Qualification of an Additively Manufactured Component for Critical Applications in H2S-Containing Oilfield Environments

Abstract

Additive manufacturing (AM) processes have long been used for prototypes and non-critical applications in sour (H₂S containing) oilfield environments. The challenge now is how to reliably qualify a product that is critical and a primary pressure boundary in more severe application environments. This paper addresses the qualification details for a critical application of an UNS N07718 nickel alloy component manufactured via the laser powder bed fusion (LPBF) process.

This paper includes qualification details with environmental cracking tests utilizing both slow strain rate testing (SSRT) and C-ring testing in a high temperature, high pressure H₂S-containing environment. The SSRT samples tested included machined gage surfaces and C-rings that were machined from the actual component being qualified. In addition to composition, mechanical property, and impact resistance measurements, microstructural evaluations were conducted as a function of location within the component being qualified.

INTRODUCTION

Precipitation hardening nickel-based alloys are a significant class of materials known for their exceptional mechanical properties and resistance to high-temperature corrosive environments. These alloys derive their strength primarily from precipitation of secondary phases (gamma prime and gamma double prime phases) during heat treatment. These microstructural features allow for high yield strengths and excellent fatigue resistance while providing good corrosion resistance. This combination of characteristics typically makes these alloys often the top choice for applications such as aerospace, oil and gas, and power generation.

Among these alloys, UNS N07718 (Alloy 718) stands out due to its high strength and corrosion resistance with the ability to withstand harsh conditions which has made it a preferred material for critical components in the oil and gas industry.

The emergence of additive manufacturing (AM) techniques has revolutionized the production of complex components from Alloy 718. Laser powder bed fusion (LPBF) is the most widely used AM method for this alloy, allowing for the creation of difficult geometries that are often impossible to achieve through traditional manufacturing processes. This technique involves selectively melting layers of powdered metal using a high-powered laser, which builds parts layer by layer, enabling significant design freedom and material efficiency.