# The words on the purchase order.

> Definitions of industrial procurement, piping, valve, flange, bolting, refractory, inspection and shipping terms such as RFQ, MTR, NPS, RTJ, PMI and Incoterms.

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Updated: 2026-10-15

Plain definitions of the terms that appear in specifications, quotations, inspection records and shipping documents.

**316 and 316L stainless steel** (Acero inoxidable 316 y 316L): Austenitic stainless steels with molybdenum for better corrosion resistance. 316L has lower carbon to reduce sensitization after welding.

**API** (API): The American Petroleum Institute, publisher of standards for the oil and gas industry, including valve standards such as API 600, 602 and 6D.

**API 6D** (API 6D): The specification for pipeline and piping valves: gate, ball, plug and check valves used in pipeline service.

**ASME** (ASME): The American Society of Mechanical Engineers, publisher of codes and standards such as B31.3 (process piping), B16.5 (flanges) and B36.10M (pipe).

**ASME B16.20** (ASME B16.20): The standard for metallic gaskets for pipe flanges: ring-joint, spiral-wound and jacketed gaskets.

**ASME B16.34** (ASME B16.34): The standard for valves with flanged, threaded and welding ends. It sets pressure-temperature ratings and covers dimensions, materials, examination, testing and marking.

**ASME B16.5** (ASME B16.5): The standard for pipe flanges and flanged fittings from NPS 1/2 to NPS 24, in classes 150 to 2500.

**ASTM** (ASTM): ASTM International, publisher of material specifications such as A105 (forged carbon steel), A106 (seamless pipe) and A193 (bolting).

**ASTM A105** (ASTM A105): The specification for carbon steel forgings for piping components, widely used for forged flanges, fittings and valves.

**ASTM A106** (ASTM A106): The specification for seamless carbon steel pipe for high-temperature service, in Grades A, B and C.

**ASTM A193 B7** (ASTM A193 B7): Quenched and tempered chromium-molybdenum alloy steel stud bolting for high-temperature and high-pressure service, used with A194 2H nuts.

**ASTM A350 LF2** (ASTM A350 LF2): Carbon steel forgings with notch toughness requirements for low-temperature piping components.

**Ball valve** (Válvula de bola): A quarter-turn valve with a bored ball that gives fast isolation and tight shutoff.

**Beveled end (BE)** (Extremo biselado (BE)): A pipe or fitting end cut at an angle, usually 37.5°, to prepare it for butt welding.

**Bid tabulation (bid tab)** (Cuadro comparativo de ofertas (bid tab)): A single sheet that compares every supplier's offer line by line on price, delivery, validity, Incoterm and exceptions.

**Bill of lading (B/L)** (Conocimiento de embarque (B/L)): A carrier's document that acts as a receipt for the goods and as evidence of the contract of carriage. A negotiable B/L also controls the goods.

**Blind flange** (Brida ciega): A solid flange with no bore, used to close the end of a line or a nozzle.

**Butt-weld fitting** (Accesorio para soldar a tope): A wrought fitting, such as an elbow, tee, reducer or cap, with beveled ends that is welded to the pipe. Dimensions are covered by ASME B16.9.

**Butterfly valve** (Válvula de mariposa): A quarter-turn valve with a disc that rotates in the line. It is compact and light in large sizes.

**Cable tray** (Bandeja portacables): A rigid structure, such as a ladder or trough, that supports power and instrument cables along a route.

**Castable refractory** (Concreto refractario (castable)): A refractory dry mix that is mixed with water and cast or gunned into place, where it sets as a single mass.

**Ceramic fiber** (Fibra cerámica): A very light, fibrous insulation supplied as blanket, board or modules, used in high-temperature linings. Handle it under occupational exposure rules.

**Certificate of conformity (CoC)** (Certificado de conformidad (CoC)): A supplier's written statement that the goods meet the order or a named specification. It does not necessarily include test results.

**Certificate of origin** (Certificado de origen): A document that states the country where goods were made, which customs may need to apply duty rates or trade agreements.

**Check valve** (Válvula de retención (check)): A self-acting valve that opens with forward flow and closes to stop reverse flow. Common types are swing, lift, dual-plate and piston.

**Commercial bid evaluation (CBE)** (Evaluación comercial de ofertas (CBE)): The review of each offer's price, payment terms, Incoterm, delivery date, validity and warranty on a like-for-like basis.

**Commercial invoice** (Factura comercial): The seller's bill for the goods, stating parties, descriptions, quantities, unit prices, currency and Incoterm. Customs uses it to assess duties.

**Conduit** (Conduit (tubería conduit)): A tube or channel that protects and routes electrical wiring.

**Control valve** (Válvula de control): A valve with an actuator that adjusts flow automatically in response to a controller signal.

**Corrosion allowance** (Margen por corrosión): Extra wall thickness that the designer adds to cover metal loss over the service life.

**Customs broker** (Agente aduanal): A licensed agent who prepares and files import or export declarations and arranges customs clearance.

**DN (diameter nominal)** (DN (diámetro nominal)): The metric designation of pipe size. NPS 2, 4, 6 and 8 correspond to DN 50, 100, 150 and 200.

**Duplex stainless steel** (Acero inoxidable dúplex): A stainless steel with a mixed austenite and ferrite structure, giving higher strength and better chloride resistance than 304 or 316.

**EN 10204** (EN 10204): The European standard that defines types of inspection documents for metallic products: 2.1, 2.2, 3.1 and 3.2.

**Expediting** (Seguimiento (expediting)): Tracking an open purchase order through manufacture, testing and release so that delays are found while they can still be recovered.

**FAT (factory acceptance test)** (FAT (prueba de aceptación en fábrica)): A test of finished equipment at the manufacturer's works, witnessed by the buyer, before shipment.

**FCL and LCL** (FCL y LCL): Full container load: one shipper fills a container. Less than container load: the cargo shares a container with other shippers' goods.

**Firebrick** (Ladrillo refractario): A shaped brick of fireclay or high-alumina material, laid with mortar to form a refractory lining.

**Flat face (FF)** (Cara plana (FF)): A flange face that is flat across its full width, used with a full-face gasket.

**Freight forwarder** (Agente de carga (freight forwarder)): A company that arranges transport, documents and handling of shipments on behalf of a shipper or buyer.

**Full bore (full port)** (Paso total (full bore)): A valve whose opening matches the pipe bore, so it adds little restriction to flow and permits pigging.

**Gas detector** (Detector de gas): A device that senses flammable or toxic gas and signals an alarm when concentration passes a set level.

**Gate valve** (Válvula de compuerta): A linear-motion valve that isolates flow with a wedge or gate. It has low pressure drop when open and is not for throttling.

**Globe valve** (Válvula de globo): A linear-motion valve with a plug and seat that regulates flow and shuts off tightly, at the cost of higher pressure drop.

**Gunning** (Proyección (gunitado)): Placing refractory by spraying it onto a surface with a gun, used for large areas and repairs.

**Hazardous area (classified location)** (Área peligrosa (clasificada)): An area where flammable gas, vapor or dust may be present, so electrical equipment must be certified for it.

**Heat number** (Número de colada (heat number)): The identifier of one melt of metal. Items made from the melt carry the number and the MTR reports its analysis.

**Heavy hex nut** (Tuerca hexagonal pesada): A hexagonal nut thicker and wider than a standard hex nut. ASTM A194 specifies grades such as 2H and 2HM for flange bolting.

**Hold point and witness point** (Punto de espera y punto de testigo): A hold point stops work until the buyer or inspector releases it. At a witness point the buyer may attend, but work can continue if they do not.

**HS code (Harmonized System code)** (Código HS (Sistema Armonizado)): An internationally standardized commodity code that customs authorities use to classify goods for duties and statistics. Countries extend it beyond six digits.

**Hydrostatic test (hydrotest)** (Prueba hidrostática (hidrotest)): A pressure test with water at a pressure set by the code or specification to check strength and leak-tightness.

**Incoterms** (Incoterms): ICC trade terms, such as FCA, FOB and DAP, that allocate tasks, costs and risk between seller and buyer in an international sale.

**Insulating castable** (Concreto refractario aislante): A lightweight castable with low density and low thermal conductivity, used as a backup layer or protected hot face.

**ITP (inspection and test plan)** (ITP (plan de inspección y ensayos)): A document that lists each inspection and test, the acceptance standard, and whether it is a witness or a hold point.

**Junction box** (Caja de conexiones (junction box)): An enclosure where cables are joined or terminated. In hazardous areas it must carry a suitable protection rating.

**Lead time** (Plazo de entrega (lead time)): The time from placing an order to receiving the goods, including manufacture, testing and transport.

**Long radius elbow** (Codo de radio largo): A butt-weld elbow whose centerline radius is 1.5 times the NPS, giving a gentler bend and lower pressure drop than a short radius elbow.

**Material requisition (MR)** (Requisición de materiales (MR)): The engineering document that states what to buy: item descriptions, quantities, specifications and the date needed on site.

**MTR (material test report)** (MTR (certificado de materiales)): The manufacturer's certificate of chemistry, mechanical properties and heat treatment for a heat of metal, linked to the items by heat number.

**NACE MR0175 / ISO 15156** (NACE MR0175 / ISO 15156): The standard for materials in hydrogen sulfide (H2S) environments in oil and gas production. It limits hardness and restricts material choices to resist sulfide stress cracking.

**NDT / NDE (non-destructive testing)** (END (ensayos no destructivos)): Examination methods that check material or welds without damaging them: radiography, ultrasonic, magnetic particle and liquid penetrant testing.

**Needle valve** (Válvula de aguja): A small valve with a tapered stem and fine thread for precise control of low flows, common on instrument lines.

**NPS (nominal pipe size)** (NPS (tamaño nominal de tubería)): The North American designation for pipe size. The number is a label; below NPS 14 the outside diameter is larger than the NPS number.

**Offer validity** (Validez de la oferta): The period during which a supplier's quoted price and terms remain open for acceptance.

**Outside diameter (OD)** (Diámetro exterior (OD)): The measured outer diameter of a pipe. It is fixed for each NPS across all schedules.

**Packing list** (Lista de empaque (packing list)): A document that lists the contents of each package or crate with quantities, weights and dimensions, used to check goods on receipt.

**Pipe spool** (Spool de tubería): A prefabricated section of pipe with fittings and flanges, made in a shop to a drawing and installed as a unit.

**PMI (positive material identification)** (PMI (identificación positiva de materiales)): A check, usually with a handheld analyzer, that the alloy of an item matches the specification.

**PPE (personal protective equipment)** (EPP (equipo de protección personal)): Equipment worn to reduce exposure to hazards, such as hard hats, safety footwear, gloves, masks and eye protection.

**Pressure class** (Clase de presión): A dimensionless rating label for flanges and valves, such as Class 300. The allowable pressure falls as temperature rises.

**Pressure relief valve (PRV / PSV)** (Válvula de alivio de presión (PRV / PSV)): A safety device that opens at a set pressure to release fluid and protect equipment from overpressure, then reseats.

**Pressure vessel** (Recipiente a presión): A closed container designed to hold fluid at a pressure different from the surroundings, built to a code such as ASME Section VIII.

**Purchase order (PO)** (Orden de compra (OC)): The buyer's binding order to a supplier, stating items, prices, terms, specifications, documents and delivery.

**PWHT (post-weld heat treatment)** (PWHT (tratamiento térmico posterior a la soldadura)): Controlled heating of a welded part after welding to relieve residual stress and temper the heat-affected zone, as the code or specification requires.

**Raised face (RF)** (Cara realzada (RF)): A flange face with a raised ring inside the bolt circle where the gasket seats.

**Reducer** (Reducción): A fitting that joins pipes of different sizes. A concentric reducer keeps the centerline; an eccentric reducer keeps one side flat.

**Refractory** (Refractario): A non-metallic material that keeps its strength and shape at high temperature and resists heat, abrasion and chemical attack.

**Refractory anchor** (Anclaje refractario): A metal or ceramic support fixed to the shell that holds a monolithic lining in place against gravity, vibration and thermal movement.

**Refractory dry-out** (Secado del refractario (dry-out)): The first controlled heating of a new lining that removes water slowly so steam does not crack or spall it.

**RFP (request for proposal)** (RFP (solicitud de propuesta)): A document that asks suppliers to propose a solution, so approach and capability are evaluated along with price.

**RFQ (request for quotation)** (RFQ (solicitud de cotización)): A document sent to suppliers asking for price, delivery and terms for a defined item to a defined specification.

**Ring-type joint (RTJ)** (Junta de anillo (RTJ)): A flange with a machined groove that seats a metal ring gasket, used for high pressure and temperature.

**SAT (site acceptance test)** (SAT (prueba de aceptación en sitio)): A test of installed equipment on site to confirm it works as specified.

**Schedule (SCH)** (Schedule (SCH)): A designation such as 40 or 80 that sets the nominal wall thickness of pipe for a given NPS.

**SDS (safety data sheet)** (SDS (hoja de datos de seguridad)): A document that describes a chemical or material's hazards, handling, storage and emergency measures.

**Seamless pipe** (Tubería sin costura): Pipe made without a longitudinal weld, by piercing and rolling or extruding a solid billet.

**Shell-and-tube heat exchanger** (Intercambiador de calor de tubos y carcasa): A heat exchanger in which one fluid flows through tubes and another flows around them inside a cylindrical shell.

**Slip-on flange (SO)** (Brida deslizante (SO)): A flange that slides over the pipe and is fillet welded inside and outside. It is easier to fit than a weld neck flange.

**Sour service** (Servicio ácido (sour service)): Service in which the fluid contains hydrogen sulfide (H2S) at levels that can cause sulfide stress cracking in susceptible materials.

**Spiral-wound gasket** (Empaque espirometálico): A gasket of V-shaped metal strip wound with soft filler, with a centering ring and optionally an inner ring. ASME B16.20 covers it.

**Stud bolt** (Espárrago (stud bolt)): A fully threaded rod used with a nut at each end to clamp a flanged joint.

**Technical bid evaluation (TBE)** (Evaluación técnica de ofertas (TBE)): The review of each offer against the technical specification: material, standard, dimensions, testing and documents.

**Thermowell** (Termopozo (thermowell)): A protective tube installed in a pipe or vessel that houses a temperature sensor so it can be removed without opening the process.

**Third-party inspection (TPI)** (Inspección por tercera parte (TPI)): Inspection by an independent agency named by the purchaser, usually at the manufacturer's works before shipment.

**Valve trim** (Interiores de válvula (trim)): The internal parts of a valve that contact the flow: seat, disc or wedge, and stem. Trim material is specified separately from the body.

**Wall thickness** (Espesor de pared): The thickness of the pipe wall. It sets pressure capacity and, with the OD, the bore.

**Weld neck flange (WN)** (Brida de cuello soldable (WN)): A flange with a tapered hub that is butt welded to the pipe. It suits high pressure, high temperature and cyclic service.