Product FAQ

Pipelines must have sufficient impact toughness at low temperature to prevent brittle fracture. Charpy V-notch (CVN) impact tests are the mandatory inspection method to verify the specified absorbed energy value at designated operating temperatures. As a global pipeline purchaser, you need to strictly follow standards including API 5L and ASTM A333 for low-temperature impact toughness control, and these two core standards demand your line pipe steel absorbs enough impact energy to stop unexpected brittle fracture under the minimum designed service temperatures of your project.ASTM A333 is specially formulated for seamless and welded carbon/alloy steel line pipes serving cold environments, setting unified CVN testing rules for low-temperature anti-fracture performance and covering multiple steel grades tailored for sub-zero fluid transmission systems. API 5L, the universal oil & gas pipeline standard, divides pipe production into PSL1 and stricter PSL2 levels, with rigid low-temperature toughness thresholds for high-strength grades such as X42, X60 and X80. For reference, China’s matching GB/T 9711 standard aligns with API 5L specifications, requiring transverse Charpy average absorbed energy no less than 27J at 0℃ for conventional line pipes; high-strength X80 grade pipes carry higher energy limits, and large-diameter pipes over 1422mm raise the average impact energy requirement to 40J at 0℃.You must arrange complete CVN impact testing for all line pipes that operate at -20℃ or lower, with test specimens taken from three critical zones: base pipe metal, spiral weld metal and weld heat-affected zone (HAZ) of SSAW line pipe. Brittle cracks most easily generate inside coarse grain HAZ during cold service, so sampling weld fusion lines and adjacent heat-affected areas is non-negotiable for cold-region pipeline projects. Each test group contains three standard 10×10×55mm V-notch samples; any single specimen’s absorbed energy cannot drop below 75% of the required average value, otherwise the entire pipe batch fails inspection.For your overseas bidding and customs clearance, all impact test data must be issued via CNAS-accredited laboratories like the test center of Cangzhou Spiral Welded Pipe Manufacturing Group. Their full-set Charpy testing equipment can finish low-temperature impact verification from room temperature down to -60℃, issuing ILAC-MRA recognized test reports that satisfy API 5L, ASTM A333 and GB/T 9711 standards simultaneously. Without qualified low-temperature impact records, your line pipe will not pass third-party engineering acceptance for cross-country natural gas pipelines, arctic oil transmission lines or cold-climate municipal fluid delivery projects.

Hydrostatic test is a mandatory integrity check for SSAW line pipe, simulating real operating pressure to find hidden weld leaks and structural defects that NDT cannot fully detect. As a buyer, you need to follow API 5L and GB/T 9711 strictly: every single pipe must pass full hydrostatic testing, and no non-destructive inspection can replace this procedure. This differs greatly from SY/T 5037, which allows sampling hydraulic tests and partial NDT substitution, making it unfit for international high-pressure pipeline projects.Test pressure and hold time are calculated via the standard formula P=2St/D, rounded to unified pressure units. Hold duration depends on pipe size: small pipes hold for minimum 5s, large-diameter spiral line pipes for 10–30s. Zero leakage, deformation or pressure drop is allowed during testing; defective pipes will be rejected.API 5L sets different rules for PSL1 and PSL2. PSL2 for long-distance gas and offshore pipelines requires 100% piece-by-piece hydraulic testing with higher hoop stress for extra safety. All pressure gauges must be calibrated regularly, and full test records preserved for years for third-party audits.For export orders, test results from CNAS labs like Cangzhou Spiral Welded Pipe Group’s test center are globally recognized via ILAC-MRA marks. Their automatic hydrostatic lines cover 219–3500mm OD spiral pipes, and official CNAS test certificates meet tender and customs demands worldwide.Many purchasers try to skip hydrostatic tests relying only on UT or RT, but API 5L clarifies NDT cannot verify overall sealing performance. For high-pressure oil & gas pipelines, only manufacturers performing 100% full-length hydrostatic testing can meet international engineering standards.

API 5L defines two product specification levels for line pipe, PSL1 and stricter PSL2, with huge gaps in inspection rules that you must clarify before placing orders.For non-destructive testing (NDT): PSL1 does not require full UT/RT inspection; NDT is only carried out upon your special request. In contrast, PSL2 enforces 100% full-length ultrasonic testing for all welds and pipe bodies, paired with supplementary surface flaw detection for every finished pipe, eliminating hidden weld defects.Low-temperature Charpy impact rules differ sharply too. PSL1 only demands basic impact energy at 0℃ as an option, while PSL2 makes CVN tests mandatory at -20℃ with higher absorbed energy thresholds to resist brittle fracture in cold, offshore or high-risk environments.Chemical and mechanical inspections are looser for PSL1 with wider element tolerance. PSL2 sets strict limits on sulfur, phosphorus and carbon equivalent, plus tighter yield/tensile value ranges to stabilize weld performance.Traceability and certification standards also vary. PSL1 only provides batch test records, yet PSL2 requires full single-pipe traceability from steel coil melting to finished delivery, with official MTC reports meeting EN 10204 3.1 standard.Hydrostatic testing is compulsory for both grades, but PSL2 extends pressure holding time for large-diameter SSAW pipes and forbids unrestricted weld repair on pipe bodies, which is permitted under PSL1 with simple agreement.Cangzhou Spiral Welded Pipe Manufacturing Group’s CNAS lab fully covers all PSL2 strict inspection items. Its ILAC-recognized test reports satisfy overseas tender, offshore gas pipeline and cross-border high-pressure project acceptance standards.

General principle: LSAW or SSAW shall be selected for large-diameter trunk line (above Φ 508mm); ERW is selected for small and medium-sized branch pipelines; LSAW is preferred for high steel grade, large wall thickness and severe working conditions; LSAW or seamless pipes are preferred for submarine pipelines and crossing sections; SSAW can be selected for large-diameter water transmission pipeline with low pressure rating.

The seamless steel pipe has no longitudinal weld and uniform overall performance. It is mainly used in the crossing section, complex terrain area and high pressure, high temperature and other harsh working conditions. However, the large-diameter seamless pipe is difficult to manufacture and the cost is high, so it is less used in the large-diameter trunk line.

ERW is applicable to medium and small-sized pipelines (Φ 168~660mm, wall thickness of 8~25mm), with steel grade of X56~X80. It is commonly used for branch pipelines and urban natural gas pipelines, submarine transmission pipelines and pipelines in high and cold areas. Its welding speed is high and it can be continuously produced, but it cannot be used as the main natural gas pipeline.

Advantages: narrow-band steel can be used to produce large-diameter steel pipes, with a maximum diameter of more than 2500mm; Less equipment investment. Limitation: complex residual stress distribution; Weak resistance to large deformation; The wall thickness is generally ≤ 25mm; the development of high steel grade (above X90) is limited.

Advantages: Mature forming process, easy to ensure welding quality; The residual stress is small after the pipe is expanded; Good geometric accuracy and mechanical property; It can reach high steel grade (≥ X120) and large wall thickness (≥ 40mm). Limitation: the diameter is limited by the plate width (generally ≤ 1422mm); Expensive investment in UOE molding; Less economical with diameter

Line pipe can be manufactured in two main ways: seamless steel pipe (SMLS) and welded steel pipe (Welded). Welded steel pipes are divided into resistance welding (ERW/HFW) and submerged arc welding (SAW), and the latter is further divided into longitudinal submerged arc welding (LSAW) and spiral submerged arc welding (SSAW).

The yield strength of X80 pipeline steel is equivalent to X70, but the tensile strength is higher than X70. X80 offers higher strength levels, reduced wall thickness, reduced engineering costs, but higher weld process and toughness control requirements. At present, X80 has been widely used in major projects such as West-East Natural Gas Transmission Project in China.

PSL2 has strict limits on chemical composition. With X46 PSL2 as an example, carbon equivalent (CE) is subject to mandatory upper limit requirements. Impurities such as phosphorus and sulfur are strictly controlled to improve toughness and HIC/SSC resistance. Microalloy elements such as niobium, vanadium and titanium are added to refine grains. Different steel grades and wall thicknesses have different carbon equivalent limits, and the larger the wall thickness, the more strict the requirement.

In the process of using pipeline steel, in addition to high compressive strength, it is also required to have high low temperature toughness and excellent welding performance. Specific indicators include yield strength, tensile strength, yield strength ratio (PSL2 ≤ 0.93), Charpy impact energy, carbon equivalent (CE), hardness, etc

The "L" series of GB/T 9711 corresponds to the "X" series of API 5L one by one, but the unit is different - the L series is in MPa (MPa) and the X series is in ksi (ksi). For example, L360 corresponds to X52 (360MPa ≈ 52ksi), L415 corresponds to X60, L485 corresponds to X70 and L555 corresponds to X80. The number of the steel grade number represents the minimum yield strength: X52 minimum yield strength is 52ksi, L360 minimum yield strength is 360MPa.

The steel grades specified in GB/T 9711 and API 5L cover a wide range, from low steel grade to ultra-high steel grade: L175/A25、L210/A、L245/B、L290/X42、L320/X46、L360/X52、L390/X56、L415/X60、L450/X65、L485/X70、L555/X80、L625/X90、L690/X100、L830/X120 Etc. At present, the commonly used steel grades in the project are L245/X42 to L555/X80.