Determination of Average Grain Size of Metals is a microscopic analysis method used to evaluate the grain size of metallic materials. Grains are the crystalline structural units inside metals. Finer grains result in higher strength and better toughness of the material; coarser grains make the material more prone to brittle fracture. Therefore, grain size is a critical indicator for evaluating the quality of steel products, especially steel for pressure vessels. The following is a systematic explanation of grain size determination: 1. Why Determine Grain Size? (Engineering Significance) Strength and Toughness: According to the Hall-Petch Equation, finer grains mean more grain…

The determination of the effective heating zone of heat treatment furnaces shall comply with GB/T 9452‑2023. The core principle is to identify the chargeable zone within the furnace chamber that meets the temperature uniformity requirements through no-load temperature measurement. The main procedure includes test preparation, arrangement of temperature measuring points, heating and soaking, data acquisition and evaluation. The detailed operation method is as follows: I. Scope of Application and Core Definitions Applicable objects:Various types of heat treatment furnaces (batch furnaces, continuous furnaces, etc.).Not applicable to continuous heating zones without fixed process temperature or temperature uniformity requirements. Key terms Effective Heating…

Determination of non-metallic inclusions in steel is a key method for evaluating steel cleanliness, judging the level of steelmaking processes, and predicting the mechanical properties of steel (especially fatigue properties). At present, the main determination methods are divided into microscopic assessment methods (the most commonly used, focusing on morphology and distribution) and separation analysis methods (focusing on composition and total content). The following is a detailed determination guide based on national standards (GB/T 10561, GB/T 20123, etc.): I. Microscopic Assessment Method (Standard Rating Chart Method) This is the most common method in industrial production. Polished metallographic specimens are observed under…

Microscopic Examination Method Using Standard Rating Charts (GB/T 10561‑2005) I. Principle Polished steel specimens are examined under an optical microscope at 100× magnification. Non-metallic inclusions in the field of view are compared with standard rating charts and graded by type, so as to evaluate the cleanliness of the steel. Applicable to:Structural steels, bearing steels, tool steels, stainless steels and other steel grades. II. Specimen Preparation Sampling Location Generally take transverse sections. Avoid surface decarburized layers and edge-damaged zones (distance from edge ≥ 1–2 mm). Mounting Small specimens are recommended for hot mounting to prevent edge chipping. Grinding and Polishing Grind…

Methods for Determination of Multi-Element Content in Stainless Steel (Practical Version) Main elements in stainless steel include: Cr, Ni, Mo, Mn, Si, P, S, C, Cu, N.Some high-end grades also contain: Ti, Nb, V, W, Co, Al. To meet different testing requirements, multi-element analysis of stainless steel generally adopts a combined approach: instrumental analysis as the primary method, supplemented by wet chemical analysis. I. Optical Emission Spectrometry (OES) – Most Common & Fastest Applicable to: Solid samples such as finished products, cast blanks, steel ingots, etc. Detectable elements:Cr, Ni, Mo, Mn, Si, P, S, Cu, Ti, Nb, V, W, etc.…

Steel Butt-Welding Fittings are key components in piping systems used to change direction, connect branch pipes, and alter pipe diameters. Their types and parameters are mainly specified in accordance with the national standard GB/T 12459 (equivalent to ISO 4200), chemical industry standards HG/T 20592 (European system) and HG/T 20615 (American system). The following is a detailed summary of types and parameters: I. Types of Fittings Based on function and shape, they are mainly classified into the following categories: 1. Elbows Used to change the direction of the pipeline. 45° Elbow: for small-angle direction change. 90° Elbow: the most commonly used,…

Steel products require different levels of inspection documents, commonly referred to as “inspection certificates” or “quality certification documents”, for delivery, acceptance inspection and trade settlement. The differences between these documents mainly lie in: the number of inspection items, involvement of third parties, and inclusion of test data. I. Commonly Used Domestic Inspection Documents (GB/T 247, GB/T 17505) Domestic standards classify inspection documents into the following categories: 1. Certificate of Quality The most common and basic document. Contents include: Product name, grade, specification and quantity Heat number, batch number Chemical composition Mechanical properties Delivery condition Production standard Inspection results Purpose: Basic…

I. Classification and Grading of Piping (Core Definitions in TSG) Pressure piping is divided into 4 major categories by application. Category GC is further graded to match regulatory intensity. Category GA: Long-Distance PipingDefinition: Oil or gas pipelines crossing provincial or municipal boundaries.Standard: GB/T 34275-2024 Code for Pressure Piping — Long-Distance Piping. Category GB: Public Utility PipingSubcategories: GB1: Urban gas piping GB2: urban heating pipingStandard: GB/T 38942-2020 Code for Pressure Piping — Public Utility Piping. Category GC: Industrial Piping (Core Grading)Grading basis: medium hazard, design pressure (P), design temperature (T).Grading determines regulatory and inspection requirements. GC1: Piping for highly toxic or…

Carbon steel refers to an iron-carbon alloy with a carbon content of less than 2.11%. In the field of pipe fittings and pipeline engineering, carbon steel is classified according to strict criteria, mainly based on carbon content, mechanical properties, and applicable temperature/pressure conditions. Below is a detailed classification system for carbon steel material grades, covering commonly used international standards (such as ASTM) and Chinese national standards (GB). I. Classification by Carbon Content (Basic Classification) This is the most universal classification method, which determines the hardness, toughness, and weldability of steel. Low Carbon Steel / Mild Steel Carbon content: ≤ 0.25%Features:…

Alloy steel refers to steel based on carbon steel, to which one or more alloying elements (such as chromium, molybdenum, nickel, vanadium, etc.) are specially added to improve its properties, including strength, toughness, corrosion resistance, and heat resistance. In the manufacture of pipe fittings, alloy steel is commonly used in extreme working conditions involving high temperature, high pressure, or low temperature. Below is a detailed classification of alloy steel material grades, mainly in accordance with international standards (ASTM) and Chinese national standards (GB). I. Classification by Alloy Element Content Low Alloy Steel Total alloy content: < 5%.Features: High strength, good…

Materials for low-temperature service are mainly classified according to their minimum service temperature and chemical composition. They are explained below in accordance with commonly used international standards (ASTM) and Chinese national standards (GB), without using tables. I. Common Low-Temperature Steel Grades under International Standards (ASTM) 1. Nickel-Based Low-Temperature Steels (Most Widely Used) Nickel is the most effective element for improving low-temperature toughness, making nickel steels the preferred materials for cryogenic service. A420 WPL3Contains 1.5% nickel, with a minimum service temperature of -73°C. Commonly used for general low-temperature pipelines and chemical processing units. A420 WPL6Contains 3.5% nickel, with a minimum service…

Austenitic Stainless Steel refers to stainless steel with an austenitic microstructure at room temperature. It features excellent corrosion resistance, good toughness, outstanding low-temperature performance (non-magnetic), and superior weldability. In pipeline engineering, pressure vessels and pipe fitting fabrication, austenitic stainless steel grades are mainly classified in accordance with ASTM (American Society for Testing and Materials) standards. The following is a detailed explanation of commonly used austenitic stainless steel material grades: I. Chromium-Nickel Series Stainless Steel (300 Series) This is the most widely used austenitic stainless steel series, which achieves an austenitic structure mainly through chromium (Cr) and nickel (Ni). 1. 304…