1、UDC 621.644.2434.14 : 628.11.3 : 662.76 : 620.1 97 DEUTSCHE NORM September 1992 External corrosion protection of buried pipes Corrosion protection systems for steel pipes DIN 30675 Part 1 uerer Korrosionsschutz von erdverlegten Rohrleitungen; Schutzmanahmen und Einsatzbereiche bei Rohrleitungen aus
2、Stahl Supersedes April 1985 edition. This standard has been jointly prepared by DIN Deutsches institut fr Normung e. V. and DVG W Deutscher Verein des Gas- und Wasserfaches e.K (German Gas and Water Engineers Association) and has been adopted into the DVGW Codes of practice on gas and water. Dimensi
3、ons in mm 1 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.1 1 3 4 4.1 4.2 4.3 Page 1 Scope and field of application . Concep s . 1 Aggressiveness of soil . 1 Fault . 1 Impressed current cathode . 1 Isolating joint 1 Cathodic protection . 2 Anodebackfill 2 Corrosion cell 2 Passive corrosion protection
4、 2 Protection potential . 2 Stray current 2 Protective coating. 2 Design parameters. 2 Corrosion protection systems . 2 Requirements for backfill material 2 Protective coatings. . 2 Cathodic protection . 3 1 Scope and field of application This standard specifies extemal corrosion protection systems
5、for buried steel pipes and gives guidelines for selection of the appropriate system as a function of the service conditions. The specifications made here may be applied by analogy to underwater steel pipes. Provided the pipes are not to be sub- jected to high mechanical stresses nor to electrochemic
6、al corrosion, the properties of the water shall be deemed the same as those of soil belonging to category I. It should be noted that the risk of corrosion is greater where the pipework is subject to electrochemical corrosion (.e. cell formation) or water-line corrosion. In these cases, the risk of c
7、orrosion and the necessary protective measures shall be assessed in ac- cordance with DIN 50 929 Part 3. 2 Concepts For the purposes of this standard, the concepts marked (*) are defined somewhat differently from DIN 50 900 Part 2. For additional concepts, see DIN 50 900 Parts 1 and 2. Page 4.4 Pipe
8、s subject to electrochemical corrosion . 4 4.4.2 Localized cathodic protection 4 4.4.3 Protection against stray currents . 4 4.5.1 Hydrogen-induced cracking . 5 4.5.2 Anodic stress corrosion cracking . 5 5 Inspection 5 5.1 Protective coatings 5 5.2 Cathodic protection. . 5 5.3 Pipes subject to elect
9、rochemical corrosion . 5 5.3.1 Protection provided by isolating joints . 5 5.3.2 Localized cathodic protection 5 5.3.3 Protection against stray currents . 5 Standards and other documents referred to Other relevant standards and documents. . 4.4.1 Protection against cell formation in the presence of
10、impressed current cathodes . 4 4.5 Protection against stress corrosion cracking 5 5 6 2.1 Aggressiveness of soil The aggressiveness of soil is the sum of all effects that can induce free corrosion (Le. corrosion in the absence of electri- cal current) in buried pipes. 2.2 Fault A fault is localized
11、damage of the pipe coating, which pro- vides passive corrosion protection, where such is no lotiger effective. 2.3 Impressed current cathode An impressed current cathode is used as an external source of electric current in an electrolyte ,e.g. soil). It has a higher electric potential than the objec
12、t it is intended to protect (such as that of the reinforcing steel embeddd in .concrete) and, in combination, they form a corrosion cell. 2.4 Isolating joint An isolating joint is a joint or coupling between two lengths of pipe, inserted in order to provide electrical discontinuity between them. Con
13、tinued on pages 2 to 7 Beuth Verlag GmbH, Berlin, has the exclusive right of sale for German Standards (DIN-Normen) 02.94 DIN 30 675 Part 1 Engi. Price group 6 Sales No. 0106 Page 2 DIN 30 675 Part 1 2.5 Cathodic protection (*) Cathodic protection is an active (as opposed to passive) means of protec
14、tion against corrosion. It functions by op- posing the natural flow of electric current from the electrolytic environment (soil) to the metal surface. The protection poten- tial (cf. subclause 2.9) must match or better the corrosion potential of the soil. 2.6 Anode backfill For the purposes of this
15、standard, anode backfill is a layer of homogeneous material belonging to soil category Ia or Ib (as specified in DIN 50 929 Part 3 or DVGW-Arbeifsblaft (DVGW Code of practice) GW 9) surrounding the pipe. In accordance with DIN 19 630 and DIN 4033, it includes the material on which the pipe rests and
16、 the backfill material. 2.7 Corrosion cell (*) A corrosion cell is an electrolytic system comprising a cath- ode and an anode in electrical contact with an electrolyte. For the purposes of this standard, the pipe material (which is subject to the risk of corrosion) is the anode, and the cathode is i
17、nserted in the soil in which the pipe is buried in order to counteract this effect. 2.8 Passive corrosion protection Passive corrosion protection is that provided by isolating the pipe from the aggressive environment (e.g. soil, water) by means of a protective coating. 2.9 Protection potential (*) T
18、he protection potential is the threshold value within the protection potential range. if this value is achieved in the case of buried pipes, it may be assumed that corrosion occurs so slowly as not to be harmful. NOTE. The subject of protection potential is covered in DIN 30 676. Further information
19、 can be found in chapter 2 of the Handbuch des kathodischen Korro- sionsschufzes (Manual of Cathodic Corrosion Pro- tection) i. The values of protection potential given there apply only to the specific type of corrosion under consideration (e.g. even or uneven attack resulting in material loss). Oth
20、er values apply to other types of corrosion behaviour (e.g. stress corrosion cracking). 2.10 Stray current (*) Stray current is that which spontaneously flows from the con- ductive elements of electrical installations into the surround- ing soil. This term is also used to designate that which flows
21、from the impressed current cathode to the object being pro- tected. 2.1 1 Protective coating For the purposes of this standard, a protective coating is an electrically insulating layer of material applied to the outside of metal substrates (in this case, pipes and fittings) in order to effect passiv
22、e corrosion protection. 3 Design parameters The following parameters must be taken into account when selecting a corrosion protection system for buried steel pipes. a) The mechanical stresses expected during transport, storage, pipelaying and trench backfilling, as the soil set- tles, and in service
23、. b) The possibility of root penetration. c) The aggressiveness of the soil in which the pipes are to be laid and that which is present during subsequent trenchwork. In accordance with DIN 50 929 Part 3 and DVGW-Arbeifsblatt GW 9, the following categories of soil are to be distinguished: Ia: not agg
24、ressive; Ib: of low aggressiveness: II: aggressive: III: highly aggressive. d) Electrochemical corrosion, such as that arising from cell formation in the presence of impressed current cathodes and from the stray currents of d.c. installations. e) The continuous service temperature. f) The tensile st
25、resses expected in service. 4 Corrosion protection systems 4.1 Requirements for backfill material Residue from refuse incineration plants or power plants, and soil with carbonaceous constituents, shall not be used as backfill material in trenchwork. Recycled or granulated ma- terial shall only be us
26、ed where the results of regular checks show that its properties correspond to those of soil cat- egory I. 4.2 Protective coatings Pipe coatings may be applied at the works, at the storage site, or in situ. Table 1 specifies environments (.e. soil cate- gories) for pipes coated with polyethylene, the
27、rmoset plastics or bitumen. The thickness of polyethylene and bitumen coat- ings shall be in compliance with the normal thicknesses specified in DIN 30 670 and DIN 30 673, respectively, that of thermoset plastic coatings being in compliance with DIN 30 671. Table 2 specifies environments for pipes p
28、ro- tected by wrapping tapes and heat-fused materials in accord- ance with DIN 30 672 Part 1, as a function of the stress classes specified therein. Table 3 specifies environments for buried valves protected in accordance with DIN 30 677 Parts 1 and 2. The continuous service temperatures given in ta
29、bles 1 to 3 are those at which adequate corrosion protection is provided by a coating alone (cf. subclause 2.8). The information given does not apply to the corrosion resistance of the steel where the coating has faults, nor to its performance under extreme service conditions (cf. subclause 4.5). Wh
30、ere the pipes will be subjected to high mechanical stres- ses, the coatings selected shall be particularly resistant to impact and indentation, such as polyethylene and bitumen coatings of increased thickness as specified in the relevant standards. In addition, the following measures may be taken: a
31、) provision of wrapping tape about the coating; b) provision of a protective mat about the pipe that does not adversely affect cathodic protection; c) coating with fibre cement mortar. Such measures are usually not necessary where the pipes are buried in sand or in soil which does not contain stones
32、. Where root penetration is likely to affect pipe protection, polyethylene or thermoset plastic coatings, or wrapping tape with a cover or inlay of plastic film in combination with fibre cement mortar, shall be used. In the case of long, electrically conducting pipelines (e.9. welded steel pipelines
33、), extensive concentration cells may form. Where the probability of corrosion is high (cf. DIN 50929 Part 3) and where cathodic protection is not provided, the entire pipeline shall be buried in material as defined in subclause 2.6. DIN 30 675 Part 1 Page 3 A 2, Up to 30 Table 1 : Environments (soil
34、 categories) for coated steel pipes Type of coating service cate- I, II, III Type N I Up to 50 I I, II, III B B Type s I Up to 70 1 I, II, III I, II, III Up to 30 Up to 50 I EP as in DIN 30 671 I Up to 30 1 I,II, III EP as in EP as in DIN 30 671 DIN 30 671 Up to 50 I,II Upto70 I PURasin DIN30671 I I
35、 Type N Type s Up to 30 I,II Up to 30 I, II, III Type N or S Type N or S Up to 50 1,II Upto70 I Type s I Up to 30 I I, II, III PUR tar DIN 30 671 as in Type N Up to 30 I,II Bitumen DIN 30 673 Normal Reinforced Up to 40 I, II, III Type N or S Type N or S 1) Where required (cf. subclause 4.5), the pip
36、e shall also be provided with cathodic protection as specified in DIN 30 676. In this case, the coatings used are suit- able for use with soil of any category, assuming normal (i. e. not heavy-duty) service conditions (cf. subclause 4.3). Up to 50 I,II Upto70 I Table 2: Environments (soil categories
37、) for coating systems as specified in DIN 30 672 Pari 1 Continuous ser- vice temp., in Soil categories) Stress class I, II, III Up to 30 I c I or50 I For l), see table 1. 2) In accordance with DVGW-Arbeitsbltter G 462 Part 2 and G 463, stress class A coatings shall not be applied in situ, except on
38、pipes or fittings with an uneven sur- face, in which case several layers of wrapping tape (cf. subclause 2.2.1 of DIN 30 672 Part I), used in combi- nation with a protective mat, are to be applied. 3, In the case of pipes used at fluctuating service temper- atures up to 70 “C, thermoset plastic coat
39、ings (e.g. liquid epoxy resin), used in combination with a suitable heat-fused material with epoxy primer, shall be applied for now. It is also advisable to isolate the pipe from the soil by means of a protective mat. A standard on coatings applied in situ for continuous service temperatures up to 7
40、0 “C is currently in preparation. 4.3 Cathodic protection Use of cathodic protection (cf. DIN 30 676) considerably improves the corrosion protection of buried pipes. Where the protection criteria specified in DIN 30 676 are satisfied, even where the coating has faults, and where such is verified in
41、accordance with DIN 50 925*), then unalloyed and low-alloy steel pipes used at continuous service temperatures of well under 50 OC shall be deemed as being fully protected from corrosion. For this reason, the relevant standards and liter- ature specify the use of cathodic protection where particular
42、 safety requirements are to be met. The distribution of current and the protective-current requirements are a function of the quality of the protective coatings in accordance with sub- clause 4.2. Where suitable coatings are selected, the effects from external systems are negligible, and the reliabl
43、e per- formance of the cathodic protection is ensured. Where the effects from high-voltage installations are to be considered, the requirements specified in AfK-Empfehlung (AfK Recommendation) No. 3 shall be taken into account. *) At present at the stage of draft. _ Used with anode Continuous backfi
44、ll service tem- (cf. subclause 2.6) Relevant Type of coating perature, in “C Soil categories No coating4) Yes Up to 30 “C Yes Coating as in I I Up to 30 “C I, II, 1173) I, II, III EP, PUR, PUR tar coating as in I NO 1 Upt070“C 1 I EP, PUR, PUR tar coating1) as in DIN 30677 I Part 2 I I I I 1 Yes I.
45、II, Ir1 coating as in I) Where cathodic protection is provided in addition, these coating types are suitable for burial in soil of any category. 2, Cf. DIN 30677 Pari 1, Explanatory notes. 3) Where cathodic protection is provided, only valves with a coating in compliance with DIN 30677 Part 2 shall
46、be used. 4) Cf. DIN 30677 Part 2, Explanatory notes. 4.4 Pipes subject to electrochemical corrosion Where electrochemical corrosion (cf. clause 3) is a possi- bility, suitable protective measures against such effects shall be taken in addition to provision of protective coatings in accordance with s
47、ubclause 4.2, since coating alone is not sufficient. In fact, in the case of pipes provided with improved passive corrosion protection, the risk of electrochemical corrosion (particularly, cell formation in the presence of impressed current cathodes) is not prevented, but rather is greater at any br
48、eaks in the coating. Coatings in accordance with subclause 4.2 do, however, serve to support the electrochemical corrosion protective measures that need to be taken. Where it is not possible to take suitable measures against electrochemical corrosion, a fault-free coating or provision of anode backf
49、ill shall be deemed sufficient in the case of short pipelines. In this case, the quality of the coating or backfill shall also be verified in service (cf. Technische Regel fr brennbare Flssigkeiten (Code of practice for combustible liquids) (TRbF) 131 Part 1). A distinction shall be made between measures taken against: a) cell formation in the presence of impressed current cathodes, and b) stray currents. 4.4.1 Protection against cell formation in the presence of impressed current cathodes Suitable protection against cell formation in the presence of impressed current cathodes
