Chemical Composition and Mechanical Property
| Grade | C% | SI% | Mn% | P% | S% | N% | B% | Cr% | Mo% | Cu% | Nb% | Ni% | Ti% | V% | Zr% |
| P355QL1 | 0.16 | 0.4 | 1.5 | 0.02 | 0.01 | 0. 015 | 0.005 | 0.3 | 0.25 | 0.3 | 0.05 | 0.5 | 0.03 | 0.06 | 0.05 |
| Steel Grade | Yield Strength, for product in mm, Mpa | Tensile Strength, Mpa | Elongation, %, min | ||||
| P355QL1 | t≤50 | 50<t≤100 | 100<t≤150 | t≤100 | 100<t≤150 | 22 | |
| 355 | 335 | 315 | 490-630 | 450-590 | |||
1. What additional quality controls are required during manufacturing?
Answer:
Beyond standard P355Q requirements:
Batch testing frequency: One set per 20 tons (vs 40 tons for P355Q)
Extended Charpy testing: 3 specimens per test at -60°C
100% ultrasonic testing (EN 10160 Class S3)
Z-direction testing (minimum 35% reduction area)
Optional CTOD testing for fracture-critical applications
2. How does the heat treatment process differ from standard quenched & tempered grades?
Answer:
Specialized Q&T process features:
Modified austenitizing (900-930°C for grain refinement)
Accelerated quenching (water spray + forced air)
Two-stage tempering:
First temper: 580-600°C × 2hrs
Second temper: 620-640°C × 1hr
Final hardness verification (max 240HV10)
3. What welding consumables and procedures are required?
Answer:
Cryogenic Welding Protocol:
Preheat: 175-225°C (for all thicknesses)
Consumables: EN ISO 16834-A G 46 5 M21 4Ni1.5Mo
Heat Input: 1.0-2.0 kJ/mm (narrower range than standard grades)
Interpass Control: 200-250°C (infrared monitored)
Mandatory PWHT: 600-620°C × 2hrs + 30min/25mm
Weld Testing: Impact tests at -60°C for both weld metal and HAZ
4. What are the key applications where P355QL1 is mandatory?
Answer:
Critical cryogenic applications including:
LNG storage tank inner shells (-162°C)
Liquid ethylene process vessels (-104°C)
Liquid oxygen/hydrogen containers
Arctic offshore structures (API 2N compliance)
Nuclear cryogenic auxiliary systems
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