Seven stages of chemical technology from creativity to industrialization (Issue 64/100 in total)--detailed design

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Seven stages of chemical technology from creativity to industrialization (Issue 64/Total 100) - Engineering Transformation: Detailed design for everyone.: Hello everyone! In the last issue, we talked about basic design, and the genes of the device were determined. This issue talks about the last link in the project transformation stage - detailed design. Detailed design is the "last mile" of construction drawings. The basic design tells you "this equipment is here and that pipe goes over there", and the detailed design answers:: How many millimeters are the mounting bolt holes of this equipment from the edge of the foundation? At what elevation does this pipe pass through the pipe gallery? Should thermal stress compensation be done when passing next to high-temperature pipelines? Will the handwheels of two adjacent valves interfere with each other? Many people think that detailed design is a "refined version" of basic design. Just enlarge the scale and mark all the dimensions. This understanding is not quite right. Detailed design is not a simple refinement, but a comprehensive spatial integration and construction transformation. Spatial conflicts, stress issues, and inconvenient operation and maintenance that may have been ignored in the basic design stage—only when all professional 3D models are put together in the detailed design stage will these problems be exposed. Every modification at this stage is far more expensive than the basic design stage. 1. The difference between detailed design and basic design. Basic design focuses on “whether it can be realized.” Can the distillation tower be separated? Is the heat exchanger area sufficient? Is the pump head sufficient? The detailed design focuses on "how to install it and how to use it." How should the pipes be routed so as not to fight, where should the valves be installed so that the operator can access them, and in which direction should the heat exchanger tube bundle be cored for ease of maintenance. The deliverables of basic design are mainly process system diagrams, equipment layout diagrams, and main equipment data sheets. The deliverables of detailed design are construction drawings that can be directly handed over to the construction team for construction according to the drawings - pipeline empty views, structural reinforcement drawings, electrical wiring diagrams, and instrument circuit diagrams. Errors in basic design can be corrected in the detailed design stage, and the cost is relatively controllable. If errors in detailed design are brought to the construction site, the cost of rework will be cutting pipes, pounding concrete, and reordering, and the cost will be magnified hundreds or thousands of times. In the basic design stage, coordination between various disciplines mainly relies on the exchange of design conditions and drawings. During the detailed design phase, all disciplines must work together in the same 3D model, and collision checks run automatically. The movement of any pipe immediately exposes conflicts with other disciplines in the model. The 3D model is the core platform for detailed design and the core means of quality control. 2. Pipe stress analysis and three-dimensional piping Pipe stress analysis and three-dimensional piping design are the two most technical tasks in detailed design and most directly affect the safety and operability of device operation. Types of pipes requiring stress analysis: High-temperature pipelines with relatively high operating temperatures, large-diameter pipelines with relatively large nominal diameters, pipelines connected to sensitive equipment nozzles with strict restrictions on the nozzle load, pipelines transporting extremely or highly hazardous media, and periodically operating pipelines that require fatigue analysis. Simply put, pipes with high temperatures, large pipe diameters, dangerous media, and pipes connected to important equipment should all be included in the scope of stress analysis. The core problem to be solved in stress analysis is: How much thermal expansion will occur when a high-temperature pipe rises from normal temperature to operating temperature? If both ends are rigidly fixed and there is nowhere to release the thermal expansion, the pipe itself will generate huge thermal stress. In severe cases, it may cause cracks in the weld or excessive stress on the equipment nozzle. Stress analysis is to reasonably set up expansion joints, spring supports, hangers, and fixed brackets on the pipeline so that the pipeline has enough flexibility to absorb thermal displacement in the thermal state, and at the same time, the load on the equipment nozzle is controlled within the allowable range. The selection of spring supports and hangers needs to be determined based on the stress analysis results - the thermal displacement of the pipeline, the load in the operating state, and the load in the installation state. The three data jointly determine the spring model and set load. Three-dimensional piping design is the art of space. Equipment models, structural models, and pipe gallery models all enter the three-dimensional platform, and automatic collision checks are run to eliminate all hard and soft collisions. Hard collision refers to the direct interference between the pipeline and the steel structure, equipment, and other pipelines in space, which must be eliminated. Soft collision is more concealed and more troublesome - although the pipe does not directly collide with any object, there is insufficient operating space for the valve handwheel, insufficient space for disassembly and assembly of flange bolts, the spacing between the insulation layers is too small, and the instrument panel is blocked by the pipe and cannot be read. These problems are extremely difficult to find on two-dimensional drawings, but they can be checked one by one in the three-dimensional model by simulating the operation path and maintenance space. In the three-dimensional model, the operator's inspection route can be simulated: When you come up from the stairs, which platform you walk to, which valves you pass, which instruments on the inspection route need to be bent down to look at, and which ones need to be looked up at. Designers first walk the path that operators need to walk every day in the model. This kind of "virtual inspection" can identify many inconvenient design problems in advance - good three-dimensional piping design is to shorten the length of the pipeline as much as possible and reduce the number of elbows and pipe fittings while meeting the stress requirements and operation and maintenance space. This is a process that requires repeated trade-offs and optimization. 3. Synchronous deepening of structural, electrical, and automatic control detailed design stages. The work of each major is parallel, and design changes in any major may trigger a chain reaction. The structural major performs frame structure calculations, pipe gallery design, pile foundation design and equipment foundation design. The core input of the structural design is the load conditions provided by the equipment professional - the self-weight of each equipment, the weight after filling with water, the weight of the medium during operation, wind load, and earthquake load. If the load conditions are submitted incompletely or with deviations, the structural calculation is based on errors. Omission or underestimation of the load of heavy equipment will lead to insufficient beam and column cross-sections. When it is discovered and adjusted at the detailed design stage, the architectural plan and foundation plan have been affected. The electrical major configures transformer capacity, distribution circuits, cable selection and laying, lightning protection and grounding, and strictly divides explosion hazard areas according to explosion-proof requirements. The explosion hazard area division map is the "safety map" of electrical design - which area uses explosion-proof motors, which area uses explosion-proof lamps, and which area cables must use explosion-proof sealed joints, all according to this map. If the area is divided incorrectly, non-explosion-proof equipment may be used in explosion-risk areas, which is a major safety hazard. The selection of electrical equipment must strictly correspond to the division of explosion-proof areas. Before power is transmitted, a dedicated person shall check the sealing integrity and grounding continuity one by one. Automation specializes in DCS and SIS configuration design, control panel design, instrument cable and bridge design. The automatic control work in the detailed design stage is to transform the control scheme and interlocking logic determined in the basic design stage into constructable and configurable design documents. The isolation of SIS and DCS is further implemented at the configuration level - the SIS logic controller is independent of DCS, SIS I/O cards and DCS cannot be mixed, and the communication between SIS and DCS must be one-way. These are stipulated in principle in the basic design stage and implemented into the configuration files and wiring diagrams in the detailed design stage. 4. In the detailed design stage of long-lead equipment technical specifications, long-lead equipment technical specifications need to be compiled and purchased first. The manufacturing cycle of long-lead equipment often takes as long as half a year to one year. If you wait until the detailed design is completed before bidding and procurement, the arrival time of the equipment will become the bottleneck of the total project period - the site has already met the installation conditions, but the equipment has not been built yet, and the entire project will be stuck waiting. The quality of technical specification preparation directly affects equipment performance and the accuracy of supplier quotations. The specifications cannot be written too vaguely - "The flow rate of the pump is several cubic meters per hour, the lift is several meters, and the material is stainless steel" - if written like this, the supplier will quote within the widest range. The price difference between high and low configurations may be very large, and the workload of subsequent bid evaluation and technical clarification will be doubled. The specification should try to clarify the key parameters and acceptance criteria - the performance curve of the pump requires that the efficiency at the normal operating point should not be lower than a certain value, the vibration value should not exceed a certain value, and the bearing design life should not be lower than a certain value. The more specific the key terms are, the less likely subsequent disputes will be. After the technical specifications of the long-term equipment are compiled, an internal review and the owner's review will be organized, and the bidding will be issued after confirmation. During the technical bid evaluation, the supplier's bidding documents must be checked item by item against the specifications, and deviations shall be evaluated item by item - whether to accept the deviation or require the supplier to make corrections, each decision must have a technical basis. 5. Review and filing of construction drawings. After all construction drawings of each major are produced, they will be sent to a third-party review agency for review. Structural calculations, equipment basic drawings, pipeline stress analysis reports, electrical system diagrams and other professional drawings are all submitted for review. The review of construction drawings is not about “finding faults”, but about “finding out the truth”. No matter how experienced designers are in their professional fields, they may still have cognitive blind spots. Third-party review agencies are independent of the project and can identify potential problems in the design from different perspectives—whether the structural design meets the strength requirements of the seismic code, whether the fire protection design meets the rigid requirements for fire separation and evacuation routes, and whether the lightning protection grounding design covers all buildings that need protection. The opinions put forward by the review agency need to be responded to one by one, and the drawings that need to be modified should be revised and resubmitted for verification. This process cannot be omitted. In order to catch up with the schedule, some projects directly use the construction without serious modifications after the review opinions come back. When the quality supervision station arrives at the site, problems are found, and the cost of stopping the work for rectification is much greater than spending a few more days to make serious revisions during the review stage. After the construction drawings are reviewed and approved, a construction permit still needs to be applied for. The construction permit is a legal prerequisite for the start of construction. Without the permit, construction cannot start legally. Prerequisites for applying for a construction permit include:: The construction drawings have been reviewed and approved, the safety facility design special article has been reviewed and passed, the fire protection design has been reviewed and approved, the construction unit has been determined, the supervision unit has been determined, and the construction funds have been secured. The preparation of these conditions requires a certain period of time and must be considered as an independent node in the project schedule. It cannot be covered up by the illusion that "construction will naturally start after the design is completed." 6. Several pitfalls in detailed design During the detailed design stage, there are several common pitfalls worth paying attention to in advance. One is the omission of the pipe stress analysis range. Some projects only perform stress analysis on the main process pipelines, ignoring the thermal stress of auxiliary pipelines - such as steam tracing pipelines and hot oil tracing pipelines. The diameter of these pipelines is not large, but the operating temperature may be relatively high. If stress analysis is not performed, the bracket may fall off or the weld may crack due to thermal displacement during operation, eventually causing leakage. Another is a 3D model review going through the motions. The 3D model review is divided into three stages: 30%, 60%, and 90%. The content and focus of the review at each stage are different. Some projects compressed three reviews into one, or people from all majors were not present during the review—piping majors came but structural majors did not come, and instrumentation majors did not come but electrical majors did the inspection. After reviewing it this way, there were still many collisions and interferences left in the model, which were only discovered on site. Regarding the specific methods of 3D model review, a special issue will be used to expand in detail later. Another is the disconnect between construction drawings and procurement data. The equipment data sheet has been updated, but the construction drawings still have old data. The purchased equipment does not match the basic dimensions reserved on the construction drawings. The root cause of this disconnect was poor change management—after the equipment data sheet was updated, all affected construction drawings were not updated simultaneously. In the detailed design stage, the change management process must be strictly implemented. The scope of impact of any modification must be assessed, all affected disciplines must be notified, and all relevant documents must be updated simultaneously. 7. Change management that needs to be strictly controlled during the detailed design stage. An entire section is used to emphasize change management because this stage is so critical. Every time a change occurs during the detailed design stage, it may affect not just one drawing, but multiple documents from multiple disciplines. If there is no strict control, there will be a situation of "changing this and forgetting that". Change management in the detailed design stage is logically connected to the MOC discussed in detail in Issue 94. Every change, no matter how big or small, should have a written record: What is the change, why is it being changed, which majors have been assessed for scope of impact, what is the list of affected downstream documents, and whether all majors have been synchronously updated and confirmed after the modification is completed. This process may seem cumbersome, but compared to the vicious cycle of "if you change it and forget it, if you forget it you make it wrong, and if you make a mistake you rework it", being more cumbersome actually saves time. Next issue preview No. 65: Pipe stress analysis and three-dimensional piping design The previous issue briefly mentioned that pipeline stress analysis and three-dimensional piping are the two most technical tasks in detailed design. The next issue will discuss these two contents in detail - the specific methods and common problems of stress analysis, the operational details of "virtual inspection" in three-dimensional piping, and the key points of the 30%, 60%, and 90% three-stage model review.