L. D. Stephenson

Thermal spray and weld repair alloys for the repair of cavitation damage in turbines and pumps: A technical note

The cavitation and erosion resistance of 21 thermal spray coatings and four weld repair materials were investigated in the laboratory using cavitation jet and slurry erosion testing. Of the thermal spray coatings, Stellite® 6 deposited by the high velocity oxyfuel (HVOF) process had the lowest cavitation rate (11.7 mg/h). This was higher than the corresponding cavitation rate (3.2 mg/h) of 308 stainless steel weld metal currently used as a reference. In the slurry erosion testing, the volume loss of Stellite® 6 applied by the HVOF process was 5.33 cubic mm/h, much lower than the corresponding loss (11.17 cubic mm/h) in the currently used stainless steel 304 reference. Furthermore, the electrochemical potential difference between the carbon steel and HVOF sprayed Stellite 6 coating was 0.25 volts, half the potential difference between the 304 stainless steel carbon steel substrate, and will result in reduced galvanic corrosion of the substrate near the contact areas. Stellite 6 deposited by the HVOF process was recommended for repair of damage resulting from erosion and subsequent cavitation by caused by surface roughening.

Demonstration and validation of stainless steel materials for critical above-grade piping in highly corrosive locations : final report on Project F07-AR15

Abstract : The problem of accelerated corrosion damage to Department of Defense (DoD) assets in marine coastal settings is greatly compounded when the affected infrastructure is critical to military mission and operational safety. Exposed piping networks that supply water for fire protection of fueling facilities require a high maintenance investment to prevent catastrophic system failure during operation. This demonstration/validation project evaluated the use of low-carbon stainless steel materials for fire-suppression water pipes at the Chimu-Wan tank farms on Okinawa Island, Japan, one of the most corrosive locations in the world for steel infrastructure. Highly corroded carbon steel pipes at the site were replaced with two grades of stainless steel, and minor corrosion-mitigation modifications were made to pipe supports. After the rehabilitated system was commissioned, the pipes were inspected and tested according to established practice. Based on a March 2017 inspection report provided by installation personnel, the stainless steel materials appear to be performing as expected after almost a decade of exposure. They will require only periodic routine inspection and maintenance to mitigate small areas of surface corrosion that may appear over the intended 30 year service life. The return on investment calculated for this project is 1.21.

Demonstration of thermally sprayed metal and polymer coatings for steel structures at Fort Bragg, NC : final report on Project F07-AR10

Abstract : The Department of Defense spends billions annually on corrosion-related maintenance. It has recently been estimated that at least 25 U.S. Army installations have severe corrosion problems with above-ground steel storage tanks. Coatings are widely recognized as a first line of defense for protecting these steel structures. Thus, the Office of the Secretary of Defense Corrosion Prevention and Control Program sponsored a project that demonstrated and evaluated new technology with two thermally sprayed coating systems for corrosion protection of steel structures in severely corrosive environments. The technologies included metallizing a steel tank with zinc-aluminum alloy and flame-spraying a polyolefin powder coating on the legs of an elevated steel storage tank. This report documents the materials and application of the two coating systems and subsequent performance evaluations. Metallizing is more costly than traditional organic coatings and is often overlooked as an option. However, life-cycle costs in highly corrosive environments can actually be lower than using organic coating systems. As this project demonstrated, the flame-sprayed polyolefin coating is too costly for use on large steel structures. Guidance documents are identified to help make decisions on the use and procurement of metallizing coating systems. The projects return on investment was calculated to be 2.94.

Fast Photolytic Release of Nano-Encapsulated Biocides for Neutralizing Bacteria

A fast-triggered photolytic technology based on the on-demand release of biocides encapsulated within phospholipid nanoparticles has been developed for the neutralization of biological contaminants such as bacteria. Fast-triggered release occurs when light sensitive molecules (photosensitizers) embedded within phospholipid particles are triggered by an external light stimulus. The photo-induced oxidation due to the stimulus causes the lipid chains to break and rapidly release their contents. When the phospholipid carriers are loaded with strong biocides, the fast-triggered release can result in the neutralization of biological contaminants in a controlled environment. It was observed that a 98% release of biocides was achieved in 12 min and 68% release achieved in 2 min through photo-induced oxidation. This method of release of biocides potentially can offer a technology for rapid decontamination inside heating, ventilation and air conditioning (HVAC) systems and surfaces such as walls, windows, etc. Moreover, biocide loaded phospholipid particles could be released as aerosols for neutralizing airborne bacteria and other biological contaminants. The appropriate choice of biocides can enable potential use in first-responder type situations and the automatic remote neutralization following bacterial contamination of air ducts or surfaces.