EFFECT OF HOT WIRE FILLER METAL ADDITION ON GTAW HEAT INPUT FOR CORROSION RESISTANT OVERLAYS
|Publication Date:||30 June 2017|
BACKGROUND AND INTRODUCTION
Steel piping, valves, blow-out preventers (BOPs), and other processing components require protection from contact with hydrogen sulfide-laden oil or gas. These "sour" products are the current norm for deep wells in the Gulf of Mexico and other areas. Corrosion-resistant alloy overlays are also used in the pressure vessel industry for various applications. Without a protective layer of a corrosion-resistant alloy, catastrophic failures, due to stress-corrosion cracking, will occur. The prominent method for application of this protective layer is to apply a CRO using some welding process. The process most favored is the gas tungsten arc welding process using an energized filler metal feed, commonly referred to as "hot wire" (GTAW-HW). By preheating the filler wire, greater deposition rates can be achieved.
ASME BPVC Section IX does not address the use of hot wire filler metal addition in terms of parameter limits or whether the power is included in the determination of heat input rate (HIR)1. In upstream (prerefinery) oil and gas applications, the tendency has been to add this secondary (hot wire) power to the primary (arc) power to calculate HIR; however, there have been questions raised in terms of whether the secondary power actually contributes to the amount of energy being supplied to the base metal or is consumed in the process of preheating the filler metal. This study will attempt to quantify what contribution, if any, is provided by the secondary power to affect the resulting HAZ properties and chemical composition of the CRO.