GALVANIZED IRON PIPE

Transcription

1 UNIVERSITY OF SAN CARLOS Technological Center Nasipit, Talamban GALVANIZED IRON PIPE SUBMITTED BY: MANDAWE, CHRISTIAN VINCENT MAGADAN, JOHN BACAY, KYLE SUBMITTED TO: DR. LORETERO

2 GALVANIZED IRON AND STEEL: CHARACTERISTICS, USES AND PROBLEMS This standard includes general information on the characteristics and common uses of galvanized iron and steel and identifies typical problems associated with these materials along with common causes of its deterioration. INTRODUCTION Galvanizing is a process of coating iron or steel with zinc in order to provide greater protection against corrosion for the iron or steel base. The process of galvanizing sheet iron was developed simultaneously in France and England in Both of these methods employed a "hot dipping" process to coat sheet iron with zinc. Like tinplate, early galvanized metals were hand dipped. Today almost all galvanized iron and steel is electroplated. The following are the most common methods for applying protective coatings of zinc to iron and steel: 1. Hot-dip Galvanizing: The immersion of iron or steel in molten zinc, after the surface of the base metal has been properly cleaned. a. This process gives a relatively thick coating of zinc that freezes into a crystalline surface pattern known as spangles. b. During the process, a multiple layered structure of ironor steel-zinc alloys is formed between the inner surface of the zinc coating and the iron or steel. These middle layers tend to be hard and brittle and may peel or flake if the iron or steel element is bent. 2. Electrogalvanizing: The immersion of iron or steel in an electrolyte, a solution of zinc sulfate or cyanide. Electrolytic action deposits a coating of pure zinc on the surface of the iron or steel. Advantages: a. The thickness of the coating can be accurately controlled using this process. Limitations: a. The thick coatings provided by the hot-dip galvanizing

3 process are not usually possible with this method. 3. Sherardizing: The placing of a thoroughly cleaned iron or steel element in an air-free enclosure where it is surrounded by metallic zinc dust. The architectural element is then heated and a thin, zinc alloy coating is produced. Advantages: a. The coating will conform to the configurations of the element. Limitations: a. This process is usually limited to relatively small objects. 4. Metallic Spraying: The application of a fine spray of molten zinc to a clean iron or steel element. The coating can then be heated and fused with the surface of the iron or steel to produce an alloy. Advantages: a. Coating is less brittle than those produced by some of the other processes. b. Coating will not peel or flake on bending. Limitations: a. The coating is more porous and becomes impermeable with time as products of corrosion fill in the pores. 5. Painting: Paint containing zinc dust pigments may be applied as a protective coating to galvanized iron and steel. Advantages: a. The paint may be applied in an situ. Limitations: a. This is a less effective method of zinc coating than the others listed above. b. Paint does not adhere well to pure zinc, nor to galvanized iron or steel. c. When paint peels from galvanized iron and steel, it

4 usually comes off completely along with the primer, exposing a clean metal surface. d. If sheetmetal features are well-painted, it is difficult to identify whether they are zinc or galvanized iron or steel. 1) If the metal is galvanized, it will have a spangled appearance and may show some rust or rust stains from the iron or steel base metal. Both galvanized iron and steel are magnetic 2) If the metal is cast or pressed zinc, it will have a grayish-white appearance. Pure zinc is not magnetic so a magnet will not stick. 3) A magnet test will also reveal whether a painted sheetmetal feature is zinc or galvanized iron or steel. Both galvanized iron and steel are magnetic, pure zinc is not. PROBLEMS AND DETERIORATION Problems may be classified into two broad categories: 1) Natural or inherent problems based on the characteristics of the material and the conditions of the exposure, and 2) Vandalism and human-induced problems. Although there is some overlap between the two categories, the inherent material deterioration problems generally occur gradually over long periods of time, at predictable rates and require appropriate routine or preventive maintenance to control. Conversely, many human induced problems, (especially vandalism), are random in occurrence; can produce catastrophic results; are difficult to prevent, and require emergency action to mitigate. Some human induced problems, however, are predictable and occur routinely. NATURAL OR INHERENT PROBLEMS CORROSION: Galvanized iron and steel's resistance to corrosion depends largely on the type and thickness of the protective zinc coating and the type of corrosive environment. The zinc coating on galvanized iron and steel may be corroded by: Acids, strong alkalis, and is particularly vulnerable to corrosion by sulfur acids produced by hydrogen sulfide and sulfur dioxide pollution in urban atmospheres.

5 1. Natural Corrosion: a. The zinc coating on galvanized iron and steel develops a natural carbonate on its surface by exposure to the atmosphere and by the action of rainwater. This coating, however, is usually not thick enough to protect the metal from further corrosion. b. The carbonate can become brittle and crusty and eventually split, exposing fresh zinc for corrosion. Since the zinc coating on the iron or steel is very thin, it can corrode up to the base metal exposing the base to the atmosphere as well. c. In industrial atmospheres, the zinc carbonate coating can be broken down by the same acids that attack zinc. These acids convert the carbonate to zinc sulfate, which is water soluble and washes away with rainwater, often staining the adjacent building elements. 2. Chemical Corrosion: a. Galvanized iron and steel have good corrosion resistance to: Concrete, mortar, lead, tin, zinc and aluminum. b. Galvanized iron and steel have poor corrosion resistance to: Plasters and cements (especially Portland cements) containing chlorides and sulfates, acidic rainwater runoff from roofs with wood shingles (redwood, cedar, oak, and sweet chestnut), moss, or lichen, condensation on the underside of zinc plates and ponded water on the exterior surfaces of the zinc features 3. Galvanic (Electrochemical) Corrosion: This type of corrosion is an electrolytic reaction between the zinc coating and dissimilar metals when in the presence of an electrolyte such as rain, dew, fog or condensation. a. To prevent the corrosion of the zinc coating due to galvanic action, contact between galvanized items and copper or pure iron or steel should be avoided. b. Galvanized iron and steel are corrosive to all metals except lead, tin, zinc and aluminum. c. Applying a protective coating such as paint to galvanized iron and steel will alleviate the problems caused by corrosion of the protective zinc coating.

6 VANDALISM OR HUMAN-INDUCED PROBLEMS Mechanical or Physical Deterioration: 1. Abrasion: Causes removal of the protective metal surface. The soft zinc coating on galvanized iron and steel make it vulnerable to abrasion damage, especially at roof valleys and gutters where the coating can be worn paper-thin by the scouring of rainwater. 2. Fatigue: A type of deterioration caused by cyclical expansion and contraction of sheet metal features, especially roofs, without adequate provisions for this movement. a. Zinc is very vulnerable to fatigue failure because it has a relatively high coefficient of thermal expansion. b. Fatigue failure may also occur when the metal sheets are too thin to resist buckling and sagging. It results in the bulging and tearing of the zinc coating and resembles a cut or a crack. 3. Creep: The permanent distortion of a soft metal which has been stretched due to its own weight. Thin areas of the metal are especially prone to failure. Creep may be prevented by the use of properly sized individual sheets and bays, properly designed joints, and an adequate number of fasteners. 4. Distortion: Permanent deformation or failure may occur when a metal is overloaded beyond its yield point because of increased live or dead loads, thermal stresses, or structural modifications altering a stress regime.

7 Connection Failure: 1. Wind and thermal stress can damage a roof by pulling joints apart and loosening fasteners. Galvanized Iron Pipe Galvanized iron pipes are actually steel pipes that are covered with a protective layer of zinc. 1960s. Galvanized pipes were installed in many homes that were built before the Galvanized Iron Pipe on Water Safety Zinc erodes from galvanized pipes. Corrosion can build-up on the inside walls of the pipes and creates the potential for lead to accumulate over time. Corrosion in galvanized pipes can lead to lower water pressure and water quality issues. Customers can identify if it is galvanized iron pipe if the scratched area of the pipe will be a silver-gray colored and have threads. Customers who have galvanized and lead service lines can have lead released in tap water from the corroded pipe lines. Although people replaced their lead service line, there can be traces of lead released from the galvanized pipes. Galvanized iron pipe can accumulate lead in water released from corroded service lines. In order to prevent lead from flowing with the water, they should replace both the corroded service line and the galvanized iron pipe. The rusted area of galvanized iron pipes can contain deep layers of iron and lead that have accumulated for years and can still contaminate the water.

8 Galvanized Steel Water Supply Piping in buildings This article discusses Galvanized iron pipe inspection, diagnosis, repair o Diagnosing & repairing clogged galvanized iron water supply pipes o Diagnosing & repairing clogged galvanized iron drain pipes o Black iron water piping o Dielectric fittings to connect copper to galvanized iron piping - avoid corrosion o Life expectancy of galvanized iron or galvanized steel water piping The articles at this website will answer most questions about water supply & drain piping, wells, & water tanks as well as many other building plumbing system inspection or defect topics. New York State License # (inception to 2008). Galvanized steel (iron) is not commonly used as a water entry service pipe, although galvanized steel fittings may be found at the point of entry into the house. Where galvanized service piping is used, it is typically at least 1 1/4-inch diameter. The word galvanized means zinc-coated. The coating helps prevent the steel from rusting. Galvanized steel (iron) piping was common until roughly This piping typically lasts 40 to 60 years. Some lower-quality pipes do not last as long and there are some oversized pipes still in use after 60 years. Where it is found today in singlefamily homes, it is usually near the end of its life. "Galvanized" refers to a metal plating process that coated iron or steel water pipe surfaces with a corrosion-resistant zinc surface.

9 Life expectancy of galvanized steel piping: Galvanized steel supply pipes are typically 1/2-inch diameter. The connections are threaded. When the pipe corrodes, the rust accumulation inside the pipe chokes down the diameter of the pipe, resulting in poor water pressure. Rust also attacks the pipe walls, making the walls thinner. Eventually, the pipe will rust through, usually at the joints first, resulting in leakage. Galvanized iron water supply pipe can also burst from freezing, and may split at seams depending on how the pipe was manufactured. Galvanized iron water supply (or drains) are more likely to burst by splitting or fracturing if pipe sections are corroded from an external cause such as corrosive water or by contact with materials or surfaces that increase the pipe corrosion rate. Our photo (above left) illustrates a galvanized iron pipe failure (and replacement) at a spa in Lourdes, Mexico. < Black Iron Piping in buildings Uncommon for water supply piping but found as gas piping, oil piping, and some other uses, is black iron pipe - essentially the same material as galvanized iron piping, but without the protective galvanized zinc coating. Diagnosing rusty galvanized steel piping As rust builds up inside the pipe, a brownish color is often noted in the water when a faucet is turned on, especially after several days of inactivity. This rust in the water usually dissipates after a few seconds. As we mentioned in our discussion of lead water entry mains piping, many of the old lead service lines were connected to a galvanized nipple a short piece of steel pipe that was often in contact with the soil. This pipe rusts on the outside and inside, and may be close to the end of its life. It is often wise to replace this as a precautionary measure. Galvanized steel piping will often leak first at the joints. Steel pipe has threads cut into it where it joins a fitting. The pipe wall is thinner at the threaded connections. As the piping rusts from the inside, the pipe rusts through first at the threaded connections, where the pipe wall is thinner. Our photo (above-left) shows silver-colored water supply piping that is probably galvanized iron. But this pipe looks a little too good. We suspect from the photo that the pipe has been painted.

10 Watch out: because it's easy to spray-paint silver or aluminum paint on metal pipes in buildings, you may need to check closely or use a magnet to be sure that the silver-colored water supply piping you are examining is really galvanized iron (magnetic) and not painted brass (not magnetic) or painted black iron pipe (magnetic, paint scrapes off). Also, as our photo above demonstrates, don't miss nearby visually obvious safety hazards like the missing discharge tube on the pressure relief valve on that water heater! If someone spray painted brass water supply piping with aluminum paint you could be fooled. Galvanized Steel Pipe to Copper Pipe Connections - Dielectric Fittings In most jurisdictions plumbing codes require the use of a dielectric fitting when joining steel piping to copper or other metals; some plumbing jurisdictions permit use of a 6-inch brass nipple in this location as an alternative to diaelectric fittings. Why? When connecting iron or galvanized iron pipes to copper in buildings, often galvanic corrosion and ultimately plumbing leaks will occur at the meeting of these two dissimilar metals. Using a dielectric fitting (misspelled as diaelectric or dieelectric) or an approved brass fitting to connect these two metals, or more commonly, using plastic or bronze fittings at the joint between these two metals will avoid future corrosion and leaks. Details about the requirement for dielectric fittings at copper to steel pipe connetions are atdielectric FITTINGS and more about the galvanic scale and corrosion between dissimilar metals is at GALVANIC SCALE & METAL CORROSION. At ELECTRICAL GROUND SYSTEM INSPECTION we discuss the need for a jumper wire around interruptions in the metal piping system, such as where a diaelect4ric fitting is installed or where a water meter interrupts continuity. Galvanized Steel Drain Piping in buildings Our photographs (below) show galvanized drain piping in use in buildings. At below left, the cleanout in a galvanized drain line has been lost, plugged with whoknows-what, and is an odor and leak source. At below-right, the rope trying to secure the galvanized drain line to the cast iron sewer piping confirm a history of leak troubles and improper plumbing connections.

11 Clogged Galvanized Steel Plumbing Drains When diagnosing clogged drain piping in a building (CLOGGED DRAIN DIAGNOSIS & REPAIR), an important distinction is between a specific point of clogging and piping that really needs total replacement. If a point-clog exists it can generally be cleared successfully. When mineral deposits or rust have decreased the interior diameter of galvanized iron pipe drains so that drainage is poor, plumbers use two methods to try to clear the lines: 1. Snaking the galvanized drain pipe, sometimes euphemistically "running a wire" through the drains. We paid Plass the Plumber a stiff fee to provide this ineffective service in Poughkeepsie, leading to a big bill and no improvement in the piping. Eventually we opened the walls and cut open the drain line to see that only a very tiny internal diameter of drainage was left in a rust and mineral-clogged pipe. 2. Using acid drain cleaners. This process might work if the drain pipes are not too badly clogged and if the steel or iron is otherwise in good condition. Beware of running acid into septic systems Galvanized steel or iron Galvanized steel or iron was the traditional piping material in the plumbing industry for the conveyance of water and wastewater. The term galvanizing once referred to hot dipped galvanizing,

12 in other words total immersion in molten zinc after pretreatment cleaning. This technology afforded a reasonable level of internal and external protection to the metal pipe. In more recent times, the use of electroplating technologies has provided a more attractive external finish, but little or no internal protection. Although still included in many codes of practice throughout the world, the popularity of galvanized piping is declining. It is still being used extensively in the fire protection industry, but overall there are increasing limitations on how and where galvanized piping may be used. Internal and external corrosion is a particular problem where galvanized steel or iron piping is connected to dissimilar materials, such as copper alloy (brass) in taps and valves. Internal corrosion can add iron, which causes an undesirable taste and may also cause unsightly precipitation of iron salts on clothes. Aesthetic guidelines contained in the WHO Guidelines for Drinking-water Quality address these matters. 10. STANDARDS FOR MATERIALS USED IN PLUMBING SYSTEMS HEALTH ASPECTS OF PLUMBING The use of galvanized steel or iron as a conduit for drinking-water is a greater problem where the water flow is slow or static for periods of time due to rust discoloration caused by internal corrosion. Galvanized steel or iron piping may also impart an unpalatable taste and smell to the water conveyed under corrosive conditions. Galvanized steel piping systems are generally accepted for outdoor use, but because of the size or bulk of the pipe and fittings, and the inflexibility of such systems overall, the material is not desirable for internal water plumbing. Galvanized pipe is heavy to handle and is generally joined by threading and screwing the components together. This is a lengthy procedure when compared to the assembly of competing non-metallic pipework systems.

13 References: Books Engineering Materials: Properties Selection by Kenneth and Michael Budinski Websites id=8c7pxhnqje4c&pg=pa696&lpg=pa696&dq=galvanized+iron+pipe+mate rial+test&source=bl&ots=tqesmgpqoa&sig=x6wsyc8iykcktm2liu4niepe _JE&hl=en&sa=X&ved=0CEYQ6AEwBWoVChMI4OSBtKTyAIVZBOmCh3pwguB#v=onepage&q=galvanized%20iron%20pipe %20material%20test&f=false r_hot-dip_galvanizing.pdf