尽管铸造技术已经有了巨大的发展，并利用计算机技术辅助优化结构设计和浇铸过程的流体几何设计，但是要达到1类或2类接受标准的X射线/MT或PT质量要求仍然是极端困难的，而这些都是核电站、热电站或石化工业内的苛刻环境所要求的标准。因此就需要进行焊接改进。
　　In spite of the enormous improvements in foundry technology, assisted by computerized processes to optimize the design of patterns and flow geometry during pouring it is extremely difficults to achieve X-Ray / MT or PT quality to Class 1 or 2 acceptance standards required in HP/HT applications in Nuclear, Thermal Power Stations or severe services in Petrochemical Industries. Upgrading by welding is required.

　　但是，在焊补后，铸件阀门的整体质量和可靠性就变得难于保证。有时所有这些问题都遗留在铸件焊接金属框架里。测试杆通常针对每个温度，但是它们的分析可能是不确定的。即使圆形测试杆表明化学特性和物理特性是可接受的，逐渐本身仍然可能存在难于察觉的有损强度或防腐能力的内部缺陷。
　　After weld repairs, however, the overall quality and reliability of a cast valve is difficult to determine. Sometimes all that is left is a skeleton casting with weld metal. Test bars are usually cast for each heat, but their analysis may be inconclusive. Even if the round test bar indicates acceptable chemical and physical properties, the casting itself may have undetectable inherent deficiencies that reduce strength or corrosion resistance.

精细 Fine

粗糙 Coarse

原始 Oriented

粗晶体 Coarse Dendrites

细晶体 Fine Dendrites

无晶体 No Dendrites

微孔性 Microporosity

合金再生相 Alloy Second Phase

包含物 Inclusions

　　根据锅炉法典第IX节的要求，在使用过程中需要定期进行检查的内容包括，逐渐金属的焊缝，管道焊缝。焊补位置的纪录因此必须保存，所以在工厂运行过程中，故障发生的信号可能与原始的制造条件和标准有关。
　　The periodic in-service inspection of Section IX of the Boiler Code includes weld repairs in cast metal, and pipe welds. Records of weld-repair locations must therefore be maintained, so signs of distress found during plant operation can be related to the original fabricated conditions and standards.

　　在铸造过程中，浇铸到模腔内的金属在凝固过程中可能会产生收缩、分离或气孔，这些问题使得“浇铸”铸件无法被苛刻环境应用领域所接受。收缩发生在两个过程中，温度高于熔点的金属冷却时产生收缩，随后在凝固过程中进一步收缩。第一次增加熔化金属补偿，但是固态冷却过程中的补偿就要靠加大尺寸。
　　Metal poured into a mold cavity during the casting process solidifies with the possibility of shrinkage, segregation or porosity, which can prevent an "as-poured" casting from being acceptable for severe applications. Shrinkage occurs in two parts - as metal superheats above the melting point and has losses, causing shrinkage, followed by further shrinkage during solification. Added melt compensates for the first part, but the contraction during cooling in the solid state must be compensated by oversized dimensions.

　　分离，或熔化物的化学分离，是在模腔内壁固化出一层后的凝固过程中发生，在很长的温度变化期间，低流动性使得小固体颗粒-晶体-以树状结构形成和生长。最初的晶体，紧靠着模腔内壁，合金含量最少。在里面的核心部分，合金含量比较高，这使得预想的成分变得没有什么相似性。在每个晶体枝杈内，也存在着微观偏析。结果导致微孔、再生相沉淀和金属和非金属成分混杂。
　　Segregation, or chemical separation of the melt, occurs during solidification when a layer forms at the mold-cavity wall and progresses inward. Low fluidity over a wide temperature range allows small solid crystals - dendrites - to form and grow in a treelike pattern. The initial crystals, freezing next to the mold walls, have the lowest alloy content. Farther in, the core has high alloy concentration, bearing little resemblance to the intended composition. Within each dendrite arm, microsegregation occurs. Result is microporosity, second-phase precipitation and inclusions of intermetallic or nonmetallic compounds.

　　在冷却过程中，溶液中的气体逸出造成多孔性，或被截留在晶体枝杈之间形成微小气孔。此外，作为晶体固化和量的收缩，熔化物的替代品一定会沿着交错的晶体网络流过一段曲折的路程。流动阻力可能太高，从而导致微孔和多孔。
　　Porosity can be caused by gases coming out of solution during cooling and becoming trapped between dentrite arms as tiny voids. Also, as dendrites solidify and shrink in volume, replacement of melt must flow along a tortuous path of interleaving dendrites. Resistance to flow may be high enough to cause microvoids and porosity.

　　铸件内部的其它一些缺点是，凝固过程中，在不均匀收缩造成的应力集中和接近熔点温度下金属的低强度的综合作用下，出现的清晰裂缝和热撕裂。较低的铸造温度会形成冷疤，熔化金属出现的沙粒或炉渣的累积会导致污点。低级的铸造作业也可能造成其它缺陷。
　　Some other defects in castings are well-defined cracks and hot tears that develop during solidification, under combination of stress concentration from uneven contraction and the metal's low strength at near-melting temperatures. Cold shots develop from low casting temperature, and dirt spots result from pickup of sand or slag by molten metal. Poor foundry practices can cause other deficiencies, too.

　　铸件的改进要满足X射线质量的要求就要靠缺陷部位的磨削，焊补，热处理和重复测试和检验。即使在这种情况下，阀座和垫圈面或碰焊端可能会显示需要通过重焊和机加工的细线裂缝。
　　Upgrading of castings to meet X-Ray quality needs relies on the grinding out of faulty areas, weld repairs, heat treatment, and retest and examination. Even then, seating and gasket faces or buttweld ends can show fine-line cracks that need more upgrading by rewelding and remachining.