MERCURY LIQUID METAL EMBRITTLEMENT OF ALLOYS FOR OIL AND GAS PRODUCTION AND PROCESSING

MERCURY LIQUID METAL EMBRITTLEMENT OF ALLOYS FOR OIL AND GAS PRODUCTION AND PROCESSING

Authors: Raymundo Case and Dale R. McIntyre, ConocoPhillips Production Assurance Technology

Source: CORROSION 2010, March 14 - 18, 2010 , San Antonio, TX

Preview ABSTRACT

Mercury is a natural component of certain hydrocarbon reservoirs, so exposure to liquid mercury can occur in oil and gas production and processing plants. This paper reports liquid metal embrittlement (LME) test results for a variety of common oilfield and processing plant alloys exposed to liquid Hg across a range of temperatures. Test methods used include slow strain rate testing and C-ring tests. A fracture mechanics approach to derive critical stress intensities for the onset of Hg LME is suggested. Test results are presented for ASTM A516 Gr 70 carbon steel, ASTM A193 Gr B7 low alloy steel, AISI type 317 stainless steel, AISI type 410 stainless steel, Types 2205 and 2507 duplex stainless steels, Gr 2, Gr 5 Titanium alloys, UNS N10276, UNS N04400 and UNS A95086. Anomalous results were obtained in slow strain rate testing of duplex stainless steels in Hg. The implications ofthese anomalous results are discussed.

INTRODUCTION

Trace amounts of mercury occur naturally in some hydrocarbon reservoirs, and when mercury is encountered in oil and gas production and processing operations it must be contained, removed and eliminated from the product stream. One of the possible problems in mercury-containing production environments is mercury liquid metal embrittlement of the production and processing equipment.

Liquid metal embrittlement (LME) is a form of environmental cracking which occurs when structural alloys come in contact with liquid metals of various sorts. The attack normally involves penetration of the liquid metal along the grain boundaries of the structural alloy and consequent loss of structural strength and ductility. Unlike other forms of environmental cracking, such as stress-corrosion cracking or sulfide stress cracking, liquid metal embrittlement may occur in the absence of net tensile stresses in the structural alloy. All alloys are not prone to LME by all liquid metals; rather, there are specific pairs of liquid metals and structural alloys which have sufficient mutual solubility to result in grain boundary penetration.

Mercury is unique in that it is liquid over a wide range of ambient temperatures common to oil and gas production and processing environments. Some alloys, such as brass and aluminum, are well known to be highly susceptible to Hg LME whereas the Hg LME susceptibility of other alloys has not been thoroughly studied. In this work a series of laboratory tests were performed to assess the risk of mercury LME in a number of alloys commonly used in oil and gas production and processing equipment.

EXPERIMENTAL PROCEDURE AND RESULTS

Three to five standard SSR specimens were machined from each material listed. The standard specimens had a 1.0 inch (25.4 mm) long gage section with a 0.150 inch (3.8 mm) diameter. The shoulder diameter of the specimen was nominally 0.25 inch (6.4 mm) and an overall length of 2.75 inches (69.9 mm). The dimensions were in accordance to ASTM G129. Uniaxial tension tests were conducted with duplicate tensile specimens procured for the materials 2205 duplex stainless steel and solution-treated-and-aged Ti-6AI-4V.

Number of Pages 10