Sanicro® 28 Extends Life Cycle of Heat Exchanger Cooler by Five Times

A peroxide mill in Brazil was experiencing regular maintenance failures in a heat exchanger cooler system due to corrosion and heat issues. Sanicro® 28 not only solved the problems but also significantly increased the cooler’s maintenance lifecycle.

The Background

Hydrogen peroxide (H2O2) is commonly used for bleaching, water treatment and hydrometallurgical processing. However, high temperatures and aggressive corrosive environments mean the materials used in its production process have to be robust enough to withstand these demanding conditions.

Sandvik was invited to support a customer in the material selection for a hydrogen heat exchanger cooler (shell-tube design). This equipment is usually located in the hydrogen gas purification and compression stage for H2O2 production.

The cooler, which previously had tubes made from 316L stainless steel, had been experiencing maintenance failure every four to six months. Operations were conducted in high levels of chloride content with design temperatures up to 280°C (536°F). The aggressiveness of this environment was leading to stress corrosion cracking (SCC) induced by chlorides, and pitting corrosion in the outside diameter of the tubes.

The Solution

It was time to look for a more robust material for the tubes. Sandvik’s Sanicro® 28, approved by ASME, is a high-alloy, multi-purpose, austenitic stainless steel designed for highly corrosive applications. Its resistance to SCC and pitting corrosion means it can withstand environments with a high chloride content, and temperatures up to 600°C (1100°F).

SAN28 microstructure _San28Cu_38x100x.jpg

Sanicro® 28’s performance relies on a balanced chemical composition of nickel, chromium and a relatively high pitting resistance equivalent number (PREN) of 38. The nickel content at 31% is responsible for increasing the material's resistance to SCC and its ability to resist deformation at high temperatures. Meanwhile, the 27% chromium-enriched oxide layer supports pitting corrosion resistance, making it an ideal material for extremely corrosive environments containing halogens.

The Result

Tubes made from Sanicro® 28 were used to replace those made from 316L in the hydrogen cooler, and have successfully increased the equipment’s life-cycle by five times. Furthermore, they are still delivering superior performance.

The inlet hydrogen temperature was the critical process feature where SCC was previously observed. SCC is temperature, stress and concentration dependent. For the 316L tubes, resistance under 0.01%Cl- (weight) has a 50°C (120°F) temperature limitation. When evaluating Sanicro® 28 as an option to increase equipment productivity, its SCC resistance was found to reach up to 240°C (464°F) with no cracks.

Since the Sanicro® 28 tubes were installed in 2018 there have been no signs of corrosion, none have required to be plugged, and no leaking has been observed.

The client’s investment in high nickel Sanicro® 28 as the ideal choice for its cooler tubes has been justified by the results - lower production costs, fewer interruptions and reduced operational risks.