The market for sand control products is very competitive, which demands that the manufacturer use economical materials and employ efficient designs. This is especially important in expandable sand control screens; this new technology must compete with existing non-expandable screens that are low cost manufacture using commodity-type raw materials. For corrosion resisting sand control screens, a key component to the success of the product is the metallurgy of the base pipe. The alloy selected must provide corrosion performance similar to 13Cr that is typically used as the base pipe in conventional sand screens. 316L (UNS S31603) is a commodity CRA material that provides the necessary ductility and strength for application to expandable screen base pipe. However, its corrosion resistance in the production environment has been questioned by many users. The basis for this concern is corrosion data and experience in non-production environments. Therefore, corrosion testing in simulated production environments is needed. This test program verified the corrosion resistance of S31603 in a mildly sour environment containing 0.50 psi (0.003 MPa) H2S and 50,000 ppm chloride at pH 3.5 and 175 °F (79 °C) as well as established some performance parameters in more severe environments of H2S, chlorides, and temperature. With these data, S31603 can now accepted for many applications where conventional 13Cr completions would be used and also in sour environments that exceed the limits now established for S31603 in ISO 15156/NACE MR0175.
Today, the material of choice for CRA base pipes used in conventional, non-expanding sand screens is 13Cr. When properly heat treated, 13Cr has reasonable resistance to embrittlement from H2S and is immune to stress corrosion cracking from hot chlorides. However, 13Cr does not have sufficient ductility to be safely expanded, and its resistance to sulfide stress cracking after expansion is reduced. S31603 is an austenitic stainless steel having excellent toughness and ductility. These are suitable mechanical characteristics for expandable screen base pipes, but S31603 may be susceptible to stress corrosion cracking in chloride-containing fluids. Data by Copson predicts rapid failure of S31603 in boiling MgCl2; other experience has been primarily in oxygen-containing environments.1 There is little data in the literature in production environments, perhaps because until this time, the low strength has prevented its widespread use.
Another barrier to the use of S31603 in production environments is the new limits established for it by ISO 15156/NACE MR0175. With a maximum temperature for exposure to sour environments of 140 °F (60 °C), there is little opportunity to use S31603 as few wells have temperatures this low. CRA's that are known to perform well in hot, sour production environments and also have the required strength and ductility are cost prohibitive. Therefore, it would be useful to extend the temperature limits
for S31603. The purpose of this test program is:
To establish suitability of S31603 in a mildly sour production environment (0.003 MPa H2S and 50,000 ppm chloride at a pH of 3.5 and 175 °F (79 °C)).
To discover environments where S31603 could replace 13Cr.
To gather test data that would allow ISO 15156/ NACE MR0175 to raise the current performance limits of S31603 in conditions of H2S, chloride, and temperature.