Linings

Along with technical and metallurgical advancement in piping materials, research on lining requirements for pipeand fittings has resulted in the development of linings to meet many different service requirements. AACCIIPPCCOO offersseveral types of linings, the most common being cement lining. Pipes and fittings furnished by AACCIIPPCCOO are offeredunlined or with linings as follows:

• Cement lined per ISO 4179 and AWWA C104 for water transmission lines and sewer force mains.

• Protecto 401 Lined – Ceramic Epoxy Lined for septic gravitysewers and sewer force mains.

• Special Linings for unusual service conditions. Please contact ACIPCO.

CCEEMMEENNTT LLIINNIINNGG Cement-mortar lining for ductile iron pipe and fittings for water service is in accordance withISO 4179 and AWWA C104. Cement-lined pipe is also furnished for sewage service and a number of other applications.

AACCIIPPCCOO applies a sulphate resisting cement-mortar lining to ductile iron pipe. The sulphate resisting cement-mortar lining is a Portland type cement per ASTM C150 and meets the chemical requirements of BS 4027. Thelining is applied by using a high-speed centrifugal process. By using this method, excellent quality control of the cement-mortar lining is maintained. The cement linings AACCIIPPCCOO produces are dense, smooth, uniform, and wellbonded to the pipe wall, and offer very little frictional resistance to the flow of water.

The pipe is spun at a very high rate accompanied by vibration to produce a dense lining. This high-speed liningbrings water and latence to the lining surface. The latence is immediately washed out of the pipe with water. Byusing this unique process developed by AACCIIPPCCOO, there is no need to grind linings or use additives to the cementmortar. The immediate result is a smooth, dense, and well-compacted cement-mortar lining.

After the application process, the linings are then cured in a controlled environment to prevent too rapid a loss ofmoisture from the mortar.

This table shows recommended thicknesses from ISO 4179 for cement-lined ductile iron pipe. Forsome service conditions, greater lining thickness may be preferred. Consult AACCIIPPCCOO for specific details.

RREESSIISSTTAANNCCEE TTOO SSOOFFTT AANNDD AACCIIDDIICC WWAATTEERRSSWhen cement-mortar linings are subjected to very soft water, calcium hydroxide, CA(OH)2, is leached. The con-centration of leachates increases with the aggressiveness of the water and its residual time in the pipe and is inversely proportional to the diameter of the pipe. These waters will also attack calcium silicate hydrates, whichform the larger portion of cement hydrates. Although calcium silicate hydrates are almost insoluble, soft waters canprogressively hydrolyze them into silica gels, resulting in a soft surface with reduced mechanical strength.

AACCIIPPCCOO 3366 IInntteerrnnaattiioonnaall PPiippee MMaannuuaall

Linings

Pipe Size Nominal Thickness(mm) (mm)

100-350 3350-600 5700-1200 61400-1600 9

Standard Cement Lining Thickness

Seal-coat will retard this leaching and attack to a great extent; however, as mentioned before, there are very fewcountries that have sufficiently aggressive waters to necessitate the use of a seal-coat. Also, such aggressive waters may cause toxic metals to leach from piping in customers’ homes, making it difficult to pass water quality standards requiring tests at first draw from customers’ taps. Therefore, water quality standards requiringbetter balanced water chemistry may cause these few communities to treat their water, and further diminish theneed for seal-coat.

Utilities or municipalities that are concerned that their water may be aggressive to cement-mortar linings without aseal-coat are encouraged to follow the procedure detailed in Section II.A., “Use of Seal-Coat,” in the Foreword tothe ANSI/AWWA C104/A21.4 Standard to determine if a cement-mortar lining without seal-coat will impart objectionable hardness or alkalinity to the water.

Also in instances where utilities or municipalities are concerned that water may be aggressive, they may want toconsider specifying thicker cement linings. Please contact AACCIIPPCCOO for details on cement linings thicker thanAWWA C104 or ISO 4179.

Standard non-seal-coated, cement-mortar-lined ductile iron pipe is generally considered to be suitable for continuous use at pH between 6 and 12. For service with pH outside this range, consult AACCIIPPCCOO.

Friction head loss or drop in pressure in a pipeline is an everyday concern for the waterworks engineer. Head-loss calculations are based on equations developed by hydraulic engineers after conducting numerous flowtests on actual working mains. Several formulas were developed by Darcy, Chezy, Cutter, Manning, Hazen-Williams,and others. Of these, the formula and tables prepared by Hazen-Williams have proved to be the most popular.

FFLLOOWW TTEESSTT RREESSUULLTTSS OONN CCEEMMEENNTT--MMOORRTTAARR--LLIINNEEDD DDUUCCTTIILLEEAANNDD GGRRAAYY IIRROONN PPIIPPEE

A pipe lining, to be satisfactory, must provide ahigh Hazen-Williams flow coefficient “C” initially and must have sufficient durability to main-tain a high flow coefficient over many years ofservice. Unless the lining meets the above requirement, its other properties, chemical orphysical, are of little significance. Numerous flowtests have been made on operating lines through-out the United States to determine how well cement-mortar linings meet these basic requirements. Tests on both new and old watermains have established the average value of “C”that can be expected of new cement-lined ironpipe, and have also provided a measure of thecontinued effectiveness of such linings over extended periods of service.

AACCIIPPCCOO 3377 IInntteerrnnaattiioonnaall PPiippee MMaannuuaall

Cement-mortar-lined ductile iron pipe has a Hazen-Williams “C” value of 140, a realistic value that is maintained over time.

For laminar, fully developed flow in a pipe, friction depends only on the Reynolds number (a function of velocity, inside pipe diameter, and the kinematic-viscosity of the fluid being transported). It is interesting to note that theroughness of the pipe wall is not considered. The reason is that, for the parabolic laminar flow velocity profile, verylittle of the flow comes in contact with the roughness elements of the wall surface; the velocities in the vicinity ofthe wall surface are quite low. When laminar flow exists, the fluid seems to flow as several layers, one on another.Because of the viscosity of the fluid, a shear stress is created between the layers of the fluid. Energy is lost fromthe fluid by the action of overcoming the frictional force produced by the shear stress.

FFLLOOWW CCOOEEFFFFIICCIIEENNTT OOFF CCEEMMEENNTT--MMOORRTTAARR LLIINNEEDD DDUUCCTTIILLEE IIRROONN PPIIPPEEFor turbulent flow of fluids in circular pipes, there is a layer of laminar flow adjacent to the pipe wall called the laminar sublayer. Even in turbulent boundary layers, this sublayer exists where laminar effects predominate. In thecase of a pipe, the greater the Reynolds number, the thinner the laminar sublayer is. It has already been noted thatthe roughness has no effect on the head loss for laminar flow. If the laminar sublayer is thicker than the roughnessof the pipe wall, then the flow is hydraulically smooth and the pipe has attained the ultimate in hydraulic efficiency.If this flow were plotted on the Moody diagram, it would coincide with the “smooth pipe” curve.

DIPRA and its predecessor, CIPRA, have long advocated a Hazen-Williams “C” value of 140 for use with cement-lined gray and ductile iron pipe. This recommendation of a “C” value of 140 for design purposes is sound. It recog-nizes that the real world of pipelines is a far cry from the gun-barrel geometry of the laboratory pipeline. Furthermore,DIPRA’s continued field testing of operational pipelines has shown a “C” value of 140 to be realistic, and one that ismaintained over time—even when transporting highly aggressive waters.

In all normally specified pipe sizes, cement-mortar-lined ductile iron pipe has an internal diameter that is largerthan the nominal diameter, which is larger than the nominal pipe size. For most substitute pipe materials, the insidediameter is equal to—or in some cases, even less than—the nominal pipe size. The head loss encountered in a piping system is much more sensitive to available pipe inside diameters than normal flow coefficients.

Cement lining will withstand normal handling; nevertheless, pipe or fittings may be found at times to havedamaged linings which need to be repaired before placing in service.

FFIIEELLDD RREEPPAAIIRR OOFF DDAAMMAAGGEEDD CCEEMMEENNTT LLIINNIINNGGSSAWWA C104, EN545 and ISO 4179 provide that damaged linings may be repaired, and the following repair procedure is recommended by AACCIIPPCCOO:

1. Cut out the damaged lining to the metal. Square the edges.

2. Thoroughly wet the cut-out area and adjoining lining.

3. With the damaged area cleaned and the adjoining lining wet, spread the mortar (see recommended on nextpage) evenly over the area to be patched. After the lining has become firm and adheres well to the surface, finishit with a wet paint brush or similar soft-bristle brush.

4. The repaired lining should be kept moist by placing a wet burlap over the required area of the pipe or fitting for at least 24 hours.

AACCIIPPCCOO 3388 IInntteerrnnaattiioonnaall PPiippee MMaannuuaall

RREECCOOMMMMEENNDDEEDD CCEEMMEENNTT MMIIXX Cement mix by volume: 3 Parts Portland Cement; 2 Parts Clean Sand; necessary water for slump of 125mm to 200mm. The sand should be free of clay and screened.

PPRREECCAAUUTTIIOONNSS1. Mortar for lining should not be used after it has been mixed for more than one hour.

2. Too rapid a loss of moisture from fresh linings due to hot weather or high wind will prevent proper cure, resulting in the lining being soft and powdery. To prevent this loss of moisture, (a) do not line hot castings and (b) close the ends of the castings with wet burlap.

3. Fresh linings which become frozen will not be serviceable. Avoid lining in freezing weather.

Pipe and fittings lined with special coatings are available from AACCIIPPCCOO on a special order basis. For more detailed information regarding lining selection, application parameters, and typical field topcoats, please contactAACCIIPPCCOO.

Ductile iron pipe is especially suited for pressure sewer applications because its standard wall thicknesses provide for high operating pressures with a minimum 20% surge allowance. Surges, or hydraulic transients, are avery serious problem for pressure sewers, as pump stations are vulnerable to power outages and surge controldevices for raw wastewater are not always dependable. The surge forces, which can rupture some piping materials, are caused by momentum in the liquid due to change in velocity.

Pressure sewers are designed much the same as water transmission lines. The Hazen-Williams formula is themost popular flow formula. The Hazen-Williams friction coefficient, C, is generally accepted as 140 for cement-mortar linings and 150 for epoxy linings. Special linings are not usually specified if the pipe is always flowing full andthe waste stream is domestic sewage. However, the designer has the option of special linings to resist H2S asdiscussed under Gravity Sewers. In either case, the hydraulic efficiency of ductile iron pipe, coupled with its larger-than-nominal inside diameter, results in reduced pumping costs over the life of the pipeline.

Piping for pressure sewers can be provided not only with push-on joints, but also with restrained joints having deflection capabilities after installation. All ductile iron force main piping can beinterfaced with pumps, lift stations, andplant piping with standard fittings andfactory-supplied spools.

AACCIIPPCCOO 3399 IInntteerrnnaattiioonnaall PPiippee MMaannuuaall

Ductile iron pipe is often used in difficult installations because of its great strength, jointintegrity, and its versatile and readily available

joints and fittings.