Welding map preparation for piping spools

To answer and support for newbie inspector about trace welding map and mark up weld joint in construction drawings without an assigned weld joint. So, I would like to make a new topic for your reference. It may hope you during fabricating and control welding activities. 

Welding map or NDE map is a document to trace the weld joint in welding summary or later traceablility. So, you need to understand isometric detail. 

Welding map preparation

Why was we mark-up the joint no. #18 as below photo >>> because the drawing have detailed type of components such as flange(F5), gasket (G10), bolt (B12) and enough information for reference, update welding summary, line check, hydrotest, assembly, final FAT.

Mark up weld joint (recommend)

Don't mark up the weld joint as below photo, because detailed drawings were lack of welding component/ assembly component such as flange, gasket, bolting material.

Don't mark up weld joint in this drawing

Assign sequence weld joint number

Next, sequence to assign the weld joint number (1, 2, 3, 4, ....)for easy check and actions later such as installation of valves, orient of equipment, line check, site inspection, arrow marking, lable number marking, etc.

So, it is a easy way to mark up the weld joint, that you may follow the stream of flow fluid service as arrow marking in the isometric (refer below photo).

Don't mark up the weld joints overlap on another details such as linear dimension, detailed components, etc.

Please keep clearance between components has detailed in drawing to make sure no missing information.


In case of 2 or more the same support name/code in on drawings, you may mark up it as S5/1 (for first one), S5/2 (for second one), S5/3, etc.

Assign spool number

Next, To easy release for hydrotest and painting activities, all spools must be identified by spool number (#1, #2, #3,...). Please don't ignore this step, because it will support for trace later of hydrotest, painting, installation, packing, etc.

How to identify the spool number? OK, that it is easy way to separate the spool number in drawing at breakdown flange joint. One spool mean a individual component (only), and separated by the flanged joint, thread joint. 

Other benefit, you can periodly release one by one for hydrotest or dimension, or update progress report properly.


To aware and understand isometric drawings, you must access to specification and details of drawing and cross-drawing. You have to experienced in site inspection and shop fabrication. Otherwise must be learn more specifications.

Nguyen Duy Bien

Enjoy learning and researching, reading book. Knowledge welding inspection painting inspection.

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