Wednesday, June 17, 2009

PV Elite User Guide 2005

Chapter 1: Introduction 1-1

What is PVElite?...................................................................................................................................... 1-2

What is the Purpose and Scope of PVElite? ............................................................................................. 1-2

What Distinguishes PVElite from our competitors?................................................................................. 1-3

What Applications are Available? ............................................................................................................ 1-4


 

Chapter 1: Introduction

1-2 PVElite User Guide 2005

What is PVElite?

PVElite is a PC-based pressure vessel design and analysis software program developed, marketed and sold

by COADE Engineering Software. PVElite is a package of nineteen applications for the design and analysis

of pressure vessels and heat exchangers, and fitness for service assessments. The purpose of the program

is to provide the mechanical engineer with easy to use, technically sound, well documented reports with

detailed calculations and supporting comments, which will speed and simplify the task of vessel design,

re-rating or fitness for service. The popularity of PVElite is a reflection of COADE's expertise in

programming and engineering, as well as COADE's dedication to service and quality.

What is the Purpose and Scope of PVElite?

Calculations in PVElite are based on the latest editions of national codes such as the ASME Boiler and

Pressure Vessel Code, or industry standards such as the Zick analysis method for horizontal drums.

PVElite offers exceptional ease of use, which results in dramatic improvement in efficiency for both design

and re-rating.

PVElite features include:

Introduction 1-3

_ Graphical User Interface, which lists model data and control with a vessel display.

_ Both horizontal and vertical vessels may be composed of cylinders, conical sections, body flanges as

well as elliptical, torispherical, hemispherical, conical and flat heads.

_ Saddle supports for horizontal vessels. Leg and skirt supports at any location for vertical vessels.

_ Extensive on-line help.

_ Deadweight calculation from vessel details such as nozzles, lugs, rings, trays, insulation, packing and

lining.

_ Wall thickness calculations for internal and external pressure in accordance with the rules of ASME

Section VIII Divisions 1 and Division 2, PD 5500 and EN-13445. Stiffener rings are evaluated for

external pressure.

_ Wind and seismic data using the American Society of Civil Engineers (ASCE) standard, the Uniform

Building Code (UBC), and the National (Canadian) Building Code, India Standards as well as British,

Mexican, Australian and European Standards.

_ User defined unit system.

_ A complete examination of the vessel's structural loads combining the effects of pressure, deadweight

and live loads in the empty, operating and hydrotest conditions.

_ Logic to automatically increase wall thickness to satisfy requirements for pressure and structural loads

and introduce stiffener rings to address external pressure rules.

_ Structural load evaluation in terms of both tensile and compressive stress ratios (to the allowable

limits).

_ Detailed analysis of nozzles, flanges, and base rings.

_ A complete material library for all three design standards.

_ A component library containing pipe diameter and wall thickness, ANSI B16.5 flange pressure vs.

temperature charts, and section properties for AISC, British, Indian, Japanese, Korean, Australian and

South African structural shapes.

_ Printed output from PVElite is exceptionally clear and complete, with user definable headings on each

page. User comments and additions may be inserted at any point in the output.

What Distinguishes PVElite from our

competitors?

COADE treats PVElite more as a service than a product. Our staff of experienced pressure vessel engineers

are involved in day-to-day software development, program support and training. This approach has

produced a program, which most closely fits today's requirements of the pressure vessel industry. Data

entry is simple and straightforward through annotated input screens and/or spreadsheets. PVElite provides

the widest range of modeling and analysis capabilities without becoming too complicated for simple

system analysis. Users may tailor their PVElite installation through default setting and customized

databases. Comprehensive input graphics confirms the model construction before the analysis is made.

The program's interactive output processor presents results on the monitor for quick review or sends

complete reports to a file, printer or Word document. PVElite is an up-to-date package that not only utilizes

standard analysis guidelines but also provides the latest recognized opinions for these analyses.

1-4 PVElite User Guide 2005

PVElite is a field-proven engineering analysis program. It is a widely recognized product with a large

customer base and an excellent support and development record. COADE is a strong and stable company

where service is a major commitment.

What Applications are Available?

The following applications are available in PVElite.

General Vessels

Wall thickness design and analysis of any vessel for realistic combinations of pressure, deadweight,

nozzle, wind and seismic loads in accordance with ASME Section VIII Division 1 rules, Division 2 rules,

PD 5500, and EN-13445. These calculations address minimum wall thickness for pressure and allowable

longitudinal stress (both tension and compression) in the vessel wall for the expected structural load

combinations.

Complete Vertical Vessels

Vessels supported by either skirts, legs or lugs can be defined for complete dead load and live load

analysis. Stacked vessels with liquid are also addressed. Hydrotest conditions may be specified for either

vertical or horizontal test positions. Vessel MAWP includes hydrostatic head and ANSI B16.5 flange

pressure limitations.

Complete Horizontal Vessels

Stress analysis of horizontal drums on saddle supports using the method of L. P. Zick. Results include

stresses at the saddles, the midpoint of the vessel, and in the heads.

The following applications are available in PVElite:

Shells & Heads

Internal and external pressure design of vessels and exchangers using the ASME Code, Section VIII,

Division 1 rules. Components include cylinders, conical sections, elliptical heads, torispherical heads, flat

heads, spherical shells and heads. This program calculates required thickness and maximum allowable

internal pressure for the given component. It also calculates the minimum design metal temperature per

UCS-66, and evaluates stiffening rings for external pressure design.

This module also includes the implementation of API-579 for Fitness For Service evaluations (FFS). Sec.

4, Local Thinning, Sec. 5, General Metal loss and Sec. 6 Pitting Corrosion, are available at this time.

Introduction 1-5

Nozzles

Required wall thickness and reinforcement under internal pressure for nozzles in shells and heads, using

the ASME Code, Section VIII, Division 1 rules and including tables of outside diameter and wall

thickness for all nominal pipe diameters and schedules. The program checks the weld sizes, calculates the

strength of reinforcement and evaluates failure paths for the nozzle. Hillside, tangential and Y-angle

nozzles can also be evaluated.

Conical Sections

Internal and external pressure analysis of conical sections and stiffening rings using the ASME Code,

Section VIII, Division 1 rules. Complete area of reinforcement and moment of inertia calculations for the

cone under both internal and external pressure are included.

Floating Head

Internal and external pressure analysis of bolted dished heads (floating heads) using the ASME Code,

Section VIII, Division 1, Appendix 1 rules. An Additional calculation technique allowed by the Code

(Soehrens calculation) is also implemented by the program.

Flanges

Stress analysis and geometry selection for all types of flanges using the ASME Code, Section VIII,

Division 1 rules. This program both designs and analyzes the following types of flanges:

_ All integral flange types

_ Slip on flanges and all loose flange types with hubs

_ Ring type flanges and all loose flange types without hubs

_ Blind flanges, both circular and non-circular

_ TEMA channel covers

_ Reverse geometry weld neck flanges

_ Flat faced flanges with full face gaskets

Users can input the external forces and moments acting on the flange and alternate mating flange loads.

Tubesheets (TEMA and PD 5500)

PVElite performs an analysis of all types of tubesheets using the 8th Edition of the Standards of the

Tubular Exchanger Manufacturers Association and PD 5500. The program takes full account of the effects

of tubesheets extended as flanges, and for fixed tubesheets also includes the effects of differential thermal

expansion and the presence of an expansion joint. Expansion joint can be designed within this module. For

a fixed tubesheet exchanger the program can analyze multiple loads cases for both the corroded and

uncorroded conditions. If an expansion joint is added, then corresponding expansion joint load cases will

also be run.

1-6 PVElite User Guide 2005

Horizontal Vessels

Stress analysis of horizontal drums on saddle supports using the L.P. Zick method. Results include

stresses at the saddles, the midpoint of the vessel and in the heads. Stiffening rings used in the design of

the vessel are also evaluated. Wind and seismic loadings are also considered. Additionally, the saddle,

webs and baseplate are checked for external seismic and wind loads. Users can also specify friction and

additional longitudinal forces on the vessel.

Legs & Lugs

Analysis of vessel support legs, support lugs, trunnions and lifting lugs based on industry standard

calculation techniques, and the resulting stresses are compared to the AISC Handbook of Steel

Construction or the ASME Code. A full table of 929 AISC beams, channels and angles is included in the

program. Users can also perform WRC 107 calculation on the trunnion and the support lug, from within

this module.

Pipes & Pads

Required wall thickness and maximum allowable working pressure for two pipes, and branch

reinforcement requirements for the same two pipes considered as a branch and a header. Based on ANSI

B31.3 rules, this program includes tables of outside diameter and wall thickness for all nominal pipe

diameters and schedules.

WRC 107/FEA

Stresses in cylindrical or spherical shells due to loading on an attachment, using the method of P.P.

Bijlaard as defined in Welding Research Council Bulletin 107, including a stress comparison to VIII Div.

2 allowables for 3 different loading conditions. This module also contains an interface to the Finite

Analysis Program (Nozzle Pro from The Paulin Research Group).

Baserings

Calculates stress and thickness evaluation for skirts and baserings. Results from both the neutral axis shift

and simplified method for basering required thickness is reported. Required skirt thickness due to weight

loads and bending moments are also displayed. Tailing Lugs attached to the basering can also be

analyzed.

Thin Joints

Stress and life cycle evaluation for thin walled expansion joints in accordance with ASME VIII Div. 1

appendix 26.

Thick Joints

Stress, life cycle and spring rate calculations for flanged and flued expansion joints in accordance with

ASME VIII Div. 1 appendix 5. The spring rate computation is per TEMA eighth edition.

Introduction 1-7

ASME Tubesheets

This program determines required thickness of tubesheets for fixed or U-tube exchangers per the ASME

Code Section VIII division 1 section UHX. You can use the program to analyze multiple loads cases for

both the corroded and uncorroded conditions.

Half-Pipe

This program determines required thickness and MAWP for half-pipe jacketed vessels per the ASME

Code Section VIII division 1 appendix EE.

Large Openings

This program analyzes large openings in integral flat heads per the ASME Code Section VIII division 1

appendix 2 and appendix 14. Required thickness, MAWP and weights are computed for geometries with

or without an attached nozzle.

Rectangular Vessels

This program analyzes non-circular pressure vessels using the rules of the ASME Code, Section VIII,

Division 1, Appendix 13. Most of the vessel types in Appendix 13 are analyzed for internal pressure,

including reinforced or stayed rectangular vessels with a diametral staying plate. All membrane and

bending stresses are computed and compared to the appropriate allowables.

WRC 297 / PD5500 Annex G

This program calculates the stress analysis of loads and attachments according to the Welding Research

Council bulletin 297 (WRC 297) and the British Standard Annex G (PD:5500). The WRC 297 bulletin,

published in 1984, attempts to extend the existing analysis of WRC 107 for cylinder-to-cylinder

intersections. PD:5500 Annex G provides an analysis of stress in cylindrical or spherical shells due to

attachment loads. Complete material databases for ASME Sec VIII and Div-1,2 are available. In the case

of PD 5500, the complete material database found in Annex K is also included.

Appendix Y Flanges

This module performs a stress evaluation of Class1 category 1, 2, or 3 flanges that form identical flange

pairs, according to the latest version of the ASME Code Section VIII Division 1 Appendix Y.

Summary

Displays a description and evaluation of all the components of a pressure vessel or heat exchanger.

Design pressure, temperature, material, actual thickness and Maximum Allowable Working Pressure are

shown for each component.

1-8 PVElite User Guide 2005

Saturday, June 13, 2009

ALLOYING ELEMENTS AND THEIR EFFECTS

Alloy Steels by Definition


 

A PLAIN carbon steel is iron combined with small amounts of carbon where the carbon content can vary between 0.008% and approximately 2.0% A plain carbon steel can also contain limited amounts of manganese (1.65% max ), silicon (0.60% max ), and copper (0.60% max ) and still be classified as a carbon steel. The more common carbon steels are the standard types such as C1005 with approximately 0.05%C up through the C1095 type with approximately 0.95%C. The C1100 steels are resulfurized and the C1200 steels are resulfurized and rephosphorized.


 

By simple definition, an alloy steel is a type of steel to which one or more alloying elements have been added to give it special properties that cannot be obtained in carbon steel. The constructional alloy steels are those generally considered to be AISI 1300 through the AISI 9800 series, although modifications of these types are also used in special applications. The chemical limitations of an alloy steel, as defined by the American Iron and Steel Institute (AISI), are as follows:


 

"Steel is considered to be alloy steel when the maximum of the range given for the content of alloying elements exceeds one or more of the following limits: manganese, 1.65%; silicon, 0.60%; copper, 0.60%; or in which a definite range or a definite minimum quantity of any of the following elements is specified or required within the limits of the recognized field of constructional alloy steels: aluminium ,boron, chromium up to 3.99%, cobalt, columbium' molybdenum, nickel, titanium, tungsten, vanadium, zirconium, or any other alloying element added to obtain a desired alloying effect."


 

To simplify the designation of alloy steels specified to chemical composition limits, a fournumeral series has been established by the Society of Automotive Engineers (SAE) and the American Iron and Steel Institute (AISI). The last two digits of the fournumeral series are intended to indicate the approximate middle of the carbon range. In some cases, five digits are given and the last three represent the carbon content as in the high carbonchromium bearing steels. The first two digits represent the alloy or alloys present. The various types of alloy steel and their numerical designations are shown on the opposite page.


 

Functions of Alloying Elements in Constructional Alloy Steels


 

As a general rule, alloy steels are specified when more strength, ductility, and toughness are required than can be obtained in carbon steel in the section or part under consideration. Alloy steels are also used when specific properties such as wear resistance, corrosion resistance, heat resistance, and special low temperature impact properties are desired.


 

Engineering reasons for the acceptance of any material can usually be justified, but it is often easy to lose sight of the fact that there must also be an economic reason for the widespread use of alloy steels. It is interesting to note that some of the largest users of alloy steels include the most costconscious industries who primarily use alloy steels because of their net advantages over carbon steels. There must, of course, be a mating of the economic and engineering factors in any given application. From a designer's viewpoint, alloy steels give greater latitudes in design, greater safety with larger payloads, and less maintenance.


 

Large tonnages of the alloying elements nickel, chromium, molybdenum, manganese, vanadium, and othersare now used annually. They are generally furnished as ferroalloys, or in some cases as the pure element, such as nickel, or as oxide compounds of the element, as with nickel and molybdenum. In these forms, they are added to molten steel in specified amounts to produce the modern constructional alloy steels.


 

Alloying elements are incorporated in steel for one or more of the following reasons, of which the first two are more important:


 

1.    To improve mechanical properties through control of the factors, which influence hardenability, and to permit higher tempering temperature while maintaining high strength and improved ductility

2.    To improve mechanical properties at elevated or low temperatures

3.    To increase resistance to chemical attack and to elevated temperature oxidation

4.    To influence other special properties such as magnetic permeability and neutron absorption.


 

Microstructure of steel can be considered as being composed of two phases:


 

1.    Ferrite, the magnetic alpha modification of iron possessing high ductility, but poor tensile strength

2.    Cementite, the ironcarbide phase, a hard, brittle constituent. The carbide phase in alloy steel is not generally pure iron carbide, hut rather a complex combination of iron and alloy carbides.


 

Alloying elements have definite effects on the properties of the ferrite and carbide phases present. They improve the mechanical properties in two ways:


 

1.    By changing the state of dispersion of the carbide in the ferrite

2.    By changing the properties of the ferrite and carbide phases.


 

The alloying elements can be classified according to their specific influence on either the ferrite or carbide phase. Some alloying elements, notably manganese, chromium, molybdenum, and vanadium, dissolve in the ferrite phase and also form carbides. Such elements as nickel, copper, and silicon do not form carbides in steel. When present in the amounts usually found in alloy steels, they dissolve in and strengthen the ferrite.


 

The highest mechanical properties of the constructional alloy steels are developed principally by quenching and tempering. If an alloy steel has been well quenched, maximum surface hardness will be developed. It is important to remember that carbon is responsible for the maximum attainable surface hardness in the section being quenched, but practical considerations necessitate the use of alloys to get maximum surface hardness and depth of hardening as section sizes increase. Alloying elements such as nickel or chromium do not, in the constructional alloy steels, make the steel surface any harder, but rather improve the hardenability and the mechanical properties of the heat treated alloy steel by influencing the rate of austenite transformation so that deephardening characteristics are obtained. In hardening 0.30% carbon steel, a quenching speed of 1800' F per second through the 1300' F temperature level on cooling must be maintained to secure the greatest hardness. Alloying elements reduce the value of this critical quenching speed to 100' F per second or less, thus permitting the steel to be cooled to temperatures of 400 to 500' F before any transformation occurs. In this range, hardening can occur completely through much heavier sections of alloy steel than could possibly be the case with the carbon steels. Depending on alloy content, sections 2, 3, 4 in., and over can be throughhardened by quenching.


 

The depth of hardness can be determined by direct readings on transverse sections through various diameter bars or can be estimated from the endquench hardenability test.


 

Even when heat is extracted from alloy steels at slower rates, maximum hardness can be attained because the reaction rates involved in the decomposition of austenite on cooling are slower in the presence of the alloying elements. In practice, this means that a less drastic quench can be employed, and that heavier sections will develop full hardness. The slower quench creates a lower thermal gradient and minimizes quench cracking and warping.


 

In the practical application of the constructional alloy steels, it has been desirable, in order to obtain the best combination of strength and ductility in the heat treated condition, to have a steel containing both a ferrite strengthener such as nickel and the carbide forming elements chromium and molybdenum, The latter elements allow higher temperatures to be used for tempering while maintaining high tensile strength and a good degree of ductility in addition to their function of promoting full-hardening at slower cooling rates.


 


 

Specific Effects of Alloying Elements in the

Constructional Alloy Steels

Manganese


 

Manganese is normally present in all commercial steels. It is essential to steel production, not only in melting but also in rolling and other processing operations. In hotworking operations, the action of manganese on sulphur improves hot working characteristics and contributes to better surface on the product.

Manganese is soluble in both alpha and gamma iron, and also forms a carbide, Mn3C. Under certain conditions the eutectoid percentage of carbon is lowered, and at 2.0% manganese, becomes 0.67%C. Manganese also lowers the critical points effectively, in a manner similar to that of nickel, and causes a pronounced hysteresis effect between the heating and cooling transformations.

In the constructional alloy steels, manganese very markedly decreases the critical cooling rate and contributes thereby to deep hardening.

With a manganese content of 11.0 to 14.0% and with a carbon content of 1.00 to 1.40%, the alloy is austenitic. This analysis is particularly resistant to wear and abrasion under high impact stresses.


 

Silicon


 

Additions of silicon raise the critical temperature on heating by amounts varying with the carbon content. Heating temperatures for quenching treatments are therefore increased. Silicon is not a carbideforming element in steel, but enters into solution in the ferrite. It increases the strength of the ferrite without loss of ductility when added in amounts up to 2.500/0. In these large quantities, however, it introduces processing difficulties, such as poor machinability, and increases susceptibility to decarburization.

One of the most important applications of silicon is its use as a deoxidizer and in molten steel. Silicon is usually present in fully deoxidized constructional alloy steels in amounts up to 0.35%, insuring the production of sound, dense ingots. Silicon increases hardenability and strengthens low alloy steels. In larger amounts it increases resistance to scaling at elevated temperatures and also raises the 500ºF embrittlement range for ultra high strength applications.


 


 


 


 


 

Nickel


 

Nickel as an alloying element in constructional alloy steels is a ferrite strengthener and is soluble in all proportions in both gamma and alpha iron. It depresses the Ac and Ar critical points. It lowers the carbon content of the eutectoid, which, with 3.5% nickel steel, is reduced to 0.70% carbon.

Since nickel does not form any carbide compounds in steel, it remains in solution in the ferrite thus strengthening and toughening the ferrite phase. In either the annealed or untreated condition, nickel will increase the internal strength and elastic limit over corresponding carbon steel. Nickel steels are easily heat treated because nickel very effectively lowers the critical cooling rate necessary to produce hardening on quenching. In heat-treated steel, nickel increases the strength and toughness. Resistance to impact stresses at subzero temperatures is also considerably improved.

In combination with chromium, nickel produces alloy steels with higher elastic ratios, greater hardenability, higher impact, and fatigue resistance than are possible with carbon steels.


 

Chromium


 

Chromium as an alloying element in constructional steels is found to form a solid solution with both the alpha and gamma phases of iron. With carbon and iron it forms a complex series of carbide compounds of chromium and iron. It is a strong carbide former, similar in this respect to molybdenum and tungsten. It raises the Ac" critical point, especially when large amounts of chromium are present. The eutectoid carbon content is found to be lowered by chromium additions, by an amount varying with the quantity present. At 2.0%, chromium, the eutectoid forms with 0.62% carbon. With 12.0% chromium, eutectoid carbon drops to under 0.40%.

Complex chromiumiron carbides go into solution in austenite slowly; therefore a sufficient heating time before quenching is necessary when treating the medium carbon grades. If the chromium is sufficiently dissolved in austenite, greater depth of hardening on quenching is obtained because the critical cooling rate required is decreased.

Chromium is essentially a hardening element, and is frequently used with a toughening element such as nickel to produce superior

mechanical properties. At higher temperatures, chromium contributes increased strength, but it is ordinarily used for applications of this nature in conjunction with molybdenum.

Two of the most important properties of steels containing chromium are wear resistance and cutting ability. These effects are primarily due to the high hardness of the chromium carbides.


 

Molybdenum


 

Molybdenum as an alloying element in steel can form a solid solution with the ferrite phase and also, depending on the molybdenum and carbon content, can form a complex carbide. Molybdenum slightly increases the electrical resistance of low carbon steels. This indicates it is largely in solid solution in ferrite. In high carbon steels, electrical resistance is decreased, which gives evidence that the molybdenum is largely confined to the carbide phase when the steel is in the annealed condition. Molybdenum raises the Ac3 critical point when added in the usual amounts (0.10 to 0.60%) for constructional alloy steels. When molybdenum is in solid solution in austenite prior to quenching, the reaction rates for the transformation of austenite become considerably slower as compared with a carbon steel, resulting in deeper hardening steel.

Molybdenum steels in the quenched condition require a higher tempering temperature to attain the same degree of softness as comparable carbon or alloy steels. This resistance to tempering conferred by molybdenum contributes to the ability of these steels to retain their strength at elevated temperatures. They show, because of this effect, a considerable resistance to "creep" under sustained loads below their elastic limit at temperatures up to 1100 F.

Alloy steels, which contain 0.15 to 0.30%, molybdenum, show a minimum susceptibility to temper embrittlement. It has been found that some quenched and tempered alloy steels become brittle when slowly cooled from the tempering temperature. This brittleness is made evident by low resistance to impact. The susceptibility of such steels to "temper brittleness" is serious when large parts are being made, for it is difficult to cool large sections rapidly enough to prevent damage. Molybdenum additions in the amounts noted prevent temper brittleness and allow usual cooling rates to be used after tempering.


 

Vanadium


 

Vanadium is one of the strong carbideforming elements. It dissolves to some degree in ferrite, imparting strength and toughness. The complex carbides formed by vanadium additions are quite stable.

Vanadium steels show a much finer structure than steels of a similar composition without vanadium. Grain growth tendencies are minimized for temperatures in the heat-treating range, thus allowing higher hardening and normalizing temperatures to be used.

As with other strong carbideforming elements, vanadium raises the critical points and decreases the carbon content of the eutectoid. This latter effect is very pronounced.

Vanadium gives other alloying effects of importance, namely: increased hardenability where it is in solution in the austenite prior to quenching; a secondarv hardening effect upon tempering; and increased hardness at elevated temperatures.


 


 


 

Boron


 

Boron is usually added to steel to improve hardenability; that is, to increase the depth of hardening during quenching. During World War 11 and the Korean conflict, boron supplanted substantial quantities of nickel, chromium, and molybdenum in a group of alloy steels, primarily to conserve these elements which are ordinarily used to increase hardenability. Boron treated steels will usually have a boron content in the range of 0.0005 to 0.003%. This small] amount of boron appears to be the optimum range for enhancing the hardenability of other alloys and because of this effect boron is designated as an alloy "intensifier." Whenever boron is substituted in part for other alloys, it should be done so only with hardenability in mind because the lowered alloy content may be harmful on some applications. Boron is very effective when used with lowcarbon alloy steels, but its effect is reduced as the carbon increases. When the carbon content is above 0.60%, the use of boron is not suggested. Boron appears to be most detrimental to impact resistance in steels with low transition temperatures; thus, if a nickel steel is to be used for low temperature applications it should not contain boron, but, conversely, boron steels should contain nickel to offset the detrimental effect of boron on low temperature transition.

Boron also has a relatively high nuclear cross section and can be used for neutron absorption.


 

Aluminium


 

Aluminium is widely used as a deoxidizer and for control of inherent grain size. When added to steel in controlled amounts, it produces a fine austenitic grain size.

In fact, of all the alloy elements, Aluminium, in prescribed amounts, is the most effective in controlling gram growth. Titanium, zirconium and vanadium are also effective grain growth inhibitors, but have adverse effects on hardenability because their carbide compounds are very stable and difficult to dissolve in austenite prior to quenching.

Aluminium is used as an alloying addition in amounts of 0.95 to 1.30% in the most popular nitriding steel. The aircraft industry uses the nitriding steel, AISI 7140, because of its high surface hardness after nitriding and its distortionfree properties up to approximately the nitriding temperature. The extremely high hardness of the nitrided case is due to the formation of a hard, stable Aluminium nitride compound. The amount of aluminium present in nitriding steels is considerably in excess of the amount necessary to produce a fine austenitic grain size in other steels.


 

Copper


 

Copper as a metal has been used since antiquity, but its use as an alloy of steel is not so well known. Copper, like nickel, does not form carbides in steel, but dissolves in and strengthens the ferrite. The use of copper in certain alloys increases the resistance to atmospheric corrosion and increases the yield strength. Low carbon alloy steels alloyed with 1.0 to 1.5% copper show precipitation hardening response during aging at approximately 900' F that markedly increases the yield strength. Copper has been used in some die steel applications and more specifically in the highstrength lowalloy steels where chemical compositions are specially developed to impart higher mechanical property values and greater resistance to atmospheric corrosion than are obtainable from conventional carbon structural steels containing copper.


 

Columbium


 

Element 41 of the periodic table has been named "niobium" by several international technical societies; however, prominent metallurgists in this country prefer to use the name columbium.

Columbium influences the properties of steel by (1) imparting a fine grain size and preventing grain coarsening as high as 1875' F, (2) by preventing air hardening, (3) by retarding softening during tempering, (4) by hastening nitriding reactions, and (5) by enabling steel to resist creep and rupture at elevated temperatures. Columbium enters into the ferrite of very lowcarbon steels and strengthens the ferrite by the formation of an intermetallic compound of limited solid solubility. Alloys containing more than 0.5%, columbium can be age hardened when the carbon content is very low. In medium carbon steels, age hardening effects may be obtained if the heat-treating temperature is high enough to effectively dissolve some of the columbium carbides.

One of the advantages of using columbium for grain refinement is that it has a low deoxidizing power and does not introduce undesirable oxide inclusions into the steel. The A3 temperature is raised by columbium and the A4, or upper austenite limit, is lowered, thus restricting the austenite temperature ranges.

Columbium decreases the hardenability of steel by carbon impoverishment as well as by grain refinement and the nucleating effect of the carbides; but columbium can inhibit transformation when in solid solution.

The fine grain size and the decreased hardenability imparted by columbium increase the ductility of steels slightly and the impact strength markedly. These improvements in properties are more noticeable in the lower carbon steels.


 


 


 


 


 


 


 


 

Titanium


 

Titanium in steel is used primarily as a deoxidizer and an effective grain growth inhibitor; but as an alloying element, it has the greatest carbideforming tendency of any of the alloying elements. Its carbideforming tendency is so strong that a 0.50% carbon steel will have practically no tendency to quench harden when 1.5 to 2.0% titanium is added. Titanium's contribution to hardenability is usually negligible because it may only dissolve in minute amounts in the presence of considerable carbon.

Titanium is now being used in some elevated temperature applications where high stress rupture and secondary hardening effects are required. In very low carbon steels, titanium has a pronounced effect on strengthening the ferrite by solid solution effects and ranks next to silicon in this respect. Titanium residuals of 0.02% can cause impairment of impact properties by shifting the transition zone to higher temperatures and may cause increased susceptibility to temper brittleness in steels fully quenched and drawn at 1200' F.


 

Zirconium


 

Zirconium is a graingrowth inhibitor and is a more potent deoxidizer than boron, silicon, titanium, vanadium, or manganese. It has been considered as a substitute for manganese in combating hot shortness, but has not been used for economic reasons.

The chief commercial use of zirconium is in lowalloy highstrength steels to improve their hot rolled properties. Improved lowtemperature properties have been reported by some investigators who have shown that zirconium is more effective than vanadium in raising the lowtemperature Izod impact property of certain steels.

Zirconium has a positive effect on hardenability, but usually it is not sufficiently great enough to use the element primarily for this purpose.

The elevated temperature properties are generally improved by the presence of zirconium nitrides which apparently are stable nitrides of low solubility that enable the steel to resist creep.


 

Cobalt


 

Cobalt is soluble in all proportions in gamma iron and has nearly 75% solubility in alpha iron. Cobalt hardens or strengthens the ferrite when it is dissolved in ferrite and thus resists softening under elevated temperature conditions. The carbideforming tendency is similar to or slightly higher than iron's carbideforming tendency.

With respect to hardenability, cobalt has a negative effect for 0.40% carbon steels and hastens the transformation to softer products rather than retarding transformation and inducing hardenability, as do most alloying elements. However, in very lowcarbon chromium steels, cobalt has been shown to increase hardenability.


 


 

Combination of Alloying Elements


 

Combinations of the alloys in all possible proportions would, of course, result in a multitude of alloy steels. However, by careful consideration of the characteristics of various alloy combinations, a relatively small list of standard alloy steels meets the requirements of steel producers and consumers. In the standard constructional alloy steels, carbon, manganese, and silicon are elements, which occur normally. A steel containing one additional alloying element, such as nickel, chromium, or molybdenum, is known as single alloy steel. When two such alloying elements are added, it is known as a double (binary) alloy steel; when three are added, it becomes a triple (ternary) alloy steel.


 

In general, it may be said that the combination of alloys in constructional steels results in no loss of the qualities which are imparted to the steel when alloying agents are added singly. For instance, if nickel strengthens ferrite when used alone, it will act to an equivalent degree when used in combination with other elements. When used in combination, alloys may in fact so complement each other as to give greater overall benefits than when used singly in much larger quantities. Thus steels of the nickel, chromium, or molybdenum single alloy types are used generally in smaller sections where throughhardening and suitable mechanical properties can be attained. When larger sections are to be handled, the double and triple alloy types are preferred because they harden deeper and offer increased resistance to tempering. The triple alloy types afford an interesting example of more uniform properties because the common residual elements are specified as alloys so that unexpected effects due to occasional variations in residual alloys are not encountered. Also, the probability that all specified elements will occur at the low limit of the specified composition is less than that for single or double alloy compositions. Closer control of hardenability and resulting mechanical properties is therefore possible.


 


 

PROSEDUR PELAKSANAAN PEKERJAAN PEMERIKSAAN INSTALASI FIRE HYDRANT


 

BAB I

I     UMUM


 

  1. LATAR BELAKANG


 

Dengan pertimbangan mengenai kondisi safety peralatan instalasi fire hydrant dan kekhawatiran mengenai kondisi instalasi . Dan juga adanya kebutuhan untuk melaksanakan program perawatan intalasi fire hydrant yang tepat, maka dilaksanakanlah pemeriksaan dengan tujuan :


 

Dengan mengacu pada fakta-fakta diatas dan standar pipe code yang ada mengenai Piping inspection, maka secara teknis dipandang perlu untuk melakukan Reliability Analysis terhadap instalasi pipa fire hydrant tersebut.


 


 

  1. Maksud dan Tujuan


 

Maksud dan tujuan Reliability terhadap instalasi fire hydrant tersebut adalah untuk melakukan evaluasi terhadap kehandalan kondisi instalasi. Untuk itu perlu dilakukan pemeriksaan-pemeriksaan antara lain


 

  1. Pemeriksaan NDT ( penetran test ) dan leak test pada instalasi fire hydrant untuk mengetahui atau meyakinkan bahwa instalsi yang dioperasikan dalam kondisi aman dan keselamatan kerja yang memenuhi syarat telah diproteksi dengan safety device yang berfungsi baik dan mempunyai perlengkapan pengukur (indikator-indikator) yang memenuhi syarat
  2. Pengukuran ketebalan pipa pada titik-titik yang berpotensi terjadi korosi terbesar, dimana mewakili kondisi pipa instalasi secara keseluruhan termasuk memperhitungkan hasil survey dengan menggunakan DM 4 DL.


 

  1. Pelaksanaan Risk Assessment yang mencakup identifikasi penyebab potensial failure dan pengaruhnya terhadap kelangsungan operasi instalasi terhadap lingkungan.
  2. Pelaksanaan Remaining Life Assessment berdasarkan kondisi riil actual pipa, parameter operasi dan lingkungan yang ada, dengan melakukan perhitungan engineering untuk memperkirakan umur pakai dari pipa tersebut .


     

Dari data hasil pemeriksaan tersebut diatas dan evaluasinya yang mengacu pada standar pipe code yang ada, maka bisa diperoleh kemungkinan-kemungkinan sebagai berikut :


 

1.    Apakah instalasi fire hydrant tersebut terus bisa dioperasikan , sampai seberapa lama dan handal untuk kondisi operasi dan lingkungan yang ada.

  1. Apakah pipa tersebut memerlukan perbaikan untuk bisa terus beropersi secara aman dan handal, adapun jenis perbaikan tersebut bisa meliputi ,

    Misalnya :

    1. Sistem Coating atau Proteksi Cathodiknya.
    2. Penggantian pipa secara partial.
    3. Penggantian / perbaikan valve yang rusak
    4. Supportnya dan sebagainya


     


     


     


     


     


     


     


     


     


     


     


     

BAB II


 

  1. PENDEKATAN ENGINEERING


 

  1. REFERENSI
    1. API 570 piping inspection Code. Inspection, Repair, Alteration and Repairing of

In – service piping system.

  1. API – RP 574 Inspection of piping system components.
  2. ASME B31G, Manual for Determining the Remaining Strength of Corroded pipelines.
  3. ASME B31.3
  4. NACE RP 0169, Control of External Corrosion Underground or submerged Metallic Piping System.
  5. NACE RP 0175, Control of internal Corrosion in Piping System.
  6. Undang-undang No 1 tahun 1970
  7. SK DIRJEN Perlindungan dan Perawatan Tenaga Kerja No Kepts. 40/1978


 


 

  1. PELAKSANAAN


 

Prosedur pelaksanaan pekerjaan ini disusun untuk menjadi panduan dalam melaksanakan pekerjaan pemeriksaan instalasi fire hydrant. Adapun teknik yang akan digunakan adalah random-thickness measurement, leak test setiap valve serta keseluruhan instalasi baik dengan metode NDT ataupun hydrotest.

Sementara itu untuk random-thickness measurement akan dipilih pada titik yang diduga berpeluang mendapat serangan korosi terberat, yakni di titik down-stream pada shinker section pipa dan setelah section valve. Pemilihan titik ini dilakukan dengan asumsi bahwa turbulensi aliran yang bisa menyebabkan kerusakan permukaan internal dinding pipa besar peluangnya untuk terjadi di titik tersebut.

Pengambilan data ketebalan dinding pipa dari pipa penyalur ini adalah untuk mengetahui kondisi terakhir ( pada saat pengukuran ) dari jaringan pipa, dimana hasil dari pengukuran akan dibandingkan dengan design ketebalan awal sehingga akan diketahui laju korosi. Dari hasil tersebut kemudian diambil langkah-langkah yang perlu guna perbaikan dan penyempurnaan jaringan pipa penyalur ini, sehingga dapat memenuhi persyaratan keamanan, Keselamatan kerja serta lindungan lingkungan.


 

IV. METODOLOGI INSPEKSI

4.1 PENGAMATAN VISUAL

Pengamatan visual dari fakta instalasi dilakukan untuk mengetahui keadaan pipa, coating ,kondisi dari support dan perlengkapan peralatan.Hasil visual akan dievaluasi sesuai dengan mode failure and deterioration serta didokumentasikan dalam bentuk table dan foto-foto.


 

4.2 UJI NDT ( Penetrant Test )

Pengujian ini dilakukan uji pada body setiap valve dan daerah sambungan secara random yang mengacu dari hasil visual.

    Pengujian tersebut dapat memberikan gambaran kondisi valve serta sambungan terhadap cacat dibawah permukaan.


 

  1. PENGUKURAN KETEBALAN PIPA

    Pengukuran ketebalan dilakukan dengan pengukuran samping secara random/acak. Lokasi pengukuran dibagi menjadi 4 (empat) section/bagian dan masiang-masing bagian diambil 3(tiga) titik pengujian sehingga keseluruhannya menjadi 12 tiik


     

    Dari masing-masing titik uji diambil 4 posisi pengambilan data pada orientasi 0, 90,135 dan 180 derajat dan masing –masing posisi tersebut diambil 10 itik yang terjarak masing-masing 1 cm sehingga pada setiap titik lokasi pengukuran diperoleh 40 data hasil pengukuran.


 

Titik –titik yang dipilih adalah lokasi yang mempunyai karakteristik sebagai tempat dengan peluang terbesar terjadinya korosi atau peluang defect tinggi, yaitu daerah low-sot, deadleg, dan elbow sehingga hasil pengukuran di titik-titik tersebut dapat mewakili gambar kondisi dilokasi yang tidak diukur. Data- data tersebut dapat memberikan gambar kondisi seluruh pipa.


 

  1. UJI KEBOCORAN

    Pengujian ini dilakukan dengan cara memberikan tekanan pada instalasi fire hydrant dan

    ditahan secukupnya untuk melakukan analisa kebocoran pada keseluruhan instalasi


     


     

V. KESIMPULAN DAN SARAN

Untuk mencapai tujuan di atas dan dikaitkan dengan metodologi pengambilan sample beberapa catatan berikut dibuat sebagai bahan pertimbangan dalam pengambilan keputusan menindaklanjuti hasil-hasil dari pemeriksaan ini :

Untuk mendapatkan gambaran yang lebih baik, jika metode yang sama akan digunakan maka sebaiknya instalasi ini dilihat dulu dalam satu kesatuan dan ditinjau perbagian seperti :

a. Penentuan berdasar kritikal area

b. Pengelompokan line number.

c. Pengelompokan valve dan peralatan penunjang lainnya


 

Data-data Penunjang

1.Instalasi fire hydrant Data Sheet

Data sheet ini dapat digunakan sebagai sumber informasi pertama karena akan memuat data-data teknis pada saat design dan pemasangan seperti Pressure yang dipakai, thickness yang digunakan, rating dari peralatan dan protection jenis coating.

  1. As-built Data

Bahan-bahan ini akan bermanfaat sebagai petunjuk untuk memilih bagian-bagian yang harus mendapat perhatian lebih dan / atau focus dan suatu program inspeksi.

3.Environmental Data

Data ini sangat bermanfaat untuk melihat pembagian klasifikasi area dimana tergantung dari faktor resiko.

4.Monitoring equipments/ tools

Mengenai keberadaan monitoring equipment/tools di dalam sistem instalasi ini seperti : fire hydrant, smoke detector , alarm, hose dan sprinkle.

.


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 

ORGANISASI PELAKSANA

Untuk mendapatkan hasil yang baik dengan efektifitas kerja yang memadai, maka pekerjaan pemeriksaan ini akan dilaksanakan oleh team kerja yang terdiri atas personil dengan tugas masing-masing yang jelas. Organisasi tersebut terdiri atas:


 

Koordinator Pekerjaan

Koordinator Pekerjaan akan memantau perkembangan pekerjaan dari kantor pusat, dan akan terjun ke lapangan jika keadaan memerlukannya sesuai dengan permintaan dari Supervisor Lapangan. Sebagai Koordinator Lapangan, tugas dan kewajibannya tidak terbatas pada satu pekerjaan, melainkan beberapa proyek yang digarap oleh perusahaan sehingga fungsinya lebih cenderung kepada kebijaksanaan.


 

Supervisor Lapangan

Selama pekerjaan lapangan berlangsung, team pelaksana akan dipimpin oleh seorang Supervisor Lapangan, yang bekerja juga sebagai Pimpinan Team. Dia berperan sebagai penerus kebijaksanaan yang digariskan oleh Koordinator Pekerjaan dan mengatur tugas team, peralatan, logistik, dan hal-hal lain yang berkaitan dengan kelancaran pekerjaan lapangan. Supervisor Lapangan akan memberikan laporan kegiatan harian kepada Koordinator Pekerjaan dan kepada wakil dari client di lapangan, serta melaporkan berbagai kelainan tehnis yang ditemukan di lapangan untuk dianalisa oleh Koordinator Pekerjaan dan dicarikan jalan keluarnya.


 

Petugas Ultrasonik

Ketebalan sisa pipa akan diukur dengan menggunakan tehnik ultrasonik DM 4 DL. Titik pengukuran akan dilakukan disekeliling badan pipa pada setiap cm dan kearah memanjang setiap cm dengan total panjang 20 cm. Hal ini disesuaikan dengan rekomendasi yang ditetapkan sesuai dengan Standar di lapangan, scanning ketebalan akan dilaksanakan oleh Petugas Ultrasonik dibantu oleh 1 orang pembantu untuk pembersihan bidang yang akan diukur.


 

Petugas NDT

Peralatan NDT akan digunakan untuk mengetahui kondisi sambungan serta peralatan lain yang menjadi target pengecekan. Seorang petugas NDT akan mengidentifikasi daerah target dan diikuti oleh team untuk kepentingan lebih lanjut


 

Team Pendukung

Team pendukung pekerjaan ini adalah tenaga pembantu. Tugas mereka akan diatur oleh Supervisor Lapangan sesuai dengan kebutuhan atau permintaan team inti.


 

STRATEGI PELAKSANAAN

Untuk memperoleh hasil kerja yang maksimal secara efektif, maka perlu diatur urutan pelaksanaan, sistim pelaporan, dan tehnik pelaksanaannya.

Urutan Pekerjaan

Pekerjaan harus dilakukan dengan urutan yang benar agar hasil pemeriksaan yang satu dengan lainnya bisa saling menunjang dan sinkron. Supaya bisa memperoleh hasil yang baik maka pekerjaan akan diurutkan seperti berikut:

  1. Supervisor Lapangan bersama-sama dengan Petugas Lapangan akan melakukan penelusuran jalur untuk menentukan dimana titik pengukuran ketebalan dan pemeriksaan NDT akan dilakukan.
  2. Akan dilakukan tindak lanjut pekerjaan apabila ditemukan kerusakan atau kebocoran.
  3. Analisa engineering akan dilakukan berdasar dari data pemeriksaan tehnis.
  4. Rekomendasi-rekomendasi untuk dijadikan acuan dan pertimbangan guna keamanan dan keselamatan dalam pengopresian instalasi tersebut.


 

Friday, June 12, 2009

New Beginning


1. POLARITY

A welder should understand the meaning of polarity, and recognize what effect it has on the welding process. For proper penetration, uniform bead appearance and good welding result, the correct polarity must be used when welding with any wire or electrode.

Incorrect polarity will cause: poor penetration, Irregular bead shape, excessive spatter, difficult to control the arc, overheating, and rapid burning of wire or electrode.

ARC BLOW
  • Occurs when the arc refuses to go where it is supposed to, blows wildly forward or back, and produces spatters badly.
  • Most frequently encountered at the start and finish of joints, and in corners and deep grooves, particularly when high amperages are being used in welding thick.
  • Makes welding very difficult, reduce speed and lowers weld quality
  • When the arc blow opposite to the direction of travel it is called back blow.
  • When the arc blows with the direction of travel, it is called forward blow.
  • Is caused by magnetic force acting on the arc, making the arc blow from its normal path.
TO REDUCE ARC BLOW:
  • Reduce current
  • Weld toward a heavy tack or toward a weld already made
  • Use back stepping on long welds
  • Place ground connection as for from joint to be welded as is possible
  • If back blow is in the problem, place ground connection at start of weld and weld towards a heavy tack
  • If forward blow causes trouble, place ground connection at the end of weld
  • Wrap ground cable around the work piece and pass ground current through it in such a direction that magnetic field will be set-up to neutralize the magnetic field causing the blow
  • Hold as short and arc possible to help the arc force counteract the arc blow
  • If the machine bring used is of type producing both AC&DC, switch to AC.

    2. THE EFFECT OF THE WELDING HEAT ON METAL

 

Metals become larger when heated and become smaller upon cooling. During welding the arc heats the metal being welded, causing it to become larger or expand. As the heat is removed, the surrounding metal and air cause a cooling effect upon the heated area, which results in the metal becoming smaller, or contracting. When this expansion and contraction is not controlled, distortion (warping) is likely to result. On the other extreme, if expansion and contraction is restrained, or controlled too rigidly, severe stress and strain may result and impair the weld.

 
Three rules can be followed to aid in the prevention and control of distortion:
  • Reduce the forces that cause shrinkage.
  • Make shrinkage forces work to reduce distortion
  • Balance shrinkage force with other forces.
Reduce the force that cause shrinkage:
  • Avoid over welding
  • Over welding causes distortion, it is a waste of time and money. In certain cases it may even weaken the joint.
  • Use proper joint preparation and fit-up
  • Use intermittent welds
  • Use "back step" welding method
Make shrinkage force work to minimize distortion
  • Pre-set parts out of position
  • Space parts to allow for shrinkage
  • Pre-bend (pre-camber)
Balance shrinkage forces with other forces
  • Balance one shrinkage force with another, i.e. by welding alternatively on both sides.
  • Peering (but no advisable)
  • Use of jigs and fixtures such as clamps, jigs, strong backs to hold the work in a rigid position during welding.
     

    3. TO STRIKE AND ESTABLISH AN ARC
The basis of arc welding is the continuous electric arc. The arc is maintained when the welding current is force across gab between the electrode tip and bar metal. A welder must be able to strike and establish the correct arc easily and quickly. 

Too long arc length
  • Increase of spatter
  • Poor penetration
  • Sound of arc will be more
of a hiss than a crackle
  • Metal will melt off the electrode
in large drops
  • Slag removal will be difficult
Travel speed too fast
  • Bead will be thin & stringy
  • Poor penetration
 Travel speed too slow
  • Weld metal will pile up and roll over
  • Excessive overlap
 Amperage too high
  • Bead will be flat
  • Excessive spatter
  • Excessive porosity
  • Electrode becomes overheated
 Amperage too low
  • Difficult in striking the arc
  • Difficult in maintaining
correct arc length
  • Weld metal pile up
  • Excessive overlap
  • Poor penetration


4. RUNNING BEAD WITH WEAVING MOTION
 

Weaving is an oscillating motion, back and forth, crosswise to the direction of travel. These motions are used to:
  • Flat out slag,
  • Deposit a wider bead,
  • Secure good penetration at the edge of the weld,
  • Allow gas to escape,
  • Avoid porosity.
Types of weaving motion:

The weave should not be wider than three times the diameter of electrode. And the purpose accomplished by both these motions is substantially the same and their usage is largely a matter of preference.

5. REHEAT AND INTERPASS CONTROL

The main reason for preheating and interpass control is to lower the cooling rate in the Weld Metal (WM) and Heat Affected Zone (HAZ). The lower cooling rate, the lesser the chance WM and Base Metal (BM) cracking. It lowers the chances of shrinkage stresses. It will maintain the desired properties of the weld and the base material.

 
PREHEAT METHODS
  • Portable heating torches with rosebud tips
  • Ceramic heating elements
PREHEAT AREAS
  • At least 3" (75mm) away from the joint towards the center of the joint.
  • Preheat both external and internal (if accessible) areas of the joint.
     
MONITORING OF PREHEAT TEMPERATURES
  • Use temperature indicating crayon (ex: tempil stick) with the appropriate preheat temperature requirements.
  • Apply to the joint at least one minute after preheated, 3" away from the joint.
MONITORING OF INTERPASS TEMPERATURE
  • Use temperature indicating crayons (tempil stick)
  • Apply to the joint at least one inch away from the welded joint. 


    7. HOW TO READ AND USE THE WELDING PROCEDURE SPECIFICATION (WPS)

 
Welding Procedure Specification is a specific guide for welders in execute their job. Welder must understand the contents of a welding procedure and must be able to identify the parameters stated in the WPS.

 
When there is doubt in executing a weld, always refer to the WPS for guidance. Always follow the parameter in the welding procedure. DO NOT WELD WITHOUT A WELDING PROCEDURE IN YOUR WORK AREAS.
 
HOW TO READ METHOD STATEMENT AND SPECIAL INSTRUCTION? 
Certainly critical applications will require additional instructions to ensure that the work will be done correctly. This instruction will supplement the welding procedure and should also be followed strictly. The method statement will be displayed in the work areas.