Abstract
Dual certified S31600/S31603 austenitic stainless steel and S31803 duplex stainless steel are widely used for the construction of compact diffusion-bonded heat exchangers. One of the unique features of the units is to join flat metal plates together through diffusion bonding. As there is no braze filler metals involved, qualified diffusion bonding joints can have parent metal properties. Space and weight savings are the major benefits of using these exchangers in the oil and gas industry.
The first part of this paper describes diffusion bonding process and presents data from mechanical testing and microstructure examination of bonded S31600/S31603 and S31803 duplex. This is to demonstrate that our diffusion bonding procedures are qualified to ASME(1) code requirements for the production of heat exchangers.
The main part of this paper deals with the qualification of diffusion bonded alloys to NACE MR0175/ISO 15156 for use in specified H2S-containing environments. For S31600/S31603 and S31803 duplex, the primary cracking mechanism in H2S-service is stress corrosion cracking (SCC). Two heat exchanger design conditions which have specified temperature, chloride concentration and H2S partial pressure were simulated for laboratory testing. Four-point bend specimens were loaded to 100% of the actual yield strength (AYS) and fully submerged to the test solutions for 720 hours. None of the samples showed any indication of SCC or pitting. Based on the results, it can be concluded that diffusion-bonded S31600/S31603 and S31803 duplex heat exchangers can be used for the specified sour service conditions.
