• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文会议>International Conference on Offshore Mechanics and Arctic Engineering 2007(OMAE2007) vol.4; 20070610-15; San Deigo,CA(US) >EXPLAINING POROSITY FORMATION IN UNDERWATER WET WELDS
【24h】

EXPLAINING POROSITY FORMATION IN UNDERWATER WET WELDS

机译：解释水下湿润区的孔隙形成

获取原文
获取原文并翻译 | 示例
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Macroscopic porosity in underwater wet welds is one of the main defects that deteriorate the mechanical properties of the wet welded joints. It is well established that weld metal porosity is a function of pressure, thus water depth. However, the mechanism of porosity formation is not well understood, therefore the problem is not yet mitigated to acceptable levels, particularly at water depths close to and beyond 100 m. To purposely produce porous welds similar to those obtained in wet welding, bead-on-plate (BOP) welds were deposited in air with gas metal arc welding (GMAW) with no shielding gas, with autogenous gas tungsten arc welding (GTAW) and GTAW with cold wire feed using insufficient shielding gas (8 CFH). During welding with both processes, oxygen from the atmosphere readily reacts with the alloying elements in the molten tip of the wire and in the weld pool. Under these conditions, droplets that detach from the wire electrode will generally contain a gas bubble, which is transported into the weld metal. These two welding processes were selected because there is no slag produced in the process. Slag slows down the cooling while giving enough time for degassing to occur, as in the case of shielded metal arc welding (SMAW) in air. Even with insufficient shielding gas, the autogenous GTAW welds did not exhibit porosity because there was no metal addition in the form of droplets. However, when a wire was fed into the arc, droplets detached from the wire in the oxidizing atmosphere transported gas into the weld pool, manifested as external and internal weld metal porosity. Similarly, the GMAW BOP welds exhibited internal porosity. When quenched in water, the droplets that detached from the electrode in these oxidizing conditions exhibited internal voids. Metal transfer analysis performed on the GMAW BOP welds associated short circuiting mode with large droplets and high porosity contents (10 pct.). Conversely, small droplets are expected to transport less gas and produce less porosity. Proof of concept welds using the pulsed current GMAW (GMAW-P) process resulted in higher droplet detachment frequency, smaller droplets and a low number of short circuiting droplets. Even though a few short circuiting events were still present, the GMAW-P process drastically reduced porosity to only 0.2 pct. Chemical reaction between oxygen and carbon generates CO gas at the bottom surface of the droplets in flat welding position, this gas ascends and is partially trapped inside the droplet. However, when the welding torch and base metal are rotated 90 degrees or in horizontal welding position, the CO gas generated escapes. Consequently there is no CO bubble in the pendant droplet or porosity in the weld metal. Wet welds were made with pulsed current using AWS E6010 electrode at a pressure equivalent to 50 m water depth. Porosity was reduced from 3.9 with constant current to 2.5 pct with pulsed current. Even when porosity was reduced with pulsed current, higher pulse frequency needs to be tested along with different peak and background current values to further reduce porosity. Flux covered electrodes with ferro-manganese, ferro-titanium and boron additions were extruded for wet welding. These electrodes produced wet welds with an average porosity of 1.2 pct., which could be further reduced to 0.85 pct. By better control of the arc at the beginning side of the weld.
机译：水下湿焊​​缝中的宏观孔隙率是使湿焊缝的机械性能下降的主要缺陷之一。公认的是，焊接金属的孔隙率是压力的函数，因此是水深的函数。但是，对孔隙形成的机理尚不十分了解，因此该问题尚未减轻到可接受的水平，尤其是在接近和超过100 m的水深处。为了有目的地生产类似于湿式焊接的多孔焊缝，使用无保护气体的气体保护金属电弧焊（GMAW），自生钨极气体保护电弧焊（GTAW）和GTAW在空气中沉积盘焊（BOP）焊缝冷焊丝进给时使用的保护气体（8 CFH）不足。在两种工艺的焊接过程中，来自大气的氧气都容易与焊丝熔融尖端和焊池中的合金元素反应。在这些条件下，从焊丝电极上脱落的液滴通常会包含气泡，气泡会被输送到焊接金属中。选择这两个焊接过程是因为在该过程中没有产生炉渣。炉渣会降低冷却速度，同时给空气提供足够的时间进行脱气，例如在空气中进行屏蔽金属电弧焊（SMAW）的情况下。即使没有足够的保护气体，自发GTAW焊缝也不会出现气孔，因为没有以液滴的形式添加金属。但是，当将焊丝送入电弧时，在氧化性气氛中从焊丝上脱落的液滴将气体输送到焊缝池中，表现为焊缝内部和外部的金属孔隙。同样，GMAW BOP焊缝显示出内部孔隙。当在水中淬火时，在这些氧化条件下从电极上脱落的液滴显示出内部空隙。在GMAW BOP焊缝上进行的金属转移分析具有大液滴和高孔隙率（10 pct。）的短路模式。相反，预计小液滴将输送较少的气体并产生较少的孔隙率。使用脉冲电流GMAW（GMAW-P）工艺的概念焊接证明，焊缝分离频率更高，焊缝更小，短路焊缝的数量更少。即使仍然存在一些短路事件，GMAW-P工艺仍将孔隙率大大降低至仅0.2 pct。氧与碳之间的化学反应在扁平焊接位置的液滴底表面产生CO气体，该气体上升并部分捕获在液滴内部。但是，当焊炬和母材旋转90度或处于水平焊接位置时，产生的CO气体会逸出。因此，悬垂液滴中没有CO气泡，焊缝金属中没有孔隙。使用AWS E6010电极在等于50 m水深的压力下以脉冲电流进行湿焊。孔隙率从恒定电流下的3.9降低到脉冲电流下的2.5 pct。即使当通过脉冲电流降低孔隙率时，也需要测试更高的脉冲频率以及不同的峰值和背景电流值，以进一步降低孔隙率。将具有铁锰，铁钛和硼添加剂的药芯焊条挤出进行湿焊。这些焊条产生的湿焊缝的平均孔隙率为1.2 pct。，可以进一步降低到0.85 pct。通过更好地控制焊缝起点的电弧。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号