Behaviour of zinc rich primer after UHP (Ultra High Pressure) waterjetting for C5M environment (or naval construction).

Transcription

1 Behaviour of zinc rich primer after UHP (Ultra High Pressure) waterjetting for C5M environment (or naval construction). Philippe LE CALVE 1 ; Christian FAVENNEC 2 ; Nicolas BOCCA 3 1 Anticorr Conseil, France, Anticorrconseil.lcp@orange.fr 2 DCNS Lorient, France, Christian.favennec@dcnsgroup.com 3 DCNS Lorient France, Nicolas.bocca@dcnsgroup.com Abstract. All standard specify that zinc rich primer shall be applied on blasting surfaces to white or near white metal. The aim of this study was to evaluate the behaviour of zinc rich primer after UHP (Ultra High Pressure) waterjetting. For that, the surface preparation was performed to obtained different flash rust levels (from 0 to 2 g/m2) less than OF1 (flash rust) regarding French standard NF T The behaviour of four zinc rich primer paints systems (ethyl silicate and epoxy) were compared themselves and also with their behaviour on abrasive blasting surface preparation (Sa 2 1/2). They were also compared with a reference paint system without zinc applied on a surface prepared by UHP and blasting. All the technical solutions including flash rust and paint system were characterized before and after accelerated ageing in accordance with ISO All the solutions built on the zinc rich primer after UHP waterjetting have performed better than the reference solution and for all the different levels of surface iron oxide. Independently of the two zinc coating technology, the study shows that the corrosion protection of the steel was improved. The scribe delamination is less than 3 mm for all cases. Work remain to be done to quantify the impact of the degree of flash rust and roughness on the performance, but zinc rich primers appear to be a valuable technology to improve the performance of coatings after UHP waterjetting in new building and maintenance for marine conditions. Keywords : Coating; surface preparation; UHP waterjetting; zinc rich primer! 1

2 Introduction. Surface preparation processes influence the performance and lifetime of coating systems applied to steel substrates. Thus, the state of the steel surface immediately prior to painting is crucial and the main factors influencing the performance are the presence of rust and mill scale, surface contaminants including dust, salts and grease, surface profile. For aggressive environments such as marine atmospheres of C5M corrosivity category and high-performance coatings that require cleaner and/or rougher surfaces, blast cleaning is often preferred (see ISO or SSPC VIS1). As an alternative to abrasive cleaning for maintenance work or complete renovation, ultra high pressure (UHP) waterjetting may be a promising strategy for surface preparation as long as the performances of the coatings on steel structures are not affected. UHP waterjetting technology has been described intensively [1-3]. It is crucial to characterise the surface quality of steel substrates prepared by UHP waterjetting, in terms of flash rust, salt contaminants or surface roughness etc. Previous works have been conducted by the team of Le Calvé et al. in order to gain more understanding on the surface preparation by UHP waterjetting and its influence on the coating performances through accelerated corrosion tests and field exposures [4, 5]. - One study was dedicated to the extraction and the measurement of iron oxides, as a function of the degree of flash rusting (OF0, OF1, OF2) as described in the standard NF T [3]. It should be remembered that original state of the support is a determining element in the concentration measured. The latter can vary between 4-6 g/m 2 for a level of flash rusting OF1 and higher than 8 g/m 2 for a level of flash rusting OF2. Similar techniques were used by Islam and co-workers [6] -A systematic investigation about the influence of flash rust on the performance of four reference paint systems applied in new construction and maintenance configuration after UHP waterjetting preparation (hand held gun, 2100 bar) showed that the method did not lead to similar performance as classical abrasive cleaning (Sa 21/2) [4]. The study showed a drop in the coating performance as a function of increasing level of flash rust degree from OF0 to OF2, which highlights the importance of the steel surface state prior to UHP waterjetting. - The performance of 13 different coating systems applied on UHP treated steel in maintenance configuration (robot, 2450 bars) was studied in field exposure and laboratory tests and compared to classical abrasive blasted steel [5]. 4 coating systems applied on UHP treated surfaces were found to give satisfying results comparable to a surface preparation by abrasive blasting. If UHP waterjetting becomes more widely used for maintenance applications, they are however some questions on the use of this technique for new construction. In particular, the surface state of hydroblasted zinc-rich shop primer coated steel (in new construction configuration) is not fully described. Thus, there is a need to better assess the efficiency of hydroblasting for such application. The influence of cleaning parameters such as flow pressure or hydroblasting tools are examined in terms of surface cleanness, roughness and remaining zinc on surface. The results are compared with classical grit blasted surfaces. [7]. All standard specify that zinc rich primer shall be applied on blasting surfaces to white or near white metal. The aim of this 2

3 study was to evaluate the behaviour of zinc rich primer after UHP (Ultra High Pressure) waterjetting. For that, the surface preparation was performed to obtained different flash rust levels (from 0 to 2 g/m2) less than OF1 (flash rust) regarding French standard NF T This study evaluates the resistance of several zinc-rich primers applied under different flash oxidation conditions obtained after surface preparation by UHP water jetting compared with a reference surface preparation consisting of abrasive blasting. Experimental. Sample!surface!preparation:!SurfacepreparationbyUHPwaterjetting! Definition of UHP water jetting According to standard NF T35-520, the selected level of preparation grade of UHP water jetting is: DHP4: Exposure of steel: elimination of all oil, grease, sludge, caking, old paint, rust and loose mill-scale, and all old coatings and foreign materials. The exposed steel has a uniform finish, with an original metal appearance. «After the water has evaporated, the exposed steel surface takes on an amber colour that will change over time to a surface oxidation that becomes powdery, depending on weather conditions. This amber colouring is called flash rust. Standard NF T defines 3 flash oxidation levels to specify and for acceptance of stripped surfaces by comparison with photos. Photo OF0: exposed steel state after the end of surface preparation and drying operations, no trace of oxidation Photo OF1: exposed steel state after the end of surface preparation operation, with a slight non-powdery surface oxidation Photo OF2: exposed steel state after state OF1, with a powdery surface oxidation. In this study, the required preparation grade is DHP4 with degree of flash rust level OF1 (standard NF T35-520). Definition of a methodology to obtain different flash oxidation levels Three oxide levels have been defined so as to determine the influence of the quantity of iron oxides on the resistance of the paint system: - quantity of oxides <1 g/m² - quantity of oxides between 1 and 2 g/m² - quantity of oxides between 2 and 3 g/m² DHP4 OF1: flash rust<1 g/m² The UHP waterjetting robot was used with continuous water aspiration. DHP4 OF1: 1 g/m² <flash rust< 2 g/m² The UHP waterjetting robot was used without aspiration. Samples were dried immediately with compressed air. DHP4 OF1: 2 g/m²<flash rust< 3 g/m² The UHP waterjetting robot was used without aspiration. 3

4 Figure 1: Photographs of UHP water jetting Figure 2: Drying of samples Characterization of surface preparation Roughness measurement: A contact roughness-measuring instrument is used to measure the roughness (standard ISO ). Determination of the concentration of soluble salts The concentration of soluble salts is obtained using the Bresle method (standards ISO and ISO ). Analysis of iron oxides The surface concentration of iron oxides (g/m²) was determined using an analysis method developed by DCNS. With this method, oxides were extracted using Bresle patches using a solution of mercaptoacetic acid. Iron oxides were then quantified using a direct reading photometer on a dilute extraction solution treated by additives selected to bring all iron into a single ionic form and to complex it. Laboratory ICP/OES (atomic adsorption) measurements were made in parallel to confirm the on-site photometer method (standard ISO 11885). Results of characterization. Therefore six surface preparation cases were defined in this study. 4

5 Initial surface Surface preparation prior to Rusting preparation painting Case 1 ASa2.5 N / Case 2 ASa2.5 N DHP4 OF1 (<1 g/m²) Case 3 ASa2.5 N DHP4 OF1 (between 1 and 2 g/m²) Case 4 ASa2.5 N DHP4 OF1 (between 2 and 3 g/m²) Case 5 Sa2.5 + PPA (zinc silicate) N DHP4 OF1 (<1 g/m²) Case 6 ASa2.5 C DHP4 OF1 (<1 g/m²) Each sample was photographed before and after surface preparation CASE 3 (DHP4 OF1 (between 1 and 2 CASE 4 (DHP4 OF1 (between 2 and 3 g/m²)) g/m²)) After surface After surface Before surface Before surface preparation by UHP preparation by UHP preparation preparation water jetting water jetting CASE 5 (DHP4 OF1 (<1 g/m²)) Before surface preparation After surface preparation by UHP water jetting CASE 6 (DHP4 OF1 (<1 g/m²)) Before surface preparation After surface preparation by UHP water jetting 5

6 Characterization results are as follows: Analysis of iron oxides (g/m 2 ) (photometer) Quantity of iron oxides requested (g/m 2 ) Roughness measurement (Ra in µm) Concentration of soluble salts (mg/m 2 ) Case 2 0 ±0.03 < ± Case ±0.01 Between 1 and ± Case ±0.23 Between 2 and ± Case ±0.04 < ± Case ±0.06 < ±1 9.2 Analyses of iron oxides Laboratory measurements were made in order to confirm that results obtained using the onsite photometer method for analysis of iron oxides are correct. Figure 3 shows the comparison between these two methods and shows that they are equivalent. Quan3ty!of!iron!oxides!(mg/L)! 7,0 6,0 5,0 4,0 3,0 2,0 1,0 0,0 Comparison!of!results!obtained!with!the!photometer!and!in!the! laboratory.! Eurofins/5enmg/l Lab/5inmg/l Photomètremg/l Photometermg/l Case5 Case5 Case2 Case2 Case6 Case6 Figure 3: Comparison of results obtained with the photometer and in the laboratory For the calculation method, some blanks measured with the photometer have values > 1 therefore resulting in negative oxide quantities. Therefore it was decided to use a blank = 0.4 in accordance with Cefracor's recommendations. The results table shows that the quantity of iron oxides for case 3 is not equal to the requested quantity. This difference is due to the difficulty in controlling the quantity of oxides created using workshop techniques and production tools. Measurement of roughness: The Ra for case 6 is higher than the other samples. This observation is consistent with rusting C on the samples before surface preparation. Concentration of soluble salts: The concentration of soluble salts for case 6 is higher than for other samples. This observation is also consistent with rusting C on the samples before surface preparation. Paint applications Five paint systems were chosen for each case studied, namely 30 combinations of samples. Case3 Case3 Case3 Case4 Case4 Case4 Blank Blank Blank 6

7 Chemistry of the primer Pore seal Intermediate Finish Reference Epoxy primer with barrier effect / epoxy PU Zinc-rich primer with Diluted System 1 epoxy PU ethyl silicate binder epoxy System 2 Zinc-rich epoxy primer / epoxy PU System 3 Zinc-rich epoxy primer / epoxy PU System 4 Zinc-rich primer with ethyl silicate binder Diluted epoxy epoxy PU Samples Samples have scribe dimensions 100x0.5mm. Artificial ageing tests The test procedure according to ISO (Volvo test standard STD ) is defined in Figure 4. This test is selected regarding the results of the study [8] where the exposure conditions on the contenair wessel compare with a different standard of aging (ISO 9227, ISO 20340) and static exposure. The best correlation was observed using the cyclic test ISO Figure 4: Cyclic test procedure It was decided to carry out a second 12-week cycle after the first 12-week cycle, considering the state of the samples. There are only very small defects at the scribe in the samples. Characterization of samples Evaluation of samples before and after ageing!! 7

8 Assessment!of!the!test!panels!as!defined!for!this!study.! Criteria! Standard! Thresholds!of!acceptance!!! Defectsbeforeand ISO4628P2 0(S0) afterweathering ISO4628P3 Ri0 DelaminationP Mx<3mmforzincprimedcoating corrosionfromthe ISO4628P8 system* scribeline Adhesionbefore artificialageing Adhesionafter artificialageing ISO4624 ISO4624 Minimumpullofftestvalue:>4MPa Noadhesivefailurebetweenthesubstrateand thefirstcoat Minimumpullofftestvalue=50%initialvalue Noadhesivefailurebetweenthesubstrateand thefirstcoatunless Remarks! Comparisonwiththe referenceonsa2½ Comparisonwiththe referenceonsa2½ Measurement of delamination after ageing 1- The Maximum delamination value Dmax around the scribe is measured at 12 weeks and at the end of the test (24 weeks), excluding 1 cm at ends (without the coating being removed) (Figure 5 A). 2- The coating is removed at the end of the test and the corroded zone on each side of the scribe is measured in 1 cm segments except for 1 cm at each end. The average D of the corroded area is calculated as described in Figure 5 B. A! B! Dmax=(VPscribe)/2 Average=(C Pscribe)/2 C =ΣC n/n Figure 5: Delamination measurement (A) before and (B) after removal of the coating Results after ageing Examination of defects after 24 weeks Samples have different degrees of rusting: a few rust points, Ri0 and Ri1. Blistering defects were observed on samples: RC5-1 and S4C6-2. These defects did not appear on the duplicate coupons and are negligible. No blistering, cracking or chalking defect was noticed. After 24 weeks ageing, the level of rusting of tests pieces is low and equal to Ri0. Furthermore, no significant blistering, cracking or chalking defect is noticed. 8

9 DMaxbeforethecoadngisremoved (mm) Variation of the maximum delamination Dmax before the coating is removed at 12 and 24 weeks Varia3on!of!delamina3on!D!Max!around!the!scribe!!(before!the!coa3ng!is!removed)!during!ageing!(at!12!and!24!weeks)! Cas1P12semaines Case1P12weeks Cas2P12semaines Case2P12weeks Cas3P12semaines Case3P12weeks Cas4P12semaines Case4P12weeks Cas5P12semaines Case5P12weeks Cas6P12semaines Case6P12weeks R R! S1 S1! S2 S2! S3! S3 S4 S4! Figure 6: Variation of the maximum delamination before the coating is removed at 12 and 24 weeks of ageing Discussion of results: - After 12 weeks of ageing, systems S1, S2, S3, S4 comply with the requirement D<3mm, regardless of the type of surface preparation. - After 24 weeks of ageing, only the reference system R applied on all surface preparations and S1-case 5 do not comply with the requirement. Partial conclusion: The zinc-rich primers used in this study clearly have better results than the reference system, regardless of the surface preparation used (except for S1-case 5). Variation of corrosion D after the coating is removed (24 weeks) Cas1P24Semaines Case1P24weeks Cas2P24semaines Case2P24weeks Cas3P24semaines Case3P24weeks Cas4P24semaines Case4P24weeks Cas5P24semaines Case5P24weeks Cas6P24semaines Case6P24weeks 3!mm! Delamina3on!D!around!the!scribe!aNer!the!coa3ng!is!removed!! aner!24!weeks!of!ageing! Daeerremovalofthecoadng(mm) 9,0 8,0 7,0 6,0 5,0 4,0 3,0 2,0 1,0 0,0 Case1 Cas1 Case3 Cas3 Case5 Cas5 R R! S1 S1! S2 S2! S3! S3 S4 S4! Case2 Cas2 Case4 Cas4 Case6 Cas6 3!mm! Figure 7: Delamination after the coating is removed after 24 weeks of ageing 9

10 Discussion of results: The delamination of systems S1, S2, S3 and S4 and of R systems cases 2, 3 and 4 is less than 3mm, regardless of the surface preparation. Figure 8 Samples RC5-1 (left) and S1C5-1 (right) -The same trend is observed for the surface preparation denoted case 5 (Sa2½ + zinc silicate (PRZ) stripped by UHP water jetting): delamination is more for all systems except S2. Partial conclusion: As above, the results for zinc-rich primers selected for this study are clearly better than the reference system for all surface preparations. Concerning the influence of the surface preparation, the observed delamination is higher for case 5 (presence of residual zinc from the shop primer) for all systems except S2. Characterization of bond before and after ageing and study of the surfaces Variation in the ultimate stress before and after ageing for each system Uldmatestress(MPa) Uldmatestress(MPa) 20,0 15,0 10,0 5,0 0,0 20,0 10,0 0,0 Variadonintheuldmatestressbeforeandaeerageingforspecimens coatedwiththereference!system! Cas1 Case1 Case2 Cas2 Case3 Cas3 Case4 Cas4 Case5 Cas5 Case6 Cas6 Variadonintheuldmatestressbeforeandaeerageingforspecimens coatedwiththereference!system!4! Case1 Cas1 Cas2 Case2 Cas3 Case3 Cas4 Case4 Cas5 Case5 Cas6 Case6 Figure 9 Variation in the ultimate stress before and after ageing for each system 4!MPa! 4!MPa! 10

11 Discussion of results: - The ultimate stress is higher than the 4MPa requirement before and after ageing, regardless of the surface preparation. Results comply with the requirement. Partial conclusion: The ultimate strength values of systems S1 and S4 are lower than the other systems (they are halved). These observations are related to their chemistry: zinc-rich primer with ethyl silicate binder and the less cohesive nature of this type of paint. Standard deviations of measured ultimate strengths for S2 and S3 are higher than for the other systems. Study of failure surface Partial conclusion: Failure surfaces of the primer (in this case zinc ethyl silicate) are largely cohesive for systems S1 and S4, which explains the low values of the ultimate strength values (5-10MPa). This phenomenon is probably due to the chemistry of these systems (ethyl silicate primer) and more precisely the nature of the primer. The remaining primer (at the failure surface) is very thin for these 2 systems: 10-20µm (nominal thickness = 60µm). Failure surfaces for systems S2 and S3 are adhesive between coat 1 and substrate for cases 1, 2 and 5 (only for S3). Therefore poor adhesion is observed. However ultimate strength values remain high (10-15MPa). Discussions After 24 weeks artificial ageing, the level of rusting of tests pieces is low and equal to Ri0. Furthermore, no significant blistering, cracking or chalking defect is observed. The zinc-rich primers used in this study clearly have better results than the reference system, regardless of the surface preparation used. Corrosion on systems S1, S2, S3 and S4 is less than 3 mm, regardless of the surface preparation (case 1 to case 6). Influence of the chemistry of the primer Two different primer chemistries were introduced in this study, namely zinc ethyl silicates and zinc epoxies. Their main difference lies in the quantity of zinc. Comparison between the 2 operating modes Barrier effect of the reference system R The primer of the reference system contains aluminium pigments in order to improve the barrier effect of the system. In general, the behaviour of the reference system is not nearly as good as the behaviour of other systems for all the tested configurations, particularly as determined by the scribe corrosion measurement. Galvanic effect of other systems o Zinc ethyl silicate The primers for systems S1 and S4 are zinc ethyl silicates. The ultimate stresses of systems S1 and S4 are lower than the other systems (they are halved). The failure surfaces are largely cohesive in the primer, which explains the low values of the ultimate strength (5-10MPa). The system is slightly cohesive (lower presence of binder in this type of primer). 11

12 Zinc salts are observed in the scribes in the samples: zinc is available and functions satisfactorily, such that zinc salts can be formed in the scribe, limiting corrosion under the coating. o Zinc epoxy Primers for systems S2 and S3 are zinc epoxies. Zinc contents are 85% and 81% for systems S2 and S3 respectively. Systems S2 and S3 (zinc epoxy) have type A/B adhesive failure surfaces for cases 1, 2 and 5 (for S3 only). However, ultimate stresses remain high (10-15MPa). The results are promising for the use of zinc-rich systems after surface preparation by UHP water jetting. Influence of surface preparation Delaminations and corrosion measured after 24 weeks of ageing of the reference system (before the coating is removed) are higher than the required 3 mm for case 1, case 5 and case 6. Although the surface contains a high oxide and salts content before surface preparation with UHP water jetting, the performances of the different applied systems is very satisfactory and is much better than the performance of the reference system on the same state. This backs up the information collected from earlier studies on surface preparation by UHP water jetting (and particularly phase 3), according to which the surface condition obtained by UHP water jetting is free of salts and oxides and other contaminants. Although it is recommended that there should be a significant roughness for zinc ethyl silicates, the different tested cases show that zinc is available for galvanic operation and the surface is sufficiently clean even for the highest concentrations of surface iron oxides. These observations show that the performances of the applied system depend on the surface preparation method and the initial level of rusting. Moreover, performances obtained after surface preparation by UHP water jetting are better than those obtained after surface preparation by abrasive blasting (case 1). Systems S2 and S3 (zinc epoxy) have A/B primer - substrate adhesive failure surfaces for cases 1, 2 and 5 (only for S3). Therefore poor bond is observed with no trace of zinc on the surface (for some configurations) Influence of the quantity of oxides Two methodologies were used to quantify surface iron oxides: - Use of Bresle patches and a UV photometer to determine the surface concentration of iron oxide, quantification made in the field. - Quantification made in the laboratory The results obtained with these two techniques are similar and confirm that the method developed (Bresle patches + UV photometer) works well and is efficient and is an on-site method that informed personnel are capable of implementing. For oxide quantities, no difference is observed between increasing oxide thresholds, and there is no cliff effect on performances for the highest thresholds. There is a tolerance for good behaviour of the tested solutions to surface iron oxide concentrations. 12

13 Conclusion The study included tests of the performance of different zinc paint systems on surface conditions obtained by surface preparation with UHP water jetting. This was done starting from surface preparation with surface preparation by UHP water jetting, and applying increasing surface iron oxide levels starting from 0 to 2g/m2 for state DHP4 < 0F1 according to NF T (French standard). The behaviour of zinc paint systems with the zinc epoxy chemistry and zinc ethyl silicate chemistry were compared for the different tested configurations and against a reference surface preparation obtained by abrasive blasting and by using a reference paint system. The behaviours of all solutions made (composed of surface iron oxide concentration / zinc paint system combinations) were characterised before and after an artificial ageing cycle according to the revised ISO The behaviours of the different solutions will then be characterised after natural ageing currently taking place on a site characterised for corrosivity class C5M.It is found that the oxide quantification method is available and gives good agreement with the laboratory method used for this study. The different technical solutions used based on zinc systems are always better than the reference paint system used for this study (barrier effect system). Zinc in the 2 chemistries used is available to limit propagation of corrosion from the scribe, with values less than 3mm each time. Failure value of pull of test are very high in each case, with a majority of type A/B failures for zinc epoxies. Although the surface preparation by abrasive blasting method does not create any roughness, it improves surface cleanliness and the behaviour obtained is equivalent to or better than that obtained using the surface preparation by abrasive blasting method. Therefore the use of a zinc primer can be envisaged, since these are the only primers that can guarantee the target high durabilities for ship building and repair. However, surface iron oxides that can vary from 1 g/m2 to 2 g/m2, as demonstrated in this study, have to be well controlled (after surface preparation by UHP water jetting). Therefore this study demonstrates that existing baselines can be revised.! References! 1- A. Momber, Hydroblasting & coating of steel structures 2003 Elsevier 2- T. Mabrouki, A. Conier, O. Hafiz, K. Raissi, Mécanique & Industries, 5 (2004) P. Le Calvé, P. Meunier P, J.-M. Lacam, Protect. Coat Europe, 19 (9) (2002) P. Le Calvé, P. Meunier, J.-M. Lacam, J.Protective Coatings & linings, 20 (1) (2003) P. Le Calvé, J.Protective Coatings & linings, volume 24 n 8 (August 2007) M. Islam, W. McGaulley, M. Adams Analitical WJTA American Waterjet Conference, August Houston, Texas, USA. 7- P. Le Calvé, J-P Pautasso, N Le Bozec, Paper 8371, Eurocorr09, September 6-10, 2009, Nice, France 8- N Le Bozec, Paper 1268, Eurocorr 2013, Estoril, Portugal, September 1-5,