Below we provide the answers to several frequently asked questions regarding Ductile Iron Pipe installation. After the air has been expelled and the valve or valves segregating the part of the system under test have been closed, pressure is then normally applied with a hand pump, gasoline-powered pump, or fire department pumping equipment for large lines. After the main has been brought up to test pressure, it is held at least two hours and the make-up water measured with a displacement meter or by pumping the water from a vessel of known volume. The hydrostatic pressure test helps to identify damaged or defective pipe, fittings, joints, valves, or hydrants, and also the security of the thrust restraint system.
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Below we provide the answers to several frequently asked questions regarding Ductile Iron Pipe installation. After the air has been expelled and the valve or valves segregating the part of the system under test have been closed, pressure is then normally applied with a hand pump, gasoline-powered pump, or fire department pumping equipment for large lines.
After the main has been brought up to test pressure, it is held at least two hours and the make-up water measured with a displacement meter or by pumping the water from a vessel of known volume. The hydrostatic pressure test helps to identify damaged or defective pipe, fittings, joints, valves, or hydrants, and also the security of the thrust restraint system.
A: Yes. Section 4. Repair is achieved by first cutting out the defective or damaged lining to the metal so that the edges of the lining not removed are reasonably perpendicular to the pipe wall or slightly undercut.
A stiff mortar is then prepared, containing not less than one part of cement to two parts of sand, by volume. This mortar is applied to the cutout area and troweled smooth with adjoining lining. To provide for proper curing of patches by preventing too rapid of a moisture loss from the mortar, the patched area is normally seal-coated immediately after any surface water evaporates, or alternatively the area is kept moist e.
Of course, in potable water-related applications, no patch or curing components should be used in the repair that would negatively affect health or water quality.
A: No. Casing pipes should normally be 6- to 8-inches larger than the outside diameter of the Ductile Iron Pipe bells. Insulating chocks, skids, or spacers normally should be placed on the Ductile Iron Pipe carrier pipe , or affixed to the casing, to ensure approximate centering of the carrier pipe within the casing pipe. In order to further stabilize the Ductile Iron Pipe, normally the area between the casing pipe and the carrier pipe is partially filled with sand or grout.
If the annulus is completely filled, it can be argued that external loads might understandably be transferred to the carrier pipe. If restrained joints are needed to resist thrust forces on a Ductile Iron Pipeline for example, to anchor unblocked bends immediately outside the casing , and the required restrained length extends into a casing pipe, it would then be necessary to install restrained joint pipe into, and often extending completely through, the casing pipe.
In normal buried service, the function of restrained joint pipe is to transfer thrust forces to the soil structure. Therefore, if the annular space between the two pipes is not grouted, the length of restrained pipe inside the casing should not normally be considered as part of the restrained length in a thrust calculation to balance the thrust force. Ductile Iron Pipe can, and has been used for both directional drilling and microtunneling installations.
The methods involve forming a hole a little larger than the outside diameter of the pipe joint. The Ductile Iron Pipe is then pushed or pulled through the hole.
When the pipe is pulled into position, restrained joints are utilized. Also, specially designed and manufactured Ductile Iron Microtunneling Pipe is currently available. Consequently, the bell sockets are different and the gaskets are not interchangeable. Proper gaskets for both designs are readily available. Therefore, the direction of the bells is not functionally related to the direction of flow within the main. It is common practice — but not mandatory — to lay pipe with the bells facing the direction in which work is progressing.
When the main is being laid up a slope, for example, the pipe is frequently laid with the bells facing uphill for ease of installation. Is this proper? A: Not necessarily. Additionally, possible damage might occur to valves and appurtenances that may be rated at lower pressures. For an example, assume a inch Ductile Iron Pipeline is to operate at psi working pressure. In addition, C states that the test pressure shall not exceed pipe or thrust restraint design pressures.
For inch diameter Ductile Iron Pipe, the lowest pressure class available is psi. A specification calling for a test pressure of 1. This would require thrust blocks to be larger and restrained joint systems to be longer than required. This could result in an unnecessarily proportional movement of the thrust restraint system, as well. Is this normal, and if so, how can field rounding be accomplished? Accordingly, pipes selected for cutting should be field gauged.
An MJ gland inserted over the barrel might serve as a convenient indicator for this purpose. Some pipes, especially in the larger diameters, may be out-of-round to the degree that they will need to be rounded after cutting by jacking or other methods to facilitate making the joint. This is a normal occurrence and does not in any way affect the serviceability of Ductile Iron Pipe. Instructions for rounding their products can be obtained from the pipe manufacturers.
Is this OK? A: Cradled supports, following the contour of the pipe, are recommended in order to minimize stress concentrations at the supports. The amount of stress is dependent on pipe size, pipe wall thickness, type of support, distance between supports, location of supports along the pipe length, loading, etc. Formulas addressing these high stress concentrations for cylindrical shells and pipes have been published in technical literature.
When applying these formulas to Ductile Iron Pipe in aboveground installations, utilizing one support per length of pipe located immediately behind the bell, the resultant stresses normally are not considered critical for small diameters. However, the stress analysis is difficult and the results are rendered uncertain by doubtful boundary conditions; therefore, the ultimate responsibility of such a design rests with the design engineer.
Supports should not be placed under spigots adjacent to bells, due to higher developed stresses and possible undesirable effects on joints. Also, flat supports are normally not used for underground installations due to possible high loadings. A: One method of installing Ductile Iron Pipe in unstable soils is to install the pipe on piers or pilings above or underground. Because of the flexibility of the joints, Ductile Iron Pipe supported at intervals usually requires that at least one support be placed under each length of pipe for stability.
Another method is to lay restrained joint pipe through the unstable soil area and anchor the pipeline on both sides outside of said area. The anchoring may be achieved by means of concrete abutments, or by continuing the restrained joint pipe an adequate distance beyond the unstable soil. In such an installation, consideration needs to be given to — among other things — maximum joint deflections, maximum axial force, anchor design, etc.
In some cases, the only consideration needed is the use of long-pattern sleeves on firm ground along with allowing the pipeline to settle. A: Unlike some substitute materials, Ductile Iron Pipe does not deteriorate and is impermeable when subjected to hydrocarbons. With a Ductile Iron Pipe system, only the gasketed joints may be subject to permeation. However, due to the relatively small contact area between the gasket and potable water, permeation through Ductile Iron Pipe gasketed joints is not likely to be a significant source of contamination unless the gasket is exposed to neat organic chemicals for long periods of time.
No incident of permeation of Ductile Iron pipe and only one incident of permeation of gaskets was reported. Some gasket materials resist permeation and degradation from hydrocarbons better than others.
While tests on other gasket materials show promise, the results to date indicate that fluorocarbon rubber gaskets are the most resistant to permeation.
Gaskets of this material are available for use with Ductile Iron Pipelines installed in areas contaminated by or susceptible to contamination by hydrocarbons. Soils contaminated with hydrocarbons should not adversely affect the performance of polyethylene encasement as a corrosion protection means for Ductile Iron Pipe. Polyethylene encasement protects the pipe by preventing direct contact with corrosive soil.
If this barrier is not violated, the corrosion protection system is not compromised. Although hydrocarbons will permeate the polyethylene they are not considered corrosive to iron pipe.
This edition approved June 6, These procedures should not be applied for air-pressure testing because of the serious safety hazards involved. Use of a test pressure greater than the rated valve pressure can result in trapped test pressure between the gates of a double-disc gate valve. For tests at these pressures, the test setup should include a provision, independent of the valve, to reduce the line pressure to the rated valve pressure on completion of the test.
Frequently Asked Questions - Installation
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