Wayne MCGaulley, Staff Engineer William Shepperson, Staff Engineer Corrpro Companies, Inc Jefferson Davis Highway, Suite 500 Arlington, VA 22202

Transcription

1 COMPARISON OF SECONDARY SURFACE PREPARATION OVER WATER JETTED SURFACES AND THE EFFECT ON COATING PERFORMANCE Wayne MCGaulley, Staff Engineer William Sheppersn, Staff Engineer Crrpr Cmpanies, Inc Jeffersn Davis Highway, Suite 500 Arlingtn, VA Fred Berry Naval Sea Systems Cmmand, Cde 05M 1333 Isaac Hull Ave. Bldg. 197, Stp 5131 Washingtn, DC Abstract. Phtgraphs f abrasive blasted and water jetted surfaces taken at micrscpic levels have shwn that the water jetted surface appears rugher as magnificatin increases, whereas the abrasive blasted surface appears smther as magnificatin increases. The subject paper is a status reprt f an nging Naval Sea Systems Cmmand (NAVSEA) study. The study investigates cating perfrmance ver water jetted surfaces with several different secndary surface preparatin methds. BACKGROUND In recent years, advances in equipment have made water jetting an effective frm f surface preparatin fr use in industry as well as in the US Navy. Currently, water jetting is used by the US Navy t remve nn-skid decking material n aircraft carrier flight decks and underwater hull catings. Current US Navy specificatins, such as the Naval Ships Technical Manual (NSTM) Chapter 634, Deck Cvering, require a measurable anchr tth prfile f 3 t 4.5 mils. Water jetting at pressures up t 40,000 psi alne cannt impart this prfile. It can nly reveal an existing prfile. When viewed under magnificatin, the surface f a water jetted substrate appears rugher than the surface f an abrasive blasted surface. The pssibility exists that the increased surface rughness f the water jetted surface may allw increased wetting f catings n the substrate. By mre effectively wetting the surface, catings can achieve greater adhesin. ~ On US Navy ships, substrates that d nt exhibit a surface prfile can be fund in varius areas, fr a variety f reasns. Prfiled steel n underwater hulls and in tanks can becme crrded, which destrys the angular prfile and leaves an irregular tpgraphy f pitted steel. On aircraft carrier flight decks, aircraft arresting cables wear away nn-skid catings and plish the underlying steel remving any existing prfile. When utilizing water jetting, the resulting surface is nt in accrdance with the current NSTM Ch. 634 requirement f 3 t 4.5 mils f anchr tth prfile. The purpse f this study is t investigate the perfrmance f catings ver smth water jetted surfaces (n a macr level) cmpared t the perfrmance f surfaces with a measurable anchr tth prfile achieved by secndary mechanical surface preparatin methds. New water jetting technlgies, such as next-generatin rbtic crawlers and imprved lance-nzzle designs allw increased prductivity fr water jetting peratins. Hwever, secndary surface preparatin t establish a macr prfile is slw and cstly, thus reducing the feasibility f using water jetting. Therefre, if it can be shwn that water jetted surfaces withut secndary surface prfiling can perfrm as well r better than thse with secndary surface preparatin, the US Navy can emply these new water jet technlgies n a brader basis fr surface preparatin, thus reducing csts. 1 Weismantel, Guy E., "Paint Handbk," McGraw-Hill, Inc. 1981

2 INTRODUCTION In rder t fully test the hypthesis that water jetting prvides an adequate surface t apply catings that will perfrm as well r better than catings applied ver an abrasive blasted surface, the testing must simulate actual field cnditins. Of the cnditins that can prvide an area where an existing prfile has been remved, the flight deck f an aircraft carrier is the wrstcase scenari. In the aircraft arresting cable area, aircraft carrier flight deck steel cnditin is defined by smth steel with n existing macrprfile. Therefre, testing f all systems was cnducted ver the wrst-case smth substrate. T simulate this cnditin, cld-rlled steel was chsen as the substrate. The surface f the cldrlled steel was a dull shine, with sme staining present. The envirnmental cnditins f an aircraft carrier flight deck cnsist f mist, saltladen air and sea spray. Additinally, flight deck catings are expsed t cnstant UV radiatin during daylight hurs. Perfrmance tests must be chsen prperly t simulate these cnditins. Three perfrmance tests were chsen t best simulate these cnditins: Atmspheric expsure Cathdic disbndment Prhesin The first step in simulating service cnditins is the atmspheric expsure test. This prvides the mst accurate data since panels are subject t a natural marine envirnment. This test is very time intensive and therefre des nt prvide immediate results. Due t the time intensive nature f atmspheric expsure, a prcedure that can simulate natural cnditins at an accelerated rate called the prhesin test was als used. This test cyclically expses test specimens t humid saltladen air, then dry, ht air. This test prvides accelerated crrsin results, typically within 2,000 hurs f testing, t identify perfrmance differences between surface preparatin r materials. is under cathdic prtectin. Additinally, if the cating is nt perfrming prperly, it may disbnd frm the substrate in damaged areas when under cathdic prtectin. The amunt f cating that disbnds can be measured directly by scribe cutback and cmpared t ther cnditins r catings. TECHNICAL APPROACH Test Matrix. Table 1 summarizes the perfrmance tests and panel cnditins that were used in this study. Nte that nly ne panel frm each surface preparatin methd was used fr metallgraphy, which is "the study f the structure f metals and allys by varius methds, especially by the ptical and electrn micrscpe, and by x- ray diffractin. ''2 Table 1. Test Matrix Test Atmspheric Expsure Prhesin Cathdic Disbndment Metallgraphy Number f Panels per Cming per Surface Preparatin Adhesin Scribe Uncated (per surface prep nly) Prcedure. The panel surfaces cntained a large amunt f ils frm the milling prcess. Panels were degreased by dipping in slvent and wiping. The primary surface preparatin methd was Ultra-High Pressure Water Jetting. The perating pressure used fr this prcess was 40,000 psi with a flw rate f 3 gallns per minute. A rtating lance, spinning at 3,000 rpm with a tw jewel, zer-degree, nn-cavitating nzzle assembly was used. The jewel rifice size was inch. Six sets f panels received a full cleaning t SSPC-SP 12, WJ- 1. Fllwing water jetting, five f the six sets f panels received secndary surface preparatin t impart an anchr tth prfile. An additinal set f panels received nly slvent cleaning, withut water jetting, t serve as Cathdic disbndment testing prvides an additinal measure f adhesin. Prly adhered catings may blister when the substrate 10 2 "McGraw-Hill Dictinary f Scientific and Technical Terms, Fifth Editin," McGraw-Hill, New Yrk, 1994

3 a cntrl. Table 2 cntains the surface preparatin matrix. Table 2. Surface Preparatin Matrix Primary Secndary N. f Surface Surface Panels Preparatin Preparatin Water Jetting; Nne 21 Water Jetting Grind 21 Water Jetting Wire Wheel 21 Water Jetting Grit Blast 21 Water Jetting Sht Blast 21 Water Jetting Rt-Peen 21 Nne Nne 21 Ttal 147 Fllwing surface preparatin, tw methds f measuring surface cntaminatin were used t characterize the resulting surface: Chlride Measurements Bresle Methd Cnductivity Measurements Mdified Bresle Methd The Bresle Methd uses a standard extractin fluid and titratin t detect nly chlride species, whereas the cnductivity measurements are made using de-inized water and a Hriba Twin Crd B-173 Cnductivity Meter, which measures the cmbined cnductivity f inic species present. Fllwing chlride and cnductivity readings, surface prfile measurements were made using Testex Press-O-Film replica tape in accrdance with ASTM D 4417 "Test Methd fr Field Measurement f Surface Prfile f Blast Cleaned Steel" Methd C. Additinally, surface prfile was measured using a Mituty S J-201 Surface Rughness Tester (prfilmeter). The prfilmeter prvides much mre data than replica tape and allws measurements t be made n much smaller prfiles, such as smth surfaces, water jetted surfaces and thse that are wire wheel plished. The data prvided by the prfilmeter are as fllws: Arithmetic mean f prfile, RA Maximum peak t valley height, Rv Mean peak t valley height, Rz Mean rt square f prfile, Rq Peak density, Rac 11 After surface prfile measurements were made, panels were cated with accepted US Navy cating systems, utlined belw in Table 3. Table 3. Cating System Matrix System 1 Cating Standard Nn-Skid Epxy Primer Military Specificatin MIL-PRF MIL-PRF First Cat F-150, Green Buff DFT 2-3 mils 3-4 mils Secnd Cat F- 151, Haze Gray Gray DFT 2-3 mils 3-4 mils Prir t further testing, all panels were allwed t cure fr a minimum f seven days at 75 F fllwing applicatin f the tpcat. Adhesin. After full cure was achieved, adhesin testing cmmenced. Adhesin testing was dne in accrdance with ASTM D 4541 "Test Methd fr Pull-Off Strength f Catings Using Prtable Adhesin-Testers," using a Paddi Jr. prtable adhesin tester capable f measuring adhesin up t 4,000 psi. A high strength epxy adhesive with theretical bnd strength f 4,290 psi at maximum cure was used t adhere the dllies t the cating. Measurements were made n fur panels frm each surface preparatin type per cating system with three readings taken per panel. Areas damaged during adhesin testing were repaired using the prper cating system and allwed t cure fr seven days prir t further testing. Fllwing adhesin testing, panels were placed in a battery f tests t measure perfrmance f the varius surface preparatin methds in simulated service cnditins. These tests are described belw. Atmspheric Testing. Fur panels f each surface preparatin per cating system were placed in atmspheric testing. This testing is cnducted at Crrpr's Atmspheric Test Site in Sea Isle City, New Jersey. Panels were placed at a 45 inclinatin, facing suth. Panels were sprayed with seawater daily at which time they were inspected fr significant crrsin changes. Tw f the panels received intentinal 45 scribes. These panels were evaluated fr scribe cutback, general paint failure, and verall rust. The remaining tw

4 panels were fr adhesin measurements. Frmal inspectins were perfrmed at regular threemnth intervals t evaluate verall perfrmance and measure adhesin. Prhesin Testing. Accelerated Crrsin testing was perfrmed in general accrdance with ASTM G85, "Standard Practice fr Mdified Salt Spray (Fg) Testing." Test samples were subjected t a standard salt fg expsure, using a 5% NaC1 slutin, fr a perid f ne-hur. The test samples were then subjected t a ne-hur dry-ff perid, where the expsure chamber is purged f the salt air and heated t 35 C. This cycle was repeated fr a ttal f 2,000 hurs. Results frm this test are typically a better indicatr f perfrmance than traditinal salt fg testing (in accrdance with ASTM B 117). Fur panels f each surface preparatin per cating system were placed in prhesin testing. Tw f the panels received intentinal 45 scribes. These panels were evaluated fr scribe cutback, general paint failure, and verall rust. The remaining tw panels were fr adhesin measurements. Frmal inspectins were perfrmed every 100 hurs fr lhe first 500 hurs and every 500 hurs fr the next 1,500 hurs t evaluate verall perfrmance and measure adhesin. Cathdic Disbndment. Tw panels f each surface preparatin per cating system were placed in cathdic disbndment testing. Testing was cnducted in general accrdance with ASTM G 8, "Test Methd fr Cathdic Disbndment f Pipeline Catings." Duplicate cated 6-inch by 12-inch by 1/8-inch test panels have a 6-inch scribe made parallel t and centered alng the 12-inch panel edge. The test panels were placed in a nn-metallic tank and expsed t natural seawater. Seawater flw int the tank was maintained t avid stagnatin. The test panels were electrically cupled t a centrally lcated magnesium ande. These panels remain in testing fr a minimum f 45 days, with electrical data (galvanic current and n/ff ptentials) taken weekly. After expsure, the panels were remved frm the tank and inspected fr blistering and cutback frm the scribe. Blistering was rated in accrdance with ASTM D 714, and scribe cutback was recrded as the maximum distance frm the scribe that the 12 cmplete cating system culd be easily remved using a razr knife. Metallgraphy. One sample f each type f surface preparatin was retained fr in-huse visual and micrscpic evaluatin. Samples will als be sent t a labratry fr Scanning Electrn Micrscpy (SEM) evaluatin. RESULTS AND OBSERVATIONS Cntaminatin. Chlride and cnductivity measurements were made n tw panels frm each type f surface preparatin within the bttm tw inches f the panel. Average readings are shwn in Table 4 and Figure 1. Table 4. Cntaminatin Data Surface Average Preparatin Cnductivity Slvent Cleaned 13 Grind 33.5 Sht Peen 10.5 Rt-peen 13 Wire Wheel 26 Grit Blast 11 Water Jet 17 Chlrides* * indicates Belw Detectable Levels Figure 1 Cnductivity ~ 25 " 2O 15 0 D Cnductivity] All chlride measurements were belw detectable limits. Cnductivity readings were within the range f micr-siemens per centimeter, with nly ne reading abve 30 micrsiemens per centimeter and the majrity f readings belw 20 micr-siemens per centimeter. Accrding t NAVSEA Standard Item , Sectin , the limits n cnductivity are 30 micr-siemens per centimeter fr immersin service and 70 micr-siemens per centimeter fr atmspheric service. Chlride limits are 3 micr-

5 grams per centimeter fr immersin service and 5 micr-grams per centimeter fr atmspheric service. Prfile Measurements. As shwn in Table 5, grit blasting, fllwed by sht blasting, cnsistently gave the rughest surfaces n a macr level. Water jetting and slvent cleaning, fllwed by wire-wheeling, cnsistently gave the smthest surfaces n a macr level. Of interest thugh, is that water jetting and slvent cleaning, fllwed by wire-wheeling, had the highest Rpc (intervals between peak & valley/abve & belw mean) behavir, by a cnsiderable amunt. Table 5. Prfile Data Rpc Surface RA Rv Rz Rq (peaks Testex Preparatin (mils) (mils) (mils) (mils) /area) (mils) ShtPeen Wire Wheel Grinder Rt-peen Water Jet Grit Blast Slvent Clean The prfile data shwn in Table 5 des nt shw any significant difference between the water jetted surface and the slvent cleaned surface. There are, hwever, scale limitatins t the prfilmeter and the true effects f water jetting n surface tpgraphy cannt be determined until metallgraphy is cmpleted. Adhesin Testing. Prir t being placed int testing, the panels withut scribes were tested fr cating adhesin. Maximum Adhesin Table 6. System 1 Standard Epxy System 2 Nn- Skid Primer Cating Adhesin Surface Preparatin Max (PSI) Water Jetting 2079 Grit Blast 2528 Sht Blast 2119 Rt-peen 2119 Wire Wheel 2079 Grinder 2201 Slvent Wipe 2038 Water Jetting 2283 Grit Blast 2119 Sht Blast 2160 Rt-peen 1956 Wire Wheel 4956 Grinder 2283 Slvent Wipe 2364 * Dentes failure t substrate Min (PSI) ' Results f the adhesin measurements, as shwn in Table 3 and Figure 2, indicate that the surface preparatin methds are perfrming at least equally with the exceptin f the wire wheel, which exhibits an extremely high adhesin f 4,956 psi. The wire wheel surface preparatin is als the nly ne that had a failure t the substrate. Prhesin Testing. Prhesin testing f the scribed panels was initiated n July 31,2001. The nn-scribed panels were placed int testing n August 20, 2001 fllwing adhesin measurements. At the time f this paper, scribed panels have been in prhesin testing fr 500 hurs, nn-scribed panels have been in prhesin testing fr 300 hurs. Figures 3 and 4 shw the results f prhesin testing t date fr scribed and nn-scribed panels, respectively. T date, there is n significant difference in the perfrmance f catings ver the varius surface preparatins. Prhesin testing will be cntinued until 2,000 hurs {11 System 2] 1000 Figure 2 13

6 Prhesin Rust Ratings After 500 Hurs With Scribes ~ _.Sys,ml 4 Sy stem 2 Figure 3 Prhesin Rust Ratings After 300 Hurs Withut Scribes CONCLUSIONS Peak density is reduced by surface preparatin that implements mechanical defrmatin f the surface, thugh withut magnificatin, water jetting des nt appear t impart a prfile. The effects f water jetting n surface prfile were undetectable using either Testex tape r prfilmeter. Future wrk in this area will include SEM phtgraphs and metallgraphy f the unpainted surfaces t determine significant differences between the prfiles imparted by the surface preparatin methds. 6 E Sy stem 4 ] I Sy stem The data in Table 6 and Figure 2 shw n significant difference between the adhesin f catings t the varius surface preparatins used. Adhesin values may change fllwing perfrmance testing. Figure 4 Other Observatins. During surface preparatin, the wetting characteristics f the surface changed significantly. Prir t water jetting, the water was bserved t bead n the surface meaning incmplete wetting was achieved and the substrate had lw surface energy. After the surface was water jetted, hwever, water was bserved t spread quickly ver the surface, meaning mre cmplete wetting was achieved, thus the surface energy f the substrate was increased. This is demnstrated in Figure 5, shwn belw.. Water jetting may affect substrate surface energy. It is nt knwn at this pint what this means fr cating adhesin, thugh it des indicate increased wettability f the surface. High wettability results in intimate cntact between cating and bare steel, which directly crrelates t increased pull-ff adhesin) The results reprted in this paper are based n the specific parameters f the water jetting equipment used, substrate and cating materials selected, and the tests perfrmed. Using ther perating pressures, nzzles designs, different substrates, cating materials, r applicatin under different envirnmental cnditins may dramatically vary the results reprted here. FUTURE WORK In additin t investigating the initial issue f cating adhesin and perfrmance ver water jetting versus ther frms f surface preparatin, this study will cntinue t investigate the effects f prfile size and density n adhesin as well as its effects n cating perfrmance. This Figure 5. Example f water wetting the surface better after water jetting. The center was water jetted at 40,000 psi with 6 gpm. Left and right f center were nly degreased. 3 Baghdachi, Jamil, PhD, "Adhesin Aspects f Plymeric Catings, Virtual Seminar," Federatin f Scieties fr Catings Technlgy, June 14,

7 will be accmplished thrugh literature searches and additinal labratry research. One f the gals f this wrk is t determine which surface characteristics result in the best cating adhesin and cating perfrmance; the abslute rughest (peak/valley values) surface r a surface which, thugh nt as rugh, exhibits a higher Rpc surface (mre peak/valley systems). T accmplish this, results frm cating perfrmance testing and adhesin measurements will be analyzed fr crrelatin t surface characteristics. Currently, panel testing is still in prgress and will cntinue thrugh Nvember 2001 fr prhesin and cathdic disbndment testing. Atmspheric expsure testing will cntinue thrugh July Results f SEM are expected in Nvember If micr-prfile is fund t influence adhesin and can be cntrlled, future implicatins f this nging study will require develpment f a prcedure and equipment t measure the surface micr-prfile in the field. Accurate field measurements will be necessary if micr-prfile f water jetted surfaces is t be cnsidered a quality cntrlled item such as macr-prfile f abrasive blasted surfaces is quality cntrlled. Testers," American Sciety fr Testing and Materials, West Cnshhcken, PA, 1997 ASTM G 85-98, "Standard Practice fr Mdified Salt Spray (Fg) Testing," American Sciety fr Testing and Materials, West Cnshhcken, PA, ASTM G 8-96, "Test Methd fr Cathdic Disbndment f Pipeline Catings," American Sciety fr Testing and Materials, West Cnshhcken, PA, Baghdachi, Jamil, PhD, "Adhesin Aspects f Plymeric Catings, Virtual Seminar," Federatin f Scieties fr Catings Technlgy, June 14, 2001 "McGraw-Hill Dictinary f Scientific and Technical Terms, Fifth Editin," McGraw-Hill, New Yrk, 1994 REFERENCES Weismantel, Guy E., "Paint Handbk," McGraw-Hill, Inc., New Yrk 1981 SSPC-SP 12/NACE 5, "Surface Preparatin and Cleaning f Steel and Other Hard Materials by High- and Ultrahigh- Pressure Water Jetting Prir t Recating," SSPC, Pittsburgh, PA, 1995 "Naval Ships' Technical Manual S9086-VG- STM-010, Chapter 634, Deck Cverings", Naval Sea Systems Cmmand, 1991 NAVSEA Standard Item , "Cleaning and Painting Requirements," Naval Sea Systems Cmmand, 2000 ASTM Standard D , "Standard Test Methd fr Pull-Off strength f Catings Using Prtable Adhesin 15