1 OZONE AND OXYGEN GAS SYSTEM CLEANING AND VERIFICATION PRESENTED BY: DARYL L. ROLL, P.E.
2 OZONE SYSTEM CLEANING Cleanliness requirements and protocol Fabrication and installation strategies Welding effects Qualified subcontractor for component and system cleaning Ozone system preparations Basic cleaning and passivation chemistries Testing and verification
3 THEORY OF PASSIVATION Passive Layer Transition Zone Base Metal SURFACE 2 Chrome: 1 Iron 1 Chrome: 4 Iron
4 CLEANING AND PASSIVATION BENEFITS Chemical cleaning and flushing removes particulate contamination and organic films Passivation increases corrosion protection at weld areas and mechanically damaged surfaces Eliminates potential oxidation of contaminants within distribution system Clean systems maintain product purity Reduction of particulate generation
5 SPECIFICATIONS FOR CLEANLINESS CGA G – 4.1, 1996 CGA G – 4.4, 1993 CGA P – 34, 2001 ASTM G93 – 96 ASTM A380 – 99 ASTM A967 – 99 ASTM F312 – 97 ASTM F331 – 98
6 OXYGEN GAS CLEANING REQUIREMENTS The CGA requirements include cleanliness testing of the system after cleaning to meet 47.5 mg/sq.ft. of contamination on the surface ASTM requirements include alkaline degreasing and passivation of welded and mechanically finished stainless steel Passivation guidelines are reviewed in ASTM A380 and A967
7 CGA G-4.1 REQUIREMENTS Cleaning Methods Steam Vapor degreasing Solvent washing Alkaline cleaning Acid cleaning Mechanical cleaning Purging Packaging and Labeling Inspection Record Keeping White light UV light Wipe test Solvent extraction Safety Safety
8 WELD AND FABRICATION EFFECTS Corrosion resistance of surface effected by grinding, welding and mechanical polishing Chrome to iron ratio of surface at weld areas or after grinding will be equal to the base metal (0.25) or less Oxidation of active surfaces will generate iron oxide particles Passivation will restore surface corrosion resistance and a chrome to iron ratio of 2.0 or greater
9 WELD SEAM ANALYSIS: BEFORE PASSIVATION Heat Affected Zone % Millimeters
10 WELD SEAM ANALYSIS: AFTER PASSIVATION Heat Affected Zone % Millimeters
11 FITTINGS & CONNECTIONS Butt Welds – Smoothest transition Flanges – Maintenance, accessibility Socket Welds – Create particle entrapment areas Preclean of Weld Areas Post Clean of Weld Areas Threaded Connections – Particle entrapment
12 VALVE CONSIDERATIONS Connection Types Flange Threads Socket weld Butt weld Valve Types Ball - Small diameter Butterfly Gate or Globe Removable spools for cleaning & replacement Components must be oxygen pre-cleaned and replaced during cleaning operations, installed under purge
13 PREOPERATIONAL CLEANING REQUIREMENTS The system must be free of metal grindings, construction debris and organics (oil and grease) The system must contain necessary low point drains and high point vents The gas distribution system within the ozone contactor chamber shall be pre-cleaned and installed clean Pneumatic gas test with all components installed Quality welds with no excessive heat effected zones Spool replacements for all components
14 CHEMICAL CLEANING PROCEDURES Initial DI flush and leak test Alkaline cleaning with detergents remove surface debris and organic films DI water rinse between stages Acid passivation solution for iron removal Final DI water rinse and particle count testing Dry with clean, dry air or nitrogen and test for dew point. Use solvent (IPA) to test for NVR and total solids. Purge system for installation of components and final pneumatic testing.
15 POST CLEANING REQUIREMENTS Precleaned and certified components Removal of spools & replacement of components within clean area & gas purge Final gas testing of system
16 SOLVENT CLEANING & DRYING PART 1: CLEANING Solvent specifications require use of non- flammable organic solvents 1,1,1 Trichloroethane and Freon are very expensive regulated solvents ($100 - $300/gal) N-Propyl Bromide, AK-225, & Vertrel MCA are replacement solvents Ozone Depleting or regulated solvents
17 SOLVENT CLEANING & DRYING PART 2: DRYING Alkaline replacement cleaners require final DI water rinse Complex piping systems = difficult to dry with traps Flushing with IPA plus nitrogen gas purge will blend residual water and lower vapor pressure Allow attainment of -30°F dew point or better
18 SUMMARY Ozone and oxygen enriched generation and distribution piping systems require a clean and organic free distribution system. Fabrication operations reduce cleanliness and corrosion resistance which is why cleaning and passivation is required. Compliance with CGA / ASTM regulations
19 SUMMARY (Contd) Proper testing and certification of cleanliness is required. Collaboration between engineering design, mechanical installation and precision cleaning contractor is needed. Systematic preparation, clean fabrication and proper cleaning methods result in improved component performance, ease of system maintenance and overall safety of operations.