Understanding Casting Products, Properties, and Process Quality: Case Study of Ductile Iron Valve Deficiency

Introduction

Casting is a manufacturing technique used to shape material, often metals, into a desired shape by pouring molten material into a mold that subsequently solidifies, forming the desired geometry. Casting products are typically tested using both destructive and nondestructive methods, ensuring compliance with the required quality standards before being assembled with other components. Casting is used to produce complex and durable components for various applications and industries, including automotive, aerospace, and facility construction projects.

Within the casting process, the concept of “charge” and “recharge” plays a vital role in maintaining efficiency and quality. The “charge” refers to the raw material introduced into the furnace for melting, such as material scraps, alloys, or virgin materials. “Recharge” occurs when additional materials are added during the melting process in the furnace, either to replenish depleted materials or adjust the chemical composition for specific properties. Proper charge and recharge control processes ensure the consistency of molten materials, reduces waste, and maintains high-quality cast components that conform to the required specifications.

This article addresses the structural failure of a cast pressure-retaining component, namely a valve, during hydrostatic testing at an oil and gas facility construction site, where the valve’s guided ribs were observed to have broken out of the valve’s body. The article focuses on identifying the root causes of the failure through a comprehensive analysis, addressing aspects of material properties and selection, manufacturing process, and quality control.

Ultimately, we utilize our detailed analysis to propose a set of recommendations aimed at preventing similar failures from occurring in the future. In essence, the findings and recommendations presented in this article are intended to serve as a reference point for foundries, manufacturers, suppliers, customers, and inspection personnel, aiming to enhance the overall reliability, integrity, and safety of cast components used in the industry.

ASTM A395 Specifications

ASTM A395 is a standard specification for ferritic ductile iron pressure retaining castings used at elevated temperatures [1]. According to this standard, castings of all grades are suitable for use up to 450°F. For temperatures above 450°F and up to 650°F, only Grade 60-40-18 castings are suitable [1]. ASTM A395 outlines the required mechanical properties for these castings, including tensile strength, yield strength, elongation, and hardness. It also specifies the necessary chemical composition for elements such as carbon, silicon, and phosphorus. Furthermore, it requires the casting components to undergo various quality control tests, such as tension tests, hardness tests, and chemical analyses, in order to confirm the components’ conformance to specifications.

ASTM A395 contains specifications for multiple grades, one of which is Grade 65-45-15. This is a type of ductile cast iron known for its excellent mechanical properties and high ductility. Grade 65-45-15 is commonly used in applications requiring high strength and ductility, including pressure-retaining castings, automotive components, agricultural machinery, and industrial equipment. The exact specification values and properties of Grade 65-45-15 will be discussed later in the article.