Manufacture and Testing of a Large Zirconium Clad Vessel

David Clift, P.Eng.

Production Manager Ellett Industries September 14, 2005

Abstract

• • Serviceability depends upon the quality of the clad corrosion liner Careful application of design details, skilled trades & systematic application of manufacturing controls and non-destructive examination.

Zirconium Clad Steel Reactor

3.6m diameter x 6.5m length (11’ 10” x 21’ 2 Shells are 22mm (7/8”) thick SA516-70 with 3mm (0.12”) nominal, 2.28mm (0.090”) minimum, thickness Zirconium 702 explosion clad liner. The hot pressed heads are of 37mm (1.5”) SA516-70 with a 4.7mm (3/16”) nominal thickness of clad liner

Design Details

Separation of Longitudinal & Circumferential Welds Advantages •Containment of possible breaches •Efficient gas purging •Simplified helium testing

Material Procurement

• • Base Metal N.D.E.

– ASME SA 578 Level C • grid pattern or continuously scanned - grid pattern is standard • three inspection levels – A- least , B - moderate, C - most demanding; allows a discontinuity smaller than can be contained within a 25mm circle Cladding N.D.E.

– full compliance with ASME Section VIII & IX • • production bend tests, PT examination and 100% RT before bonding PT after bonding and, in the case of the heads, after forming. All clad surfaces were visually examined

Ultrasonic Examination of Bonding

ASTM B 898 Acceptance Criteria Inspection Class A Inspection 100% Single Indication Allowable Size <25mm B C 100% 230 mm grid <75mm < 58cm 2 Minimum Area of Sound Bond 99% 97% 95% •Class C is the standard Inspection Class of B 898 •Class B was specified for this project

Explosive Cladding

•

Current Practice

– an interlayer of titanium when zirconium cladding exceeds 6.4 mm (1/4”) nominal thickness – Explosion detonation (booster) locations • • corner, side or center of plates an area of ultrasonic non-bond is typically located under the detonation point • non-bond related to the size of charge

Vessel Plate Manufacture

• Central explosion detonation points for both shell and head plates on this unit – thin cladding, thick backing plates – ASTM B 898 Inspection Class B ultrasonic inspection (75mm maximum indication size) • Results – non-bond areas in shell plate were acceptable – head plate detonation points were removed as cut-outs for centrally located nozzles

Plate Surface Defects

• Damaged areas of clustered gouges were noted on three of the six shell plates – Gouge depth ranged from 1.2mm (0.047”) to 2.4mm ( 0.094”) deep – Gouge size varied –less than 13 cm 2 (2 in 2 ) in area • Root cause - “rock fall” that occurred during underground explosive blasting

Repair Plan

• Weld repair – shallow gouges (<1.2mm deep) were weld repaired in conformance with ASTM B 898 . – Controls • customer approval • carbide burr removal • qualified weld overlay repair • PT inspect • fully documented

Repair Plan - cont’d

• • Deep gouges Individually ported batten style covers

Vessel Seam Weld & Test Sequence

• • • • • Carbon steel welds are applied and specified NDE performed prior to batten strap attachment UT the cladding bond adjacent to the end of the longitudinal seam filler strips to find potential leak paths Fit & weld longitudinal batten strips, silver braze to isolate and helium bubble test @ 1 bar pressure Circumferential welds performed in a similar manner Confirming PT of all ZR welds per ASME

Fabrication - Cleanliness

• • • Tool surfaces to be of alloy, plated or hardened steel • Rolls & brake forming surfaces - confirmed free of all surface defects & contamination Weld joint design should minimize carbon steel welding & grinding on process surfaces Zirconium weld zones are mechanically and chemically cleaned prior to welding

Final Cleaning

• • • Contaminated areas abrasively ground Acid wash with HF/HNO3 Ferroxyl test per ASTM A 380 – spray application of the potassium ferricyanide test solution on suspect areas – reacts with free iron to form a blue indication

Helium and Hydro Testing

• • • Helium Mass Spectrometer testing per ASME Section V, Article 10, Appendix IV was performed before and after hydro testing Purging batten strip cavities – helium from bubble testing conducted up to a month earlier had to be purged with clean & dry air to eliminate false indications Test conditions – 25% of the vessel’s maximum allowable working pressure (50 psig) – approx 20% helium concentration

Test Results

• Results – All purge vents located behind nozzle liners, seams and internal batten style patches were vacuum sniffed – All readings remained at a background or atmospheric helium concentration - equivalent to a leak of 5 x 10 -6 atm cc/sec

Additional Research

• Preparation and analysis of a zirconium weld overlaid coupon to assess built-up metal quality • CS - TI - ZR construction Prepared block – ready to weld overlay After welding and step machining

Results

• • • • ZR overlay welding on both the titanium interlayer and the zirconium cladding, min thickness .76mm

Test results confirm a composition containing titanium and zirconium No detectable iron was present in any of the test samples 100% Zr when a 0.76mm thick layer was applied over a combined thickness of Ti and ZR of 3.05mm. The actual thickness of the ZR alone in this case was 1.3mm

Questions