Sabtu, 28 November 2015
Jumat, 27 November 2015
NDT
Methods
NDT methods may rely upon use of electromagnetic radiation, sound, and inherent properties of materials to examine samples. This includes some kinds of microscopy to examine external surfaces in detail, although sample preparation techniques for metallography, optical microscopy and electron microscopy are generally destructive as the surfaces must be made smooth through polishing or the sample must be electron transparent in thickness. The inside of a sample can be examined with penetrating radiation, such as X-rays, neutrons or terahertz radiation. Sound waves are utilized in the case of ultrasonic testing. Contrast between a defect and the bulk of the sample may be enhanced for visual examination by the unaided eye by using liquids to penetrate fatigue cracks. One method (liquid penetrant testing) involves using dyes, fluorescent or non-fluorescent, in fluids for non-magnetic materials, usually metals. Another commonly used NDT method used on ferrous materials involves the application of fine iron particles (either liquid or dry dust) that are applied to a part while it is in an externally magnetized state (magnetic-particle testing). The particles will be attracted to leakage fields within the test object, and form on the objects surface. Magnetic particle testing can reveal surface & some sub-surface defects within the part. Thermoelectric effect (or use of the Seebeck effect) uses thermal properties of an alloy to quickly and easily characterize many alloys. The chemical test, or chemical spot test method, utilizes application of sensitive chemicals that can indicate the presence of individual alloying elements. Electrochemical methods, such as electrochemical fatigue crack sensors, utilize the tendency of metal structural material to oxidize readily in order to detect progressive damage.
Analyzing and documenting a non-destructive failure mode can also be accomplished using a high-speed camera recording continuously (movie-loop) until the failure is detected. Detecting the failure can be accomplished using a sound detector or stress gauge which produces a signal to trigger the high-speed camera. These high-speed cameras have advanced recording modes to capture some non-destructive failures.[5] After the failure the high-speed camera will stop recording. The capture images can be played back in slow motion showing precisely what happen before, during and after the non-destructive event, image by image.
Applications
NDT is used in a variety of settings that covers a wide range of industrial activity, with new NDT methods and applications, being continuously developed. Non-destructive testing methods are routinely applied in industries where a failure of a component would cause significant hazard or economic loss, such as in transportation, pressure vessels, building structures, piping, and hoisting equipment.
Weld verification
1. Section of material with a surface-breaking crack that is not visible to the naked eye.
2. Penetrant is applied to the surface.
3. Excess penetrant is removed.
4. Developer is applied, rendering the crack visible.
In manufacturing, welds are commonly used to join two or more metal parts. Because these connections may encounter loads and fatigue during product lifetime, there is a chance that they may fail if not created to proper specification. For example, the base metal must reach a certain temperature during the welding process, must cool at a specific rate, and must be welded with compatible materials or the joint may not be strong enough to hold the parts together, or cracks may form in the weld causing it to fail. The typical welding defects (lack of fusion of the weld to the base metal, cracks or porosity inside the weld, and variations in weld density) could cause a structure to break or a pipeline to rupture.
Welds may be tested using NDT techniques such as industrial radiography or industrial CT scanning using X-rays or gamma rays, ultrasonic testing, liquid penetrant testing, magnetic particle inspection or via eddy current. In a proper weld, these tests would indicate a lack of cracks in the radiograph, show clear passage of sound through the weld and back, or indicate a clear surface without penetrant captured in cracks.
Welding techniques may also be actively monitored with acoustic emission techniques before production to design the best set of parameters to use to properly join two materials.[6] In the case of high stress or safety critical welds, weld monitoring will be employed to confirm the specified welding parameters (arc current, arc voltage, travel speed, heat input etc.) are being adhered to those stated in the welding procedure. This verifies the weld as correct to procedure prior to nondestructive evaluation and metallurgy tests.
Structural mechanics
Structure can be complex systems that undergo different loads during their lifetime, e.g. Lithium-ion batteries.[7] Some complex structures, such as the turbo machinery in a liquid-fuel rocket, can also cost millions of dollars. Engineers will commonly model these structures as coupled second-order systems, approximating dynamic structure components with springs, masses, and dampers. The resulting sets of differential equations are then used to derive a transfer function that models the behavior of the system.
In NDT, the structure undergoes a dynamic input, such as the tap of a hammer or a controlled impulse. Key properties, such as displacement or acceleration at different points of the structure, are measured as the corresponding output. This output is recorded and compared to the corresponding output given by the transfer function and the known input. Differences may indicate an inappropriate model (which may alert engineers to unpredicted instabilities or performance outside of tolerances), failed components, or an inadequate control system.
Radiography in medicine
Chest radiography indicating a peripheral bronchial carcinoma.
As a system, the human body is difficult to model as a complete transfer function. Elements of the body, however, such as bones or molecules, have a known response to certain radiographic inputs, such as x-rays or magnetic resonance. Coupled with the controlled introduction of a known element, such as digested barium, radiography can be used to image parts or functions of the body by measuring and interpreting the response to the radiographic input. In this manner, many bone fractures and diseases may be detected and localized in preparation for treatment. X-rays may also be used to examine the interior of mechanical systems in manufacturing using NDT techniques, as well.
Notable events in early industrial NDT
1854 Hartford, Connecticut: a boiler at the Fales and Gray Car works explodes, killing 21 people and seriously injuring 50. Within a decade, the State of Connecticut passes a law requiring annual inspection (in this case visual) of boilers.
1880 - 1920 The "Oil and Whiting" method of crack detection[8] is used in the railroad industry to find cracks in heavy steel parts. (A part is soaked in thinned oil, then painted with a white coating that dries to a powder. Oil seeping out from cracks turns the white powder brown, allowing the cracks to be detected.) This was the precursor to modern liquid penetrant tests.
1895 Wilhelm Conrad Röntgen discovers what are now known as X-rays. In his first paper he discusses the possibility of flaw detection.
1920 Dr. H. H. Lester begins development of industrial radiography for metals.
1924 — Lester uses radiography to examine castings to be installed in a Boston Edison Company steam pressure power plant.
1926 The first electromagnetic eddy current instrument is available to measure material thicknesses.
1927 - 1928 Magnetic induction system to detect flaws in railroad track developed by Dr. Elmer Sperry and H.C. Drake.
1929 Magnetic particle methods and equipment pioneered (A.V. DeForest and F.B. Doane.)
1930s Robert F. Mehl demonstrates radiographic imaging using gamma radiation from Radium, which can examine thicker components than the low-energy X-ray machines available at the time.
1935 - 1940 Liquid penetrant tests developed (Betz, Doane, and DeForest)
1935 - 1940s Eddy current instruments developed (H.C. Knerr, C. Farrow, Theo Zuschlag, and Fr. F. Foerster).
1940 - 1944 Ultrasonic test method developed in USA by Dr. Floyd Firestone, who applies for a U.S. invention patent for same on May 27, 1940 and is issued the U.S. patent as grant no. 2,280,226 on April 21, 1942. Extracts from the first two paragraphs of this seminal patent for a nondestructive testing method succinctly describe the basics of ultrasonic testing. "My invention pertains to a device for detecting the presence of inhomogeneities of density or elasticity in materials. For instance if a casting has a hole or a crack within it, my device allows the presence of the flaw to be detected and its position located, even though the flaw lies entirely within the casting and no portion of it extends out to the surface. ... The general principle of my device consists of sending high frequency vibrations into the part to be inspected, and the determination of the time intervals of arrival of the direct and reflected vibrations at one or more stations on the surface of the part."
1946 First neutron radiographs produced by Peters.
1950 The Schmidt Hammer (also known as "Swiss Hammer") is invented. The instrument uses the world’s first patented non-destructive testing method for concrete.
1950 J. Kaiser introduces acoustic emission as an NDT method.
(Basic Source for above: Hellier, 2001) Note the number of advancements made during the WWII era, a time when industrial quality control was growing in importance.
1963 Frederick G. Weighart's[9] and James F. McNulty’s[10] co-invention of Digital radiography is an offshoot of the pairs development of nondestructive test equipment at Automation Industries, Inc., then, in El Segundo, California. See James F. McNulty also at article Ultrasonic testing
1996 Rolf Diederichs founded the first Open Access NDT Journal in the Internet. Today the Open Access NDT Database NDT.net
Kamis, 26 November 2015
Corrosion in nonmetal
Corrosion in nonmetals
Most ceramic materials are almost entirely immune to corrosion. The strong chemical bonds that hold them together leave very little free chemical energy in the structure; they can be thought of as already corroded. When corrosion does occur, it is almost always a simple dissolution of the material or chemical reaction, rather than an electrochemical process. A common example of corrosion protection in ceramics is the lime added to soda-lime glass to reduce its solubility in water; though it is not nearly as soluble as pure sodium silicate, normal glass does form sub-microscopic flaws when exposed to moisture. Due to its brittleness, such flaws cause a dramatic reduction in the strength of a glass object during its first few hours at room temperature.
Corrosion of polymers
Ozone cracking in natural rubber tubing
Polymer degradation involves several complex and often poorly understood physiochemical processes. These are strikingly different from the other processes discussed here, and so the term "corrosion" is only applied to them in a loose sense of the word. Because of their large molecular weight, very little entropy can be gained by mixing a given mass of polymer with another substance, making them generally quite difficult to dissolve. While dissolution is a problem in some polymer applications, it is relatively simple to design against. A more common and related problem is swelling, where small molecules infiltrate the structure, reducing strength and stiffness and causing a volume change. Conversely, many polymers (notably flexible vinyl) are intentionally swelled with plasticizers, which can be leached out of the structure, causing brittleness or other undesirable changes. The most common form of degradation, however, is a decrease in polymer chain length. Mechanisms which break polymer chains are familiar to biologists because of their effect on DNA: ionizing radiation (most commonly ultraviolet light), free radicals, and oxidizers such as oxygen, ozone, and chlorine. Ozone cracking is a well-known problem affecting natural rubber for example. Additives can slow these process very effectively, and can be as simple as a UV-absorbing pigment (i.e., titanium dioxide or carbon black). Plastic shopping bags often do not include these additives so that they break down more easily as litter.
Corrosion of glasses
Glass is characterized by a high degree of corrosion-resistance. Because of its high water-resistance it is often used as primary packaging material in the pharma industry since most medicines are preserved in a watery solution. Besides its water-resistance, glass is also very robust when being exposed to chemically aggressive liquids or gases. While other materials like metal or plastics quickly reach their limits, special glass-types can easily hold up.
Glass corrosion
Glass disease is the corrosion of silicate glasses in aqueous solutions. It is governed by two mechanisms: diffusion-controlled leaching (ion exchange) and hydrolytic dissolution of the glass network.[10] Both mechanisms strongly depend on the pH of contacting solution: the rate of ion exchange decreases with pH as 10−0.5pH whereas the rate of hydrolytic dissolution increases with pH as 100.5pH.[11]
Mathematically, corrosion rates of glasses are characterized by normalized corrosion rates of elements NRi (g/cm2·d) which are determined as the ratio of total amount of released species into the water Mi (g) to the water-contacting surface area S (cm2), time of contact t (days) and weight fraction content of the element in the glass fi:
.
The overall corrosion rate is a sum of contributions from both mechanisms (leaching + dissolution) NRi=Nrxi+NRh. Diffusion-controlled leaching (ion exchange) is characteristic of the initial phase of corrosion and involves replacement of alkali ions in the glass by a hydronium (H3O+) ion from the solution. It causes an ion-selective depletion of near surface layers of glasses and gives an inverse square root dependence of corrosion rate with exposure time. The diffusion-controlled normalized leaching rate of cations from glasses (g/cm2·d) is given by:
,
where t is time, Di is the i-th cation effective diffusion coefficient (cm2/d), which depends on pH of contacting water as Di = Di0·10–pH, and ρ is the density of the glass (g/cm3).
Glass network dissolution is characteristic of the later phases of corrosion and causes a congruent release of ions into the water solution at a time-independent rate in dilute solutions (g/cm2·d):
,
where rh is the stationary hydrolysis (dissolution) rate of the glass (cm/d). In closed systems the consumption of protons from the aqueous phase increases the pH and causes a fast transition to hydrolysis.[12] However, a further saturation of solution with silica impedes hydrolysis and causes the glass to return to an ion-exchange, e.g. diffusion-controlled regime of corrosion.
In typical natural conditions normalized corrosion rates of silicate glasses are very low and are of the order of 10−7–10−5 g/(cm2·d). The very high durability of silicate glasses in water makes them suitable for hazardous and nuclear waste immobilisation.
Glass corrosion tests
Effect of addition of a certain glass component on the chemical durability against water corrosion of a specific base glass (corrosion test ISO 719).[13]
There exist numerous standardized procedures for measuring the corrosion (also called chemical durability) of glasses in neutral, basic, and acidic environments, under simulated environmental conditions, in simulated body fluid, at high temperature and pressure,[14] and under other conditions.
The standard procedure ISO 719[15] describes a test of the extraction of water-soluble basic compounds under neutral conditions: 2 g of glass, particle size 300–500 μm, is kept for 60 min in 50 ml de-ionized water of grade 2 at 98 °C; 25 ml of the obtained solution is titrated against 0.01 mol/l HCl solution. The volume of HCl required for neutralization is classified according to the table below.
Amount of 0.01M HCl needed to neutralize extracted basic oxides, mlExtracted Na2O
equivalent,
Economic corrosion
Economic impact
The collapsed Silver Bridge, as seen from the Ohio side
In 2002, the US Federal Highway Administration released a study titled "Corrosion Costs and Preventive Strategies in the United States" on the direct costs associated with metallic corrosion in the US industry. In 1998, the total annual direct cost of corrosion in the U.S. was ca. $276 billion (ca. 3.2% of the US gross domestic product).[7] Broken down into five specific industries, the economic losses are $22.6 billion in infrastructure; $17.6 billion in production and manufacturing; $29.7 billion in transportation; $20.1 billion in government; and $47.9 billion in utilities.[8]
Rust is one of the most common causes of bridge accidents. As rust has a much higher volume than the originating mass of iron, its build-up can also cause failure by forcing apart adjacent parts. It was the cause of the collapse of the Mianus river bridge in 1983, when the bearings rusted internally and pushed one corner of the road slab off its support. Three drivers on the roadway at the time died as the slab fell into the river below. The following NTSB investigation showed that a drain in the road had been blocked for road re-surfacing, and had not been unblocked; as a result, runoff water penetrated the support hangers. Rust was also an important factor in the Silver Bridge disaster of 1967 in West Virginia, when a steel suspension bridge collapsed within a minute, killing 46 drivers and passengers on the bridge at the time.
Similarly, corrosion of concrete-covered steel and iron can cause the concrete to spall, creating severe structural problems. It is one of the most common failure modes of reinforced concrete bridges. Measuring instruments based on the half-cell potential can detect the potential corrosion spots before total failure of the concrete structure is reached.
Until 20–30 years ago, galvanized steel pipe was used extensively in the potable water systems for single and multi-family residents as well as commercial and public construction. Today, these systems have long ago consumed the protective zinc and are corroding internally resulting in poor water quality and pipe failures.[9] The economic impact on homeowners, condo dwellers, and the public infrastructure is estimated at 22 billion dollars as the insurance industry braces for a wave of claims due to pipe failures.
Microbial corrosion
Microbial corrosion
Main article: Microbial corrosion
Microbial corrosion, or commonly known as microbiologically influenced corrosion (MIC), is a corrosion caused or promoted by microorganisms, usually chemoautotrophs. It can apply to both metallic and non-metallic materials, in the presence or absence of oxygen. Sulfate-reducing bacteria are active in the absence of oxygen (anaerobic); they produce hydrogen sulfide, causing sulfide stress cracking. In the presence of oxygen (aerobic), some bacteria may directly oxidize iron to iron oxides and hydroxides, other bacteria oxidize sulfur and produce sulfuric acid causing biogenic sulfide corrosion. Concentration cells can form in the deposits of corrosion products, leading to localized corrosion.
Accelerated low-water corrosion (ALWC) is a particularly aggressive form of MIC that affects steel piles in seawater near the low water tide mark. It is characterized by an orange sludge, which smells of hydrogen sulfide when treated with acid. Corrosion rates can be very high and design corrosion allowances can soon be exceeded leading to premature failure of the steel pile.[5] Piles that have been coated and have cathodic protection installed at the time of construction are not susceptible to ALWC. For unprotected piles, sacrificial anodes can be installed local to the affected areas to inhibit the corrosion or a complete retrofitted sacrificial anode system can be installed. Affected areas can also be treated electrochemically by using an electrode to first produce chlorine to kill the bacteria, and then to produced a calcareous deposit, which will help shield the metal from further attack.
Corrosion passivated material
Corrosion in passivated materials
Passivation is extremely useful in mitigating corrosion damage, however even a high-quality alloy will corrode if its ability to form a passivating film is hindered. Proper selection of the right grade of material for the specific environment is important for the long-lasting performance of this group of materials. If breakdown occurs in the passive film due to chemical or mechanical factors, the resulting major modes of corrosion may include pitting corrosion, crevice corrosion and stress corrosion cracking.
Pitting corrosion
Main article: Pitting corrosion
The scheme of pitting corrosion
Certain conditions, such as low concentrations of oxygen or high concentrations of species such as chloride which complete as anions, can interfere with a given alloy's ability to re-form a passivating film. In the worst case, almost all of the surface will remain protected, but tiny local fluctuations will degrade the oxide film in a few critical points. Corrosion at these points will be greatly amplified, and can cause corrosion pits of several types, depending upon conditions. While the corrosion pits only nucleate under fairly extreme circumstances, they can continue to grow even when conditions return to normal, since the interior of a pit is naturally deprived of oxygen and locally the pH decreases to very low values and the corrosion rate increases due to an autocatalytic process. In extreme cases, the sharp tips of extremely long and narrow corrosion pits can cause stress concentration to the point that otherwise tough alloys can shatter; a thin film pierced by an invisibly small hole can hide a thumb sized pit from view. These problems are especially dangerous because they are difficult to detect before a part or structure fails. Pitting remains among the most common and damaging forms of corrosion in passivated alloys[citation needed], but it can be prevented by control of the alloy's environment.
Pitting results when a small hole, or cavity, forms in the metal, usually as a result of de-passivation of a small area. This area becomes anodic, while part of the remaining metal becomes cathodic, producing a localized galvanic reaction. The deterioration of this small area penetrates the metal and can lead to failure. This form of corrosion is often difficult to detect due to the fact that it is usually relatively small and may be covered and hidden by corrosion-produced compounds.
Weld decay and knifeline attack
Normal microstructure
Sensitized microstructure
Main article: Intergranular corrosion
Stainless steel can pose special corrosion challenges, since its passivating behavior relies on the presence of a major alloying component (chromium, at least 11.5%). Because of the elevated temperatures of welding and heat treatment, chromium carbides can form in the grain boundaries of stainless alloys. This chemical reaction robs the material of chromium in the zone near the grain boundary, making those areas much less resistant to corrosion. This creates a galvanic couple with the well-protected alloy nearby, which leads to weld decay (corrosion of the grain boundaries in the heat affected zones) in highly corrosive environments.
A stainless steel is said to be sensitized if chromium carbides are formed in the microstructure. A typical microstructure of a normalized type 304 stainless steel shows no signs of sensitization while a heavily sensitized steel shows the presence of grain boundary precipitates. The dark lines in the sensitized microstructure are networks of chromium carbides formed along the grain boundaries.[3]
Special alloys, either with low carbon content or with added carbon "getters" such as titanium and niobium (in types 321 and 347, respectively), can prevent this effect, but the latter require special heat treatment after welding to prevent the similar phenomenon of knifeline attack. As its name implies, corrosion is limited to a very narrow zone adjacent to the weld, often only a few micrometers across, making it even less noticeable.
Crevice corrosion
Main article: Crevice corrosion
Corrosion in the crevice between the tube and tube sheet (both made of type 316 stainless steel) of a heat exchanger in a seawater desalination plant.[4]
Crevice corrosion is a localized form of corrosion occurring in confined spaces (crevices), to which the access of the working fluid from the environment is limited. Formation of a differential aeration cell leads to corrosion inside the crevices. Examples of crevices are gaps and contact areas between parts, under gaskets or seals, inside cracks and seams, spaces filled with deposits and under sludge piles.
Crevice corrosion is influenced by the crevice type (metal-metal, metal-nonmetal), crevice geometry (size, surface finish), and metallurgical and environmental factors. The susceptibility to crevice corrosion can be evaluated with ASTM standard procedures. A critical crevice corrosion temperature is commonly used to rank a material's resistance to crevice corrosion.
Resistance to corrosion
Resistance to corrosion
Some metals are more intrinsically resistant to corrosion than others (for some examples, see galvanic series). There are various ways of protecting metals from corrosion (oxidation) including painting, hot dip galvanizing, and combinations of these.[2]
Intrinsic chemistry
Gold nuggets do not naturally corrode, even on a geological time scale.
The materials most resistant to corrosion are those for which corrosion is thermodynamically unfavorable. Any corrosion products of gold or platinum tend to decompose spontaneously into pure metal, which is why these elements can be found in metallic form on Earth and have long been valued. More common "base" metals can only be protected by more temporary means.
Some metals have naturally slow reaction kinetics, even though their corrosion is thermodynamically favorable. These include such metals as zinc, magnesium, and cadmium. While corrosion of these metals is continuous and ongoing, it happens at an acceptably slow rate. An extreme example is graphite, which releases large amounts of energy upon oxidation, but has such slow kinetics that it is effectively immune to electrochemical corrosion under normal conditions.
Passivation
Main article: Passivation (chemistry)
Passivation refers to the spontaneous formation of an ultrathin film of corrosion products, known as a passive film, on the metal's surface that act as a barrier to further oxidation. The chemical composition and microstructure of a passive film are different from the underlying metal. Typical passive film thickness on aluminium, stainless steels, and alloys is within 10 nanometers. The passive film is different from oxide layers that are formed upon heating and are in the micrometer thickness range – the passive film recovers if removed or damaged whereas the oxide layer does not. Passivation in natural environments such as air, water and soil at moderate pH is seen in such materials as aluminium, stainless steel, titanium, and silicon.
Passivation is primarily determined by metallurgical and environmental factors. The effect of pH is summarized using Pourbaix diagrams, but many other factors are influential. Some conditions that inhibit passivation include high pH for aluminium and zinc, low pH or the presence of chloride ions for stainless steel, high temperature for titanium (in which case the oxide dissolves into the metal, rather than the electrolyte) and fluoride ions for silicon. On the other hand, unusual conditions may result in passivation of materials that are normally unprotected, as the alkaline environment of concrete does for steel rebar. Exposure to a liquid metal such as mercury or hot solder can often circumvent passivation mechanisms.
Corrosion removal
Corrosion removal
Main article: Rust removal
Often it is possible to chemically remove the products of corrosion. For example, phosphoric acid in the form of naval jelly is often applied to ferrous tools or surfaces to remove rust. Corrosion removal should not be confused with electropolishing, which removes some layers of the underlying metal to make a smooth surface. For example, phosphoric acid may also be used to electropolish copper but it does this by removing copper, not the products of copper corrosion.
Galvanic corosion
Galvanic corrosion
Main article: Galvanic corrosion
Galvanic corrosion of aluminium. A 5-mm-thick aluminium alloy plate is physically (and hence, electrically) connected to a 10-mm-thick mild steel structural support. Galvanic corrosion occurred on the aluminium plate along the joint with the steel. Perforation of aluminium plate occurred within 2 years.[1]
Galvanic corrosion occurs when two different metals have physical or electrical contact with each other and are immersed in a common electrolyte, or when the same metal is exposed to electrolyte with different concentrations. In a galvanic couple, the more active metal (the anode) corrodes at an accelerated rate and the more noble metal (the cathode) corrodes at a slower rate. When immersed separately, each metal corrodes at its own rate. What type of metal(s) to use is readily determined by following the galvanic series. For example, zinc is often used as a sacrificial anode for steel structures. Galvanic corrosion is of major interest to the marine industry and also anywhere water (containing salts) contacts pipes or metal structures.
Factors such as relative size of anode, types of metal, and operating conditions (temperature, humidity, salinity, etc.) affect galvanic corrosion. The surface area ratio of the anode and cathode directly affects the corrosion rates of the materials. Galvanic corrosion is often prevented by the use of sacrificial anodes.
Galvanic series
Main article: Galvanic series
In any given environment (one standard medium is aerated, room-temperature seawater), one metal will be either more noble or more active than others, based on how strongly its ions are bound to the surface. Two metals in electrical contact share the same electrons, so that the "tug-of-war" at each surface is analogous to competition for free electrons between the two materials. Using the electrolyte as a host for the flow of ions in the same direction, the noble metal will take electrons from the active one. The resulting mass flow or electric current can be measured to establish a hierarchy of materials in the medium of interest. This hierarchy is called a galvanic series and is useful in predicting and understanding corrosion.
Cara hitung vol piping
Rumus Menghitung Berat Pipa Besi
BERAT (kg)= (OD(mm)-TEBAL(mm)) x TEBAL(mm) x 0.02466 x PANJANG(m)
Pipa mempunyai ukuran yang standar, artinya ukuran pipa tetap sama walaupun pabrik pembuatnya berbeda-beda. Pipa baja banyak digunakan untuk instalasi pemipaan baik itu di pabrik, industri pertambangan, minyak dan gas, maupun untuk instalasi pipa air bersih untuk rumah tangga seperti yang di suplai oleh PDAM. Material untuk pipa baja, dalam hal ini untuk standar industri proses adalah A-106-Gr.B dan juga A-53.
Standar ukuran pipa baja berdasarkan ANSI B36.10 dalam inchi adalah 1/4”, 3/8”, 1/2”, 3/4”, 1”, 1-1/4”, 1-1/2”, 2”, 2-1/2”, 3”, 3-1/2”, 4”, 5”, 6”, 8”, 10”, 12”, 14”, 16”, 18”, 20”, 22”, 24”, 26”, 28”, 30”, 32”, 34”, 36”, 38”, 40”, 42”, 44”, 46”, 48”. Untuk satu batang pipa di pasaran standar panjangnya yaitu 6000mm (6 meter).
Untuk satu jenis ukuran, pipa memiliki schedule sendiri-sendiri. Masing-masing pipa dengan schedule tertentu memiliki ukuran tebal dinding yang berbeda-beda. Schedule pipa yaitu 5S, 5, 10S, 10, 20, 30, 40S, STD, 40, 60, 80S, XS, 80, 100, 120, 140, 160, XXS.
Biasanya toko atau perusahaan penjual pipa selalu memberikan katalog untuk ukuran pipa dan beratnya. Sehingga kita tidak perlu lagi untuk menghitung manual satu persatu, akan tetapi tentu saja kita juga harus mengetahui cara untuk menghitung berat pipa apabila memang kita tidak memiliki buku katalog tersebut. Berikut adalah rumus yang digunakan untuk menghitung berat pipa besi atau baja.
1. Kita ketahui bahwa Baja memiliki berat jenis ρ = 7850 kg/m3
2. Rumusan untuk mencari berat suatu benda adalah
m = ρ * V
dimana: m = massa (berat), kg
ρ = berat jenis, kg/ m3
V = Volume dari benda tersebut, m3
3. Untuk mendapatkan volume dari benda yang akan kita hitung beratnya maka formulanya adalah luas area penampang dikalikan dengan panjang benda tersebut.
V = A * L
dimana: A = luas area penampang, m2
L = panjang, m
Pipa memiliki penampang yang berbentuk lingkaran , maka rumus area untuk lingkaran adalah:
A = (π*D2 ) / 4
Dimana: π = 3.14 (koefisien tetap)
D = diameter, m
Karena dalam hal ini pipa memiliki dimensi diameter luar (OD) dan diameter dalam (ID), maka rumus untuk luas area penampangnya adalah:
A = ((π*OD2 ) / 4) – ((π *ID2 ) / 4)
Maka Volume untuk pipa dapat dicari dengan rumus:
V = (((π*OD2 ) / 4) – ((π *ID2 ) / 4)) * L
5. Setelah kita ketahui rumus untuk mendapatkan harga dari volume satu buah pipa dengan panjang tertentu, maka dapat kita masukkan rumus volume pipa ke dalam rumus berat. Sehingga kita dapatkan rumus yang langsung bisa kita gunakan untuk menghitung berat daripada pipa yang ingin kita hitung beratnya.
Rumus tersebut yaitu:
m = ρ * ((((π*OD2 ) / 4) – ((π *ID2 ) / 4)) * L)
Berikut ini kita ambil contoh untuk menghitung berat satu batang pipa 2” Sch 40.
Parameter yang bisa kita ketahui adalah :
Satu batang pipa, L = 6000 mm = 6 m
Pipa 2” Sch 40, memiliki:
OD = 60.3 mm = 0.0603 m
ID = 52.3 mm = 0.0523 m
Berat jenis pipa baja, ρ = 7850 kg/m3
Dari parameter yang telah kita ketahui tersebut, maka langsung saja kita input ke dalam rumus berat pipa baja:
m = ρ * ((((π*OD2 ) / 4) – ((π *ID2 ) / 4)) * L)
m = 7850 * (((π*0.06032 ) / 4) – ((π *0.05232 ) / 4)) * 6)
m = 33.323 kg
Maka kita dapatkan berat untuk pipa 2” Sch 40 panjang 6 meter adalah 33.323 kg
Cara Menghitung piping
Cara Menghitung Ketebalan Pipa Menurut Asme B31.3
Dalam menghitung thickness pipe, atau kita menyebutnya dengan schedule pipe. Sebenarnya mudah saja, kita tinggal melihat dalam tabel pipe schedule dan otomatis kita akan tau tebal dari pipa tersebut.
Kalau dilihat dari sector fabrikasi, memang tepat dengan metode melihat schedulenya kita tau berapa ketebalan pipa tersebut. Namun kita perlu menghitung, sebenarnya pipa yang kita gunakan itu memerlukan tebal berapa si? Apakah schedule yang kita tentukan sudah tepat atau jangan jangan kurang dari yang dibutuhkan. Oleh karenanya, kita perlu tau bagaimana menghitung ketebalan pipa secara manual.
Untuk menghitung ketebalan pipa, sudah disebutkan dalam asme B31.3, tentang process piping. Asme yang saya gunakan disini adalah tahun 2010, tujuannya untuk mempermudahkan dan menyamakan presepsi, karena saya akan menyebutkan referensi halamanya pula dalam kalkulasi di bawah ini supaya anda benar benar paham caranya. Jadi kita gunakan acuan, asme yang 2010.
Dalam ASME tersebut, dihalaman 44, tepatnya para 304.1.1 disebutkan :
tm = t + c
Dimana :
tm adalah minimum thicknes, termasuk pula mechanical atau corrosion alowacnce.
C adalah jumlah dari mechanical allowance, misalnya thread (ulir), kedalaman grove atau coakan. Dapat pula corrosion atau erroseion allowace.
t adalah thickness berdasarkan pressure design, yang harus dicari sebelum menentukan tm.
Nilai t ditentukan dengan :
Masih di halaman yang sama, yaitu para 304.1.2. Untuk notasi dari yang disebutkan diatas, adalah sebagai berikut :
Pertanyaan selanjutnya kita akan langsung ke soal, contoh soal maksudnya. Tapi mungkin nanti ada yang belum paham di dapatnya dari mana, kita akan jelaskan setelah contoh soal itu selesai. Ok.
Misalnya diketahui :
Material A106
P = Desain Pressure = 260 Psig (Rating =150#), untuk suhu 200F
D = Diameter pipa = 10 inc.
Ditanya,
Berapakah tm (thicknes yang diperlukannya)?
Dijawab :
t = P*D/(2(S*E*W+P*Y)
P = 260 Psig
D = 10 inc = 10,7 (diameter actual)
S = 20 Ksi = 20.000 Psi
E = 1
W = 1
Y = 0.4
Jadi,
t = 260*10,7/ (2*(20.000*1*1+260*0.4)
= 0.069 inc
Sekarang seperti janji saya, kita saya akan menuntunya bagaimana nilai nilai tersebut ditemuan dalam asme b31.3.
Pertama, untuk nilai P yaitu pressure design dan nilai D, diameternya. Dua nilai itulah yang kita tentukan sendiri. kalau diameternya, ya dari diameter pipa berapa yang kita ingin tau schedule nya. kalau P nya, biasanya dari piping material class, atau orang proses yang sudah menentukannya.
Yang kedua. nilai S dari data di atas adalah nilai stress dari material yang di peroleh dari table A-1. Silahakan ke table A-1, halaman 176. Cari dengan temperature 200 F. Didapatlah nilai 200, nilai duaratus itu satuannya dalam ksi, lihat lah halaman selanjutnya. Jadi kalau mau di jadikan psi, kita mengalikannya dengan seribu. Lihat gambar di bawah agar lebih paham mencarinya.
Sekarang nilai E adalah factor kualitas untuk sambungan pipanya, didapat dari table A-1B yang ada di halaman 227 (sambil lihat gambar di bawah ya gan). Nilai yang kita ambil berdasarkan materialnya, yaitu A106 dan kita dapat dua jenis biasanya, seamless dan welded. Namun untuk material ini, kita menemukan satu jenis yaitu seamless.. jadi kita ambil nilainya 1.
W adalah nilai factor pengurangan kekuatan dari pengelasan, didapat dari para 302.3.5(e) yang nilai umumnya adalah 1 untuk occasional load sekelas wind dan seismic, silahakan lihat di halaman 43.
Sedangkan nilai Y adalah Coefficent dari table 304.1.1, halamnya masih sama dengan rumus yang tercantum. Lihat di pojok kanan atas, kita mendapatkan nilai 0.4. Dua nilai W dan Y, sama sama koefisien, jadi tidak memiliki satuan, kita masukan saja apa adanya.
Kembali lagi ke hasil perhitungan yang telah kita tentukan nilai t nya 0.069, apakah sudah selesai perhitungannya? ternyata belum. Masih ada beberapa langkah lagi, kita baru menemukan nilai t, kita harus mencari tm.
Nilai tm, yang merupakan penjumlahan dari = t + c. dimana nilai c adalah corrosion alowace yang diperhitungkan. Misalnya untuk carbon steel kita tentukan CA nya adalah 3mm (0.118 inc) , c-nya adalah 0.118inc.
Jadi nilai tm = 0.069+0.118 = 0.128 inc
Namun perhitungan tersebut biasanya masih ditambahkan dengan mill tolerace, yaitu sebesar 12.5 %
Jadi nilai tm+mill tolerace = 0.128+12.5% = 0.210 inc
Jadi, tebal yang dibutuhkan untuk pipa berdasarkan desain pressure yang ditentukan yaitu 0.21 inc.
Sekarang kita tinggal melihat table schedule pipa, kira kira sechedule mana yang sesuai dengan tebal pipa ini, ternyata schedule yang mendekati adalah schedule 20 dengan ketebalan 0.25 inc. Jadi pipa yang kita gunakan, 10 inc dengan schedule 20.
Kurang lebih itulah pemaparan sederhana mengenai cara menghitung ketebalan pipa, berdasarkan ASME B31.3, semoga bisa bermanfaat.
Krawu
Selamat pagi kawan kawan kali ini saya akan bahas makanan tradisional cirebon yg biasa di sebut krawu.
Krawu untuk sebagian orang sudah lupa dengan makanan ini.krn sudah jarang kita temui baik di pdagang sarapan keliling maupun warung warung keci
Ank sekarang mungkin bekum mendengar apalagi memakanya.
Krawu sejenis makanan ringan yang dlu buasa buat sarapan pagi sebelum kita beraktifitas.
Krawu terbuat dari jagung yang di rebus dan di kasih parutan kelapa ditambah sdkit garam mnrt selera kita.
Krawu lebih enak kalau kita kasih sayur.
Masih adakah sekarang krawu di sekitar kita????
Selamat pagi met aktifitasss
Klemer/lomah lameh
Sebagian orang mungkin tdk tau apa itu klemer atau lomah lameh.
Klemer atau lomah lameh mungkin hanya bisa di jumpai di cirebon bagian barat.seperti kec arjawinangun.kec susukan jec kaliwedi dan kec gegesik.
Karena selain di daerah yg telah saya sebutkan diatas tidak mengenal nama camilan klemer dan lomah lameh itu.
Klemer adalah camilan yg terbuat dari opak aci yg di masaj seperti masakan ikan atau daging.
Kalau di goreng pake pasir di sebut kerupuk melarat kalau di goreng pake minyak disebut kerupuk kalau diolah seperti masakan lain spt bumbu rendang .bumbu pedesan dan bumbu apa saja sesuai selera kita di sebut klemer atau lomah lameh.
Buat vegetarian klemer adalah makanan faforit karena bkn dari daging dan ikan tp rasa sama spt ikan dan daging...penasaran datang ke daerah kami..kab cirebon bagian barat..
Buat yg blm mencoba ayooo
Kerupuk Melarat
Nama yg unik untuk nama makanan ringan yang satu ini.di cirebon disebut kerupuk melarat kalau sudah di goreng.tp kalau di goreng dengn minyak goreng namanya bukan lagi kerupuk melarat.
Kerupuk melarat di cirebon sendiri punya banyak nama ada yg sebut opak aci.
Dinamakan kerupuk melarat karena di gorwng dengan pasir.
Makanya dinamakan kerupuk melarat.
Kerupuk melarat dlu memang makanan orang melarat tp sekarang seiring bantajnya orang berduit yg takut makan makanan hasil gorengan karena takut dengn penyakit yg mungkin timbul karena pemakaian minyak gorwng.
Seharusnya sekarang sudah naik pangkat bukan melarat lagi tapi kerupuk kaya..
Selamat pagi
Rabu, 25 November 2015
Jalabia
Jalabiah mungkin hampir mirip dengan makanan yg datangnya dari luar negeri donat.
Jalabiah terbuat dari tepung beras ketan sedangkan fonat dari tepung terigu.
Jalabiah diolah secara sederhana sedangkan donat diolah lebih moden
Di era th 90 ke bawah jalabiah jd makanan faforit di semua kalangn baik kota apalagi di desa
Jalabiah punya nama brrbeda di lain daerah.
Tp donat hanya satu nama
Kembali komsumsi jalabiah lebih enak dan kenyang.
Spa yang blm pernah makan jalabiah
Geblog
Geblog mungkin asing buat orang yg berdomusili di wilayah perkotaan.
Geblog makanan ringan yg terbuat dari ubi kayu yang di haluskan
Geblog jg sangat mengenyangkan dan bisa intuk sarapan pagi buat masyarakat pedesaan di kab cirebon jabar di era sebelum th 90 an
Geblog sekarang sudah jarang di jumpai sudah tergantikan roti dan donat yg praktis dan dan mungki higienis.
Apakah masih ingat geblog???