In a Titanium Tube Bundle Heater Reboiling a 10% Diethanolamine (DEA) Solution at 110°C for Gas Sweetening, How Does the Hydrogen Sulfide (H₂S) Loading (0.1 vs. 0.5 mole/mole) Change the Rate of Titanium Sulfide (TiS) Formation and the Risk of Hydrogen Embrittlement?
Leave a message
In 10% diethanolamine at 110 C with H 2 S loading, titanium forms a titanium sulfide (TiS) layer on the surface. With a loading of 0.1 mole/mole H2S, the TiS layer is thin (0.1-0.5 µm) and does not prevent hydrogen uptake. The hydrogen absorption rate is 20-50 ppm/1,000 hours. The layer of TiS is thicker (1-3 µm) and more protective at 0.5 mole/mole of H2S loading. Hydrogen absorption rate falls to 5-15 ppm after 1,000 hours. The sulfide layer serves as a barrier against hydrogen ingress. But for cracked (by heat cycling) layer hydrogen absorption increases.
Mechanism of Protection of Sulfide Layer
Ti + H 2 S → Ti S + H 2 Hydrogen sulfide interacts with titanium. The TiS layer is a semiconductor and may be protective when dense and adherent. The rate of production rises with the concentration of H₂S. The dense and continuous TiS layer acts as a barrier of atomic hydrogen recombination sites and restricts hydrogen ingress.
Quantitative H2S Loading Hydrogen Uptake
H₂S Loading (mole/mole) TiS Layer Thickness (µm) H Absorption (ppm/1,000 h)Time to H 200 ppm (hrs)
0.05 0.05-0.1 50-100 2,000-4,000
0.1 0.1-0.5 20-50 4,000-10,000 0.25 0.5-1.0 10-20 10,000-20,000 0.5 1.0-3.0 5-15 13,000-40,000 1.0 2.0-5.0 3-8 25,000-65,000
H 2 S Loading Guide for DEA Reboilers
H 2 S Loading (mole/mole) Hydrogen Embrittlement Risk Recommended Grade <0.1 High Grade 7 0.1-0.3 Moderate Grade 7 0.3-0.7 Low Grade 2 or Grade 7 >0.7Grade 2 Very low
The Specification in Knowledge
The greater H 2 S loading (0.3-0.7) is for DEA/H 2 S service titanium reboilers and enhances the creation of a protective TiS layer that minimizes hydrogen absorption. The benefit of sulfide passivation can be taken keeping H 2 S loading >0.3. The engineer controls the loading of H2S to avoid hydrogen embrittlement.
