Maintenance Bills of Material (BOM)

Stephen J. Thomas, Subject Matter Expert

What is a BOM?
A Bill of Material or BOM for short is a list of the repair materials needed to restore a failed asset to full functionality. This list may be very comprehensive and list every part that could ever be needed, or just a list of critical or asset specific material excluding the miscellaneous standard parts that are used in multiple asset repairs. This list can be retained by the maintenance organization in an asset file or preferably as part of your plant’s computerized maintenance management system (CMMS) linked to specific applicable assets. If this data is stored in a paper file or even in a separate application such as Excel, it can quickly become obsolete causing serious problems and delays when you try to make repairs. For many reasons, the latter is far better than the former.

Why is a BOM Valuable?
There are several reasons that a BOM is of immense value to your organization. First is that it improves the effectiveness and efficiency of the repair operation because there already exists a list of the specific parts that are required. Second, it goes a long way to avoiding errors. The planners or mechanics don’t have to try to find the specific parts they need; the list is readily available. This really helps when time is of the essence and the equipment must be returned to service in an expeditious manner. Last, if the parts are not stored in the plant warehouse it makes ordering them simple and accurate since the list will not only specify the part information in detail but often provide the name of the supplier and an estimated cost.

Where Do BOMs Apply?
Before we discuss how they are created, let’s talk about what assets they are created to support. Assets in this discussion are the assets that support your plant’s manufacturing process. They can be pumps, vessels, instruments, electrical equipment and many other types that when they fail need to be repaired.

Every asset in your plant that is “repairable” should have a unique non-intelligent asset number associated with it. Non-repairable items are typically referred to as “parts’ and are replaced with new ones when they fail. The asset number is tied to the physical asset from the day you purchase it until the day it is retired from service and often longer. Don’t confuse this with the location identifier which often is a “smart” ID that relates to a specific plant location, the type of equipment and a unique reference number for the unit with which it is associated. The asset number and Location ID sometimes get confused but they are different! For example, a pump on a crude unit many have a unique asset number like 12345678, while the physical location in which it resides could be 45P-101A where 45 is the unit distinction, “P” means pump, 101 is a location ID, and the “A” is telling you that there is a primary and back up. You should be able to see the Location ID on your P&ID diagrams; never the asset number because that will change as the asset is replaced.

How are BOMs Created?
Typically, BOMs should be created when your asset is purchased. Along with all of the other paperwork you receive from the vendor is the recommended spare parts list which gives you accurate information about the parts needed for repair. Many time vendors “overkill” the recommended spare parts list and it is so long that stocking all of the spare parts they recommend is extremely expensive and not always value added. As you review this list you should realize that not all of the parts are needed since the potential failure of certain specific parts is unlikely. For this reason, your maintenance engineer needs to conduct a comprehensive review and identify only what they want in stock before your purchase everything on the list.

Once the list of what you want in the asset’s BOM has been identified the next question is do you need to actually purchase and store all of the parts in your warehouse or just identify specific ones for future ordering from the vendor when needed. If delivery in a timely manner from the vendor is not an issue, then you can just list the item in your BOM for future ordering. Many plants identify these parts in their stores catalog as being “On Request Only.” While you don’t have the part in stock ordering in this manner makes getting the correct part easy since the part’s specification is already set up in the CMMS.

While the optimum time to create a BOM is when the asset s purchased, this is not always possible for equipment that already exists on site. These BOMs need to be created by the maintenance engineer and reviewed by the maintenance execution team. Once established the parts list can be added as that asset’s BOM. This review effort requires careful analysis of what you already have in your warehouse since in a plant some of the equipment may be duplicated. You also need to identify what new parts are needed on site and what parts can be listed in you inventory as “On Request Only” and purchased later.

Building the list of BOM parts is only the beginning. The BOM list needs to be linked to the specific assets to which they apply. Notice I said assets. The reason is that you most likely have multiple assets that can have the same BOM. In this case most CMMS tools have a “where used” application that allows for this identification. Be careful. You may need to change the quantity of a specific part held in stock if the number of assets needing that part for repair increases.

Once this task has been completed, any work order tied to a specific asset with a linked BOM can be used to order what is required for the repair. This is a task most often performed by your planners as they develop job plans. The BOM can also be used by field execution when during the course of repair, they discover that a needed part was not ordered as part of the planning process.

Adding, Changing and Deleting BOM Data
BOM data is not static; it changes over time and needs to be maintained or the assets for which the BOM was created will have the wrong parts listed. There are many reasons for this need; the supplier develops new and improved parts, older parts become obsolete, vendors change and often catalog numbers are modified. All of these changes need to be accounted for in the BOM otherwise when you order the parts you want; the vendor won’t be able to supply them or they will be incorrect and the problem won’t be discovered until they are needed.

These changes need to be updated in the asset’s BOM as they arise. The question is who can make the change? You may think that the ability to change BOMs should be open to various groups and a multitude of individuals. On the surface this sounds like a good idea, but is it? The more people that can go into the CMMS and change BOM information, the more likely that unintentionally they may make a mistake rendering the BOM useless when you need it the most.

Some firms restrict BOM modification to a team who has the responsibility for plant asset data integrity. The problem here is that in order to provide the needed changes to the data integrity team there needs to be a work process either electronic, through e-Mail or even via paper, each of which introduces potential errors. Other firms allow the maintenance engineers to make the changes. This seems to be the most productive solution. These individuals know the equipment and are accountable not only for entering the correct data to the BOM, but they also have responsibility for the repair process. If they make a mistake with the BOM they most certainly will hear about from the field execution team.

In Conclusion
BOMs if managed correctly have immense value to the organization and go a long way to improving repair effectiveness and efficiency. The thing to remember to make it work correctly is that the BOMs require work to maintain them up to date and usable for the planners and repair teams that count on them for getting the correct parts to the job.