Quench Polish Quench (QPQ) Coating Behavior Under Dynamic Loads

Abstract

The selection of coating or surface treatments is a crucial step in the design of oil and gas equipment to protect against the deterioration caused by wear, corrosion, galling, fatigue, etc. Quench polish quench (QPQ) nitriding is a superior candidate to increase surface hardness for abrasion and galling resistance in carbon or stainless steels. The increased surface hardness improves the wear and corrosion resistance but reduces the surface material ductility. It is generally not recommended for application to V-shaped threads or sharp notches subjected to high stress. During well perforation in cased-hole completion, the detonation of the gun string along with the induced pressure wave in fluids generates a large-magnitude dynamic motion in the gun string. The peak load of a perforating event, from detonation to fluid-structure interaction, happens in the range of microseconds to milliseconds. The coupled wellbore hydrodynamic and structural dynamic shock load may cause an overstress failure in the millisecond scale but is usually overlooked in engineering practice. In this work, we investigated the behavior of QPQ coating under transient dynamic loads, employing both physical test and finite element analysis. We designed a combination of drop test fixture and specimens to simulate a notched specimen subjected to dynamic tensile loads. Two types of specimens were prepared in this study, QPQ-coated specimens and bare metal specimens without coating. The specimens without coating were tested to serve as a baseline for comparison. The methodology in this study provides a generic guideline for design of equipment potentially subjected to transient mechanical shock loads.