Reading and Interpreting Blueprints

May 2024

I think before we dive into blueprint reading, we need to understand that blueprints and engineering drawings are a graphical language. As a language, blueprints have their own grammar, syntax, and semantics. As practitioners of this language, we need to embrace them wholeheartedly because we are using this language to communicate very complex ideas in a graphical form that take their shape in the creative spaces inhabited by designers and engineers. These ideas and calculations are then transferred into the language of lines to eventually be built by the ironworkers, welders, and pipefitters tasked with turning the dream into a reality.  

Why Blueprints Matter 

Now that we have established that blueprints are a language, a medium used for communicating very complex ideas and concepts from one group to another, we need to reflect on the importance of literacy in this language. One of the primary reasons reading blueprints is essential in industrial operations is that it ensures compliance and accuracy in project execution. Engineering drawings and blueprints can be simple and clear-cut or complex and complicated documents that sometimes border on the realm of what some might deem madness. The documents are representations of designs that detail dimensions, materials, and specifications crucial for the successful completion of a project. Whether you are working in a manufacturing plant, construction site, or any other industrial setting, a thorough understanding of blueprints is vital for your work or end product meeting the requirements of the intended design. This precision is especially critical when working on projects with tight tolerances and specific client requirements.  

Moreover, the ability to interpret blueprints is fundamental for effective communication among team members in an industrial setting. Blueprints serve as a universal language that enables professionals from various disciplines — engineers, architects, fabricators, and technicians — to collaborate seamlessly. By providing a standardized visual representation of the project, blueprints facilitate clear communication, reducing the likelihood of errors and misunderstandings. This collaborative aspect is particularly crucial in industrial settings where projects often involve multiple concurrent teams. 

Project Phases 

There are multiple phases during any project when a mistake or misinterpretation of the blueprints can lead to costly mistakes. First and foremost, this starts with the bidding process of a project, when the initial drawing package is released to the companies bidding on the project that the end customer is paying to be constructed. In this phase of the project life cycle, there’s an opportunity to make a mistake and lose money if those putting together the bid package miss a detail or some piece of crucial information that could cost the company money later on. We need engineers, estimators, and sales staff to be able to read and interpret construction drawings. 

Once that hurdle is cleared, and if the company gets the bid, the project enters the planning phase, during which skilled construction professionals break out the sticky notes along with colored pencils and proceed to dissect the project plans down to the smallest details. These professionals are looking for that one detail missed in the bidding phase because that one missed detail might turn this project into a money-losing quagmire. This is where decisions are made on construction methods, planning, and equipment choices. An example might be needing a very large crane to make a critical lift of a significant component or structure; this might need a high-dollar crane, which, if missed, would have far-ranging impacts. 

Sequence of Events 

As an inspector and field engineer, being able to correctly read and interpret blueprints as well as engineering drawings is one of the most important elements of the job. You are on the job to assist the skilled trades in making sure all the features and components of what is being built are laid out correctly and that mistakes are not made that will cost the company valuable time and large amounts of money plus have implications on cost and schedule. 

In my personal experiences, the important role I often filled was to be a resource to the boots on the ground. Many times, I was providing opportunities to learn and hone blueprint-reading skills. I filled this role by helping some of the newer skilled trade members learn some of the intricacies of blueprint reading. Most of the time, this wasn’t in a formal classroom setting; it was a one-on-one experience that might have taken a couple of minutes to explain a small piece of the blueprint-reading puzzle, including revision blocks, dimensioning, or some other small stumbling block that needed clarification. 

When reading and interpreting a blueprint or engineering drawing, here is my sequence of events: 

• Title block. Usually located in the lower right corner, the title block reveals essential details and information about what is being constructed. Make sure that you are not constructing the wrong component or structure.  

• I then move on to notes and keynotes. Notes on the blueprint provide additional information or specifications. An example of this might be a note near a specific beam that states “W21 x 44,” indicating the size and type of the beam. Pay attention to these notes as they offer crucial details for construction and manufacturing.  

• Revision numbers. Revision numbers are vital for tracking changes. I cannot overestimate how important revision numbers are, as the revision number will communicate if the blueprint has multiple revisions. Each revision number (Rev. 1, Rev. 2, etc.) should be checked to understand how the design has evolved. Revision clouds or symbols often highlight modified areas, and there is nothing worse than working off an old revision; that is going to cost time and money to correct. Always check the revision number before work starts. 

• Dimensions and sizes. Dimensions are marked with lines and arrows, specifying the length, width, and height of structural elements or components. For instance, a dimension line between two columns might indicate a distance of 20 ft. In structural work, we would pay attention to the sizes of beams, columns, and other structural components for accurate construction. 

• Last, we get to the workers and boots-on-the-ground individuals on the shop floor who are building and manufacturing our component structure. Of course, this is a phase with plenty of opportunities for mistakes to be made if the skilled crafts don’t read and interpret the drawings and prints correctly. The dimensions and details as outlined on the blueprint are not merely arbitrary instructions; they are calculated design choices put into the drawings to achieve a specific visual and functional outcome. The need for precision in fabrication cannot be overstated; precision is needed for ensuring that every component aligns with the intended dimension and specification to deliver what the customer ordered. This attention to detail is what transforms a set of blueprints into a victory, where each element contributes to the overall success of the project. 


This article was written by Garry A. Pace (an AWS CWI and welding engineering consultant based out of Katy, Tex.) for the American Welding Society.