Expansion-Cone Material: Heat-Treatment Effects
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper IPTC 14784, ’Effect of Heat Treatment on Mechanical Properties of Expansion-Cone Material,’ by Sayyad Zahid Qamar and Tasneem Pervez, Sultan Qaboos University, prepared for the 2011 International Petroleum Technology Conference, Bangkok, Thailand, rescheduled to 7-9 February 2012. The paper has not been peer reviewed.

To withstand repeated high-level thermomechanical stresses, expansion-cone material must have specific properties. This work covered heat treatment and mechanical testing of tensile and impact specimens of American Iron and Steel Institute (AISI) D6 (DIN 1.2436) tool steel. The heat-treatment process comprises annealing, hardening/austenitizing, air or oil quenching, and single or double tempering. Mechanical testing includes hardness, tensile properties (elastic modulus, yield strength, ultimate strength, and ductility), and impact strength. An optimal heat-treatment sequence was developed for the AISI D6-steel expansion mandrel.

Introduction

Solid-expandable-tubular (SET) technology is applied for completion and production purposes. SET systems can optimize fracturing parameters by maintaining larger diameters, and they can provide effective sealing for isolating multizone environments. Expandable tubulars can help in first-time fracturing, refracturing, and multizone fracturing, and in refurbishing older wells, thus providing enhanced production and fracturing applications.

Maintenance of many oil and gas wells requires workover operations ranging from simple interventions to costly remediations. These operations include correcting production or injection profiles, converting wells from producers to injectors (or vice versa), mitigating cementation problems, repairing corroded casings, fracturing or refracturing of zones, and perforating or reperforating new or existing zones. SET systems enable such strategies. Also, SET technology can assist techniques such as smart completions, multifracturing strategies, steam-assisted gravity-drainage applications, and unconventional enhanced-oil-recovery methods.

SET technology uses cold expansion of a tubular by forcing a conical mandrel made from special tool steel through it. The tubular is cold worked beyond its elastic limit, causing permanent plastic deformation, as shown in Fig. 1. An SET test rig was designed, fabricated, and commissioned for full-scale expansion tests of SETs. Expansion cones, shown in Fig. 2, used at this facility are made from cold-worked AISI D6 tool steel.

AISI D6 tool steel is a high-carbon high-chromium steel with 2.0–2.25% car-bon, 0.2–0.6% manganese, 0.2–0.4% silicon, 11–13% chromium, 0.15–0.3% vanadium, and 0.8–1.25% tungsten. This steel is known for its high wear resistance, high compressive strength, high surface hardness after hardening, good through-hardening properties, and good stability during hardening. Published work on AISI D6 steel focused on surface-hardening methods and wear-related issues. However, little published literature was available about an optimum heat-treatment strategy, especially for AISI D6 steel used as a mandrel for expanding petroleum tubulars. The main objectives of this work were to investigate mechanical properties of AISI D6 steel after various heat-treatment operations and to develop an optimum heat-treatment strategy.