Walk into any fabrication workshop serving the oil and gas sector and you’ll hear the same handful of abbreviations thrown around all day — WPS, PQR, MTR, NDE, ITP, MDR. For an experienced engineer, these terms are second nature. For a new inspector, a junior QA/QC coordinator, or a workshop owner trying to understand why a client keeps asking for documents they’ve never heard of, the alphabet soup can be genuinely confusing.
This crash course breaks down the core terminology used across welding, material verification, inspection, and code compliance in industrial fabrication. Whether you’re preparing for vendor approval with a major operator, studying for an inspection role, or simply trying to read a project specification without reaching for Google every five minutes, this guide gives you the working vocabulary you need.
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Why Terminology Matters Before the Technical Details
Most fabrication and inspection problems aren’t caused by a lack of technical skill — they’re caused by miscommunication. A workshop that doesn’t fully understand what a client means by “ITP” may submit the wrong inspection sequence. A junior engineer who confuses a WPS with a PQR may struggle to explain why a weld procedure needs requalification. Getting comfortable with the terminology isn’t academic — it’s the foundation that everything else in pressure vessel fabrication, quality control, and vendor approval is built on.
The terms below are grouped into four practical categories: welding and procedure qualification, material verification, inspection and testing, and documentation and code compliance.
1. Welding and Procedure Qualification Terms
Before a single weld is made on a pressure-retaining component, the welding process itself has to be proven and the welder has to be qualified to perform it. These three documents work together to demonstrate that.
| Term | What It Means |
| WPS (Welding Procedure Specification) | A written instruction that defines exactly how a weld should be made — process, filler metal, joint design, preheat, current, travel speed, and post-weld heat treatment. It tells the welder how to weld a specific joint in a way that meets code requirements. |
| PQR (Procedure Qualification Record) | The record of what actually happened when a test weld was made to support a WPS, along with the mechanical test results (tensile, bend, impact) that prove the procedure produces a sound weld. A WPS is only valid if it’s backed by a qualifying PQR. |
| WPQ / WQR (Welder Performance / Welder Qualification Record) | Proof that an individual welder can produce an acceptable weld using a qualified WPS, demonstrated through a test weld and the required examinations. This is tied to the welder, not the procedure. |
In short: the PQR proves the process works, the WPS tells the welder how to follow it, and the WPQ proves the welder can execute it. All three are referenced together in Section IX of the ASME Boiler and Pressure Vessel Code.
2. Material Verification Terms
Pressure vessels and piping are only as reliable as the raw material they’re built from, so every plate, pipe, and fitting needs documented proof of its properties and a way to trace it back to its source.
| Term | What It Means |
| MTR (Material Test Report / Mill Test Report) | A certificate issued by the material manufacturer showing the chemical composition and mechanical properties (yield strength, tensile strength, elongation) of a specific batch of material. It’s the document a fabricator checks before accepting incoming steel. |
| Heat Number | A unique identifier stamped or marked on a piece of material, linking it back to the specific production batch (“heat”) and its corresponding MTR. This is the backbone of material traceability. |
| Material Traceability | The documented chain that connects a finished component, back through fabrication records, to the original heat number and MTR — a requirement most operators (including Saudi Aramco) audit closely during vendor approval. |
3. Inspection and Testing Terms (NDE/NDT)
Once material is welded and fabricated, it has to be examined for flaws without damaging the component. This is where non-destructive examination comes in.
| Term | What It Means |
| NDE / NDT (Non-Destructive Examination / Testing) | A family of inspection methods used to detect flaws in materials and welds without cutting, breaking, or otherwise damaging the part. |
| RT (Radiographic Testing) | Uses X-rays or gamma rays to produce an image of the internal structure of a weld, revealing porosity, slag, lack of fusion, or cracking. |
| UT (Ultrasonic Testing) | Sends high-frequency sound waves through the material; reflections from internal flaws are read on a screen, making it effective for detecting subsurface discontinuities, especially in thicker sections. |
| MT (Magnetic Particle Testing) | Applies a magnetic field and fine iron particles to a ferromagnetic part; particles cluster at surface and near-surface cracks, making them visible. |
| PT (Liquid Penetrant Testing) | A dye penetrant is applied to a clean surface, drawn into surface-breaking defects by capillary action, then revealed with a developer — commonly used on non-ferrous materials and welds. |
| Hydrostatic Testing | A pressure test using water, performed at a pressure above the vessel’s design pressure, to confirm there are no leaks and the component can safely withstand its intended service conditions. |
4. Documentation and Code Compliance Terms
All of the welding, material, and inspection records above eventually feed into a structured documentation package that proves the finished component meets code requirements.
| Term | What It Means |
| ITP (Inspection and Test Plan) | A document that lays out every inspection and test activity required during fabrication, in sequence, along with who performs each one and which steps require a witness or hold point before work can continue. |
| MDR (Manufacturer’s Data Report) / Data Book | The complete compiled record handed over at project completion — WPS, PQR, WPQ, MTRs, NDE reports, hydro test records, and the final certification form — serving as proof that the component was built and verified to code. |
| Form U-1 | The specific Manufacturer’s Data Report form used for pressure vessels built to ASME Section VIII, Division 1. It’s signed by both the manufacturer and the Authorized Inspector as the formal certification of code compliance. |
| ASME BPVC (Boiler and Pressure Vessel Code) | The set of ASME standards governing the design, fabrication, inspection, and testing of boilers and pressure vessels, organized into multiple sections covering everything from materials to welding qualification. |
| U Stamp | The ASME certification mark that authorizes a manufacturer to fabricate and stamp pressure vessels in accordance with Section VIII, Division 1, after passing an ASME survey of its quality control system. |
| AI (Authorized Inspector) | An inspector commissioned through an Authorized Inspection Agency who verifies, on behalf of the code, that fabrication and testing comply with ASME requirements before signing the Form U-1. |
| ISO 9001 | An internationally recognized quality management system standard. Many fabrication workshops maintain ISO 9001 certification as the structural backbone of their QA/QC system, alongside ASME compliance. |
Putting the Terms Together
These categories aren’t isolated — they form a single chain of evidence. A WPS and PQR prove the welding process is sound. An MTR and heat number prove the material is what it claims to be. NDE methods like RT and UT prove the finished weld is free of unacceptable flaws. An ITP governs when each of these checks happens. And the MDR, anchored by Form U-1 and the U Stamp, bundles everything into the final proof of compliance that gets handed to the client — or reviewed by an operator during vendor approval.
Understanding this chain is what separates someone who can recite definitions from someone who can actually manage a fabrication project, prepare a vendor approval package, or step into an inspection role with confidence.
| Want the deeper dive? This crash course is the starting point. Our ASME Standards and Industrial Documentation series go deeper into each of these terms — including a full breakdown of the U Stamp process and how to assemble a complete MDR data book. Browse the series on FreeDocumentsHub.com. |