How to determine the offset amount of steam pipe supports

Structural Analysis and Selection of Pipe Supports and Hangers. Publication date: April 21, 2016. Source: Article from the 10th issue of “Power Equipment” in 2015. Authors: Liu Xiaolong, Kong Xianghao, Inner Mongolia Electric Power Survey and Design Institute Co., Ltd. The article introduces the proper steps for designing pipe supports and hangers, as well as their classification and components； It also elaborates in detail on the selection and installation of pipe supports and hangers, as well as the precautions to be taken. (Inner Mongolia Electric Power Survey and Design Institute Co., Ltd.? 010020) Abstract: Pipe support and hanger designers are one of the key figures in pipe design. This paper introduces the proper procedures for designing pipe supports and hangers, as well as their classification and composition ； It also elaborates in detail on the selection and installation of pipe supports and hangers, as well as the precautions to be taken. Keywords: pipeline ； Brackets and supports ； Design ??????? 1 Scope of design and main functions of pipe supports and hangers ??????? 1.1 The supports used to hold pipes are generally divided into two parts; one part is part of the main civil engineering structure, and is commonly referred to as “pipe racks” and “pipeline galleries”” ； The other components are the various supports, braces, and hangers that connect the pipes to the main structural elements of the building; these include various brackets fixed to the building itself, as well as standalone brackets with a height of 2 meters or less. These are collectively referred to as \"pipe supports and hangers\". The pipe supports and hangers referred to in the text are the latter, and their design is the responsibility of the piping specialty. ??????? 1.2 The main functions of pipe supports and hangers can be summarized as: bearing the loads on the pipes, restricting the displacement of the pipes, and controlling pipe vibrations. Among these, bearing pipeline loads is the most important and common function of supports and hangers. ??????? 2. Reasonable steps in the design of pipe supports and hangers ? ??????? The design of pipe supports and hangers should be carried out concurrently with the piping layout design. If the design of pipe supports and hangers is delayed until after the completion of the piping layout drawings, it will delay the preparation of equipment specifications as well as the issuance of construction drawings by the civil engineering department. This will inevitably prolong the overall construction schedule. Moreover, the design of pipe supports and hangers cannot be completed simultaneously with the piping design, thereby affecting the planned commissioning date. Therefore, proper organization of the design phase for pipe supports and hangers should be regarded as a very important methodological issue. The relationship between the design arrangement of these supports and hangers and the progress of piping work is shown in Figure 1. ??????? 3 Classification and composition of pipe supports and hangers Based on the three main functions of pipe supports and hangers—load bearing, positioning, and vibration control—as well as their respective characteristics and applications, they can be classified into three categories: load-bearing supports and hangers, positioning devices, and vibration control devices (see Table 1). Pipe support and hanger assemblies consist of components mounted on the pipe (pipe section structure), components fixed to the load-bearing structure (building structure or equipment) (root structure), and intermediate components that connect these two types of components. ??????? 4 Key Points for Setting Pipe Supports and Hangers ??????? During the pipeline layout process, consideration must be given to the location of supports and hangers, as well as their feasibility, rationality, and cost-effectiveness; these are requirements applicable to both those who design the pipelines and those who design the supports and hangers. Stress analysts and pipeline support and hanger designers should study the entire piping support system, and after reaching a consensus, determine the location and type of the pipeline supports and hangers. ??????? 4.1 Determination of the spacing between pipe supports and hangers ① The placement of pipe supports and hangers must meet the requirements regarding the maximum allowable span of the pipes. The maximum spacing between supports and hangers for horizontal pipes should be determined by calculating based on strength and stiffness criteria; the smaller value shall be adopted. The strength condition is that the bending stress caused by the pipe’s own weight must not exceed half of the allowable stress of the material at the design temperature. The stiffness condition limits the bending deflection caused by the pipe’s own weight. In general pipeline design, the deflection inside the fitting should not exceed 15 mm, and the deflection outside the fitting should also not exceed 38 mm. For steam pipes laid without slope, their deflection shall not exceed 3 mm. ②For pipes with pressure pulsations, the spacing between supports should be determined based on the required natural frequency of the pipe, in order to prevent resonance. ??????? 4.2 Determination of the location of pipe supports and hangers: When there are concentrated loads, the supports and hangers should be placed near these loads in order to reduce eccentric loads and bending stresses ； Brackets and supports should be installed near sensitive equipment to prevent the equipment connections from bearing excessive pipeline loads; these brackets and supports are preferably placed close to the equipment’s pipe openings ； Pipelines that experience intense vibration should be equipped with separate supports that are firmly fixed to the ground, in order to prevent the transmission of vibration ； Apart from vibrating pipes, the beams and columns of existing buildings should be utilized as much as possible as anchorage points for the supports ； For the sake of easy maintenance, pipe supports and hangers should be installed in locations that do not interfere with the connection of pipes and equipment as well as maintenance activities ； For pipes subjected to flexible analysis, the positions of supports and hangers are determined based on the analysis, taking into account the feasibility of providing such support ； When the flexibility of the pipeline is too high, supports and hangers should be added to prevent excessive stress as well as excessive movement and amplitude of the pipe ； When the support and hanger are equipped with special functional components, there should be sufficient space between the pipeline and the anchoring members at the installation location. ??????? 5 Considerations for the Design of Pipe Supports and Hangers ??????? 5.1 When designing pipe supports and hangers, standard and common types should be given priority; ordinary supports and hangers should be preferred as much as possible, with spring-based supports and hangers used sparingly. Since spring supports are more expensive than ordinary supports, they also suffer from failure issues under long-term operation; they are not as durable and reliable as ordinary rigid supports. Moreover, the excessive use of spring supports can cause the displacement directions at various points in the piping system to get out of control, resulting in poor stability. ??????? 5.2 The materials used for pipe supports and hangers should meet the requirements of the working environment. Choosing the wrong material may result in insufficient mechanical properties of the pipe support components under specific operating conditions. The material of the supports and hangers in contact with pipeline components shall be selected according to the design temperature of the pipeline. The material of the support and hanger components welded directly to the pipeline must be compatible with the material of the pipeline components. The allowable shear stress of the material should be 0.6 times the allowable stress of the material at the design temperature ； The allowable tensile stress of the tie rod material shall be reduced by not less than 25% compared to the allowable stress of that material. ??????? 5.3 It should be noted that the horizontal displacement of pipes affects the performance of supports and hangers. As a general requirement, the length of the adjustable rods in rigid rod hangers should be at least 20 times the amount of horizontal displacement, and the vertical angle of the rods should not exceed 3 degrees ； The length of the adjustable tie rod in the flexible hanger shall be no less than 15 times the horizontal displacement, and the vertical angle of the hanger rod shall not exceed 4 degrees ； Attention should also be paid to sliding brackets to prevent them from becoming dislodged due to excessive displacement. When the horizontal displacement of the pipeline has a significant impact, the supports and hangers should be installed offset. The so-called misalignment of supports and hangers refers to the installation of their bases at a certain horizontal distance away from the pipe section, in order to reduce the impact of horizontal displacement at the support points on those supports and hangers. The support brackets can be installed off-center; they can be offset at the root or at the pipe section. Root offsetting is possible; it can be offset in both the X and Y axes simultaneously. The pipe can only be offset along the centerline of the pipeline, and as a result the actual support points will shift, increasing the errors in the static analysis of the pipeline; unless the analysis is recalculated using the actual support points. Therefore, it is advisable to offset the supports and hangers entirely at their roots; the amount of offset for these supports and hangers should be such that the deflection angle of the hanger rods in the cold state is equal to that in the hot state. ??????? 5.4 The type of pipe supports and hangers selected should meet the requirements of pipe layout and pipe flexibility calculations; effective pipe support and hanger systems should be chosen. When selecting such supports and hangers, attention should also be paid to the impact of their own weight. Compared to the loads imposed by the pipes, the weight of the pipe section in supports and hangers accounts for approximately 1% to 3%; the weight of spring support and hanger assemblies is about 2% to 20%; the weight of constant-force support and hanger assemblies is roughly 6% to 35%; and the weight of the auxiliary structural elements at the base is about 1% to 3%. The self-weight of the entire support and hanger assembly ranges from 3% to 40% of the pipeline load. Therefore, the self-weight of supports and hangers is an important component of the loads on them that cannot be ignored, and it should be calculated based on the actual conditions of each component within each support or hanger; it cannot be estimated using a fixed ratio. For constant-force spring hangers, care must be taken in selecting the displacement value. Given that there may be discrepancies between the calculated thermal displacement and the actual thermal displacement, a certain margin should be incorporated when determining the specifications of the hanger. The selected displacement value is generally 1.2 times the calculated displacement value, with this margin being no less than 20 mm ； For variable spring hangers, the rate of change of load should not exceed 25%. Considering economic considerations, when thermal displacement is upward, the working load should be selected above the center line; when thermal displacement is downward, the working load should be selected below the center line. ??????? 5.5 Attention should be paid to pipeline vibration control; under the action of dynamic loads, pipelines can experience varying degrees of swaying and vibration. From the perspective of preventing pipeline vibration, when selecting pipe supports, rigid round steel hangers should be used as little as possible, or not used at all. In areas where forced vibration and/or impact vibration occur during operation, it is still necessary to install appropriate bracing rods, struts, shock absorbers, or dampers to ensure the safety of pipeline vibration. ??????? 6 Conclusion ??????? In summary, the design of pipe supports and hangers is closely related to the safe operation of pipes. By installing such supports and hangers, it is possible to control the stress levels in the piping system, as well as the forces and moments exerted on the equipment, thereby keeping the piping system in a safe state and ensuring the long-term safe operation of the pipes and equipment. In a sense, the piping planning process is actually the planning of piping supports and hangers. It can be seen that the design of pipe supports and hangers plays a very important role in pipeline design. References: “Design and Calculation of Pipe Supports and Hangers” TC42B2-94, Chemical Process Piping Design Technology Center, Ministry of Chemistry, October 1994. “Code for Design of Pipe Supports and Hangers in Petrochemical Industries” SH/T3073-2004, National Development and Reform Commission, 2004. Lin Qilue and Zhou Meifang, editors. Pipe Support Technologies. Shanghai Science and Technology Press, 1994. “Standard Drawings for Pipe Supports” HG/T21629-1999, Petroleum and Chemical Industry Bureau, 1999. Qu Zhaojia, Wang Jin, and Qu Shengwei, editors. Concise Manual on Calculation and Design of Pipe Supports. Machinery Industry Press, August 2002. Author’s profile: Liu Xiaolong: Born on April 16, 1988; male, Han ethnicity; from Yu County, Hebei Province. Holds a bachelor’s degree and is an assistant engineer. His area of expertise is the design of thermal power plant equipment in design institutes. Second author ； Kong Xianghao, born on December 10, 1990, is a male of Mongolian ethnicity. His place of origin is Hohhot, Inner Mongolia. He holds a bachelor’s degree and works as an assistant engineer. His research interests lie in the mechanical engineering design for thermal power plants at design institutes.

It is the result of pipeline stress analysis. After analyzing the steam pipes using CAESAR 2, the report indicates the displacement at the support points; it is based on this displacement that the pipe supports should be positioned.

Indeed. In the design process, attention is often overlooked regarding the design and material selection of supports for small pipes and non-thermodynamic pipes. The corrosion issues that arise at the junctions between stainless steel pipe supports and pipe trays are also frequently neglected. Corrosion over time can lead to serious problems, resulting in accidents; this is something that deserves caution

Determined based on the displacement amount and installation direction