Houston: Peng Engineering, p. Introduction Strength of Materials Basics Thermal Expansion and Piping Flexibility Code Stress Requirements. Pipe Stress Engineering - L.C. Peng - Ebook download as PDF File .pdf) or view presentation slides online. Pipe Stress Engineering - L.C. Peng. Pipe Stress Engineering By Liang Chuan L C Peng And - [Free] Pipe Stress Engineering By. Liang Chuan L C Peng And [PDF] [EPUB] -. PIPE STRESS.
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Pipe stress engineering / by Liang-Chuan (L.C.) Peng and Tsen-Loong (Alvin) Peng Peng, New York, NY ): American Society of Mechanical Engineers . PDF | This paper presents engineering decision-making on pipe stress analysis through the application of knowledge-based systems (KBS). Stress analysis, as. We deliver engineering and technology training that will maximize your business goals. . Codes Governing Piping Design and Pipe Stress Analysis
Evaluate the loads on structural anchors e. Evaluate the loads on pipe supports f.
Evaluate piping movements from thermal expansion or contraction 5 Step 1: What do you wish to achieve? Cont d g. Evaluate the effects of wind loads on the piping system and attached equipment h. Evaluate the effects earthquake loads on the piping system and attached equipment i. Evaluate the effects of wave loads on the piping system and attached equipment j.
Evaluate the effects of soil resistance to piping system movements and stresses k. Which Piping Code will govern the design of the piping system? Collect all plan and elevation drawings 4.
Stress analysis of parallel oil and gas steel pipelines in inclined tunnels
Nominal Pipe Diameter b. Corrosion Allowance d. Specific Gravity of contents e. Branch Connection Type n. Location b. Stiffness or Flexibility c.
In the s and s, when engineers started analyzing piping systems, they had only one thing in mind: calculating the stress due to thermal expansion.
In other words, they checked the piping layout to see if the piping system was flexible enough to absorb the thermal expansion due to temperature change. The analysis was referred to as piping flexibility analysis. Books [3—6] and articles [7—9] written during this period dealt mainly with flexibility analysis. Later on, as technology progressed, pipe stress analysis encompassed much more than just checking flexibility; yet nowadays many engineers still refer to pipe stress analysis as flexibility analysis.
This slight mix-up in terms is not important. However, the concept that flexibility is the only consideration in piping stress analyses can lead to an expensive, and unsafe, sub-standard design.
For instance, many engineers tend to consider that providing additional flexibility in the piping is a conservative approach. In reality, additional flexibility not only increases the material cost and pressure drop, it also makes the piping prone to vibration, the biggest problem area of the piping in operation.
These facts should serve as clues toward designing better piping systems. Consider, for example, the piping installed to move the process fluid from the storage tank to the process unit as shown in Fig. This temperature-independent displacement and rotation will exert a great influence on the connecting piping. Furthermore, the tank nozzle connection is far from rigid.
Its flexibility has to be estimated and included in the analysis. Then, after the pipe forces and moments at the connection are calculated, they have to be evaluated for their acceptance. These items, using Fig. The next items we come across are flanges and valves. Can they maintain the tightness under piping forces and moments? Can valves operate properly under pipe forces and moments?
These need to be checked even though the pipe itself is strong enough for the same forces and moments. We know the support friction can also have a significant effect on piping movement. The situations and methods to include the friction effect also need to be considered. In addition to the average pipe temperature, the pipe might also have a temperature gradient across the pipe cross-section due to stratified flow or blow off of low-temperature fluid.
Even radiant energy from the sun on empty un-insulated pipe can cause this type of temperature difference. This type of bowing phenomena can create a great problem in the piping and needs to be considered.
The piping connected to rotating equipment also needs the consideration of potential water hammer, pulsation, and other dynamic phenomena. Proper spring hangers will need to be selected and placed to ensure that the piping is properly supported under all operating conditions. At the vessel connection, again, the flexibility and displacement at the connection have to be included in the analysis.
After pipe forces and moments at the connection are calculated, vessel local stresses have to be evaluated to see if they are acceptable. Then, of course, if the structure is located in an earthquake or hurricane zone, earthquake and wind loading have to be considered when designing the piping system.
In general, the purpose of pipe stress analysis can be summarized into two broad categories: a Ensure structural integrity: This involves the calculation of stresses in the pipe due to all design loads. Necessary procedures are taken to keep the stress within the code allowable limits. This code stress check is the basic assurance that failures from breaks or cracks will not occur in the piping. Flange leakage, valve sticking, high stress in the vessel nozzle, and excessive piping load on rotating equipment are some of these problems.
The work required in maintaining the system operability is generally much greater than that required in ensuring the structural integrity. This is mainly attributable to the lack of coordination between engineers of different disciplines. Rotating equipment manufacturers, for instance, design non-pressure parts, such as support and base plate, based mainly on the weight and the torque of the shaft.
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Then they specify the allowable piping load with that design, disregarding the fact that some practical piping load always exists and needs to be accommodated. The allowable loads they provide are generally much too small to be practical.
Unfortunately, these allowable values go unchallenged, mainly because the industry as a whole gives no incentives to manufacturers to produce equipment that can resist the extra piping load. If more and more engineers would request the extra strength or give preferential treatment to manufacturers that produce stronger equipment, an optimal solution might eventually be reached.
Until such time comes, piping mechanical engineers should be prepared to spend three times as many man-hours in stress engineering the piping system connected to rotating equipment. And because a separate chapter is dedicated to pipe supports and restraints, we shall not include them in this discussion. In the following, we use Fig.
Starting with the main pipe, we have to know the pipe material, which is generally given by the American Society of Testing and Materials ASTM  specification number. The pipe is generally identified by its nominal diameter and nominal thickness. For pipes 12 in. However, for sizes 14 in. For each pipe size, the outside diameter is fixed for a given nominal diameter. This is done so that all pipes with the same nominal size can use the same pipe support attachments such as clamps, and insulation blocks.
Each pipe size also has several commercially available thicknesses called nominal thickness. In the United States, these thicknesses are also represented by weight grades as standard Std , extra strong XS , and double extra strong XXS , and by schedule numbers ranging from schedule 10 Sch to schedule Sch For instance, a 6-in.
The schedule number itself dose not represent any thickness; it has thickness assigned only when tagged with a pipe diameter. See Appendix A for standard nominal pipe wall thicknesses.
Pipe Stress Engineering
The pipe material involves different manufacturing processes that might implicate some stress risers and tolerances. The pipe can be broadly classified via the method in which it was manufactured: seamless or welded.
Welded pipes, which are somewhat weaker than seamless pipes due to the weld, are further classified into several categories. From the seam position, we have longitudinally welded and spirally welded two main types.
From the welding process, we have furnace butt welded, electric resistance welded, and electric fusion welded three methods. Each type of welding has its unique joint efficiency that needs to be included in the pressure design. For tolerances, we are mostly concerned with thickness under-tolerance, which can reduce the pressure resisting capability of the pipe. Under-tolerance is the allowable amount of thickness in which a manufactured pipe can be made thinner than the nominal thickness.
In general, seamless pipes and electric resistance welded pipes have a higher under-tolerance of about This under-tolerance needs to be included in the stress design of the pipe. To connect piping components together, we use either circumferential weld or flange connections. The circumferential weld, also called girth weld, is for a permanent connection, whereas the flange is used for locations requiring occasional separation.
The girth weld also has a joint efficiency that works against longitudinal stress. This joint efficiency does not affect pressure design, which is controlled by circumferential hoop stress. For loadings other than pressure, this girth weld joint efficiency is implied in the stress intensification factor. Therefore, in most piping codes, circumferential weld joint efficiency is seldom mentioned. It is also often overlooked by stress engineers.
In addition to the joint efficiency that affects the general strength of the piping, the weld also hastens creep failure at creep temperature. The additional reduction of creep strength over the non-weld-affected body is called the weld strength reduction factor.
This is the factor applied, over the joint efficiency, at high temperature ranges. The same factor is applied at both longitudinal welds and circumferential welds.
However, longitudinal weld affects only the calculation of wall thickness, which is governed by the circumferential hoop stress. On the other hand, circumferential weld affects only the sustained longitudinal stress due to pressure, weight, and other mechanical loads. The weld strength reduction factor is not applicable to occasional stress due to the generally short duration of the stress. It also does not affect thermal expansion and displacement stress range due to the self-limiting nature of the stress.
However, B Details of the application are given in Chapter 4, which deals with code stress requirements. Flanges are available in several different types.
From the structural construction point of view, it can be classified as welding neck, slip-on, or lap joint three types.
Pipe Stress Engineering-lc Peng
Each type has its length, weight, and stress intensification factor, all of which have to be identified and considered in the stress analysis. Flanges are also identified by classes. Each class has its set of pressure-temperature ratings, relating allowable pressures with operating temperatures.
At a given operating temperature, the selected flange class shall offer an allowable pressure that is either equal to or greater than the design pressure. Table 1. The table also shows the flange thickness required for each class, for 6-in. It also gives some idea about the magnitude of flange thickness, excluding hub. It is also interesting to note that the flange classes were originally called pounds. Class flanges were called pound flanges, and so forth.
This was because, originally, Class flanges were rated for pounds per square inch psi pressure at a benchmark temperature.
Pound lb meant psi, and had nothing to do with the weight of the flange. The benchmark temperatures used were different for different materials. However, as more accurate material data became available and more accurate stress calculations became possible, the original ratings also appeared less accurate. It is obvious that current pressure-temperature ratings no longer correspond to the original benchmark idea.
Although the pound classification is not very meaningful right now, it is still used by many engineers. See Appendix E for layout dimension and weight of valves and flanges. The turning of the pipe is accomplished by bends.
Bends have several general types. The most common bend is the so-called long-radius elbow, which has a bend radius equal to 1. The same standard also includes a short-radius elbow, which has a bend radius equal to the nominal pipe diameter.
Short-radius elbows are used in tight spots where available space is not enough for long-radius elbow. The cited factory-made forged elbows are quite expensive and also incur high flow friction loss due to the small bend radius. One alternative is to make the bend directly by bending the pipe. To avoid excessive thinning and potential wrinkling, the bend radius of this type is generally bigger than three nominal pipe diameters. The one shown in the figure is a 5-D bend.
Another alternative, mainly to save cost, is to cut the pipe into angled miters and bring them together to form the bend.
This type of bend is called a miter bend. All these different bends have different wall thickness requirements, flexibility factors, and stress intensification factors to be considered in the design and analysis.
Branch connections are used to form the branches of the piping. The most common full-size branch connection is the forged welding tee, which is made according to ASME B Generally, the welding tee is quite expensive, but provides the smoothest flow passages and least stress intensification factor among all branch connections.
Besides the welding tee, the most economical and readily available branch connection is the un-reinforced fabricated tee. Generally called a stub-in connection, this type of connection is made simply by cutting a hole on the run pipe and welding the branch pipe to it. A stub-in connection is cheap and easy to make, but can handle only about one-half of the pressure that the pipe can.
It also has a very high stress intensification factor. To improve both the pressure resisting capability and stress intensification, proper reinforcement is required. When designed properly, the reinforced fabricated branch connection can take the same pressure as a run pipe can, and also substantially reduce stress intensification from the un-reinforced branch connection. Other branch connections include extruded tee, integrally reinforced weld-on, contoured weld-on, and half coupling.
Each of these branch connections has its pressure design requirements and stress intensification that need to be considered in the design and analysis. See Table 3.
See also Appendix B for layout dimension of butt-welding fittings. The piping also consists of many types of valves. For valves, we have to know the type, end-to-end length, and weight, for inclusion in the analysis. The valve itself is generally approximated to an equivalent pipe of the same length with three times the stiffness of the connecting pipe.
For valves with a heavy operator, such as motor-operated ones, the operator weight and off-center location has to be included in the design analysis. This is especially important in analyzing dynamic effects such as earthquakes.
For safety-relief valves, we also have to consider the dynamic effect due to the sudden discharge of the fluid when the safety valve pops open. Valves share the same classification as flanges. They have the same pressure-temperature rating as flanges for a given class and material. To increase the flexibility of the system, the piping may also include some types of flexible connections. The one shown in the figure is a tied bellow expansion joint.Bellows are intended to control the pipe stresses and strains caused by the natural thermal expansion of material as it changes from ambient temperature to steady state temperature during start up and in reverse direction during shut down.
I agree that this is a landmark piece of work. Class flanges were called pound flanges, and so forth.
Seismic Loads the method to be used to simulate the seismic event RSA or percentage of gravity and the magnitude of the seismic event e. Peak stresses are the highest stresses in the region under consideration and are responsible for causing fatigue failure.
Its a long story. The ring and groove design actually uses internal pressures to enhance the sealing capacity of the connecting flanges. However, B As you learn, the more you will understand in the next reading.