Large and Small Scale SCC Testing of 316L Clad at 135 C

The use of 316L clad pipes is currently limited to 120 deg C to avoid stress corrosion cracking (SSC). This work has been undertaken to explore the possibility of extending the limits of 316L to higher operating temperatures. The testing is divided into a large scale test and a small scale test. The work is also meant to investigate a relationship between the test methods. It is the intention to determine small scale tests which gives similar results as the large scale test.
The large scale test consists of a full ring pipe which is stressed externally and exposed to the test fluid at the internal surface.
The small scale tests are four-point-bend tests in accordance with ISO15156-3. The test specimens are made of approx. 3mm thick clad material where the carbon steel backing has been machined off.
The test parameters are as follows:

• Temperature: 135 deg C
  
• Gas compositon: 11 bar CO2 and 0.02 bar H2S
  
• Cl-: 41800 mg/l
  
• HCO3- : 600 mg/l
  
• pH: 5.5
  

The tests are currently ongoing, Results are expected by August ’08.