PRESSURE VESSEL:Perancangan, Fabrikasidan InspeksiIr. Tri Prakosa, M.Eng.

LAPI-ITB (22-25 Oktober 2009)*

ASME Career Development Series

PRE-TESTSebutkan 2 jenis bentuk pressure vesselSebutkan 2 jenis proses fabrikasi pressure vesselApakah yang disebut dengan fracture toughness?Apakah yang disebut sebagai yield strength suatu material?Apakah yang disebut dengan hydrogen attack?Beban luar apa saja yang dialami oleh pressure vessel?Apakah yang disebut dengan pressure testing (hydrostatic testing)?Sebutkan 3 contoh non-destructive testing (NDE) pada pressure vessel*

4. INSPECTION AND TESTING*

ASME Career Development Series

Inspection and TestingInspection includes examination of:

Base material specification and quality

Welds

Dimensional requirements

Equipment documentation*

Pengujian Daya Lekat Coating*

Beberapa Jenis Kelainan Cacat/Cacat Permukaan Bejana*

Hydrotest*

Uji Pneumatisdengan gas N2 atau He*

Pemantauan Hot Spotsecara On-stream*

Pemantauan Hot Spotsecara On-streamdengan Kamera Infra Merah*

Tangential Radiography*

Pemantauan Dini melalui Radiographic Sensing*

INDIKATOR PELUMAS, PRESSUSRE GAGE, DLL*

Pengecekan Kebocoranpada Packing Gland*

Common Weld Defects*Gambar 7.1

Weld DefectsPresence of defects:

Reduces weld strength below that required

Reduces overall strength of fabrication

Increases risk of failure*

Types of NDE*Gambar 7.2

Typical RT Setup*Gambar 7.3

Pulse Echo UT System*Gambar 7.4

Pressure TestingTypically use water as test mediumDemonstrates structural and mechanicalintegrity after fabrication and inspectionHigher test pressure provides safety marginPT = 1.5 P (Ratio)*

Pressure Testing, contdHydrotest pressures must be calculated:

For shop test. Vessel in horizontal position.For field test. Vessel in final position withuncorroded component thicknesses.For field test. Vessel in final position and withcorroded component thicknesses.PT Flange test pressureStress 0.9 (MSYS)Field test with wind*

SummaryOverview of pressure vessel mechanical designASME Section VIII, Division 1Covered Materials Design Fabrication Inspection Testing*

*5. Naval Materials Definition - normal load, shear load - tension, compression - stress, strain Stress and Strain Diagram Material Characteristics - ductility - brittleness - toughness - transition temperature - endurance limit

* Normal Load (Axial load) : Load is perpendicular to the supporting material. - Tension Load : As the ends of material are pulled apart to make the material longer, the load is called a tension load. - Compression Load : As the ends of material are pushed in to make the material smaller, the load is called a compression load.TensionCompression5.1 Classifying Load

* Shear Load : Tangential load5.1 Classifying Load (cont)pulling apartPressureCargo

* 5.2 Stress and Strain In order to compare materials, we must have measures. Stress : load per unit AreaF : load applied in poundsA : cross sectional area in in : stress in psiAFF

* 5.2 Stress and Strain (cont) Strain : - Ratio of elongation of a material to the original length - unit deformatione : elongation (ft)Lo : unloaded(original) length of a material (ft) : strain (ft/ft) or (in/in)Elongation L : loaded length of a material (ft)LoeL

*Baldwin Hydraulic Machine for Tension & Compression test

* 5.3 Stress-Strain Diagram A plot of Strain vs. Stress.The diagram gives us the behavior of the material and material properties. Each material produces a different stress-strain diagram.

* 5.3 Stress-Strain Diagram Strain ( ) (e/Lo)41235Stress (F/A)Elastic RegionPlasticRegionStrainHardeningFractureultimatetensile strength

Slope=EElastic region slope=Youngs(elastic) modulus yield strengthPlastic region ultimate tensile strength strain hardening fractureneckingyieldstrength

*A36 SteelStress and Strain Diagram

* 5.3 Stress-Strain Diagram (cont) Elastic Region (Point 1 2) - The material will return to its original shape after the material is unloaded( like a rubber band). - The stress is linearly proportional to the strain in this region. : Stress(psi)E : Elastic modulus (Youngs Modulus) (psi) : Strain (in/in) Point 2 : Yield Strength : a point at which permanent deformation occurs. ( If it is passed, the material will no longer return to its original length.) or

* Plastic Region (Point 2 3) - If the material is loaded beyond the yield strength, the material will not return to its original shape after unloading. - It will have some permanent deformation. - If the material is unloaded at Point 3, the curve will proceed from Point 3 to Point 4. The slope will be the as the slope between Point 1 and 2. - The distance between Point 1 and 4 indicates the amount of permanent deformation.5.3 Stress-Strain Diagram (cont)

* Strain Hardening - If the material is loaded again from Point 4, the curve will follow back to Point 3 with the same Elastic Modulus(slope). - The material now has a higher yield strength of Point 4. - Raising the yield strength by permanently straining the material is called Strain Hardening.5.3 Stress-Strain Diagram (cont)

* Tensile Strength (Point 3) - The largest value of stress on the diagram is called Tensile Strength(TS) or Ultimate Tensile Strength (UTS) - It is the maximum stress which the material can support without breaking. Fracture (Point 5) - If the material is stretched beyond Point 3, the stress decreases as necking and non-uniform deformation occur. - Fracture will finally occur at Point 5.5.3 Stress-Strain Diagram (cont)

*Example 1.

Mooring line length =100 ft diameter=1.0 in Axial loading applied=25,000 lb Elongation due to loading=1.0 inmooring lineloading1) Find the normal stress.2) Strain?

*Example 2. - Salvage crane is lifting an object of 20,000 lb. - Characteristics of the cable diameter=1.0 in, length prior to lifting =50 ft1) Normal stress in the cable?2) Strain?

*3) Determine the cable stretch in inches.

* 5.4 Material Properties Strength Hardness Ductility Brittleness ToughnessCharacteristics of Material are described as

* 5.4 Material PropertiesStrength - Measure of the material property to resist deformation and to maintain its shape - It is quantified in terms of yield stress or ultimate tensile strength. - High carbon steels and metal alloys have higher strength than pure metals. - Ceramic also exhibit high strength characteristics.

* 5.4 Material Properties 2) Hardness - Measure of the material property to resist indentation, abrasion and wear. - It is quantified by hardness scale such as Rockwell and Brinell hardness scale. - Hardness and Strength correlate well because both properties are related to in-molecular bonding.

* 5.4 Material Properties 3) Ductility - Measure of the material property to deform before failure. - It is quantified by reading the value of strain at the fracture point on the stress strain curve. - Example of ductile material : low carbon steel aluminum bubble gum

* 5.4 Material Properties 4) Brittleness - Measure of the materials inability to deform before failure. - The opposite of ductility. - Example of brittle material : glass, high carbon steel, ceramicsDuctileBrittleStressStrain

* 5.4 Material Properties 5) Toughness - Measure of the material ability to absorb energy. - It is measured by two methods. a) Integration of stress strain curve - Slow absorption of energy - Absorbed energy per unit volume unit : (lb/in) *(in/in) =lbin/in b) Charpy test - Impact toughness can be measured.

* 5.4 Material Properties - Charpy V-Notch Test

* 5.4 Material Properties Charpy V-Notch Test (continued) - The potential energy of the pendulum before and after impact can be calculated form the initial and final location of the pendulum. - The potential energy difference is the energy it took to break the material. absorbed during the impact. - Charpy test is an impact toughness measurement test because the energy is absorbed by the specimen very rapidly. - Purpose : to evaluate the impact toughness as a function of temperature

* Charpy V-Notch Test (continued)Temperature (F)Charpy Toughness(lbin)BrittleBehaviorDuctile BehaviorTransition Temperature5.4 Material Properties

* Charpy V-Notch Test (continued) At low temperature, where the material is brittle and not strong, little energy is required to fracture the material. At high temperature, where the material is more ductile and stronger, greater energy is required to fracture the materialThe transition temperature is the boundary between brittle and ductile behavior. The transition temperature is an extremely important parameter in selection of construction material.5.4 Material Properties

*High Carbon SteelCharpy TestStainless Steel

* 6) Fatigue5.4 Material Properties The repeated application of stress typically produced by an oscillating load such as vibration. Sources of ship vibration are engine, propeller and waves. Cycles N at Fatigue FailureStress (psi)SteelAluminumEndurance Limit : A certain threshold stress which will not cause the fatigue failure for the number of cycles. Aluminum has no endurance limit

*Evaluation of fatigue curveA - Endurance limit of each material :- Case 1) stress level= 30x103 psi, max cycles=104 :- Case 2) stress level= 30x103 psi, max cycles=106 :- Case 3) stress level= 30x103 psi, max cycles=106 :- Case 4) stress level= 50x103 psi, max cycles=106 : Number of cycles020406080Stress (x10) psiB C 103104105106107

* Factors effecting Material Properties5.4 Material Properties Temperature : Increasing temperature will decrease - Modulus of Elasticity - Yield Strength - Tensile Strength Decreasing temperature will: - Increase ductility - Reduce brittleness Environment - Sulfites, Chlorine, Oxygen in water, Radiation

* 5.5 Non-Destructive Testing (NDT) NDT : Inspections for material defects External Inspection Technique - Visual Test (VT) - Dye Penetrant Test (PT) - Magnetic Particle Test (MT) Internal Inspection Technique - Radiographic Test (RT) - Ultrasonic Test (UT) - Eddy Current test - Hydrostatic Test

* - Can be used to examine only the surface of a material. - Should be done during the all phases of maintenance (QAI). - Can be performed quickly and easily and at no virtually cost. - Often performed under some magnification to locate defects. - Sometimes photographs are needed for a permanent record.Visual Testing (VT)

Dye Penetrant Test (PT)* - Can be used for location and identification of only surface defects : cracks, seams, laps, laminations or porosity - Uses dyes to make surface flaws visible to naked eye. - Can be used as a field inspection for glass, metal, castings, forgings and welds. - Simple and inexpensive

* Dye Penetrant Test (PT) (contd.)

* Magnetic Particle Test (MT) Method that can be used to find surface and near surface flaws in ferromagnetic materials such as steel and iron. The technique uses the principle that magnetic fields (flux) will be distorted by the presence of a flaw.

* Radiographic Test (RT) - The x-ray (gamma) rays are used. - The rays pass through the material and exposes film. - RT requires trained technicians. - RT may have large effect on ship access and watchstanding. The picture shows the integrity of welding for the 2.5mm thick steel plate

* (Ultrasonic Test UT) UT uses high frequency sound waves to detect flaws, measure material thickness, or level in a tank or vessel. Can be used on all metals and nonmetals. Excellent technique for detecting deep flaws in tubing, rods, adhesive-joined joints. It is used on aircraft to detect cracks in structure

* Ultrasonic Test (UT)

* Eddy Current Test Involves the creation of a magnetic field in a specimen and reading the field variations on an oscilloscope. Can only be used on conductive materials and is only good for limited penetration depth. Used for measurement of wall thickness, cracks of tubes, wire, or ball bearings.

* Eddy Current TestElliptical Crack

Hydrostatic TestsSystem being tested is isolated and pressurized by a pump.System is inspected for leaks at welds, valve bodies, valve seats, etc.Automatic and manual pressure reliefs are used to prevent overpressurizing system beyond desired test pressure.*

Hydrostatic Test Pump*

FRACTURE TOUGHNESSPlastic Zone SizePlane stress and plane strain conditionsMonotonic plastic zone sizeCyclic plastic zone size Fracture Toughness*

Plastic Zone SizeMaterials develop plastic strains as the yield stress is exceeded in the region near the crack tip (see Fig. 1). The amount of plastic deformation is restricted by the surrounding material, which remains elastic. The size of this plastic zone is dependent on the stress conditions of the body. *

Plastic Zone Size,contd*Gambar 1. Yielding near crack tip

Plane stress andplane strain conditionsIn a thin body, the stress through the thickness (sz) cannot vary appreciably due to the thin section. Because there can be no stresses normal to a free surface, sz = 0 throughout the section and a biaxial state of stress results. This is termed a plane stress condition (see Fig. 2). In a thick body, the material is constrained in the z direction due to the thickness of the cross section and ez = 0, resulting in a plane strain condition. Due to Poisson`s effect, a stress, sz, is developed in the z direction. Maximum constraint conditions exist in the plane strain condition, and consequently the plastic zone size is smaller than that developed under plane stress conditions. *

Plane stress andplane strain conditions,contd*Gambar 2. Plane stress and plane strain conditions