If your metal stock is not clearly marked and color coded, every EN 10204 certificate, every PMI test and every inspection report becomes a guessing game.
Plates with no heat number, pipes with only a spray-paint grade, mixed bars on the rack and “mystery pallets” in the yard are some of the most common root causes behind receiving NCRs, late projects and certification problems. Weak metal marking and ad-hoc color coding usually show up later as nonconformities, rework and delays in final documentation.
This guide is a practical, in-article reference for:
- What you must mark on plates, pipes, bars and forgings
- How to combine permanent metal marking with simple color coding
- How to build a short, realistic SOP for marking and color coding metals
Why Metal Marking and Color Coding Matter at Receiving
For raw materials (plates, pipes, bars, forgings), you need two things at receiving:
If marking is missing or incorrect, you cannot prove:
- that the material matches the purchase order
- that it belongs to the MTC on file
- that it is suitable for the intended service
Color coding is not a replacement for proper metal marking and certificates. It is a second layer that makes life easier for stores, inspectors and fabricators. A good system combines both:
- Permanent marking → identity and EN 10204 traceability
- Simple color coding → quick recognition and reduced mix-ups
Used correctly, metal marking and color coding will reduce:
- re-testing and re-identification
- receiving NCRs related to “wrong material” or “missing heat number”
- time spent matching materials to certificates during audits and dossier close-out
What Must Be Marked on Plates, Pipes, Bars and Forgings
Before worrying about paint colors, make sure your minimum marking requirements are clear.
For each product type, define at least:
Plates and sheets
- Standard and grade (e.g. EN, ASTM or project-specific steel grade)
- Heat number or batch number
- Dimensions (thickness, width, length – optional but helpful)
- Manufacturer identification
- Marking method: stamping, etching or durable stencil near the plate edge
Pipes and tubes
- Standard and grade
- Heat or batch number
- Size and schedule / wall thickness
- Manufacturing method if relevant (seamless or welded)
- Manufacturer
Marking can be continuous along the length or repeated at intervals, but it must stay visible after cutting into typical lengths used in your project.
Bars, sections and forgings
- Grade
- Heat or batch number
- Manufacturer
- Size or diameter where practical
If individual pieces are too small or the process does not allow direct stamping, use durable metal tags attached to small bundles, with clear rules for how long the tag must remain attached and how traceability is maintained once cutting or machining starts.
For all products:
- the heat number on the metal must match the heat number on the MTC
- marking must be legible and reasonably permanent under normal handling
- temporary chalk alone is never sufficient as the only identification
Heat numbers, traceability and certificate matching expands these principles into a step-by-step method for matching MTCs and material during receiving and fabrication.
Approved Marking Methods: What Inspectors Should Accept
From an inspection and QA/QC standpoint, acceptable metal marking methods share three properties:
- they are durable
- they are easy to read
- they are linked to the PO and certificates
Typical marking methods you can include in your procedures:
- low-stress stamping on plates, forgings, flanges
- dot-peen marking for bars and components
- chemical or electro-etching where stamping is not allowed (for example, specific stainless surfaces)
- industrial stencilled paint with permanent ink
- engraved or stamped metal tags securely attached to bundles
Good practice:
- keep primary identity (grade, standard, heat number, manufacturer) in a durable method (stamping, etching, permanent stencil, metal tag)
- use paint or chalk only as supplementary identification or status marking
If a delivery arrives with no durable marking and only colored paint stripes, your receiving inspection should treat it as a traceability problem and record it in the incoming inspection/NCR system.
The Role of Color Coding for Metals
Color coding is useful, but it must stay in its place:
- it is a visual shortcut, not the legal identity of the metal
- it supports people working in yards, stores and fabrication shops
- it reduces the chance of picking the wrong material family at a glance
Color coding can be used to indicate:
- material family (carbon steel, stainless steel, non-ferrous, alloy)
- special service (sour service, subsea, cryogenic)
- inspection status (quarantine, accepted, rejected)
There is no single universal color code for all steel grades. Many mills and stockholders publish their own grade charts, but your site should treat those as supplier-specific and still define its own rules.
The main principle:
- Metal marking and certificates establish identity.
- Color coding provides quick recognition and status information.
A Simple Internal Color Coding System for Raw Materials
If your site does not yet have a standard, start with a simple, easy-to-remember scheme and build from there.
By material family
- Carbon and low-alloy steels: one common base color band
- Stainless steels: a different base color band
- Non-ferrous metals (copper, aluminium, nickel alloys): another color band
Example approach (you can adapt the colors):
- carbon / low-alloy: blue band
- stainless: green band
- non-ferrous: yellow band
By material status
Add a second, very simple layer for status:
- quarantine / on hold: large red band or “HOLD” paint mark
- accepted: small green dot or small green band after incoming inspection
- rejected: clear red cross or “REJECTED” label and separate storage location
By special service
If you handle a lot of special materials:
- sour service materials: one additional distinctive color dot
- subsea or cryogenic: another color dot or band
Whatever scheme you adopt:
- write it down in the marking/color-coding SOP
- show it on printed charts in stores and fabrication areas
- train receiving and warehouse staff to use the same legend
Color coding only helps if it is consistent. If every shift creates its own interpretation of colors, your system will become more confusing, not less.
How to Apply Color Coding on Plates, Bars and Sections
For color coding to work in practice, define where and how to apply it.
Plates and sheets
- apply a short color band along two adjacent edges
- keep band width consistent (for example 20–30 mm)
- do not paint over the stamped or etched markings
- ensure color is visible when plates are stacked on edge
Bars and sections
- paint bands on both ends of each bar or section
- if you use two bands (family + status), keep the order and spacing consistent
- in bundles, ensure at least some bar ends with full color can be seen
Bundles and tags
- attach durable tags with grade, standard, heat number, dimensions and PO
- add a small color mark on the tag itself matching your legend
- define when and by whom tags may be removed or replaced
Clear, repeatable rules for where to place bands and tags will help inspectors quickly confirm that pieces in the middle of a stack still match the top labels and certificates.
Color Coding for Installed Piping vs Raw Materials
The color coding you use on loose raw materials is not the same as the color coding used for installed plant piping.
For installed piping:
- industrial facilities typically follow well-known pipe identification standards
- text legends on pipe markers and arrow direction are the primary identification
- color bands around pipes indicate broad categories (water, steam, gases, oils, chemicals, fire-fighting media, etc.)
Your internal scheme for raw steel should:
- avoid reusing the exact combinations used for pipe contents, to prevent confusion
- focus on material family and inspection status, not process fluid
Keep the two systems conceptually separate in your procedures: one for pipe content identification and one for material identification and traceability.
Building a One-Page SOP for Metal Marking and Color Coding
A good SOP for metal marking and color coding should be short enough that people read it and clear enough that auditors can follow it.
A practical structure:
Scope
- which products: plates, pipes, fittings, bars, structural steel, forgings
Minimum permanent marking
- what must be marked on each product type
- acceptable marking methods (stamping, etching, stencil, metal tags)
- how heat numbers, grades and standards must appear
Color coding legend
- clear table with each color and its meaning
- separate sections for material family, status and special service
- notes on where to apply bands and dots on each product type
Responsibilities and timing
- who checks marking and certificates at receiving
- who applies or verifies color coding
- how information is recorded on the incoming inspection form and in the inventory system
Records and photos
Linking this SOP to your EN 10204 and MTC procedures ensures that metal marking, color coding and certificates form one consistent traceability chain. If you need a broader structure for raw material receiving controls, start with building a raw material checklist and align it with your certificate review approach in the MTC interpretation guide.
Integrating Marking and Color Coding into Receiving Inspection
To make color coding and metal marking part of a real system, integrate them into your receiving inspection workflow:
Before delivery
- purchasing specifies marking and EN 10204 requirements in the PO
- supplier confirms they can meet those requirements
At receiving
- stores/QA checks permanent marking against the purchase order and MTC
- bundle tags are checked for grade, standard, size, heat number and PO
- basic visual and dimensional checks are carried out (use your site’s Visual & Dimensional checklist logic)
- results are recorded using a controlled incoming inspection form (see Incoming Inspection Form Template)
- status color is applied: quarantine color until checks are complete; acceptance color only after documentation and marking are verified
After receiving
- inventory records are updated with heat numbers, locations and status
- any issues are raised as NCRs; recurring marking failures should be trended via your SQS system (see SQS KPIs)
Done consistently, this process significantly reduces “mystery steel” and emergency re-identification work.
Typical Mistakes in Metal Marking and Color Coding
Common issues that inspectors and QA/QC teams see again and again:
- relying entirely on paint stripes with no stamped or etched heat number
- marking only bundles and not individual pieces, then losing traceability after cutting
- inconsistent use of colors between shifts, yards or subcontractors
- no written legend or SOP, only “tribal knowledge”
- EN 10204 certificates that do not match the actual markings on the steel
- no photo evidence to prove how material looked at receiving
Most of these issues are cheap to fix with:
- a short, clear SOP
- one unified color legend
- training for receiving and stores personnel
- simple forms that link marking, color coding and certificates together
Quick Checklist for Metal Marking and Color Coding
You can use this checklist as a one-page reminder near your goods-in area:
- Each plate, pipe, bar or forging shows: grade, standard and heat/lot number.
- Markings on metal match the purchase order and EN 10204 MTC.
- Acceptable marking methods (stamping, etching, stencil, tags) are used.
- Color coding follows the site legend for material family and status.
- Quarantined and rejected material is clearly marked and physically segregated.
- Bundle tags are present and readable until cutting or fabrication.
- Photos of marking and color coding are taken at receiving and stored with incoming inspection records.
If you can honestly tick these items for every delivery, your traceability and audit readiness are already ahead of many facilities.
From Paint on Steel to a Controlled System: NTIA’s Role
Metal marking and color coding look simple on paper, but implementing them consistently across mills, stockholders, fabricators and sites is where many organisations struggle.
That is why NTIA includes these topics in its raw material inspection training:
- how to read EN 10204 certificates and challenge doubtful data
- how to design practical marking and color-coding rules for metals
- how to integrate those rules into receiving inspection, NCR handling and final dossiers
- how to make sure purchasing, vendor inspection, stores and site QA all use the same language
If you are responsible for qualifying suppliers, inspecting incoming steel or closing out documentation packs, structured training with NTIA on raw material inspection and traceability will save you significant time and rework – and will turn color coding and metal marking into a robust, auditable part of your quality system, not just paint on steel.
