316L stainless steel is the backbone of hydrogen equipment—used in hydrogen storage tanks, pipelines, and fuel cell components for its excellent corrosion resistance. But hydrogen equipment operates in high-pressure, high-purity environments, making 316L vulnerable to hydrogen embrittlement. Hydrogen embrittlement (HE) causes the steel to become brittle and crack unexpectedly, even under low stress—posing catastrophic risks for hydrogen systems. The key to preventing HE lies in two critical areas: accurate 316L hydrogen-induced cracking (HIC) testing and strict control of welding processes using low-hydrogen welding wire. This article breaks down these two core points with simple language, real hydrogen industry cases, and actionable tips—no overly technical jargon.
Why 316L Stainless Steel for Hydrogen Equipment?
Hydrogen equipment demands materials that can handle hydrogen’s unique properties—316L stands out for these practical reasons:
Corrosion resistance: It resists attack from high-purity hydrogen and trace impurities (e.g., sulfur), which can damage other metals.
Low carbon content: The “L” in 316L means low carbon (≤0.03%), reducing the risk of intergranular corrosion—critical for welding, which is common in hydrogen equipment.
Ductility: 316L has good ductility (elongation ≥40%) in its normal state, but hydrogen embrittlement can strip this away quickly.
Cost-effectiveness: It balances performance and cost, making it the most widely used stainless steel for mid-to-high pressure hydrogen equipment.
What Is Hydrogen Embrittlement in 316L Stainless Steel?
Hydrogen embrittlement is simple to understand—here’s how it affects 316L in hydrogen equipment:
How it happens: Hydrogen atoms seep into the 316L steel’s grain structure during welding, high-pressure hydrogen exposure, or chemical reactions.
Impact: These tiny hydrogen atoms get trapped in grain boundaries, weakening the steel’s internal bonds. Over time, this causes brittle cracking (hydrogen-induced cracking, HIC)—often without warning.
Risk in hydrogen equipment: A single HIC crack can grow rapidly under high hydrogen pressure, leading to equipment leakage or explosion—why testing and welding control are non-negotiable.
316L Hydrogen-Induced Cracking (HIC) Test: Key to Detecting HE Resistance
HIC testing is the only way to confirm if 316L can resist hydrogen embrittlement in real-world hydrogen equipment. Here’s how it works in practice:
1. Common HIC Test Method (NACE TM0284)
The NACE TM0284 standard is the industry go-to for HIC testing of hydrogen equipment materials:
Test setup: Immerse 316L test samples in a hydrogen-saturated solution (simulating hydrogen equipment environments) at 25℃ for 96 hours.
Key measurements: After testing, check for cracks and measure three critical indicators: crack length ratio (CLR), crack thickness ratio (CTR), and crack sensitivity ratio (CSR).
Pass criteria for hydrogen equipment: CLR ≤15%, CTR ≤5%, CSR ≤2%—these values ensure 316L can resist HIC in high-pressure hydrogen systems.
2. Test Results & Real-World Implications
Test data example: A 316L sample from a reliable supplier passed with CLR=8%, CTR=3%, CSR=1%—safe for use in 70MPa hydrogen storage tanks.
Failed sample impact: A low-quality 316L sample failed with CLR=22%—using this in hydrogen equipment would lead to HIC cracks within 6 months of operation.
3. When to Conduct HIC Testing
Before equipment manufacturing: Test all 316L raw materials to avoid using HE-susceptible steel.
After welding: Welding can introduce hydrogen—test welded 316L samples to confirm no post-weld HE risk.
Welding Process Control: Low-Hydrogen Welding Wire Is Critical
Welding is the biggest source of hydrogen introduction in 316L hydrogen equipment. Using low-hydrogen welding wire and controlling the process prevents HE:
1. Why Low-Hydrogen Welding Wire Is Non-Negotiable
Regular welding wire contains moisture, which breaks down into hydrogen during welding—this hydrogen seeps into 316L and causes embrittlement.
Low-hydrogen wire specs: Choose ER316L-Si low-hydrogen welding wire (moisture content ≤0.2ml/100g). It’s specially dried and packaged to minimize hydrogen.
Benefit: Low-hydrogen wire reduces weld hydrogen content by 70% compared to regular wire—eliminating the main cause of post-weld HIC.
2. Key Welding Process Control Tips
Pre-weld preparation: Dry 316L workpieces at 150-200℃ for 1 hour to remove surface moisture—another source of hydrogen.
Welding parameters: Keep welding current at 180-220A, voltage at 22-24V, and travel speed at 5-8cm/min. Avoid high heat input (causes grain growth, increasing HE risk).
Post-weld heat treatment (PWHT): Anneal welded joints at 800-850℃ for 2 hours. This releases trapped hydrogen and reduces internal stress—critical for HE resistance.
3. Welding Quality Inspection
Visual inspection: Check welds for cracks, porosity, or incomplete fusion—these defects trap hydrogen and increase HIC risk.
Ultrasonic testing (UT): Use UT to detect internal weld cracks (too small to see visually) that could lead to HE failure.