrolyzed in a CDU during the heating process to form hydro- chloric acid (HCl), resulting in tremendous Organochloride Contamination in a Refinery Naphtha Hydrotreater Unit Nayef M. a la N azi, f rederick M. a da M , a N d Muthuku M ar Nagu, Saudi Aramco, Dhahran, Saudi Arabia