Author: Beijing Guojie Pipeline Co., Ltd.
Abstract: The API standard is a specialized specification system for the petroleum industry widely adopted in long-distance oil and gas transmission and refining and petrochemical projects. It is distinct from the general ASME process piping standard, and is fundamentally based on API Spec 5L line pipe, accompanied by a series of requirements for welding, anti-corrosion, and inspection.Domestic petrochemical procurement often confuses API pipeline standards with ASME fitting standards, leading to problems such as incorrect selection of PSL grades, missing toughness indicators, incomplete documentation chains, and non-compliant adoption of domestic special equipment requirements.This article outlines the API standard system architecture, grading logic, inspection and traceability requirements, distinguishes the boundaries between API, ASME, and SH petrochemical standards, and establishes an API fitting procurement control process suitable for domestic refining and oil and gas transmission projects to avoid selection and acceptance risks.
I. Introduction
In petrochemical engineering projects such as crude oil transmission, refined product pipeline networks, oil and gas gathering, and large-scale refining and chemical integration, API (American Petroleum Institute) standards are the most internationally recognized specialized pipeline technical system, and a large number of foreign-related EPC projects, CNOOC projects, and overseas export projects all specify the use of API series standards.Many procurement personnel have cognitive misconceptions, simply equating API with fitting product standards and mistakenly believing that fittings such as elbows, tees, and reducers themselves have independent API product standards. In reality, the API system focuses on transmission line pipe steel, pipeline welding, pipeline pressure testing, and pipeline service evaluation;Pressure-bearing fittings supporting petrochemical projects are usually implemented in accordance with ASME B16.9 and MSS SP75, used in combination. This is the most fundamental and also the most frequently occurring cognitive blind spot in API standard procurement.
In the domestic petrochemical industry, multiple systems operate in parallel: SH/T petrochemical standards, GB national standards, ASME, and API. The applicable scenarios, material acceptance, impact toughness, and non-destructive judgment logic of different standards differ enormously.Some procurement directly applies GB/T12459 or general ASME procurement experience to execute API projects, ignoring the distinction between the two product specification levels PSL1 and PSL2 in API 5L, and neglecting the mandatory constraints of pipelines on low-temperature impact, crack arrest toughness, carbon equivalent, and weldability;There are also projects that judge products as qualified upon obtaining an API certification certificate, without distinguishing the scope of the API monogram license and the coverage of type testing. Only at the stages of special inspection acceptance, hydrostatic testing, and non-destructive acceptance do they discover that indicators are not met, causing material return and schedule delays.
The core cognitive points of API standard procurement can be summarized as: API controls the transmission pipeline body and pipeline welding, while supporting pipe fittings implement the ASME pipe fitting series standards;API 5L is divided into two levels, PSL1 and PSL2. PSL2 is the high-requirement level and is the commonly used level for high-pressure, sour media, and long-distance trunk pipelines;When API standards are used for domestic special equipment projects, compliance comparison with TSG 31, GB/T20801, and SH/T3059 must be completed; foreign standards cannot be directly copied and used.
II. Architecture of the Core API Standard System for Petrochemical Pipelines
The most commonly used core API standard in petrochemical pipeline procurement is API Spec 5L "Specification for Line Pipe," which is the core basis for steel pipes in long-distance transmission pipelines and gathering pipelines. The standard specifies the manufacturing, dimensions, materials, mechanical properties, chemical composition, inspection and testing, marking, and documentation requirements for seamless steel pipes, submerged arc welded steel pipes, and high-frequency electric resistance welded steel pipes, and establishes two product specification levels, PSL1 and PSL2.PSL1 belongs to the basic grade and meets conventional transportation working conditions;PSL2 adds upper limit control of yield strength, low-temperature Charpy impact test, carbon equivalent limit, hardness control, and increased proportion of non-destructive spot inspection. It is suitable for high-pressure, large-diameter, sour medium, and main pipelines in densely populated areas. During procurement and selection, the grade must be strictly specified in accordance with the design documents, and PSL1 must not be used to replace PSL2.
The supporting standards mainly include API STD 1104 "Pipeline Welding Standard", which specifies the procedure qualification for pipeline butt welding, welder qualification, non-destructive testing, and defect acceptance criteria. It is different from the ASME Section IX welding system, and the pipeline welding defect tolerance and repair rules form their own system;Recommended specifications such as API RP 5L2 and API RP 570 provide guidance for pipeline coating and in-service pipeline inspection, respectively.For pipe fittings such as elbows, tees, reducers, and caps, as well as flanges, API itself has no independent product specification standards. Engineering practice adopts ASME B16.9 and MSS SP-75, and flanges adopt ASME B16.5. In the procurement technical agreement, it is stated that "pipeline steel pipes shall comply with API Spec 5L, and supporting pipe fittings shall comply with ASME B16.9". This is the standard wording for the standard combination of API petrochemical projects.
For process pipelines inside domestic refining and chemical plants, most implement the SH/T 3059 petrochemical pipeline material selection specification and ASME B31.3 process piping. Only off-site long-distance transmission pipelines, gathering and transportation pipelines, and oil and gas export trunk lines give priority to the API 5L system.Many purchasers confuse "refining and chemical process pipelines" with "oil and gas transmission pipelines", and forcibly apply API standards to process pipelines within the plant area, resulting in standard mismatch.
III. Key points of API 5L steel grade, PSL classification, and material procurement control
API 5L steel grades are named by minimum yield strength, with common grades X42, X52, X60, X65, X70, and X80, corresponding to domestic steel grades L290, L360, L415, L450, L485, and L555; the higher the steel grade, the higher the strength requirements, toughness control, and welding difficulty.PSL2 line pipe is a key focus of procurement control; it mandatorily requires Charpy impact testing. For low-temperature environments and H₂S-rich sour service conditions, hydrogen-induced cracking (HIC) and sulfide stress cracking (SSC) tests must also be added. The procurement technical agreement must clearly specify the ambient temperature, corrosive service conditions of the medium, impact test temperature, impact energy requirements, and HIC test requirements; it must not merely state the steel grade and PSL level.
For API line pipe, chemical composition control focuses on carbon, sulfur, and phosphorus content as well as carbon equivalent, for the purpose of ensuring field welding performance.PSL2 line pipe has an upper limit constraint on carbon equivalent to reduce the risk of cold cracking;whereas PSL1 does not mandate carbon equivalent or impact testing and only needs to meet basic tensile testing.During procurement, a common mistake must be strictly avoided: simply because the steel pipe has the same steel grade, directly substituting PSL1 steel pipe for PSL2 steel pipe; the two quality levels are not equivalent or interchangeable.
At the same time, it is necessary to distinguish line pipe from pipes used for boilers and chemical pressure vessels.API 5L line pipe is designed for long-distance transportation, with emphasis on weldability, crack-arrest toughness, and field installation;Heat-resistant steel pipes such as A335 and 15CrMoG are intended for high-temperature process pipelines, with emphasis on high-temperature creep rupture performance; the design starting points of the two are completely different and they cannot be substituted at will.
IV. Supplier admission, API monogram, and domestic special equipment compliance audit
API monogram authorization is an important supplier qualification, but procurement needs to clarify the boundaries: the API monogram only indicates that the manufacturer's quality management system and products meet API standard requirements, and does not mean automatic compliance with domestic special equipment licensing.For petrochemical projects implemented in China, API line pipe and supporting pressure-bearing pipe fittings are pressure piping components, and manufacturing enterprises still need to obtain the domestic Special Equipment Pressure Piping Component Manufacturing License, with the license scope covering the corresponding materials and specifications;Imported API steel pipes also require implementation of type testing and standard compliance statements, and advance communication with special inspection agencies on the standard adoption plan.
When auditing supplier qualifications, it is necessary to verify the valid authorization certificate of API Spec 5L, the steel pipe steel grades, pipe diameter ranges, and production processes (seamless/submerged arc welding/ERW) covered by the certificate. Many manufacturers' API certificates only cover small diameters or a certain type of process; products beyond the certificate scope are non-compliant even if a quality assurance certificate is issued.Under the distributor supply model, the API original manufacturer quality certificate must be issued and stamped by the steel pipe manufacturer; traders are not allowed to reissue the certificate themselves. Heat numbers, melt numbers, and stamp markings must correspond one-to-one, achieving full-chain traceability from billet, rolling, non-destructive testing, to hydrostatic testing.
Non-destructive testing and hydrostatic test requirements also distinguish PSL grades. The sampling ratio for ultrasonic and radiographic testing of PSL2 line pipe is higher than that of PSL1, and there are also specification requirements for hydrostatic test holding time and pressure values. The procurement technical agreement should clearly specify the non-destructive testing execution standards and acceptance grades, and cannot leave the acceptance criteria to the manufacturer's own choice.
V. Procurement Technical Agreements, Incoming Acceptance, and Material Substitution Control
The API project procurement technical agreement is the core of control; it cannot merely specify API 5L and steel grade X70. It must clearly state: PSL level, steel grade, delivery condition, impact test temperature and impact energy, whether HIC/SSC sulfide resistance testing is required, welding per API 1104, standards for matching pipe fittings, marking requirements, quality assurance document list, and domestic special equipment certification requirements.For overseas projects, the adopted standard version and addenda/amendments must also be specified, as different versions of API 5L differ in their indicators.
Incoming acceptance is divided into three modules: document verification, appearance and dimensions, and physical-chemical re-inspection.Document verification focuses on checking the API original mill quality certificate, heat number, hydrostatic test report, non-destructive testing report, and impact test report;Appearance inspection checks the steel pipe bevel, surface lamination, cracks, and scabs;Dimension inspection checks outer diameter, wall thickness, and ovality.For PSL2 and sour service pipelines, after arrival, spectral re-inspection and impact re-testing shall be carried out according to project requirements;For acid service pipelines, review the HIC test specimen reports as required.
The control of material substitution for API pipeline materials is strict. Any change in steel grade, PSL level, delivery condition, or sour service requirement is not a simple specification replacement. The design institute must perform strength verification, fracture toughness assessment, and welding procedure qualification confirmation, and issue a formal substitution document. Implementation may proceed only after confirmation by the supervision unit, the owner, and the inspection agency. The purchaser and supplier have no right to substitute on their own.
VI. Summary of High-Frequency Misconceptions in API Standard Procurement
First, conceptual confusion: elbows and tees are considered API fittings, ignoring that API only covers line pipe steel pipe, while supporting fittings are governed by ASME B16.9;Second, arbitrary replacement of PSL levels, substituting PSL1 for PSL2, lacking impact and toughness control;Third, obtaining an API certificate is regarded as meeting domestic special equipment requirements, lacking domestic manufacturing licenses and conformity documents;Fourth, using API line pipe for high-temperature process pipelines in refining and petrochemical plants, mixing it with ASME B31.3 process piping;Fifth, the technical agreement lacks special clauses for impact and sour service, and the manufacturer only provides routine tensile reports;Sixth, confusing the API 1104 welding system with ASME IX welding qualification, resulting in incorrect welding acceptance criteria;Seventh, the documentation chain is broken; distributors resell supplied goods, and original manufacturer API quality certification documents are missing.
VII. Conclusion
API standard procurement for petrochemical pipelines is essentially a procurement system oriented toward oil and gas transmission pipelines that prioritizes toughness and welding, and it differs significantly from the selection logic for chemical process piping and power station piping.Procurement personnel must first establish a clear understanding of the boundaries: the core object of API specifications is line pipe steel for long-distance transmission, while supporting pipe fittings and flanges rely on the ASME system;PSL classification is the most important classification indicator in API procurement and directly determines all additional requirements such as toughness, corrosion, and non-destructive testing;API international certification cannot replace domestic special equipment regulatory requirements.Only through closed-loop control of the entire process—supplier API authorization verification, tiered preparation of technical agreements, factory documentation traceability, incoming physical and chemical re-inspection, and material substitution approval—can risks of standard mismatch, grade downgrading, and acceptance rejection be avoided.
Beijing Guojie Pipeline Co., Ltd. has deep expertise in pipeline ancillary supply for petrochemical and long-distance oil and gas transmission projects, and is familiar with the combined application of API Spec 5L, API 1104, and supporting ASME fitting standards. The company can prepare API pipeline procurement technical agreements, verify API original factory documentation, and assist with incoming acceptance for EPC general contractors. It supplies API line pipe, ASME standard elbows, tees, reducers, flanges, and other pressure-bearing components, suitable for domestic oil and gas gathering and long-distance pipelines as well as overseas petrochemical projects, ensuring that pipelines meet the delivery requirements for hydrostatic testing, non-destructive testing, and special equipment supervision inspection.
References:
[1] API. API Spec 5L-2020 Specification for Line Pipe. Washington: API, 2020.
[2] API. API STD 1104-2021 Welding of Pipelines and Related Facilities. Washington: API, 2021.
[3] State Administration for Market Regulation. TSG 31-2025 Safety Technical Supervision Regulations for Pressure Piping—Industrial Piping. Beijing: China Metrology Publishing House, 2025.
[4] State Administration for Market Regulation, Standardization Administration of China. GB/T 20801-2020 Pressure Piping Code—Industrial Piping. Beijing: Standards Press of China, 2020.
[5] National Energy Administration. SH/T 3059-2012 Specification for Selection of Piping Design Materials in Petrochemical Industry. Beijing: China Petrochemical Press, 2012.
[6] ASME. ASME B16.9-2021 Factory-Made Wrought Buttwelding Fittings. New York: ASME Press, 2021.
[7] Song Keke. Manual for Selection of Pipes and Pipe Fittings for Long-Distance Oil and Gas Pipelines. Beijing: Chemical Industry Press, 2023.