This is a recurring question. Here is how I have answered it in the past.
MTO, BOM & BOQ
What is the meaning of MTO, BOM and BOQ and how do I start this ..... I mean some useful tips to make a BOM, MTO, BOQ...like what are the things to be considered, what all are mandatory... etc. ?”
My answer: (Based on my experience)
MTO means Material Take-Off. This is the action of counting of the pieces and parts needed to fabricate, purchase and or construct something. (“Have you started the MTO yet? - Have you completed the MTO yet?”)
BOM means Bill of Material. This is normally a listing of only the material shown on an individual specific drawing such as a piping Isometric. (“Have you checked all the BOM’s for the Area 10 Isometrics?)
BOQ means Bill of Quantity (also called Material Summary). This is the totaling of all the quantities from all the BOM’s from all the project to send to a piping supplier for pricing or purchase.
There are normally three material take-offs sessions during a process plant project. These are preliminary, secondary and final.
What is it? – A preliminary MTO is a material take-off very early in the design process when only a limited amount of information is known and very little detail has been developed.
Why is it done? - A preliminary MTO is normally done for two reasons. The first is to assist with the early "order-of-magnitude" (+/- 10%) estimate for the overall project. The second reason is to issue early order of magnitude "RFQ's" (Request for Quote) for piping materials
When is it done? - The preliminary MTO is only possible when there is a Plot Plan that is "Approved" by the Client or has been issued to the client for approval. This is done long before there is any detailed work started on the 3D design model.
Who does it? - A preliminary MTO is best done by very strong well experienced senior piping designers who are familiar with the project.
How is it done? - For the preliminary MTO we used a formatted form on which we could indicate the number or amount of material required for each line. On the form I would identify the line number along with the line class. I would then look at this line on the P&ID and on the Plot Plan and determine the routing of the pipe. Then in the boxes (on the form) I would then mark the amount of pipe required for each size required for that line. Then I would count the number of fittings required, starting with 90 degree elbows. Then continuing through all the other inline fittings and online fittings. After the fittings I would count all the flanges by size. Then I would count all the valves from the P&ID. The high point vents and low point drains would be made last based on an educated guess. Then I would take another form and do another line. As I did each line I would "Yellow" off the line on the P&ID so at the end all the lines are accounted for. As the forms were completed they would be reviewed by the Area Supervisor and then forwarded to the Material Control Group who would process the data to produce the RFQ's
Why is it done? - The primary reason for the Secondary MTO is to update quantities for the issue of the actual Purchase orders for piping material. A second reason is to update the project estimate.
When is it done? - The Secondary MTO can only be done when there is significant progress completed on the 3D design model (or other electronic design method). However it must be done early enough to insure that the procurement (purchase and delivery) of the piping material to the field will fit the overall project schedule.
Who does it? - The Material Control Group.
How is it done? - The Material Control Group would access the electronic data base and down-load all the material available at that time. Some factoring would be done by the Material Control Group and the Piping Design Leads to allow for work not done yet.
Final MTO –
Why is it done? - The final MTO is done first to identify any item added late in the project or anything that was missed on the Preliminary or Secondary MTO's. The second reason for the Final MTO is to get a fix on the final job costs.
When is it done? - The Final MTO is done when the last Isometric has been issued.
Who does it? - The Material Control Group.
How is it done? - The Material Control Group would access the electronic data base and down-load all the material. Any differences between the Final MTO and the Secondary MTO would be identified. Purchase orders would be issued for the updated quantities.
Please remember this is only how it was done where I was. Use it as a guide but please do not be misled that this is the only way an MTO can be done.
You must want to succeed before you can.