SANS 10120-3 L-1983 Code of practice for use with standardized specifications for civil engineering construction and contract documents Part 3 Guidance for design Section L Medium-.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. SABS 0120 : Part 3 Section L-1983 Medium-pressure pipelines PART 3 : GUIDANCE FOR DESIGN SECTION L CONTENTS Clause 1 . 1.1 1.1.1 1.1.2 1.1.3 1.1.4 1.1.5

4、1.2 1.2.1 1.3 1.3.1 1.3.2 1.3.3 1.3.4 1.3.5 1.3.6 1.3.7 1.3.8 1.3.9 1.3.10 2 . 2.1 2.1.1 2.1.2 2.1.3 2.1.4 2.2 2.2.1 2.2.2 2.2.3 2.2.4 2.2.5 2.3 2.3.1 2.3.2 2.4 2.4.1 2.4.2 2.4.3 2.5 2.5.1 2.5.2 2.6 2.6.1 2.7 2.7.1 2.7.2 2.7.3 3 . 3.1 4 . 4.1 5 . 5.1 5.2 Page Number PRE-TENDER CONSIDERATIONS 1 Inves

5、tigations 1 Type of pipe and corrosion protection 1 AC pipes. COD type . 1 Protection against electrolytic corrosion 1 Laying. depths. and cover 1 Brickwork 1 . Administration 1 Payment for trench excavation 1 Documentation 1 General 1 Protection of steel pipes l . Specifying and selection l . Excav

6、ation 1 . Valve chambers 1 Clearances inside chambers and manholes 1 Brickwork for manholes and chambers 1 Disinfection of potable water pipelines 1 Test pressures . 1 Measurement and scheduling of excavation quantities 1 DESIGN CONSIDERATIONS 2 Design criteria . 2 General 2 Design of bedding for pi

7、pes . 2 . Detail on drawings 2 Intersecting services 2 Materials 2 Flexible pipes . 2 AC pipes 2 Steel pipe wall thickness 2 . Flexible couplings 2 Protection of bolts. etc 2 Depths and Covers 2 . Depth of water mains in reticulation and wrks layouts 2 Measurement and payment considerations 3 Valves

8、 . 3 Bypass valves 3 Air valves . 3 Fire hydrants 3 Ancillaries 3 Concrete encasing 3 Thrust blocks 3 Tolerances . 5 Tolerances in manholes and other structures 5 Testing 5 Test pressures . 5 Test requirements 5 Leakage rates 5 APPLICABILITY OF OTHER CODES . 5 General . 5 TEST PROCEDURES 5 General 5

9、 OIJALITY CONTROL b) certain plate thicknesses are to be preferred because they are stock sizes and more readily available than other thicknesses. Non-standard thicknesses require special rolling6 and even though the mass of steel involved is lower than for pipes of standard thickness, the pipes may

10、 be more expensive. The use of non-standard thicknesses may also lead to expensive delays on the works because of supply problems. Flexible Couplings (Subclause 3.8.2) The coupling arrangement shown on Drawing 13.1 is expensive and is not intended for use where long lenqths of pipe are coupled toget

11、her. It is specifically meant for use in positions where it is desirable to be able to uncouple a joint relatively quickly and without complications, either to gain access to the pipeline or to replace a valve or special during make-and-break maintenance operations. Under these conditions it pays to

12、 have a machined collar onto which the coupling can seal. Because only relatively few such couplings are used, the additional expense is warranted. Do not use machined collars as shown on Drawing L-3.1 where standard (flexible) couplings with centre register are scheduled. Where RC pipes and steel s

13、pecials are used, a machined collar is essential because the AC triplex coupling cannot tolerate ovality. Use (and schedule separately) pipes with machined collars and slip-on couplings without a centre register but with centre locating studs as shown on Drawing L-3.1, at the entry to each pump stat

14、ism, on one side of each important in-line valve, and in other locations where relatively frequent make an9 break maintenance operations are likely to occur. Use (and schedule separately) slip-on type couplings without a centre reqister and conforning to Drawing L-3.1 (except that the collars do not

15、 have to he machined) where closure pieces are required. Protection of bolts, ekc. (Subclause 3.9.6). Specify suitable painting procedures (or stainless steel) for bolts, etc., to be used inside pumpstations and the like. Protection of bolts and nuts against corrosion in all areas facilitates mainte

16、nance. DEPTHS AND COVERS Depth of Water Mains in Reticulation and Works Lay_uw (Subclause 5.1.4). Because the depths of cover .- over water mains, elect.rica1 service ducts, and stormwater pipes are normally kept to a minimum, and because these services frequently cross one another, conflict between

17、 specified covers an3 other requirements is common in reticulation and similar projects. Anticipate these problem areas and prepare detail drawings and project specification clauses to dispose of the problems. A typical example of a solution tn such a problem is set out in Subclauses 3.2.6 and 3.2.7

18、 of Section I. of Part 2 of the code. (See also 2.4.3 below and Subclause 3.2.5 of Sect-ion L of Part 5 of the code.) 3) In course of preparation for the Uepartmet of Communsty Develupmrnt. 4) GLASS WL, Bactella in steel plpellnes, Thr rlvil englneer sn South hfrica, Vol. 23, No. 9 September 1981. P

19、- 5) Bedding pipes). 6) Electric welded low carbon steel plpes for aqueous flusds (ordinary duties). SABS 0120 : Part 3 Section L-1983 Medium-pressure pipelines Measurement and Payment Considerations. Determine and schedule a minimum depth of excavation that slightly exceeds the depth needed for the

20、 bulk of the route of the pipeline after allowing for the specified depth of bedding and outside diameter of the pipe. By so doing, the payment of the next incremental rate for minor increases in trench depth can be avoided. VALVES Bypass Valves (Subclause 5.3). Consider the fitting of a separate by

21、pass valve (of cross-sectional area about 10-15 % of that of the main valve) to each valve of nominal diameter over 300 mm. This should be standard practice as the bypass not only helps to equalize the pressure on the valve faces but also helps to reduce water hammer, provided that first the main va

22、lve and then the bypass valve are closed. Air Valves. Where an air valve is so located that it may be subject to inundation by ground or surface water, ensure (if possible) that the air valve cover is above ground level. This is necessary to prevent dirty water from beinq drawn into the pipeline sho

23、uld it empty. Fire Hydrants. Consider the merits of the design of fire hydrants using concrete pillars as shown on Drawing L-3.0 to overcome depth and other problems. ANCILIARIES Concrete Encasing. Concrete encasing of AC, concrete, and plastics pressure pipes is generally not advisable. The pipelin

24、e is liable to shear failure as the inherent flexibility of the pipe is lost. Stabilizing of the subsoil or the use of a protective sleeve or a stronger type of pipe is preferable. Thrust Blocks (Subclause 5.5). Because thrust blocks for bends, reducers, tees, valves, offsets. hydrants, and end caps

25、 are a vital part of pipeline colrstruction, give particular attention to their design. This is not the contractors responsibility. The area of the thrust face varies according to the pressure in the pipeline, the internal diameter of the special or fitting, and the bearing capacity of the soil agai

26、nst which the thrust face bears. In the case of end caps, tees, and bends the area of the thrust face is calculated from the formula A = 0,785 FC b where A = area of thrust face, m 2 p = rated working pressure of the pipes adjacent to the special/fitting, kPa F = factor of safety d = nominal interna

27、l diameter of the fitting, m b = bearing capacity of the soil, kPa C = factor obtained from Table 1 NOTE: In certain cases the engineer may prefer to use the actual working pressure for p because a heavier class of pipe is to be used for reasons other than pressure. 0 TABLE 1 - VALVE OF C (= Sin - f

28、or bends) 2 I Angle of bend (8) I I In the case of a reducer it is important that the surface against which the thrust block acts is in undisturbed material (not in the trench backfill) and that adequate reinforcement is provided against bending. Frequently, the thrust at a reducer is taken in the p

29、ipe itself, in the same way that the thrust acts against a closed valve in a straight pipeline. The thrust area needed to support the unbalanced force is calculated from the formula where A, F and b are as given above, and d and ti are the larger and smaller nominal internal diameters of the reducer

30、, respectively, in metres. 1 2 Bearing in mind that the pipeline will be tested to 1,s times the specified working pressure, and that the selected bearing capacity of the soil b may have a safety factor in it, values must be determined for b, the safe bearinq capacity ot the soil, and F, the safety

31、factor. In the case of a valve a bearing area is needed below the block to support the mass of the valve. In addition to a thrust area to resist the pressure induced in a pipeline when the valve is closed, unless this pressure is absorbed by the wall of the pipe. Table 2 serves as a guide to obtaini

32、ng values of b for vertical loads. The figures in the table relate to undisturbed soil, a condition which is rarely achieved in trenches. The permissible horizontal load at shallow (600 mm) depths may be significantly lower than the values given in Column 3 of Table 2 for vertical loads. End caps an

33、d tees 11 1/4 O 22 1/2 O 45 O 90 O SABS 0120 : Part 3 Section L-1983 Medium-pressure pipe1 ines TABLE 2 - MAXIMUM SAFE REARING CAPACITY OF SUBSOIL UNDER HORlZONTAL FOUNDATICONS AT 60C mm DEPTH BELOW FINISHED GROUND LEVEL AND SUBJECT TO VERTICAL STATIC LOADING Type of rock or soil Artificially occurr

34、ing soils I Cohesive soils I Non-cohesive soils 1,escription of rock or soil Made-up qround, compacted flls, waste dumps,and the like - Very stiff clays, sandy clays, silty clays sandy silts, silty sands Stiff clays, sandy clays, silts, silty sands Firm clays, sandy clays, sandy silts, silty sands S

35、oft clays, sandy clays, sandy silts, silty sands Very soft clays, sandy clays, silty clays, clayey silts, and clayey sands Compact, well graded gravels, sands, and gravel-sand mixtures; permanently above all water tables Compact, well graded sands, gravels, and gravel-sand mixtures; possibly below t

36、he water table at any stage of the life of the structure Compact but poorly graded sands, gravels, and gravel-sand mixtures; permanently above all water tables Loose sands Fresh rock, massively bedded, intact, igneous, metamorphic, or sedimentary, requiring blasting for excavation Fresh rock, fractu

37、red or jointed, which can be excavated with difficulty by pneumatic picks, hut which normally requires light blasting Decomposed rock: to be assessed as a SOLI as above 3 Maximum safe bearing capaeil for vertical lcads, kPa By test only P- 390 - 490 195 - 390 l00 - 200 SO - l00 0 - 50 200 - 390 By t

38、est only Where the nominal diameters of pipelines are under 300 mm, a series of A4 sized specification drawings similar to Drawings L-3.2 - L-3.4 may he adequate provided that the applicable table of dimensions is completed. Typical tables of dimensions (applicable to Drawings L-3.2 - L-3.4) for asb

39、estos cement ipes to be field-tested to 1 800 kPa and subsoil with a maximum horizontal hearing capacity of 55 kPa are a9 01 lows: DRAWING 14-3.2 225 ZOO 1640 150 1210 100 740 530 Pipe liameter DRAWING L-3.3 DRAWING L-3.4 iameter SABS 0120 : Part 3 Section L-1983 Medium-pressure pipelines In the cas

40、e of pipelines of nominal diameter 300 mm and larger, high maximum working pressures, and bad soil conditions, give careful consideration to the means of support. Thrust or tie-back piles may be necessary. TOLERANCES Tolerances in Manholes and Other Structures (Subclause 6.4). State which of the dim

41、ensions shown on the drawings may not be reduced because they are minimum for clearance purposes and are therefore subject to a tolerance of ;!. When determining, from pipe layouts, the internal dimensions of manholes and other structures and when stating clearance dimensions on drawings, give caref

42、ul consideration to the minimum clearance dimensions that are practicable, not only for fixing bolts and nuts into flanges and couplings before and after walls have been built, but also for subsequent maintenance. Take flange and coupling diameters and thicknesses and widths into account. TESTING Te

43、st Pressures (Subclause 7.3.1). Calculate the maximum working pressure at each critical point on the route of the pipeline. Relate the test pressures to the actual design working pressures. Do not use figures that are unrealistic as they may lead to unnecessarily large anchor blocks, valves of highe

44、r pressure class than would otherwise be required, etc. Show test pressures on design drawings where possible. Test Requirements. To avoid problems that frequently occur during testing on site because different test pressures are required for different parts of the pipeline system, ensure that the h

45、ydraulic pressure test requirements for the pipes, the specials, and the valves in the pipeline are not in conflict. Leakage (Subclause 7.3.3). Subclause 7.3.3(b) of SABS 1200 L is based on the assumption that the parameters that determine permissible leakage rates are the same for non-absorbent pip

46、es (such as steel or PVC) as for absorbent pipes (such as AC). (See Subclause 3.2.9 of Section L of Part 5 of the code). APPLICABILITY OF OTHER CODES GENERAL. The relevant requirements of SABS 0100) are applicable. TEST PROCEDURES GENERAL. Apply the procedures specified in SABS 1200 L. QUALITY CONTR

47、OL AND OTHER CONSIDERATIONS GENERAL. Apply the relevant kecommendations of SABS 0157) to the design of medium-pressure pipelines. DISPUTES. Subclause 5.1.1 of SABS 1200 L was framed to reduce the risk of disputes in regard to identification of pipes and in regard to bedding. Refer also to Subclause

48、5.1 of Section LB, particularly in the case of large diameter flexible pipes. - 7) Structural use of cotrcretc. 8) Qual ity management systems. JOINT PROTECT W TO SAME SPECIFICATION AS PlPE COATING !/ CENTRE LOCATING STUDS (MIN 3) SLIP-ON COUPLING WITHOUT CENTRE REGISTER, 3 X M 20 316 STAINLESS STEE

49、L SET SCREWS (END OF SHANK TURNED EPOXY RESIN MINTED, AND MANUFACTUREDo) TO REMOVE THREAD FOR LENGTH OF 20) SPACED AT 1209 ON CLOSER GENERALLY IN ACCdRMNCE WlTH BS 534 ROUND ClRCUM FERENCE AND SEALED W lTH PTFE TAPE CC_- MACHINED COLLAR. FACE ZINC SPRAY COATED. FIBRE WASHER-“ MINIMUM THICKNESS 0.15 mm WHERE COATING PIPE COATING AS IS CEMENT MORTAR. FOR OTClER TYPES OF SPEClFlE D PROTECTION PAINTING SHALL BE COMPATIBLE WlTH COATING ,-,-,- -7 _- LINWO AS SPECIFIED is0 150 PIPE WALL THICKNESS (I) AS SPECIFIED IN SUBCLAUSE 3.4 .3 (