Experience Counts!   Stainless steel has been accepted within the industry as the “standard” for metallic casing spacer for a number of years, but stainless steel casing spacers were initially introduced strictly as a marketing ploy to undermine the excellent market position PSI had in the PVC Coated Casing Spacer market. At the time, PSI did not fabricate a stainless steel casing spacer. We have both now, but offer the following for consideration in deciding the value of stainless steel versus an excellent quality PVC coated mild steel. Below are various referenced statements on the concerns with stainless steel in conditions similar to a cased road crossing as well as documentation of the corrosion resistance of the PVC coating: Failure Avoidance - Austenitic stainless steels can crack on exposure to media containing low concentrations of chloride ions. Key factors for CL- SCC (stress corrosion cracking) are: oxygen and water(2) (PSI Note – Oxygen and water usually available inside casings. Cl- often present from road salts) What caused the failure? The severity, rapidity and nature of the pitting clearly pointed to microbiologically influenced corrosion (MIC) as the failure mechanism. Lesson ...It is not acceptable to leave any untreated water in type 300 series austenitic stainless steels for long time periods. These alloys are particularly susceptible to pitting attack(3) (PSI Note – Does one believe it is likely to have “untreated water” inside a buried casing?) Many grades of stainless steel are likely to fail under the combined effects of an aggressive environment and static loading (stress corrosion cracking).(4) Loss of corrosion resistance by the stainless steel (304) possibly due to: incorrect welding, cold or hot working(5) (PSI Note – Casing Spacers are cold worked, & welded. They undergo static loading once installed within a casing,) Another problem is the presence of microorganisms such as iron bacteria…these bacteria greatly accelerate the corrosion process of SS(6) (PSI Note – Great likelihood of iron bacteria inside a steel casing or with a ductile iron pipe?) A Warning….Although the results obtained in the MontBlanc Tunnel cannot be generalized, use of type 303 (stainless steel) especially where chlorides are present and acid conditions could develop, must be strictly avoided” Although differences exist between 303 & 304 stainless, “so far they do not allow any reliable conclusions as to whether type 304 would be resistant to SCC in the long term in the conditions existing in the tunnel(7) ( PSI Note - Tunnel conditions may closely correlate with a casing application.) Be advised that although stainless steel generally has excellent corrosion control characteristics when exposed to atmospheric environments, it is not always recommended for underground or submerged applications. Stainless steel is susceptible to localized corrosion, e.g. pitting, crevice corrosion, and possibly stress corrosion cracking (in the presence of chlorides) where anaerobic sulfate reducing bacteria are present.(8) Typical Material Cost Savings on Casing Spacer Materials by switching from 304 stainless steel to PSI Fusion Bonded PVC Coated Casing Spacers POTENTIAL SAVINGS 100' CROSSING 300' CROSSING 12” Pipe $ 500.00 $ 1,500.00 36" Pipe $2,800.00 $ 8,400.00 48" Pipe $4,000.00 $12,000.00 C12GN-2 86.5 X 102" CR - Symmetrical (3) Crossings - 223', 142' and 142' - Designed to rotate during installation. PSI PVC Coating has been subject to a salt spray test up to the full 3000 hrs as specified by ASTM B117 method. The coating as applied in a 15 mil thickness withstood the full 3000 hrs of salt spray exposure cycled in 24 hr intervals. The coated sample is analyzed after each 24 hr cycle and results noted. Once the maximum 3000 hrs test duration was met the test was discontinued. No compromised surfaces were discovered.(9) PSI PVC coated and 304 stainless steel casing spacers have a good performance track record. However either could corrode. Likely, in the PVC coated mild steel, it would cause only a “pin hole” after a long period of time. This is not critical as it would be on a pipeline that has to hold pressure. However if stainless steel corrodes, it is conceivable that it could be more catastrophic as it will likely be at a stressed point such as a weld; which in turn could fail. PSI has been successfully providing the PVC coated casing spacers on cased road crossings for in excess of 40 years. We have also been providing 304 stainless steel casing spacers for in excess of 15 years. There have been no documented reports of any failures due to corrosion related issues. PSI PVC Coated Mild Steel Casing Spacers are the most specified in North America for oil or gas pipelines. Many of our oldest installations are on oil or gas pipelines where corrosion control is a high priority. Both PSI stainless steel and PVC coated casing spacers are proven products for use in casings; however greater economies can be obtained with the PSI Fusion Bonded PVC Casing Spacers. Author: Jay Keldsen – 30+ year member of NACE International, a Corrosion Control Society. He is a contributing member of the “Steel-Cased Pipeline Practices” Standard RP0200-200 Committee, and has published numerous technical papers relating to corrosion control practices. Jay is also past General Chairman of the Appalachian Underground Corrosion Short Course and the Liberty Bell Corrosion Short Course. References- Copies of all referenced articles or letters are available upon written request. Verbal conversation with Bill Lyons who claims to have invented the concept of stainless steel casing spacers. Bill further mentioned that the company he worked for only used stainless steel in their other product lines. Materials Selection & Design Article by Lawrence E. Drake MP/February 1990 Hydrotest water can cause MIC pitting by William G. Ashbaugh, Cortext Engineering Services, Inc . – MP/July 1989 The Metropolitan Water District of Southern California Corrosion Control Section Report Failure Analysis of Corroded 303 Stainless Steel Fasteners by W. McMillian September 1989 Reference: Corrosion Failures of Types 304 & 316 Stainless Steels in the Food Industry by G.C. Page – MP/ July 1989 Petroleum Research Center - Various Authors – Materials Performance September 2003 Stress Corrosion cracking of Type 303 Stainless Steel in a Road Tunnel Atmosphere , Helmut Haselmair – MP /June 1992 Letter – Jim Lary, NACE Corrosion Technologist, Corrpro Companies, Inc., September 08, 2003 ASTM B117, Salt Spray (Fog) Testing - ASTM B117 is the oldest and most widely used of the salt spray cabinet tests.