FAQ: Can AC power lines cause corrosion of Ductile Iron pipe?
Because buried Ductile Iron pipelines are electrically discontinuous and are essentially grounded for their entire length, overhead AC power lines normally don't impose corrosion or safety concerns.
A consequence of AC power lines and buried pipelines sharing rights-of-way is that AC voltages and currents can be induced by magnetic induction on the pipelines. The magnitude of the induced voltage and current on the pipeline is a function of a number of variables, including the length of pipeline paralleling the AC power line, the longitudinal resistance of the pipeline, and the resistance of the pipeline coating.
Ductile Iron pipe is manufactured in nominal 18- and 20-foot lengths and employs a rubber-gasketed jointing system. These rubber-gasketed joints offer electrical resistance that can vary from a fraction of an ohm to several ohms but nevertheless is sufficient for Ductile Iron pipelines to be considered electrically discontinuous. In effect, the rubber-gasketed joints normally segment the pipe, restricting its electrically continuous length, and prevent magnetic induction from being a problem. Also, in most cases, Ductile Iron pipelines are installed bare with only a standard 1-mil asphaltic coating and therefore are effectively grounded for their entire length, which further prevents magnetic induction on the pipeline.
During construction of Ductile Iron pipelines in the vicinity of overhead AC power lines, certain safety precautions should be followed, e.g., "limit of approach" regulations governing construction equipment, grounding straps, chains attached to rubber-tired vehicles to provide a ground, grounding mats, etc., especially if safety concerns are heightened due to the use of joint bonding and dielectric coatings.
FAQ: Can cement-mortar linings be repaired in the field?
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.g. with wet rags or burlap over the area or with the ends of the pipe or fitting taped over with plastic film, etc.). 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.
FAQ: Can Ductile Iron products be glass lined?
Yes, Ductile Iron products can be successfully Glass lined. Glass lined pipe and fittings have been specified and utilized as a deterrent to interior build-up and clogging of problematic sludge and scum piping systems in wastewater and sewage treatment facilities for over 40 years. Not only is the excellent non-stick characteristic effective in combating the build-up of grease, sludge, and scum, but has been found to be the only deterrent to Struvite and Vivionite build-up as well.
FAQ: What lining is typically used for Ductile Iron pipe transporting seawater?
Double thickness cement mortar lining in accordance with ANSI/AWWA C104/A21.4, Section 4.7.2., with seal coat in accordance with section 4.11. The cement in the cement mortar lining shall conform to ASTM C150, Type V. The internal joint areas coming in contact with the seawater, the "wetted areas", should be coated with Induron PE-54 epoxy or they can be wrapped with Denso tape. Denso tape can be purchased through DENSO NORTH AMERICA, INC. in Houston, TX - Phone No. 281-821-3355 or www.densoa.com.
FAQ: What means of joint restraint are available?
U.S. Pipe's primary method of thrust restraint are restrained joints.
A column of liquid moving through a pipeline has momentum or force that tends to separate the joints at changes in direction (bends and tees), stops (plugs, caps, or closed valves), and changes in size (reducers). Some means must be used to prevent joint separation to maintain the integrity of the pipeline. Three such means are thrust blocks, tie rods, and restrained joints.
Thrust blocks are usually poured-in-place concrete. They must be engineered with full knowledge of the pipeline operating characteristics and of soil type and bearing strength. They must bear against virgin soil, because thrust forces in the pipeline are transmitted through the thrust block to the soil. Depending on these conditions, thrust blocks can be quite massive. The use of thrust blocks can delay completion of the project to allow the concrete to cure adequately before applying test pressure to the pipeline. If future construction disturbs the thrust block or the surrounding soil, joint restraint and the integrity of the pipeline can be jeopardized.
Tie rods usually involve some sort of fabricated steel harness on either side of the joint held together by tie-rods. This type of joint restraint is generally labor intensive. A tie-rod type of joint restraint must be adequately protected against weakening by corrosion, or else the joint restraint and integrity of the pipeline can be jeopardized.
Restrained joints are designed to hold the joint together against a rated pressure while the pipeline transfers the thrust force to the surrounding soil envelope. In order to calculate the footage of restrained pipeline necessary for the thrust force to be fully dissipated to the soil, it is necessary to know pipe diameter, maximum anticipated internal pressure, depth of cover, soil type, and trench construction type, as well as the configuration (e.g., bend angle) requiring restraint. The calculated restrained footage must be installed on each side of the fitting. Since polyethylene encasement for external corrosion protection reduces the friction between the pipeline and the surrounding soil, the calculated restrained footage is usually multiplied by a factor of 1.5 for pipelines where polyethylene encasement is to be installed.
Mechanical joint retainer glands, both common and proprietary design, are available for use where such devices must be used (e.g., a special valve or meter). However, U.S. Pipe does not recommend their use. Restrained push-on joints manufactured by U.S. Pipe are less susceptible to external corrosion, offer appreciably more deflection, and are much less labor-intensive to install.
FAQ: What types of joints can be buried?
USP recommends that only flexible joints be buried i.e. Mechanical Joint, TYTON JOINT® and TR FLEX®.
FAQ: What are the UL and FM listings for U.S. Pipe products?
If possible, the pipe can be inserted to make–up the joint, after assembly the jack can be removed. If the pipe will be inserted into a Mechanical Joint bell, the gland can be slid over the end to hold the pipe round while the joint is made. TYTON JOINT® and TR FLEX® bells are designed to round the pipe as long as the pipe will start into the throat of the bell. Once the pipe is pushed past the gasket it will seal.
FAQ: Where can I find information on safe Ductile Iron pipe handling when unloading from trucks and/or railroad cars?
This information can be found in U.S. Pipe's guide Safe Packaging and Shipping and also the Installation Guide for Ductile Iron Pipe, published by the Ductile Iron Pipe Research Association (DIPRA). Copies can be obtained from your local U.S. Pipe Sales Representative.
FAQ: Which way should the bells face in relation to the flow?
Some Ductile Iron users specify that pipe be installed with the bell end facing the direction of flow. This theory emanates from the pre-pressure joint era, when common joint sealing materials were cement mortar and jute, asphalt and jute, just asphalt, and various other materials. The theory is predicated on the liquid flowing into the next pipe length prior to leaving the existing length.
Since the introduction of the TYTON JOINT® Pipe in 1956, it has been subjected to various tests. From this testing it has been determined the properly assembled joint will withstand a 14 psi vacuum, a 1,000 psi internal pressure, and a 430 psi external pressure without leakage. Given these results, it is obvious flow direction within the pipeline is not an installation factor.