DL/T 439-2018 in English
VALIDThe technical guide for high-temperature bolt of fossil-fired power plant
- Issued on:2018-04-03
- Implemented on:2018-07-01
- File Format:PDF
- Delivery:Via email within 1~3 business days
$321.00
Introduction
Analysis of the key points of the standard revision
| Revision dimensions | 2006 version | 2018 version | Technical impact |
|---|---|---|---|
| Material range | Covering up to 570℃ | Expanded to 677℃ (new high-temperature alloys such as GH6783) | Adapt to the needs of ultra-supercritical units |
| Test methods | Mainly traditional hardness testing | New DL/T 1719 portable Brinell hardness test | On-site testing efficiency increased by 40% |
| Organization Assessment | Main text includes requirements for 20Cr1Mo1VNbTiB | Moved to Appendix C and refines grain grading | Assessment operability is enhanced |
Key Technological Innovations
Material Selection Matrix
For the first time, the standard establishes a temperature-material correspondence table. For example, 20Cr1Mo1VNbTiB steel is clearly suitable for operating conditions up to 570°C, with its endurance ductility requirements: unused>5%, used ≥3%. Hardness gradient control requirements are established for 12%Cr steel bolts (nut hardness is 20-50 HBW lower).
Implementation Difficulties and Countermeasures
Case Study: Analysis of Main Steam Valve Bolt Fracture on a 1000MW Unit
Failure analysis using Section 4.2.7 of this standard revealed black reticular grain boundaries in 25Cr2MoVA bolts due to hot brittleness. After recovery heat treatment at 700°C for 4 hours in accordance with Section 4.3.1, the hardness was restored from the excessive HBW302 to HBW265, and the metallographic structure met the standard.
Comparison of the New and Old Standards
The 2006 version did not specify lubrication restrictions for high-temperature alloy bolts. Section 5.1.5 of the 2018 version specifically emphasizes the prohibition of using sulfur- and lead-containing lubricants on nickel-based alloys such as GH4145 to avoid the risk of stress corrosion cracking.
Appendix C Technical Highlights
Innovatively proposed a 7-level grain evaluation system, where:
Levels 1-5 are non-nested grain structures (qualified)
Levels 6-7 are nested grain structures (scrapped)
Rapid judgment under a 100× microscope is achieved through the typical graphs in Figures C.1-C.7.
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