1、BRITISH STANDARD CONFIRMED FEBRUARY 1991 BS3900-F11: 1985 Cathodic disbonding (land-based) Methods of test for paints Part F11: Determination of resistance to cathodic disbonding of coatings for use on land-based buried structures It is recommended that this Part be read in conjunction with the gene
2、ral informationin the Introduction to BS3900, issued separately. UDC667.637.2:667.636.22:620.197.527BS3900-F11:1985 This British Standard, having been prepared under the directionof the Pigments, Paintsand Varnishes StandardsCommittee, waspublished underthe authorityof the Board ofBSIandcomes intoef
3、fecton 28February1985 BSI04-1999 The Committees responsible for this British Standard are shown inBS3900: Introduction. The following BSI references relate to the work on this standard: Committee reference PVC/10 Draft for comment82/55585 DC ISBN0 580 14162 4 Foreword This Part of BS3900 is one of a
4、 series of standards dealing with the sampling and testing of paints, varnishes and related products. It has been prepared under the direction of the Pigments, Paints and Varnishes Standards Committee. The method of test described in this Part permits the assessment of the ability of paint and other
5、 organic coatings applied to metallic substrates to withstand cathodic disbonding. This method may also afford a basis for the comparison of particular coatings. The conditions of the test are more severe than those likely to be normally encountered and thus coating failure may be accelerated. It is
6、 recommended that the test should be carried out for a period of28 days and hence this method is not suitable as a means of achieving quality control. In order to carry out the method of test described in this Part it is necessary for certain supplementary information, itemized in clause3, to be mad
7、e available or to be agreed between the parties. The procedure described in this Part is suitable for coatings to be used for the protection of land-based structures, such as pipelines; it is based on the procedure developed by the British Gas Corporation. The procedure described in Part F10 is base
8、d on that developed and evaluated by COIPM (ComitInternational Permanent pour la Protection des Matriaux en Milieu Marin) and should be used for coatings that are intended for the protection of ships and structures exposed to marine environments. It has been assumed in the drafting of this British S
9、tandard that it will be used and applied by those who are approximately qualified and experienced. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard d
10、oes not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This
11、 will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date of issue CommentsBS3900-F11:1985 BSI 04-1999 i Contents Page Foreword Inside front cover 1 Scope 1 2 Definitions 1 3 Supplementary information 1 4 Sampling 1 5 Electrolyte 1 6 Appar
12、atus 1 7 Preparation 2 8 Procedure 2 9 Test report 3 Appendix A Method for producing artificial holidays 5 Appendix B Detection of accidental holidays 5 Figure 1 Stabilized d.c. power unit (see6.1) 4 Figure 2 Arrangement of test cells and the electrical connections (see8.2) 4 Publications referred t
13、o Inside back coverii blankBS3900-F11:1985 BSI 04-1999 1 1 Scope This Part describes a method of test for determining the resistance to cathodic disbonding of a single coating or multi-coat system of paint, varnish or other organic coating applied to metallic substrates when the surface coating cove
14、ring the metal substrate may contain or develop discontinuities. It is applicable to coatings that are to be applied to land-based structures, such as buried pipelines. NOTE 1For coatings that are to be used in marine environments on ships or partially exposed marine structures, the conditions of th
15、e test differ from those for coatings to be used in land-based applications. BS3900-F10 describes a method suitable for assessing coatings applied to marine structures. NOTE 2The test result may be influenced not only by the properties of the coating system under test, but also by the nature and pre
16、paration of the substrate, the method of application of the coating system and other factors. NOTE 3The titles of the publications referred to in this standard are listed on the inside back page. 2 Definitions For the purposes of this British Standard, the definitions given in CP1021 and BS2015 appl
17、y, together with the following cathodic disbonding the failure of adhesion between a coating and a metallic surface that is directly attributable to cathodic protection conditions and that is often initiated by a defect in the coating system, such as accidental damage, imperfect application or exces
18、sive permeability of the coating 3 Supplementary information For any particular application, the following supplementary information shall be provided for this method of test. This information shall be derived, partly or totally, from the product specification, British Standard or other document for
19、 the product under test or, where appropriate, should be agreed between the parties. a) Material, dimensions and surface preparation of the test surface or substrate (see clause7). b) The nature of the coating and the environment for which the coating is intended. c) Method of application of the tes
20、t coating to the substrate or test surface and its thickness. d) Duration and conditions of drying or curing of the coating (or conditions of stoving and ageing, if applicable) before testing. e) The specific method of measurement of the thickness of the dry coating, in micrometres, in accordance wi
21、th BS3900-C5, and whether it is a single coating or a multi-coat system (see7.5). f) Duration of the test and any special conditions for testing (see8.2), including the electrolyte used (see clause5). g) Details of the preparation of the artificial holiday (see7.6). 4 Sampling A representative sampl
22、e of the product to be tested (or of each product in the case of a multi-coat system) shall be taken as described in BS3900-A1. Each sample shall be examined and prepared for testing as described in BS3900-A2. 5 Electrolyte 5.1 Sodium chloride,30g/L solution, prepared by dissolving30g of analytical
23、grade sodium chloride (NaCl) in water complying with the requirements of BS3978 and diluting the solution to1L. 6 Apparatus 6.1 Stabilized d.c. power unit having either a) a controlled voltage output of between0V and12V and a current capacity sufficient to supply 20mA simultaneously to each test spe
24、cimen in circuit; orb) a cathodic protection circuit, as described in6.5 of BS3900-F10:1985. 6.2 Voltmeter, with minimum resistance of10M7 and capable of measuring in the range0V to2V to the nearest1mV. 6.3 Variable resistors,0k7 to1k7 10%,1W (one required for each test site). 6.4 Fixed resistor,17
25、1%,1W (one required for each test site). 6.5 Anodes, of minimum length75mm and of platinum wire of0.8mm nominal diameter or of platinized titanium strip, nominally6mm wide and1.5mm thick. Each test site shall have one anode. 6.6 Reference electrode, saturated calomel type, constructed from glass or
26、plastics with a porous plug. The diameter shall be less than10mm. 6.7 Equipment for maintaining the temperature of the specimens and test sites at23 2 C. 6.8 Rigid plastics tube, of50mm nominal bore (onelengthof approximately60mm for each test site). 6.9 Elastomeric adhesive 1)for sealing the plasti
27、cs tube(6.8) to the surface of the test specimen. 1) Suitable materials are two-part polysulphide rubber and silicone rubber. “Silastic” silicone rubber, grade RTV738 or RTV732 has been found to be suitable.BS3900-F11:1985 2 BSI 04-1999 7 Preparation 7.1 Test substrates Test substrates shall be subs
28、tantially flat and representative of the substrate to which the test coating is to be applied. If flat samples of the typical substrate are not available, test panels shall be used. The test panels shall be of steel and shall comply with the requirements of BS3900-A3. NOTEIt may be necessary for the
29、 surface finish of the panels to correspond to that of the typical substrate to be used seeclause3 a). 7.2 Dimensions The minimum dimensions of each of thetestsubstrates(7.1) shall be200mm 100mm 2mm, unless otherwise specified see clause3 a). 7.3 Preparation and coating of the test substrates Either
30、 prepare and coat each substrate in accordance with the supplementary information given in the appropriate product standard or in the agreement between the parties (see clause3) or blast clean each test panel (see note to7.1) in accordance with BS3900-A3 and coat in accordance with the manufacturers
31、 instructions for the product or system under test. Prepare two test specimens for each product or system under test. Prepare control specimens, which are not to be connected to the cathodic protection system, in duplicate. 7.4 Drying and conditioning of the specimens Dry (or stove and age) the coat
32、ed test and control specimens for the time and under the conditions specified for the product under test (see clause3). Unless otherwise specified, condition the specimens at23 2 C and at a relative humidity of505% for a minimum of16h, with free circulation of air. Do not expose them to direct sunli
33、ght. Carry out the determination of the coating thickness (see7.5), formation of the artificial holiday (see7.6) and test sites (see7.8) and the test procedure (see clause8) as soon as possible after completion of conditioning see clause3 d). 7.5 Thickness of the coating Determine the thickness, in
34、micrometres, of the dry coating on each test and control specimen in accordance with BS3900-C5 see clause3 e). 7.6 Artificial holiday Prepare two artificial holidays each of6mm diameter on each test specimen either by drilling a hole through the coating in accordance with the method described in App
35、endix A or by using the procedure described in7.7 of BS3900-F10:1985. NOTEIf preferred, the artificial holiday may be prepared after fixing the plastics tubes to the test specimens (see7.8). 7.7 Accidental holidays Test the coating on each specimen for freedom from accidental holidays as described i
36、nAppendix B. 7.8 Test sites Form a test site around each artificial holiday on each coated test specimen by attaching a60mm length of rigid plastics tube(6.8) using the elastomeric adhesive(6.9). Place the tubes at a minimum distance of33mm from the ends of the specimen and from each other, with the
37、ir centres on the centreline of the specimen width. Place each tube perpendicular to the coated surface and centrally about an artificial holiday. Leave the test specimens for a minimum of12h to allow the adhesive to become fully cured. 8 Procedure 8.1 Determinations Carry out the procedure on two t
38、est specimens for each test coating. NOTEThis will provide four test sites. 8.2 Conditions of the test 8.2.1 Fill each plastics tube to a depth of approximately50mm with the electrolyte(5.1) and connect the apparatus as shown in Figure 1. Ensure that the temperature of each specimen and test site is
39、 at23 2 C, and switch on the d.c. power unit(6.1). Connect the voltmeter(6.2) as shown in Figure 2 and, with the porous tip of the calomel reference electrode(6.6) placed within10mm of the holiday in the coating, adjust the electrical input by means of the variable resistor(6.3) until the voltmeter
40、indicates1 5005mV with respect to the calomel electrode. (If conventional potentiostats are used, adjust the potential as described in8.3 of BS3900-F10:1985.)BS3900-F11:1985 BSI 04-1999 3 At intervals of24h, record the voltmeter reading and adjust the variable resistor to correct any drift from the1
41、 500 5mV setting. Check the potential frequently during the first8h and, thereafter, check the potential at least once every24h. Also, every24h, record (see note) the current flow by measuring the voltage drop across the17 fixed resistor(6.4). NOTEAlthough there is no requirement to report the curre
42、nt flow, a rapid rise in its magnitude is an early indication of disbonding of the coating. Check each of the plastics tubes every24h for loss by evaporation and, if necessary, add distilled water. As it is essential that there is no leakage at the seal with the test specimen (see6.9), if leakage oc
43、curs, discontinue the test. 8.2.2 Unless otherwise specified, continue the test for7 days, maintaining the temperature at23 2 C. After this period assess disbonding at one test site on each specimen by the method described in8.3. If the disbonding is less than the limit specified, continue the test
44、using the second test site for a further21 days. Then assess the disbonding by the method described in8.3. 8.3 Inspection and assessment of the coating Inspect and assess each coating immediately after the test period. Detach the plastics tube from the test site. Using a lint-free paper towel, wipe
45、along the surface of the coating and cathode area to remove moisture. NOTEAs alkalis may be formed beneath the coating during the test, care should be taken when handling the specimen. While rinsing may reduce the alkali concentration beneath a blister, the concentration may still be sufficient to c
46、ause skin burns. Make about12 radial incisions using a sharp knife 2)through the coating to the substrate extending outwards from the holiday for a distance of20mm. Make these incisions at an angle of approximately30 from each other. Insert the knife point into the centre portion of the holiday down
47、 to the metal substrate. Using a gentle levering action, peel away slowly a radial section of coating, continuing until firm adhesion is encountered. As loss of adhesion is not always obvious, carefully examine the substrate for signs of residual coating which indicates that disbonding has not occur
48、red. Repeat with each radial segment. 8.4 Reporting of results Either a) report the extent of disbonding as the average distance in millimetres between the edge of the holiday area and the positions of firm adhesion; or b) if the coating is strongly adherent to the substrate, take the average distan
49、ce at which the coating breaks as the extent of disbonding. 9 Test report The test report shall include the following information: a) the type and identification of the coating under test; b) a reference to this British Standard, i.e.BS3900-F11; c) the items of supplementary information referred to in clause3; d) the British Standards or other published documents supplying the information referred to in c); e) the period of the test and interruptions during the test including any required for the intermediate examination of the coating (see8.2.2
