I. Introduction
Pressure pipelines are widely used in industries such as petrochemicals, long-distance oil and gas transmission, power and thermal power, new energy storage, pharmaceutical chemicals, metallurgy, and municipal heating. As special equipment, their operating media often possess characteristics such as high temperature, high pressure, flammability, explosiveness, toxicity, and strong corrosiveness. Once rupture or leakage occurs, it is highly likely to cause major safety accidents such as fires, explosions, and poisoning.The national special equipment regulatory system implements tiered management for pressure pipelines. Pipelines of different grades differ greatly in corresponding safety risks, design specifications, material standards, manufacturing licenses, and inspection and supervision requirements. Procurement work must take pipeline grade as the core guiding principle, rather than uniformly procuring materials according to general industrial pipelines.
In the practical operation of numerous engineering projects, the most prominent problem on the procurement side is vague awareness of pressure pipeline grades.Some procurement personnel only refer to the pressure and diameter marked on the design drawings, do not distinguish the risk differences among GC1, GC2, and GC3 pipelines, and directly use ordinary industrial pipe fittings for high-risk GC1 pipelines;some projects excessively raise the grade for procurement, causing unnecessary waste of procurement costs.There are also many projects where, although material parameters meet the working conditions, they lack quality certification documents, non-destructive testing reports, heat treatment records, and spectral re-inspection data required for special equipment, and are rejected during the special equipment installation supervision inspection, completion acceptance, and registration stages, causing schedule stagnation.
The classification of pressure pipeline grades is essentially an implementation method of risk-based hierarchical control.The grade determines the material access threshold, the qualification of the manufacturing unit, the inspection items, the document list, and the re-inspection requirements upon arrival at the site.Procurement personnel must thoroughly understand the grading determination rules and establish a procurement logic of "first determine the grade, then select the standard, then determine the material, and provide supporting inspections," so as to achieve precise graded procurement and compliant procurement.Based on TSG 31-2025 "Supervision Regulation on Safety Technology for Pressure Piping—Industrial Piping" and the GB/T 20801 pressure piping code, this article systematically sorts out the rules for determining pressure piping grades, clarifies by grade the mandatory procurement requirements for pressure-bearing components such as pipes, fittings, flanges, gaskets, and bolts, sorts out typical procurement misunderstandings, and builds a full-process graded procurement control mechanism.
II. Industrial Pressure Piping Grade Classification Rules and Determination Elements
According to the TSG 31 code, industrial pressure piping is divided into three grades, GC1, GC2, and GC3, based on four core indicators: design pressure, design temperature, degree of medium toxicity, and medium flammability, with risk decreasing from high to low.Long-distance pipelines GA and utility pipelines GB do not fall within the scope of industrial GC piping; their procurement standards and supervision and inspection rules are independent and must be distinguished from industrial GC piping, and procurement requirements must not be mixed.
GC1-grade piping is the highest risk grade and can be determined if any one of the following conditions is met: conveying extremely hazardous media;conveying highly hazardous gas media;Transporting highly hazardous liquid media at a working temperature higher than their standard boiling point;Transporting Class A and Class B combustible gases, or Class A combustible liquids, with a design pressure greater than or equal to 4.0MPa;Transporting combustible fluids or toxic fluids with a design pressure greater than or equal to 10.0MPa;Fluid piping with a design pressure greater than or equal to 4.0MPa and a design temperature greater than or equal to 400°C.GC1 piping carries highly hazardous media and operates under severe conditions, making it the piping category with the strictest regulatory oversight and the highest procurement threshold. All pressure-containing component manufacturers must hold the corresponding pressure piping component manufacturing license, and there are numerous inspection items with complete documentation chain requirements.
GC2 piping is medium-risk piping; all industrial pressure piping that is neither GC1 nor GC3 is classified as GC2.Common scenarios include medium- and low-pressure steam piping, ordinary combustible media piping, and moderately hazardous media piping; this is the piping type with the highest proportion in chemical and thermal power projects.GC2 control requirements are lower than those for GC1, but it still belongs to special equipment and cannot be procured according to ordinary plumbing and heating piping standards; materials, inspection, and documentation must likewise meet pressure piping specifications.
GC3 pipelines are low-risk pipelines that only transport non-toxic, non-flammable fluid media, with a design pressure less than or equal to 1.0MPa, and a design temperature greater than -20°C and less than or equal to 185°C, typically such as ordinary circulating cooling water and room-temperature soft water pipelines.GC3 has the lowest risk, and inspection requirements are simplified, but it still falls within the scope of special equipment, and non-standard parts cannot be purchased arbitrarily completely outside the pressure pipeline specifications.
Grade determination cannot rely solely on pressure values; the properties of the medium are often the decisive factor. At the same pressure of 1.6MPa, transporting ordinary circulating water is GC3, while transporting highly hazardous toxic media is directly determined as GC1; this is also the place where procurement is most prone to pitfalls. In the early stage of procurement, the four parameters of medium hazard, flammability, pressure, and temperature must be extracted from the design specification and the medium description in the P&ID drawings; the grade confirmation must be completed first, and then the material requisition can be initiated.
III. Mandatory procurement requirements corresponding to pressure pipelines of different grades
(I) Procurement requirements for GC1 pressure pipelines
The first bottom line for GC1 pipeline procurement is supplier qualification compliance; manufacturers of pressure-bearing components such as pipes, elbows, tees, reducers, flanges, and branch outlets must hold a special equipment pressure pipeline component manufacturing license, with the licensed scope covering the corresponding materials and product categories.Non-standard parts from unqualified small factories are strictly prohibited from entering GC1 pipelines.
For material selection, the requirements of the material chapter of GB/T 20801 must be strictly implemented, and the material grade, impact test, and high-temperature mechanical properties must meet the working conditions.Low-temperature GC1 pipelines must be subject to additional low-temperature impact tests;For heat-resistant steel materials such as high-temperature alloys and chrome-molybdenum steel, the supplier must provide supporting heat treatment process records.In addition to meeting pressure calculation requirements, the wall thickness margin must additionally reserve corrosion allowance and erosion allowance, and the Sch wall thickness grade must not be downgraded in selection.
Regarding inspection requirements, GC1 pipe fittings and pipes need to undergo non-destructive testing (NDT) in the proportions specified by the code, with the UT and RT inspection proportions following design and code requirements, and chrome-molybdenum steel and austenitic stainless steel must undergo intergranular corrosion tests as required;After arrival on site, the project side must arrange spectral re-verification to check the material grade, and key pipe fittings must undergo additional hardness testing.Quality certification documents must include heat number, melt number, mechanical property reports, non-destructive reports, heat treatment records, and corrosion test reports, and all documents must correspond one-to-one with the heat number and be traceable.
Flanges, fasteners, and gaskets shall be upgraded accordingly. For high-pressure GC1 pipelines, preference shall be given to welding neck flanges and RJ ring joint faces; bolts shall be high-temperature, high-strength alloy steel bolts; gaskets shall be metal ring gaskets or spiral wound gaskets. Ordinary rubber and cheap non-metallic gaskets are prohibited for high-risk GC1 medium pipelines.
(II) Procurement requirements for GC2 pressure pipelines
GC2 pipelines likewise require the supplier to hold a pressure pipeline component manufacturing license, with qualifications matching the product category; unlicensed non-standard parts are not permitted.Materials shall meet the basic requirements of GB/T 20801; carbon steel, stainless steel, or low-alloy steel shall be selected according to medium temperature and corrosion characteristics; wall thickness shall be determined according to the pressure calculation sheet, and the corrosion allowance shall be taken according to the medium corrosion rate.
The non-destructive testing proportion is lower than that for GC1 and shall be implemented in accordance with the design documents;Conventional carbon steel pipe fittings may be subject to sampling inspection according to standards.Incoming spectral re-inspection may be conducted by sampling according to the project plan and does not require 100% full inspection, but for GC2 pipelines conveying toxic or flammable media, it is recommended to increase the sampling proportion.The quality certificate shall include the heat number, mechanical properties, and dimensional inspection report; non-destructive testing reports shall be provided according to the sampling batch.
Flanges are mainly RF raised-face neck butt-welding and neck flat-welding types, matched with flexible graphite composite gaskets and spiral wound gaskets;Bolts are selected as carbon steel or alloy steel bolts according to temperature.The key point of GC2 procurement is to eliminate arbitrary standard reduction; many purchasers mistakenly believe that GC2 has low risk and procure ordinary building pipe fittings, resulting in failure to pass supervisory inspection.
(III) Procurement requirements for GC3 pressure pipelines
The medium in GC3 pipelines is non-toxic and non-flammable, and the operating conditions are mild; manufacturing license requirements still need to be met, and inspection for some categories can be simplified according to specifications.Materials are mainly 20# carbon steel and ordinary stainless steel, sufficient to meet strength requirements at room temperature and low pressure, and corrosion allowance is appropriately reserved according to water quality.Non-destructive testing is generally reduced or exempted according to design requirements; many GC3 pipeline designs do not require RT/UT inspection of pipe fittings.
Documentation is simplified; the quality certificate ensures that material and dimensions are qualified, and the heat number is traceable.Incoming inspection is mainly based on appearance and dimensional measurement, and spectral testing may be conducted as appropriate on a sampling basis.Flanges are mostly plate-type flat welding flanges, with matching rubber gaskets and composite gaskets, and fasteners are ordinary carbon steel bolts.The key focus of GC3 procurement is to distinguish the boundaries; once the medium changes or the pressure and temperature rise, it must be upgraded to GC2, and the procurement standards must be adjusted accordingly.
IV. General control points for graded procurement of pressure pipelines
1. Lock the grade first based on drawings and design documents.Before preparing procurement material requisitions, extract the pipeline classification table from the general design specifications, mark each pipeline as GC1/GC2/GC3, bind the pipeline number, medium, pressure, temperature, and grade one by one, and mark the pipeline grade on the list to avoid mixed-batch procurement.
2. Establish procurement list templates by grade.Create separate lists for GC1, GC2, and GC3; the GC1 list shall include mandatory columns for non-destructive testing, heat treatment, spectral testing, and document traceability;GC3 simplified inspection column to achieve differentiated control.
3. Materials of different grades in the same batch shall be supplied separately, marked separately, and stacked by zone.GC1 pipe fittings shall be sprayed with exclusive markings, and heat numbers shall be managed separately to prevent on-site mixing and misuse of low-grade pipe fittings in high-grade pipelines.
4. Unify the standards system.Within the same pipeline class, national standards, American standards, and European standards shall not be mixed arbitrarily. If an overseas-related project adopts the ASME system, it is necessary to check ASME B31.3 Process Piping Code, match the corresponding domestic special equipment supervision and inspection requirements, and confirm the standard adoption rules with the supervision and inspection agency in advance.
5. Changes require synchronous grade upgrades.If the medium, pressure, or temperature changes during the project implementation stage, the pipeline class must be re-determined, and the material, inspection, and documentation requirements must be adjusted accordingly; the original procurement plan cannot be continued.
V. Summary of High-Frequency Procurement Misconceptions
First, the pressure-only approach: looking only at pressure values while ignoring medium properties, misjudging low-pressure toxic media as low-grade piping, and procuring ordinary fittings, leaving major safety hazards.
Second, after grade classification, failing to verify manufacturing license qualifications and procuring uncertified non-standard fittings, which directly makes it impossible to pass special equipment supervision and inspection.
Third, mixing and using fittings of different GC grades together, using GC2 fittings on GC1 pipelines, with mismatched material inspection grades.
Fourth, focusing on the pipe body itself while ignoring pressure-bearing accessories such as branch outlets, lap-joint stubs, and reducers, and not procuring accessories according to the corresponding grade.
Fifth, weak awareness of documentation, requesting only certificates of conformity while lacking heat-number traceability, non-destructive testing, and heat treatment reports, resulting in a broken documentation chain and obstructed special equipment registration.
Sixth, confusing the procurement specifications for industrial GC piping, public utility GB piping, and long-distance transmission GA piping, and applying GB gas piping rules to GC chemical piping.
VI. Conclusion
Pressure piping grade classification is the foundational framework for special equipment safety management, and behind each grade correspond a full set of differences in risk level, regulatory requirements, material thresholds, inspection standards, and documentation systems.The GC1, GC2, and GC3 classifications are not paper labels, but rather hard mandatory guidance for procurement work.Procurement personnel must not treat pressure piping with the ordinary piping procurement mindset; they must insist on first determining the classification, then defining technical conditions, screening qualified suppliers, specifying inspection items, and closing the loop on documentation traceability.
Precise classified procurement, on the one hand, ensures the intrinsic safety of pipelines carrying high-risk media and avoids the risk of leakage and explosion;on the other hand, it avoids excessive procurement that drives up costs, achieving a balance between safety and cost.Beijing Guojie Pipeline Co., Ltd. is familiar with pressure piping regulations and standards such as TSG 31 and GB/T 20801, and can provide complete sets of piping materials, fittings, and flanges at all GC1/GC2/GC3 classifications for chemical, energy storage, thermal power, and oil and gas projects, assisting customers in organizing piping classification lists, verifying procurement technical conditions, and checking factory documentation, so as to meet the full-process compliance requirements of special equipment supervision and inspection, completion acceptance, and registration.