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Enhanced Efficiency with Duplex Heat Exchangers
Yatinder Suri, Country Head, Outokumpu India Pvt Ltd. The material design of heat exchangers plays a very important role not only in the improved strength and reduced corrosion but also in enhancing effi cient heat transfer. This case study gives an outlook of how Outokumpuís duplex stainless steel heat exchangers solved the problem of Gansu Lanke Petrochemical Equipment, a Chinese company.

Gansu Lanke Petrochemical Equipment, one of China s largest manufacturers of heat exchangers for the petrochemical industry, has extended the service life of its oil refineries from 1-3 months to 2 years and beyond thanks to Outokumpu s grade 2205 duplex stainless steel in plate air-cooler and plate shell heat exchangers.

China's crude oil import continues to grow by double digits year-on-year. Total import for 2012 is estimated at 266 million metric tons. The strong increase is paralleled by fast growing oil-refining capacity in China.

The Problem
In the past, the steel normally used in the plate air-cooler and plate shell heat exchangers was the grade, austenitic 1.4404. These plates normally have a service life of no more than 3 months (6 months in some operating environments). Using austenitic 1.4404, severe corrosion was detected after only 1 month in operation. Plate air-cooler and plate shell heat exchangers are exposed to operating conditions with temperatures of up to 140 degress Celsius and 170 degrees Celsius respectively as well as chloride content of hundreds of parts per million (ppm). Lanke engineers first started experimenting with duplex 2205 as a replacement for austenitic 1.4404 six years ago, attracted by the high strength and corrosion resistance of the duplex grade. The engineers wanted to change the plate design to increase heat transfer in the heat exchangers.

The Solution
When first considering duplex stainless steel for plate air-cooler and plate shell heat exchangers, Lanke turned to Outokumpu. The Lanke team hit a problem with their new design, which required complicated for ming. Duplex grades feature only moderate elongation and limited formability compared to austenitic grades. But with help from Outokumpu, they were provided with information on the metallurgical properties of 2205, samples, examination of test plates, and various other tests. Lanke were then able to develop a new shape, pressing technique, and production route applicable for 2205 sheet, 0.6 mm thick.

The Results
The company has now successfully replaced conventional austenitic stainless steel of type 316L (1.4404) in plate air-cooler and plate shell heat exchangers with duplex 2205 (1.4462) from Outokumpu.

Using duplex heat exchanger plates, oil refineries reap major financial benefits as maintenance shutdowns become fewer and shorter. The use of the duplex steel will extend the service life of the refineries from 1-3 months to beyond 2 years. The result is a marked increase in refinery efficiency.

Lanke's first plate air-cooler heat exchanger using duplex 2205 was installed at the Guangzhou Petrochemical Oil Refinery in early 2006. It is still in operation today, two years after start-up.

Today, Chinese oil refineries widely use tubular heat exchangers. The plate heat exchangers achieve the same heat transfer effect with only 30 per cent of the space and weight, and 50 percent of the cost, compared to tubular heat exchangers. These savings equate to higher efficiency are important when oil refinery capacities increase, so there is no need to expand heat exchangers. As a result, plate heat exchangers are expected to replace more and more tubular units.

The cooperation between Lanke and Outokumpu continues. The two companies are currently investigating the possibilities of using Outokumpu's duplex grades LDX 2101® (1.4162) and 2304 (1.4362) in plate heat exchangers.