The Third Generation Shop Primer and Japanese Shipbuilding Construction Process

Transcription

1 The Third Generation Shop Primer and Japanese Shipbuilding Construction Process Yasuyuki SEKI, Katsumi KONDOU and Osamu HARADA Chugoku Marine Paints, 1- Meijishinkai Otake Hiroshima, Japan ABSTRACT Inorganic zinc silicate primer shows excellent adhesion property to a steel surface and to over coat such as epoxy paints, because hydroxyl functional group of silicate derived by hydrolysis while curing process. The adhesion property of inorganic zinc silicate primer is retarded by white rust, salt deposit and other contaminants. Secondary surface preparations are required to remove such contaminants, which causes delay of construction process. Deduction of white rust and retention of anti-corrosive performances, not only improvement of weldability, cutting and heat resistance, had been requested for inorganic zinc silicate shop primer. The Third Generation Shop Primer has developed to meet the construction process of Japanese shipyards where shop primer is retained without blasting off, and has widely adopted by Japanese shipyards. The Third Generation Shop Primer keep intact surface while construction process and could be over coated with epoxy main coat, to provide enough performance to comply with ANNEX-1 test of PSPC requirements. 1. INTRODUCTION In 150 s, shop primer was developed as a long durable etching primer based on polyvinyl butyral resin. In 10 s, epoxy zinc-rich primer and epoxy non-zinc primer based on epoxy resin was developed as more durable shop primer. In s, inorganic high-zinc paint was developed to improve in heat-resistance and weldability, which provided less heat damage than before, and reduced second surface treatment work. We call this the First Generation Shop Primer. In the latter half of the 's, low-zinc shop primer was launched into a market. We call this the Second Generation Shop Primer. The Second Generation Shop Primer was widely accepted to ship building market as consequence of the expansion of ship-building market. In 2000, development had been continued to introduce high-heat-resistant low-zinc shop primer which could provide welding speed of 00-00mm/min (Twin-Single welding) and high welding speed of over 1,200mm/min (Twin-Tandem welding). We call this the Third Generation Shop Primer. 2. PERFORMANCE OF THE FIRST, SECOND AND THIRD GENERATION SHOP PRIMER 2-1.Comparison of each paint composition Specific features of the Third Generation Shop Primer are introduced by the use of weldabilitive pigments and zinc protector. Paint composition of each generation and characteristic are shown in Table-1. Table-1. Example of sample composition generation 1st 2nd 3rd Base hydrolysis of TES-40 Zinc powder (solids cont.) 5%wt 55%wt 50%wt Silica powder (*1) Pigments Silica powder (*1) Talc (*2) (*4) Paste Fluorite powder (*3) Additives Wax Acrylic Bentonite Bentonite - - Organic resin - Add - Zinc protector - - Add *1: Silica powder (ignition loss: 2.0% 300 o C, 3.% 500 o C, 4.5% 00 o C) *2: Talc (ignition loss: 1.2% 300 o C, 1.0% 500 o C,.% 00 o C) *3: Fluorite powder (ignition loss: 0.% 300 o C, 1.5% 500 o C, 1.% 00 o C) *4: Weldabilitive pigment (ignition loss: 0.% 300 o C, 1.02% 500 o C, 1.13% 00 o C) 200: JASNAOE-RINA 3

2 2-2. Designing Both Reduction of second surface preparation and high-speed weldability is essential to achieve improvement of productivity at shipbuilding construction process Studies to achieved to reduce second surface preparation Zinc generates white rust easily when zinc is exposed to a corrosion atmosphere (e.g. moisture, wet, electrolyte, and electric current) and an oxidation atmosphere (e.g. high temperature, and oxygen). (Figure-1 upper path) Excessive corrosion of zinc Zn 2+ Zn2+ Zn Zn2+ Zn Zn2+ Zn Zn2+ Zn Zn2+ Zn Formation of silicate film Contraction of silicate Zn White rust Zn hydrolysis Zn corrosion factor the 3rd Generation Zn Zinc protection Figure-1 Generation of white rust model To prevent the generation of white rust, we combined zinc protector as the composition of the Third Generation Shop Primer. The mechanism is not clearly, but it looks the zinc protector cover zinc surface and even if zinc melts by welding heat, zinc will not be oxidized (Figure-1 lower path). If zinc is not treated by zinc protector, zinc is oxidized and needle crystals (zinc oxide) are generated on the surface of zinc particle. (Photo-1) Photo-1. The surface of zinc after heating 1st and 2nd 3rd Zinc particle in an inorganic zinc shop primer is covered consecutive films of the ethyl silicate binder just after coated, but this film shrinks with progress of hardening and the surface of zinc particle crop out form the surface of shop primer. 200: JASNAOE-RINA 3

3 If the film is exposed to a corrosion atmosphere, the zinc particle begins to dissolve and electric current is generated. This electric current is caused by ionization potential between zinc and iron, which works to protect iron from corrosion, but excess current accelerate the generation of white rust. By this reason, ionization potential could be used as an indicator of anti-corrosive property and white rust. We have prepared test panels coated by each generation shop primers at average dry film thickness 15μm, and dried at room temperature (23 o C) for seven days. One of the test panels were kept at room temperature and others were heated to 300, 500 and 00 o C. The panel was immersed into salt water (3% NaClaq) and ionization potential was measured. The panel of First, Second and Third Generation Shop primer which kept at room temperature, respectively shows potential 0, 0 and 0mV at 0.1hrs, 0, 0 and 40mV at 24hrs, 0, 0 and 0mV at 4hrs. The Third Generation Shop primer showed lower potential compared to the First and Second Generation, which generation of white rust will be controlled (Figure-2, 3, 4). The panel heated at 300, 500 and 00 o C showed same tendency as the panel kept at room temperature. (-mv) Figure-2. Protective potential of 1st generation (hours) (-mv) Figure-3. Protective potential of 2nd generation (hours) (-mv) Figure-4. Protective potential of 3rd generation (hours) The anti-corrosive property and anti-white rust property of each shop primer was tested by the exposure test with combination of natural weathering and water spray. The anti-corrosive property is evaluated based on ASTM D-01, and anti-white rust property is evaluated based on ASTM D-01 using our own criteria 1. All shop primer has outstanding anti-corrosive property when kept at room temperature (23 o C). The Third Generation Shop Primer, of which 1 Anti-white rust grade: White rust generates to : less than or equal to 1%; : greater than 1% and up to 5%; : greater than 5% and up to %; : greater than % and up to 15%; : greater than 15% and up to 20%; 5: greater than 20% and up to 30% 200: JASNAOE-RINA 3

4 zinc consumption controlled, has outstanding anti-corrosive property and anti-white rust property even after heated at 300, 500, or 00 o C. On the other hand, the First and Second Generation Shop Primer generate large amount of white-rust. White-rust on the steel surface of the First and Second Generation Shop Primer flow out as time passes, white-rust is improved, but anti-corrosive property is decreased (Figure-5 to ). The weldabilitive pigments and zinc protector provided to the Third Generation Shop Primer has properties to control the generation of zinc ion excessively by forming insoluble film by reacting with zinc ion. Figure-5. Anti-corrosive property of 1st Figure-. Anti-white rust property of 1st days 15days 30days 0days 0days 5 4 days 15days 30days 0days 0days Figure-. Anti-corrosive property of 2nd days 15days 30days 0days 0days 5 4 Figure-. Anti-white rust property of 2nd days 15days 30days 0days 0days Figure-. Anti-corosive property of 3rd Figure-. Anti-white rust property of 3rd days 15days 30days 0days 0days 5 4 days 15days 30days 0days 0days The test result of the Third Generation Shop Primer tested the exposure test with combination of natural weathering and water spray shows good anti-white rust property as expected by the effective protective potential test. When steel panels are piled up and water penetrates into the interspaces of panel, much electric currents are provided by electric crevice corrosion, and generate much white-rust. We prepared panel coated by the First, Second, and Third Generation Shop primer and dried at room temperature 200: JASNAOE-RINA 40

5 (23 o C) for seven days. Two peaces of test panel were piled and raped with a vinyl sheet with 50ml water, them exposed to incubator and keep at 50 o C for seven days. After testing, the Third Generation Shop primer showed much less white rust than the First and Second Generation Shop primer (Photo-2). Photo-2. Comparison of white rust by accelerated test 1st 2nd 3rd Studies to achieve high-speed weldability (a) Reduction of organic components Organic compounds in film induce welding defects, because of it is gasificated by heat at welding. The organic compounds provided in the inorganic shop primer are mainly additives to improve storage stability to adjust settling of the pigment. The organic compounds in the Third Generation Shop Primer are reduced as much as possible. (b) The reduction of crystalline water in pigments Pigments used for paints normally adsorb atmospheric water. Some pigments include crystalline water. The water adsorbed to the pigment becomes estranged when exceeded the boiling point, and does not affect weldability seriously. Crystalline water becomes estranged at 400 o C or higher temperature. Crystalline water causes gasification while welding and cause welding defect. Crystalline water in the pigment was measured using differential thermal analysis. The pigments used for the Third Generation Shop Primer shows ignition loss at 00 o C with about 1.1 % but Silica, Talc and Fluorite which used for the First and Second Generation shows ignition loss with 4.%,.0% and 1.% respectively (Table-1). We tested the Weldability of the First, Second and Third Generation Shop primer, using CO 2 arc welding. Weldability of all generations was good when dry film thickness is thin. When dry film thickness is thick, the Third Generation Shop Primer shows good weldability, but the First Generation Shop Primer occurred to a lot of welding defects at welding speed 00mm/min. The Second Generation Shop Primer increased welding defects regardless of welding speed that resulted from organic resin of paint film (Table-3). Table-3. Weldability test Generation 1st 2nd 3rd 1st 2nd 3rd Welding speed (mm/min.) Dry flm thickness (μm) Second Pit (number) bead Groove (mm) Blow hole (%) * Blow hole (%) = {(Blow hole's width height)/(test-piece's width: 500mm height: 4mm)} 0 * Welding condition: Welding position: horizontal fillet weld, Welding method: CO 2 gas shielded automatic arc welding, Welding direction: ahead method, Welding wire: KOBELCO, MX Z-200, Φ=1.2mm, Welding speed: 00mm/min, 00mm/min, Distance between torches: 0mm, Degree of torch: 45 o, forward 5 o, Wire extension: 25mm, Root gap: zero, route gap zero make tack welding with three points at end face and centre of first bead while pressurized, Leg of a fillet weld: ±1mm 200: JASNAOE-RINA 41

6 Over coatability We prepared the test panels blasted at Sa2.5 and coated by the Third Generation Shop Primer with the average dry film thickness. 15μm and dried at room temperature (23 o C) for seven days. One of the test panels was kept at room temperature and other panels were heated to 300, 500 and 00 o C. Epoxy main coat is coated over the each test panel with the average dry film thickness. 300μm. The test panel was exposed to salt spray (JIS K ), artificial sea-water immersion tests (JIS K ), artificial sea-water immersion test with cathodic protection and humidity chamber test (JIS K ). After exposure, the panel was dried for a few minutes and its appearance, knife test, rust at cut area, and blister was checked. Also the pull-off strength is measured using MOTOFUJI s pull-gauge. The Painting system using the Third Generation shop primed showed good results. (Table-4) Table-4. Over coatability of "3rd Generation Shop Primer"+"Epoxy paint" after 2months Resistance to contenuous salt srpay at 35 o C (5% NaCl aq) (JIS K ) Test Item Appearance Knife cutting Rust width of cut area Pull-off test Blister (general) Epoxy paint only no change no peel sometimes rust 4.Mpa no blister 3rd S/P + Epoxy paint no change no peel no rust 4.3Mpa no blister Resistance to 3% NaCl aq immersion at 40 o C (JIS K ) Test Item Appearance Knife cutting Rust width of cut area Pull-off test Blister (general) Epoxy paint only no change no peel sometimes rust 4.3Mpa no blister 3rd S/P + Epoxy paint no change no peel no rust 4.5Mpa no blister Resistance to 3% NaCl aq immersion with cathodic protection at 40 o C Test Item Appearance Knife cutting Rust width of cut area Pull-off test Blister (general) Epoxy paint only no change no peel no rust 3.Mpa no blister 3rd S/P + Epoxy paint no change no peel no rust 4.0Mpa no blister Resistance to contenuous condensation at 50 o C ( >5%RH) (JIS K ) Test Item Appearance Knife cutting Rust width of cut area Pull-off test Blister (general) Epoxy paint only no change no peel - 4.0MPa no blister 3rd S/P + Epoxy paint no change no peel - 3.5Mpa no blister * Paint system: 3rd S/P (15μm) + Epoxy paint (300μm), 2.3mm-thick test panel * Evaluation is based on ASTM D-01 for rust, ASTM D14- for blister * Cathodic protection: Zn (Φ=15mm/test panel 4) * Failure area of pull-off test: all test panels have cohesion break of Epoxy paint (0%). We have arranged test panel coated by shop primer and heated with gradation at 23, 300, 500, 00 o C. Four of the panel is coated by epoxy main coat. The pull-off strength of the shop primer heated and epoxy main coat coated on heated shop primer are measured using MOTOFUJI s pull-gauge. The First and Second Generation Shop Primer heated below 500 o C showed cohesive failure in shop primer layer, but that heated at 00 o C showed interface detachment with the substrate and shop primer. The Third Generation Shop Primer showed cohesive failure in shop primer layer even heated up to 00 o C. Over coatability (to epoxy coat) of the Third Generation Shop Primer heated at 00 o C is better than that of the First and Second Generation Shop Primer, because of the detachment was caused cohesive brake down and detachment between glue and dolly. The First and Second Generation Shop Primer showed interface detachment between shop primer and the substrate at 00 o C (Table-5, Figure-11, 12). 200: JASNAOE-RINA 42

7 Table-5. Comparison in over coatability of each generation by pull off test Heat temp. coating 1st generation 2nd generation 3rd generation single film 3.4MPa, 0%B 3.3MPa, 0%B 5.0MPa, 0%B overcoat.0mpa, 0%D, 40%E 5.MPa, 0%B, 30%D.0MPa, 0%D, 20%E single film 3.MPa, 0%B 4.0MPa, 0%B 4.MPa, 0%B overcoat.1mpa, 5%D, 25%E.1MPa, 30%B, 40%D, 30%D.2MPa, 0%D, %E single film 4.0MPa, 0%B 3.MPa, 0%B 5.0MPa, 0%B overcoat.2mpa, 0%D, %E.0MPa, 5%D, 5%E.0MPa, 0%D, 40%E single film 3.5MPa, 0%A 3.5MPa, 0%A 4.0MPa, 0%B overcoat 5.MPa, 15%A, 5%D 5.MPa, 25%A, 5%D.1MPa, 0%D, 40%E [nature of failure area] A: Interface detachment between steel plate and shop primer, B: Cohesion break of shop primer, C: Interface detachment between shop primer and epoxy paint, D: Cohesion break of epoxy primer, E: Interface detachment between glue and dolly 5.5 Figure-11 Tensile stress of single film after heat Figure-. Tensile stress of single film after heat Figure-12 Figure-. Tensile stress stress of of overcoated film afterheat file after.5 strength (MPa) st 2nd 3rd generation strength (MPa) st 2nd 3rd none primer generation From these results, the Third Generation Shop Primer shows better resistance property to ignition damages than the First and Second Generation shop primer. 3. CONCLUSION The Third Generation Shop primer shows improved anti-white rust property and anti-corrosive property compared to the First and Second Generation Shop primer. It is also proved that the Third Generation Shop primer shows good weldability comply with high speed welding. Painting system including intact inorganic zinc paints has adopted than over 20 years. The Third Generation Shop Primer has developed to meet the construction process of Japanese shipyards, and has widely adopted. The Third Generation Shop Primer keeps intact surface while construction process, controlling white rust and rust, and provide over coatability to epoxy main coat. The Third Generation shop primer could comply with ANNEX-1 test of PSPC requirements. 200: JASNAOE-RINA 43

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