Producing accurate pictorial and orthographic drawings of chemical engineering components is a vital skill for professionals working in Kenya’s chemical processing and manufacturing industries. These drawings serve as universal communication tools that convey detailed information about component shapes, sizes, and assembly relationships. Mastery of drawing conventions, dimensioning, and software tools ensures that chemical engineers can effectively collaborate with fabricators, contractors, and quality inspectors to realize safe and efficient plant installations.
Symbols and abbreviations are standardized graphic representations used in chemical engineering drawings to simplify communication and reduce clutter while maintaining clarity. In Kenya’s chemical processing plants, these symbols represent instruments, valves, pipe fittings, and material types, enabling engineers and technicians to interpret complex systems quickly.
Pictorial sketches and drawings provide a three-dimensional representation of components to help visualize the shape and relationship between parts. This is especially important in chemical engineering where complex equipment such as reactors, heat exchangers, and pumps require clear visualization for design and maintenance.
Isometric drawings present a three-dimensional object on a two-dimensional plane with all three axes equally foreshortened. This technique is widely used in chemical engineering to represent piping layouts, equipment, and assemblies.
Orthographic elevations provide detailed multi-view representations of components, showing exact shapes and dimensions from different angles. In chemical engineering, orthographic drawings are essential for fabrication and inspection of equipment and piping.
Dimensioning provides critical information about size, location, and tolerances of features on engineering drawings. Accurate dimensioning is essential for fabrication and quality control in chemical engineering projects.
Freehand sketching is a fundamental skill for chemical engineers to quickly convey ideas, troubleshoot, or document field observations without relying on software.
| Name | Specification | Use |
|---|---|---|
| Mechanical Pencil | 0.5 mm lead, HB grade | Precise lines and shading |
| Eraser | Soft rubber | Correcting mistakes |
| Sketch Pad | A4 size, grid or plain paper | Surface for drawing |
| Ruler | 30 cm, transparent plastic | Drawing straight lines |
| Compass | Adjustable, metal | Drawing circles and arcs |
AutoCAD software is extensively used in Kenyan chemical engineering to produce precise pictorial and orthographic drawings. Its capabilities enhance accuracy, editing efficiency, and documentation management.
This chapter covers the essential symbols and abbreviations used in engineering drawings to ensure clear and standardized communication. It then explores the creation of pictorial sketches and drawings, focusing on representing components accurately in three-dimensional views. The process of drawing objects in isometric view is detailed to aid visualization of complex shapes. Orthographic elevations are examined with emphasis on both first angle and third angle projection methods, explaining their conventions and applications. Proper dimensioning techniques are discussed to provide precise measurements and tolerances on drawings. The chapter also highlights the importance of freehand sketching as a foundational skill for quick and effective design communication. Finally, the use of AutoCAD software is introduced for producing both pictorial and orthographic drawings, demonstrating modern tools that enhance accuracy and efficiency in engineering design.
Question 1 key points:
Question 2 key points:
Kenya Pipeline Company is upgrading its chemical storage facility and requires detailed pictorial and orthographic drawings of new pump assemblies and piping components.
Tasks:
a) Produce a freehand sketch of a centrifugal pump used in chemical transfer, showing main components. (10 marks)
b) Create an isometric AutoCAD drawing of the pump assembly with all relevant symbols and dimensioning according to BS ISO standards. (15 marks)
c) Interpret the orthographic drawings provided for the piping layout and identify any missing dimensions or symbols. (10 marks)
a) Begin by outlining the pump casing, impeller, shaft, and inlet/outlet. Use light strokes for initial shapes and label components clearly. Add approximate dimensions reflecting typical pump sizes in chemical plants.
b) Use AutoCAD to construct the isometric view: start with base geometry, add details such as flanges, bolts, and valves using standard symbols. Apply dimensioning with correct line types and scales (e.g., 1:10). Include title block with project details and drawing date.
c) Review the orthographic views (front, side, top) for completeness: verify all critical dimensions are present, check use of correct symbols (valves, joints), and ensure hidden lines are properly dashed. Note any omissions or inconsistencies for correction.
Common symbols include:
Isometric drawings show a 3D pictorial view with equal angles between axes, providing a realistic representation; orthographic drawings show multiple 2D views (front, top, side) for precise measurement and fabrication.
Examples:
Dimensioning provides exact sizes and locations of features, ensuring correct manufacture and assembly of heat exchanger parts, avoiding errors and rework.
Freehand sketch shows the impeller blades radiating from the central hub at an angle, with the shaft and casing outlines, labeled accordingly.
First angle projection places the object between the observer and the plane of projection; third angle projection positions the plane between the observer and object. Third angle is commonly used in Kenya.
Procedure:
1) Draw front view of base plate with dimensions
2) Project lines to top view
3) Draw top view showing bolt hole positions
4) Label views according to third angle symbols
Advantages:
Abbreviations and symbols reduce ambiguity, simplify complex information, and facilitate faster interpretation by engineers and technicians.
Steps:
1) Scan or digitize the freehand sketch
2) Set up drawing scale and units in AutoCAD
3) Trace main outlines using line and arc tools
4) Add dimensions and annotations with standard symbols
5) Review and finalize the drawing for accuracy
Question 11 (Compulsory - 20 marks)
Kenya Pipeline Company is designing a new chemical storage facility.
a) Draw to scale an isometric pictorial sketch of a cylindrical chemical storage tank with a conical roof and a manhole on the side. Include all relevant symbols and abbreviations. (10 marks)
b) Produce orthographic elevations (front, side, and top views) of the tank using third angle projection. Dimension the drawing fully, including tank diameter, height, and manhole size. (10 marks)
Question 12 (20 marks)
Explain the step-by-step procedure for creating an orthographic drawing of a shell and tube heat exchanger base plate using first angle projection. Include the standard line types and dimensioning conventions as per BS/ISO standards.
Question 13 (20 marks)
A chemical plant engineer needs to convert a freehand sketch of a distillation column into a detailed AutoCAD drawing. Describe the process, highlighting how to ensure accuracy in symbols, abbreviations, and dimensions. Provide an example of three symbols used in the drawing.
Question 14 (20 marks)
Compare and contrast the use of first angle and third angle projection methods in chemical engineering drawings. Discuss which method is preferred in Kenya and justify your answer with examples from chemical equipment drawings.
Question 11
a) The isometric sketch should depict a vertical cylindrical tank with a conical roof sloping uniformly to the center. The manhole is shown as an oval or circle on the side shell. Use standard symbols for manhole and welding. Include abbreviations such as DN for manhole diameter. The sketch must be dimensioned proportionally.
b) Orthographic views should show:
Question 12
Procedure:
1) Begin with the front view of the base plate showing bolt hole layout
2) Project vertical and horizontal lines to form top and side views
3) Use continuous thick lines for visible edges, dashed lines for hidden features
4) Apply dimensioning rules: dimension from datum points, use correct units (mm), and place dimensions outside the views
5) Label views and add title block with scale and drawing details
Standard line types include thick continuous lines for visible edges, thin continuous for dimension lines, dashed for hidden edges.
Question 13
Process:
Question 14
First angle projection places the object between the observer and the projection plane; commonly used in Europe and some parts of Asia. Third angle projection places the plane between the observer and the object; it is the preferred method in Kenya and the USA.
In chemical engineering drawings, third angle projection is favored because it aligns with international standards used by most Kenyan industries such as KPLC and KenGen. For example, third angle projection allows clear interpretation of complex equipment like heat exchangers and reactors by Kenyan engineers and fabricators, reducing errors in fabrication.
Time: 1 Hour | Type: Individual
Resources Required:
You are working as a trainee draftsman at the Nairobi City Water & Sewerage Company. You have been tasked with familiarizing yourself with the standard symbols and abbreviations used in chemical process drawings to prepare for a process diagram update.
Tasks:
i. Identify and list 15 common symbols and abbreviations used in chemical engineering drawings from the provided chart.
ii. Match each symbol with its correct meaning or equipment type.
iii. Sketch freehand the symbols for a valve, pump, heat exchanger, and reactor.
iv. Interpret a short section of a process flow diagram and label three components using correct symbols and abbreviations.
Assessor Observation Criteria:
Time: 1.5 Hours | Type: Individual
Resources Required:
At a chemical manufacturing factory in Mombasa, you have been asked to produce freehand sketches of key process components for a quick design meeting.
Tasks:
i. Observe the physical components provided and sketch each to scale approximately 1:5 on A4 paper.
ii. Annotate each sketch with the component name and one key function.
iii. Use correct line weights and shading to indicate material surfaces.
iv. Submit sketches for review.
Assessor Observation Criteria:
Time: 2 Hours | Type: Individual
Resources Required:
You are a trainee draftsman at a chemical plant in Nakuru upgrading piping layouts. You are required to produce an isometric drawing of a simple pipe fitting assembly.
Tasks:
i. Using the provided isometric grid paper, manually draw an isometric view of a pipe assembly consisting of a straight pipe (150mm length), an elbow bend (90°), and a flange connection.
ii. Apply correct isometric projection principles and line conventions (visible, hidden lines).
iii. Dimension the assembly using standard dimensioning practices.
iv. Label each part clearly.
Assessor Observation Criteria:
Time: 3 Hours | Type: Individual
Resources Required:
At a chemical processing plant in Eldoret, you are assigned to produce detailed orthographic views of a cylindrical chemical reactor for maintenance documentation.
Tasks:
i. Draw the front, top, and side elevations of the reactor in first angle projection to scale 1:10. The reactor measures 1200mm diameter and 3000mm height, with a manhole and flanged inlet/outlet nozzles.
ii. Use the correct line types for visible, hidden, and centre lines as per BS EN ISO 128.
iii. Include title block with all required information according to Kenya Standards.
iv. Dimension all relevant features.
Assessor Observation Criteria:
Time: 3 Hours | Type: Individual
Resources Required:
Working as a draftsman at a tea factory in Kericho, you need to prepare orthographic drawings of a shell and tube heat exchanger for fabrication.
Tasks:
i. Produce front, top, and side views of the heat exchanger using third angle projection. The shell diameter is 1000mm, length 2500mm, with two inlet and two outlet nozzles.
ii. Apply correct projection standards, line conventions, and dimensioning.
iii. Include the projection symbol for third angle in the title block.
iv. Annotate all views with key features.
Assessor Observation Criteria:
Time: 1.5 Hours | Type: Individual
Resources Required:
At a chemical engineering design office in Nairobi, you are tasked with completing the dimensioning of a distillation column drawing to prepare for fabrication.
Tasks:
i. Review the provided orthographic drawing and add missing dimensions according to KS ISO 129 standards.
ii. Use correct dimension lines, extension lines, and arrows.
iii. Ensure all critical features including height, diameter, nozzle positions, and flange sizes are dimensioned.
iv. Check for clarity and absence of dimension overlaps.
Assessor Observation Criteria:
Time: 1 Hour | Type: Individual
Resources Required:
At a refinery in Mombasa, you are asked to produce a freehand sketch showing a process control valve mounted on a pipeline including the actuator and positioner.
Tasks:
i. Sketch the valve assembly including the actuator and positioner from observation.
ii. Indicate flow direction and annotate key parts.
iii. Use appropriate line weights to differentiate components.
iv. Submit the sketch for review.
Assessor Observation Criteria:
Time: 3 Hours | Type: Individual
Resources Required:
You are a CAD technician at a chemical plant design firm in Nairobi. You need to produce an isometric piping drawing for a new chemical feed line.
Tasks:
i. Using AutoCAD, reproduce the provided hand-drawn isometric piping layout, including pipes, elbows, flanges, and valves.
ii. Apply layers for different components and use correct line types and colours.
iii. Add dimensions and annotations as per BS EN ISO 128.
iv. Save and submit the drawing in DWG and PDF formats.
Assessor Observation Criteria:
Time: 3 Hours | Type: Individual
Resources Required:
At a chemical storage facility in Kisumu, you have been asked to prepare detailed orthographic drawings of a storage tank for client approval.
Tasks:
i. Create front, side, and top orthographic views of the tank using third angle projection in AutoCAD.
ii. Include all standard line types, centre lines, and hidden lines as appropriate.
iii. Add dimensions and title block following Kenya Standard KS ISO 7200.
iv. Plot and submit the drawing in PDF format.
Assessor Observation Criteria:
Time: 1.5 Hours | Type: Individual
Resources Required:
At a county hospital in Nakuru, you are required to interpret equipment drawings to prepare installation instructions.
Tasks:
i. Examine the orthographic and isometric drawings provided and identify all components.
ii. Note the dimensions critical for installation.
iii. Prepare a step-by-step installation checklist referencing the drawings.
iv. Highlight any safety considerations visible in the drawings.
Assessor Observation Criteria:
Time: 1 Hour | Type: Individual
Resources Required:
At a TVET college in Kisii, you are tasked with preparing a standard title block and projection symbol to be used in all chemical engineering drawings.
Tasks:
i. Construct a title block including fields for drawing title-scale, date, drafter’s name, checker, and revision history.
ii. Draw the first angle and third angle projection symbols neatly.
iii. Ensure all text is legible and aligned.
iv. Submit the sheet for evaluation.
Assessor Observation Criteria: