Plant Design-Introduction to Basics and Role Of Piping Engineer

An Onshore Plant Piping View

A Piping Engineer/Piping department of a company holds a key position in the life cycle of a process plant. An assortment of never ending network with various dimensions, various end joints, fittings, sealing and insulation. What are the deciding factors behind this huge and heavy engineered structure? Does Piping Engineer can independently take the decision about every aspect of Piping? In this Blog, I am trying to give light to some basic aspects of detailed engineering pertaining to Piping Engineering. The bare minimum theoretical background each and every Piping Designer should know about the trade.
Going back my question in the last paragraph, the answer will be obviously “NO”. Every man-made marvels need good team efforts and so is the case of Process/ Refinery and another n number of Plants. The course of action from concept to commissioning and beyond involves the group efforts by process Engineering, Mechanical & Vessel, Civil & Structural, Instrumentation and Electrical Departments.A Plant life cycle involves majorly 

a) feasibility study stage, 

b) Designing stage, 

c) Construction stage, 

d ) Commissioning, 

e) Operation and Maintenance. 

Feasibility study involves economic feasibility (Majorly), risk and environmental effects. If the plant of a new product, then technical feasibility will be a major concern. It is because all thermodynamically feasible reactions won’t be practical. A “controllable” reaction is the desired one. Once such a chemical route is finalized, and then the foundation stone will lay, i.e. the Block Flow Diagram (B.F.D).The first estimates of Temperature, Pressure, Composition, Flow Rates etc can be marked on this diagram.

The conceptual design will be final with this activity which can give a rough idea of Equipment sizes, inputs, and outputs via products and by products-A sufficient lead to ascertain about the economics of the project.With this information in hand, the next task is Design Stage.

Design Stage Involves Rigorous calculation of Chemical and Mechanical Engineering and the crop will be complex and absolute information in the form of Drawings and text format.One of the first Phase of designing is the detailed study of the Chemical and Metallurgical aspects together. This material and energy balance calculation will establish operating conditions, equipment size, and utilities. When we add those to the BFD, we will get the Process Flow Diagram (P.F.D).Information in the form of Steady state Values will now go to the HAZOP team. This hazardous and operability checkers will ask questions, as to what will happen if the steady state value deviates from the expectations. This is a qualitative and experience intensive activity.At the same time, PFD will modify with more precise details such as standby equipment, storage, instrumentation details, pipe size requirements, valves and equipment elevations.Diagrammatic representation of these values can be called as P&ID, the nomenclature and representation may vary from company to company but the information content is unique. This will be referred throughout the life of a Process. P & ID will be extensively used while design stage and is the basis of Equipment Design, Plant Layout, Piping Layout, insulation calculation and Bill of Material (BOM) etc.A Piping Engineer Starts with P& ID, not necessary to have extensive knowledge about the process engineering aspects. But some idea about the process background will always help him to follow good engineering practices and take effective decisions.Mechanical/ Vessel department start at the early stage by rigorous study of process requirement and finalize vessel fabrication drawing and hand over to vessel manufacturer. Pressure vessel manufacturing is a very time-consuming work and piping fabrication at the site can only be started after locating the vessels. Similarly, Piping Wall thickness and lengths ca be theoretically calculated, this can carry out by considering piping as cylindrical vessels. The first Bill of Material can also be prepared at this stage without finalizing the actual routing and isometric drawing preparation. Additional requirements can be met after establishing the 3D Layout.Final approved blueprint of the three-dimensional plant layout is required to start the construction stage. 

Construction is the process of converting the 3D model into reality and involves placement of Equipment in position, routing of pipelines, welding, painting, thermal insulation, etc..   Plant site locations and constraints might have considered in the design stage itself. Some inputs may obtain from the site at the construction stage too, and incorporated after proper assessment.

Commissioning is the cold-state assessment of the constructed plant. It involves checking of the plant’s compliance with the design on paper.Those changes in the field from the design, which took due to site constraints, difficulties in getting a delivery and many other practical difficulties should be thoroughly probed. A plant is meant for steady state operation for its lifetime. But at the time of start-up, the characteristics of operation may entirely from the steady state operation. This is a big challenge for the Commissioning Engineer. A well optimized Start-up policy reduces his struggles up to a great extent.A Piping Engineer will actively involve at the stage of commissioning to take care of the mechanical Problems that may pop up during the Startup.Once the steady state operation establishes, chances of troubles are minimal if the design is optimized one. Even though sometimes operational errors may lead to troubles, and timely maintenance shouldn’t affect the smooth operation/Production. Bypassing, equipment and standby routes might be there, which may not affect the process. But from the Mechanical point of view, very small changes in the normal operational mode can affect the system greatly and if not considered properly lead to catastrophe.

Large Bore Pipeline

It is evident from the above points that a piping Engineer actively involves all stages of Plantlife right from Design to Operation. To meet the expectation of responsibilities, a Piping Engineer should have great ideas of Basic Engineering, the rigorous mathematical analysis involved in the design stage and general idea about all other disciplines. We will come across some of those in brief in the coming posts.