Mechanical Properties Terms for Seamless Pipe

Index analysis of mechanical properties of seamless pipes (smls pipe):

1. The performance index analysis of seamless pipe--plasticity.
Plasticity refers to the ability of metal materials to produce plastic deformation without being damaged under load.

2. Analysis of performance index of seamless pipe--hardness.  
Hardness is a measure of the hardness of metal materials. At present, the commonly used method for measuring hardness in production is the indentation hardness method, which uses a certain geometric indenter to press into the surface of the metal material to be tested under a certain load, and the hardness value is determined according to the degree of indentation. Commonly used methods are Brinell hardness (HB), Rockwell hardness (HRA, HRB, HRC) and Vickers hardness (HV) and other methods.

3. The performance index analysis of seamless pipe--fatigue.
The strength, plasticity, and hardness discussed above are all indicators of the mechanical properties of metals under static load. In fact, many machine parts are working under cyclic loads, under which conditions the parts will fatigue.

4. Seamless performance index analysis--impact toughness.  
The load acting on the machine at a very large speed is called impact load, and the ability of metal to resist damage under impact load is called impact toughness.

5. Analysis of the performance index of seamless pipes--strength.  
Strength refers to the ability of metal materials to resist damage (excessive plastic deformation or fracture) under static load. Since the load acts in the form of tension, compression, bending, shearing, etc., the strength is also divided into tensile strength, compressive strength, flexural strength, and shear strength. There is often a certain connection between various strengths, and tensile strength is generally used as the basic strength indicator in use.

How to determine the mechanical properties requirements of seamless pipes?

Step 1: First understand the "working conditions" - determine the performance level

Working condition characteristics	Key mechanical concerns	Examples
Normal temperature and low pressure fluid	Yield, elongation	Water and air pipes
Low temperature environment (≤-20°C)	Low temperature impact toughness KV2	LNG pipelines
High-pressure boiler/steam	High temperature yield and endurance strength	Main steam pipe 600 ℃
Dynamic load, fatigue	Impact energy, fatigue limit	Marine and wind turbine towers
Corrosion with H₂S/CO₂	Upper limit of SSC resistance hardness	Oil and gas well casing

Step 2: Lock in the "product standard" - the standard gives all mechanical indicators at one time

Use	Implementation Standards (Latest Version)	Mandatory mechanics items
High-pressure boiler	GB/T 5310-2025	Rm, ReL, A, KV2, hardness, endurance strength
Petrochemicals	GB/T 9948-2025	Rm, ReL, A, KV2, hardness, grain size
Structural pipes	GB/T 8162-2018	Rm, ReL, A, flattening, flaring
Cryogenic fluid	GB/T 6479-2013	Rm, ReL, A, KV2 (-20 ℃/-40 ℃)
Oil casing pipe	API 5CT 11th Edition	Rm, ReL, A, hardness, impact (SR16)

Step 3: Extract “quantitative indicators” – convert standard clauses into tables
Take 15CrMoG (GB/T 5310-2025) for high-pressure boilers as an example:

Index	Required value	Test temperature
Tensile strength Rm	440-640 MPa	Room temperature
Yield strength ReL	≥235 MPa	Room temperature
Elongation A	≥21 %	Room temperature
Impact absorption energy KV2	≥40 J	20 ℃
Hardness HBW	135-195	Room temperature
600 ℃ 10⁵ h rupture strength	≥100 MPa	600 ℃

Step 4: Clarify the “test method” – ensure data traceability

Pilot projects	Method standards	Sampling location	Remark
Stretch	GB/T 228.1-2021	1 set each vertically and horizontally	Gauge length 50 mm
Impact	GB/T 229-2020	Vertical V-notch	Low temperature requires keeping warm for ≥10 min
Hardness	GB/T 231.1-2018	Three-point average of the outer surface	Avoid welds
Flattening/flaring	GB/T 246-2017	Pipe end 100 mm	Structural pipe must be done
Lasting strength	GB/T 2039-2021	3 pieces from the same batch	High temperature long time test

Step 5: Add a “verification clause” to the contractCertificate: EN 10204 3.1/3.2 or GB/T 247 quality assurance certificate.
Lossless: UT (GB/T 5777 C5), ET (GB/T 7735 Class A).
Re-examination: If any indicator fails, double sampling will be conducted for re-examination. If it fails again, the entire batch will be scrapped.
Identification: Spray code "furnace batch number + standard number + impact temperature" for easy traceability.