無機鋅粉漆誘發316L不銹鋼管於銲接後之洩漏

Failure Analysis of Pre-commissioned Stainless Steel Pipe Lines

本文探討不銹鋼管線受到無機鋅底漆附著，於高溫銲接作用下所引發的破裂現象。分析方法包含背景資料蒐集、外觀觀察、電子顯微鏡分析、截面顯微組織及硬度量測等。由於鋼管裂縫位置曾為銲接的接地處，且銲接前曾有無機鋅底漆滴落於該表面，使得通電銲接時，該處因接觸電阻大而造成電流加熱作用，產生高於鋅熔點以上的高溫環境，使液態鋅原子得以沿著不銹鋼晶界侵入，降低晶界結合力而引發沿晶破壞。綜合以上特徵研判不銹鋼鋼管之破裂肇因為液態金屬脆裂所致。

Leakage of a stainless steel pipe was investigated by background information collection, visual inspection, electron microscopic analysis, metallographic examination and hardness measurement. The cracked location on the pipe was previously subject to resistance heating since it was used as a grounding conjunction during arc welding. This location was also contaminated by an inorganic, zinc-rich primer which was used to protect a nearby steel structure. The zinc-rich primer resulted in intergranular cracking of the stainless steel pipe during welding. At high temperature zinc diffused relatively easily along grain boundaries and weakened the bonding strength of the grain boundaries, which eventually resulted in disintegration of the pipe material. Accordingly, fracture in the stainless steel pipe was caused by liquid metal embrittlement.