SANS 10120-3 HC-1988 Code of practice for use with standardized specifications for civil engineering construction and contract documents Part 3 Guidance for design Section HC Corro.pdf

1、 Collection of SANS standards in electronic format (PDF) 1. Copyright This standard is available to staff members of companies that have subscribed to the complete collection of SANS standards in accordance with a formal copyright agreement. This document may reside on a CENTRAL FILE SERVER or INTRA

2、NET SYSTEM only. Unless specific permission has been granted, this document MAY NOT be sent or given to staff members from other companies or organizations. Doing so would constitute a VIOLATION of SABS copyright rules. 2. Indemnity The South African Bureau of Standards accepts no liability for any

3、damage whatsoever than may result from the use of this material or the information contain therein, irrespective of the cause and quantum thereof. Clause 1 . 2 . 3 . 3.1 3.2 4 . 4.1 4.2 4.2.1 4.2.2 4.2.3 4.3 4.4 4.4.1 4.4.2 4.4.3 4.4.4 APPENDlX A . APPENDIX B . SABS 0120 : Part 3 Section HC-1988 Cor

4、rosion protection of structural steelwork PART 3 : CUIDANCE FOR DESIGN SECTION HC CO WE NIs SCOPE PROCEDURE FOR SELECTION OF PROTECTLVE SYSTEMS CHOICE OF CANDIDATE SYSTEMS Design Life of Structure and Coating System(s) . Environment(s) . CHOICE BETWEEN CANDIDATE SYSTEMS . Experience . Functional Req

5、uirements and Maintenance Functional requirements Compatibility with engineering and metallurgical features Maintenance Cost Effectiveness . Fabrication and Construction Constraints Relating to Coating Systems . Location of fabrication and coating operations . Health and safety Constraints relating

6、to coating system . Transit constraints SELECTION CHART DETAILS OF THE COATING SYSTEMS AND SYSTEM VARIANIS IN THE SELECTION CHART GOOD STRUCTURAL DESIGN PRACTlCE FOR CORROSION PUEVENCION . PROTECTIVE SYSTEMS AND THEIR COMPONENTS Pa5e number 1 1 1 1 2 2 2 2 2 2 2 2 2 3 3 3 4 5 6-10 June 1988 Approved

7、 by the COUNCIL OF THE SOUTH AFRICAN BUREAU OF STANDARDS ISBN 0 826.07993-4 SABS 0120 : Part 3 Section HC-1988 Corrosion protection of structural steelwork SABS 1200 tIC : CORROSION PROTECTION OF STRUCTURAL STEELWORK SCOPE This part of the code gives guidance on how to select and specify the most su

8、itable corrosion-protection system for a particular set of circumstanres. The systems presented in the Selection Chart are those most commonly recommended for use on structural steelwork. This code may not adequately cover the selection of protective systems For those parts oi structures that are lo

9、cated in severely aggressive environments, such as portions of chemical plants, offshore oil rigs, harbours, dam installations and mine shafts. Should the engineer using this code find that he cannot confidently select the appropriate protective system(s) For his project, specialist advice should be

10、 sought. NOTE: For some situations, stainless or alloy steels may be used as an alternative to ordinary coated structural steel. No detailed recommendations on the use of these steels are given in this code and when their use is contemplated, advice should be sought from the steel industry. For roof

11、ing and cladding, the recommendations of SABS 0120 HB) should be followed. However, under highly corrosive conditions, suitable systems from this code may be preferred. PROCEDURE FOR SELECTION OF PROTECTIVE SYSTEMS For corrosion prevention, no protective system can adequately compensate for poor str

12、uctural design detai 1s. Therefore, review detailed design aspects with reference to Appendix A. Then a) With the desired life of the structure(s) in mind, identify the environment(s) (the humidity isograms in SARS 06423 may be an aid) and, with reference to Clause 3, identify suitable candidate sys

13、tems in the Selection Chart. It should be noted that Lhe “time to first major maintenance“ quoted in the Selection CharL is for guidance only. b) Select the preferred system from the candidate systems with reference to the additional criteria set out in the left-hand column of the Selection Chart an

14、d with reference to Clause 4. A system should not be used if the Selection Chart shows a bar against an essential or a desired criterion. For convenience, weighted numerical ratings can be assigned for the descriptive terms used in the chart for relevant criteria and the aggregate of these weighted

15、ratings can be used to aid in the selection process. Any additional criteria that may be important on a specific project can be inserted and weighted on the blank lines. c) Define tle sysLem(s) as completely as possible with reference to Clause 5. d) Draw up the detailed specification and compile th

16、e schedule of quantities, using the guidelines set out in Parts 2 to 4 of this code. CHOICE OF CANDIDATE SYSTEMS NOTE: When choosing candidate systems From the Selection Chart, consider the factors set out in 3.1 and 3.2. DESIGN LIFE OF STKUCTUKE AND COATING SYSTEM(S) a) For low long are the structu

17、re and coating systems required to fulfil their functions? MO.; structures are designed Tor a speriric functional life whlch can be achieved by choice of materials and design factors. In rare cases where access for repair or maintenance of the protective coating is impossible, the coating will be re

18、quired to have the same life as the structure. It will not normally be economical to choose materials and coating systems which gives freedom from major maintenance for the design life of the structure; reasons of hygiene or aesthetics may dictate shorter maintenance periods. It therefore becomes pr

19、artical to use a protective system which will require periodic maintenance during the design life of the structure. All systems qhould be inspected for possible maintenance needs at regular planned intervals, e.g. at com- missioning, after 1 year, and thereafter at suitable intervals. Periodic maint

20、enance embraces running and major maintenance. 1) Running maintenance is the ad hoc repair of isolated areas necessitated by design, application and maintenance deficiencies, together with eclranical damage, spillages and latent defects. There is at this stage no indication of general system failure

21、 and the work can be managed by the usual maintenance staff. 2) -r maintenance, usually beyond the scope of running maintenance, becomes necessary when early signs of rusting (red or white) appear aL weak spots and at critical areas such as welds, sharp edges or ronden- sation zones. These affected

22、areas will need to be cleaned back to the substrate (steel or metallic base coat) and the complete paint system reapplied. In addition, the whole surface of the steelwork should then be completely overcoated with a top coat. These operations should be carried out before the primer or metallic base c

23、oat shows general failure. For duplex systems which incorporate zinc-rich, galvanized and sprayed metal base coats, the total life of the coating system is the sum of the time to breakdown of the top coats plus the life of the underlying metallic coating. However, the expected “time to first major m

24、aintenance as given in the Selection Chart is the tlme to breakdown of the top coat. In severe corrosive environments where long life to first major maintenance is required, attention to design is of the utmost importance. Crevices, stitch-welding and fasteners are weak links in the protec- tive sys

25、tem. Twenty plus (20+) years to first major maintenance can be achieved on the main structural steel but in some instances (e.g. moving parts and fasteners), regular maintenance and greasing is necessary. b) What access is there going to he for cffecctive maintenance after erection? 1 jcladding and

26、sheeting. 2YPreparation ot steel surfaces for coating. SANS 0120 : PnrL 3 2 SecLion IIC-1988 Corrosion protection of structural sreelwork In addition to obvious examples such as the inside sufaces of box sectio?, it is necessary to assess Lbe life of each part OF a structure separately. Fur example,

27、 in a simple column-and-truss building, the upper flanges OF the roof trusses and outward-racing surfaces of columns, purlins and sheeting rails can easily receive appropriate protection against titis microclimate whilst they are accessible, before claddind and whilst erection damage is being repair

28、ed or Cinal coats are being applied (or both). After cladding, these siriaces would become acressible only aL great expense and with potential damage to the cladding. ENVLRONME,M(S) a) What is the general climate (macroclimate) at the site of the structural component? (:;ee the hutnidi ty isograms i

29、n SABS 064). Note LhaL the charted humldity values are those measured in a standard meteorologi- cal box (Stevenson screen) 1,23 m above the ground.) The most common types of environment are: 1) =or - dry. Normally dry. Very litLle corrosion. Ilelatlve humidity generally below 60 X . 2) Exterior inl

30、and - low pollut b) Colour: i ) decorat ive 2) statutory (colour coding) c) Resistance to damage (roS li ng, impact, scratching and abrasion); cl ) Temperature; e) Lmmersion; f) Chemical attack, etc. ; a) ttvniene. .- Compatibility -U- with Engineering and Eietallurgiral Features - - - a) IS the pre

31、ferred coating system compatible with the design and detail of the structure? e.g. galva- izing of thin elements or sealed joints, site welding and friction-grip joints. b) 1s the chosen surface preparation method compatible with the mechanical properties of the component? e.g. possible hydrogen mbr

32、ittlemrnt during pickling. Distortion of thin plate during abr,asive blasting of thin plaLe. C) IS the system compatible with cathodic protection? (See the Select ion Chart.) Mdi ntenance. Can the chosen system be trasily maintained? (See the Select ion CharL - RECOAJXNG, and 3. l(b) , keeping in mi

33、nd that. single-pack materials are easier and nlore convnient to use.) COST EFFECTIVF,W.SS. 1s the life cycle cost of the chosen system the most economical7 Take into account a) LIIP initial applied cost; h) Lhe mi rkenance costs during the life ryrle chosen, including production losses and dijmantl

34、i ng costs; A budget esLimatc using the dsired specification(s) should be compared with the capital vote for the project. If the vote is insufficienl, ideally it must be increasd, or Lhe specification(!;) (performance or expected life CO first maintenance) must be changed to meet the money available

35、. Alterjlatively, cost priority may initially be given to critical areas, and less critlcal areas built up under maintenance budget S. FABRICATION AND CONS CRIIGTION CONSrRAI NTS RELATING TO COATING SYSTEMS. When choosing between candidate systems and when deciding the location and sequence of opera

36、tions to suit the candidate systems, consider the following advantages and constraints: 3 SABS 0120 : Part 3 Section HC-1988 Corrosion protection of structural steelwork Location of Fabrication and Coating Operations. There are many options whin deciding in which location the coating system is to be

37、 applied. a) At Lhe fabricators shop (or a coating contractors yard); b) On site before erection; c) On site after erection; d) Combinations of (a)-(c) above. 4.1.1.1 Application at fabricators shop (or coating contractors yard). Shop application has the following advantages: a) The atmosphere is re

38、latively clean and unpolluted. b) Early protection of new steelwork is possible. c) The surFace of the steelwork is more easily accessible. d) Better equipment is available, e.g. mechanical handling and conveyors. e) Surface preparation using centrifugal abrasive cleaning is cheaper. f) More efficie

39、nt use can be made of supervisors, giving better quality. g) A more highly trained fixed labour forc is available, giving better productivity. h) The supply line for materials and technical service is shorter. i) Full shop coating reduces intercoat contamination. j) Shop application is less dependen

40、t on the weather. 4.4.1.2 Application on site a) Site anolication has Lhe following advantages: . . 1) Damage during handling, loading, hauling, unloading and storing on site is eliminated. 2) Wider use can be made of softer coatings such as alkyds and chlorinated rubber. 3) Centralized quality cont

41、rol of multisource supplies is possible. h) It is convenient for site fabrication, e.g. galleries, pipework and flooring. 5) The responsibility For coating and erection damage is undivided. h) Despite the above-listed advantages, certain overriding considerations may apply, e.g.: 1) The limitations

42、on open site blast cleaning; 2) the availability of acceptable blast-cleaning medium; 3) the availability of electric power at suitable voltage, phase and freqcency; 4) the availability of potable water; 5) the availability of accommodation; 6) the availability of skilled or other labour; 7) climati

43、c problems; 8) the cost of site establishment; 9) site administration costs; 10) the accessibility of the site; 11) international border problems; 12) currency controls; 13) the construction program; 14) the cost of inspection. 4.4.1.3 - Combined shopfsite application. A combined shop/site applicati

44、on permits the optimization of the advan- tages given in 4.4.1.1 and 4.4.1.2(a). Inorganic zinc and metal coatings in general have excellent resistance LO handling damage, combined with excellent self-weathering for periods of a year or more, without a Lop coat. It is possible therefore to have the

45、whole of the priming application completed centrally and the remaining coats applied on site where the ideal is probably to apply the intermediate coat (or undercoat) whilst the steelwork is on the ground befure erection and to apply the final coat after erection but before cladding. This sequence o

46、f coatlrgs has the great advantage of keeping the blast-cleaning operation off site and greatly reducing the risk of contaminating the coats applied on site. There is also less danger of exceeding the critical overcoating periods of hard coatings such as epoxies and polyurethanes. 4.4.2 Health and S

47、afety. Are any problems to be taken into account during coating Operatlons?idr aspects such as safety requirements, operation in closed spaces, local authority limitations on sand blasting, fire hazards, or explosion risks and toxicity of materials. Constraints Relating to Coating System 4.4.3 - 4.4

48、.3.1 Time intervals B) mat intervals can be allowed between coating operations, taking account of climatic considerations7 b) Do any of the candidate systems have critical overcoating intervals? The short pot-life of mixed two-componenl materials such as solventless epoxy snd inorganic zinc may caus

49、e diFficulties or even preclude their use in very hot conditions on sites exposed to direct sunlight. (See SINGLE(S) or MUI.TIPLE(M) PACK entries in the Selection Chart.) The use of slow-curing materials such as alkyds, some epoxy tars during the winter and some inorganic zincs under very low humidity conditions, may result in 1) shipment, erection and recoating schedules being impossible to meet; 2) hold-ups due to weather; 3) extra covered working area being required; 4) extra scaffolding and staging being required; 5) lower productivity with increase