A material requisition, or MR, is the document that turns an engineered instrument list into something a buyer can put out for bid and then purchase. It carries a cover sheet identifying the requisition and its purpose, the scope of supply, an itemised quantity list keyed to tag numbers from the instrument index, the datasheet for each tag or instrument type, the specifications and standards that govern the equipment, a supplier document requirements list, inspection and testing requirements, spares and special tools, delivery and packing requirements, and a register of the deviations and clarifications raised while the package is out to bid.
This is a reference for the instrument or project engineer assembling an MR package, or checking one before it goes out: what it carries, how it moves from inquiry to purchase, and where quantities drift from the instrument index.
Key takeaways
- An MR packages an engineered instrument list into something biddable and purchasable: a cover sheet, scope of supply, itemised quantities, datasheets, specifications, and supplier requirements.
- The itemised quantity list is keyed to tag numbers from the instrument index. A tag on the index with no corresponding MR line is unrequisitioned scope.
- An MR is issued at least twice: an inquiry MR for bidding, and a purchase MR after technical bid evaluation selects a compliant bidder. A further revision often follows vendor drawing review.
- The MR is neither the purchase order nor the datasheet. Each document in the package answers a different question and is produced by a different party.
- Quantities drift at predictable points: a P&ID reissue after the inquiry MR is out, a count taken by instrument type instead of by tag, spares folded into the main line, or a skid-mounted instrument requisitioned twice.
- Every MR line should trace back to a tag on the current P&ID revision. A line that cannot be traced is either a duplicate or already stale.
What the MR package carries
The cover sheet. The requisition number, its revision, the purpose of the issue (inquiry or purchase), and the project and unit it belongs to. That purpose field is what separates a bid response from a manufacturing instruction.
Scope of supply. What the vendor furnishes versus what the purchaser furnishes: manifolds, mounting hardware, cabling. Split-of-responsibility errors here, not missing hardware, are the usual cause of a bracket or a manifold missing at installation.
The itemised quantity list. One line per tag or per group of identical tags, keyed to the tag numbers on the instrument index so a reviewer can confirm every requisitioned line has a source and every tagged instrument has a requisition line. This is the list a bid responds to and the vendor manufactures against.
Datasheets. One per tag, or one per type where identical tags share a single sheet. The datasheet, covered field by field in ISA S20 datasheet fields and defined in what is an instrument datasheet, is the requirement the MR exists to carry.
Specifications and standards. The project instrument specification, any applicable piping or electrical specifications, and the public standards they invoke, referenced by number rather than reproduced in full.
The supplier document requirements list. What the vendor must submit, in what format, and by when: certified datasheets, general arrangement drawings, calibration records, test reports. It makes document delivery a purchased requirement rather than a courtesy.
Inspection and testing requirements. Witnessed or unwitnessed factory tests, hydrostatic tests, calibration checks, and any third-party inspection the specification calls for.
Spares and special tools. Commissioning and operating spares, listed and quantified separately from the main line so a spare is never mistaken for an installed instrument.
Delivery and packing requirements. Packing for the shipping route and site storage, marking and tagging of crates, and the delivery schedule the vendor commits to.
Deviations and clarifications register. Every question a bidder raises and every deviation from the specification, tracked through disposition, so the record shows what was actually agreed, not only what was first specified.
The MR lifecycle
| Stage | Purpose | What changes |
|---|---|---|
| Inquiry MR | Issued to bidders for technical and commercial response | Scope, quantities, and datasheets as understood at the point of issue |
| Technical bid evaluation | Each offer checked against the MR and its datasheets, one requirement at a time | No new document; a verdict per bidder, feeding the next issue |
| Purchase MR | Issued to the selected vendor after evaluation | Accepted deviations and any datasheet changes agreed during bidding are incorporated |
| Revision after vendor drawing review | Issued once the vendor's own drawings come back | Vendor-confirmed dimensions, weights, and connection details replace as-specified values |
The inquiry and purchase MRs are not two different documents so much as two revisions of the same one. The gap between them is exactly the technical bid evaluation: nothing in the MR itself changes during that step, but its outcome, the accepted deviations, decides what the purchase MR will say.
MR vs purchase order vs datasheet vs SDRL
Four documents travel together through the requisition and are easy to conflate because they share tag numbers and requisition numbers. They answer different questions.
| Document | What it is | Issued by | Keyed on |
|---|---|---|---|
| Material requisition | The technical package: scope, quantities, datasheets, specs, supplier requirements | Instrument or project engineer, with procurement | Tag numbers from the instrument index |
| Purchase order | The commercial instrument that buys against the MR | Procurement | The MR number |
| Instrument datasheet | The per-tag technical requirement | Instrument engineer | The tag number |
| Supplier document requirements list | What the vendor must submit and when | Instrument or document control engineer | The MR and the purchase order |
The MR is the widest of the four: the only one carrying the datasheets, the specifications, and the SDRL together. The purchase order narrows to the act of buying; the datasheet narrows to one tag; the SDRL narrows to the document obligation alone.
Where the count drifts
The quantity list is the part of the MR most exposed to error, because it is assembled once and rarely re-checked once the package is out.
Tags added on a P&ID reissue. A reissue after the inquiry MR is out can add tags to the unit. On an operating asset that reissue runs through management of change; on a project, an unreconciled quantity list simply never requisitions the added tags or puts them on a purchase order.
Quantities counted by type instead of by tag. Twelve pressure transmitters is not twelve named tags: a type count can run short or long against the index with no way to tell which tag is missing.
Spares folded into the main quantity. A spare transmitter listed on the same line as the installed ones inflates the apparent instrument count and can cause a duplicate purchase order line if the discrepancy is caught late.
A datasheet revision not carried into the purchase MR. The datasheet revises during bidding to reflect an accepted deviation, but the purchase MR ships from the earlier revision, and the vendor manufactures against a requirement nobody agreed to anymore.
Package instruments requisitioned twice. An instrument mounted on a purchased package, a skid-mounted analyzer or a pump's own seal-flush transmitter, is supplied within that package's scope, not the instrument MR, the same split covered in equipment datasheet vs instrument datasheet. If the tag also sits on the instrument MR's quantity list, it is bought twice.
The engineering record
An MR quantity is only defensible if every line traces to a tag on the current P&ID revision. Reconciling the requisition against the instrument index before issue, and again before the purchase MR is cut, is what catches an added tag, a duplicated skid instrument, or a miscounted spare before it becomes a purchase order for the wrong thing. An instrument index built from the P&ID set is the register that check runs against.
Related
- Running a technical bid evaluation for an instrument package. Between the inquiry MR and the purchase MR
- Instrument index template. What the MR's quantities are keyed to
- Instrument datasheet template. The form the MR carries per tag