Determining Wall Thickness

I he following formulas are used in the ASME Code Section VIll, Division 1 for determining wall thickness  

Maximum Allowable Stress Value for Common Steels 

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To determine wall thickness and stiffening requirements for straight pipe under external pressure, the procedure outlined in ASME BPV Code Section VIII, Division 1, UG-28 through UG-30 shall be followed, using as the design length, L, the running centerline... 

Steel vessels which are to receive a masonry lining must conform to ASME boiler and pressure vessel code. Section VIII Division 1, and in particular the design detailed in paragraph UG-22 item 4, which states that in lined vessels, loading due to the lining itself (such as weights and stresses) must be taken into account to determine wall thickness and supports. 

DOT and TC regulations require the hydrostatic testing of compressed gas cylinders by water jacket or other suitable methods that provide accurate data [1, 2]. The hydrostatic test determines the total expansion and permanent expansion under specified test pressure. These expansion readings determine wall thickness, average wall stress, and level of yield strength of the steel. DOT or TC must approve in writing the type and operation of the test apparatus. 

Figure 9-12. This infrared system determines wall thickness by measuring how much IR radiation passes through the wall of the container.

Some cylinders have thicker walls due to differences in manufacturing methods and inspection procedures. Values shown are for absolute minimums allowed by specifications. Higher values may be used if information showing thicker walls than those listed is obtained from the manufacturer of the cylinder. Use of ultrasonic testing is suggested for determining wall thickness. 

Choosing a pipeline size and determining wall thickness represent a major target in the design of piping system. In this respect, one should be aware of two fundamental concepts... 

Ultrasonic inspection is capable of locating both internal and surface-connected defects however, it will not detect narrow cracks oriented parallel to the beam. Turbine manufacturers employ ultrasonics to qualify the internal soundness of critical forgings such as shafts and discs and to determine wall thickness for cooling passages. 

The large temperature difference of the remarkable borehole, opposite other boreholes and their environment is significant. This high temperature difference is a typical feature for a small wall thickness between borehole and blade surface. For technical reasons, precise eroding of the boreholes is difficult. Due to this, the remaining wallthickness between the boreholes and the blade surface has to be determined, in order to prevent an early failure, Siemens/Kwu developed a new method to determine the wallthickness with Impulse-Video-Thermography [5],... 

Fig. 1 Simulated, profiles across a pipe in the tangential projection technique and the results of different filters for determination of the projected wall thickness...

The accuracy of the presented methods was verified using test pipes with various diameters and wall thickness of which the wall thickness was measured independently using a slide-rule. Both on film and on the monitor the wall thickness could be determined within an accuracy of ca. 0.2 - 0.3 mm. 

Basically it is only possible to determine a wall thickness change in penetration direction from a density variation of a radiographic film. No absolute wall thickness values can be obtained in this way contrary to the tangential method. 

After this calibration step (the effective absorption coefficient is determined from a known wall thickness change and the corresponding variation of the optical film density) the evaluation of local wall thickness changes Aw (corresponding to De,o) from the nominal wall thickness w o , (corresponding to Dnom) can be done according to ... 

Wall Thickness Determination in Digital Radiography, T. Wawrzinek, U. Zscherpel, C. Bellon, COFREND Congress on NDT, Nantes 1997, conference proceedings, vol. l,pp. 79-83... 

By request of the owner, two concrete test cores (0 15cm) were drilled out of the building. The wall thickness was determined at 25cm, with the maximum aggregate size being about 32mm. 

These two transducer pairs are activated alternating. For this purpose an ultrasonic instrument is combined with a two channel multiplexer. Figure 8 presents a modified standard instrument USN52 which also implies a modified software. This system performs four measurements per second - alternating the velocity and the thickness are determined. The probe can be scanned over the surface and in every position both, the velocity and the wall thickness are indicated Using the serial interface of the instrument finally a two-dimensional map of velocity or thickness can be generated. 

Through the use of lab tests implemented by the pulp and paper companies in the United States and Canada it was determined that all but one manual technique were both unrepeatable and inaccurate. During some years ago the operators of black liquor recovery boilers have been able to take advantage of the latest teehnology to inspect the wall thickness of the near drum generator tubes. The technology utilises immersion ultrasound and automated computer... 

The values of CJs are experimentally determined for all uncertain parameters. The larger the value of O, the larger the data spread, and the greater the level of uncertainty. This effect of data spread must be incorporated into the design of a heat exchanger. For example, consider the convective heat-transfer coefficient, where the probabiUty of the tme value of h falling below the mean value h is of concern. Or consider the effect of tube wall thickness, /, where a value of /greater than the mean value /is of concern. 

Equations 1 to 3 enable the stresses which exist at any point across the wall thickness of a cylindrical shell to be calculated when the material is stressed elastically by applying an internal pressure. The principal stresses cannot be used to determine how thick a shell must be to withstand a particular pressure until a criterion of elastic failure is defined in terms of some limiting combination of the principal stresses. 

It is assumed that process conditions and physical properties are known and the following are known or specified tube outside diameter D, tube geometrical arrangement (unit cell), shell inside diameter D shell outer tube limit baffle cut 4, baffle spacing and number of sealing strips N,. The effective tube length between tube sheets L may be either specified or calculated after the heat-transfer coefficient has been determined. If additional specific information (e.g., tube-baffle clearance) is available, the exact values (instead of estimates) of certain parameters may be used in the calculation with some improvement in accuracy. To complete the rating, it is necessary to know also the tube material and wall thickness or inside diameter. 

Once the mould is removed from the oven the mould starts to cool at a rate determined by the type of cooling - blown air (slow) or water spray (fast). There may be a overshoot in the internal air temperature due to the thermal momentum of the melt. This overshoot will depend on the wall thickness of the plastic product. In Fig. 4.61 it may be seen that the inner air temperature continues to rise for several minutes after the mould has been taken out of the oven (at about 13.5 minutes). 

The wall thickness of the pipe or plate used for the shell is normally determined from the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. TEMA standards also specify some minimum wall thicknesses for the shell. 

In order to adequately describe the size of a heater, the heat duty, the size of the fire tubes, the coil diameters and wall thicknesses, and the cor lengths must be specified. To determine the heat duty required, the maximum amounts of gas, water, and oil or condensate expected in the heater and the pressures and temperatures of the heater inlet and outlet must be known. Since the purpose of the heater is to prevent hydrates from forming downstream of the heater, the outlet temperature will depend on the hydrate formation temperature of the gas. The coil size of a heater depeiuLs on the volume of fluid flowing through the coil and the required heat duty. 

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