Corrosion Evaluation of SAW Welded API 5L X-80 Joints in H2S-Containing Solution

Adriana Forero Ballesteros,I S Bott,José Antônio Ponciano Gomes

doi:10.1590/1516-1439.368714

Abstract

The H2S corrosion resistance of API 5L X80 steel and its welded joint (WJ) were evaluated using the weight loss method in a 5%wt brine solution and different corrosive environments based on a sodium thiosulphate solution (10–3 and 10–2 mol/l). The weight loss method, scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) were applied to measure the effects of different H2S concentrations and pH (3 and 5) on the corrosion process and formation of corrosion product films. The results showed that the obtained corrosion rate and corrosion product films for both API 5L X80 steel and its submerged arc welding (SAW) WJ depend on the pH, H2S concentration and metal surface microstructural characteristics. The corrosion product film consists of two layers with different morphologies. The heat affected zone (HAZ) shows severe localized corrosion attack relative to the base metal (BM) and weld metal (WM), which is attributed to the microstructural characteristics of this region.

Highlights

The corrosion evaluation of metallic materials in oil and gas refinery environments is important because corrosion can cause economic and human losses
The results show that the obtained corrosion rates and characteristics of the Materials Research corrosion product films for all regions of the welded joint (WJ) (BM, weld metal (WM) and heat affected zone (HAZ)) and the base metal (BM) alone depend on the solution pH, H2S concentration and steel microstructure; for example, a severe attack in the HAZ was evidenced, which indicates the effect of the microstructure on the corrosion attack mechanism
The average corrosion rates obtained in the loss weight tests of both materials (BM and WJ) in different H2S-containing solutions are recorded in Table 3 and Figure 4

Summary

Introduction

The corrosion evaluation of metallic materials in oil and gas refinery environments is important because corrosion can cause economic and human losses. In Brazil, the manufacture and use of high-strength low-alloy steel pipelines have been implemented in recent decades; these pipelines are nationally produced using thermomechanical controlled processing (TMCP) without accelerated cooling and fabricated using the UOE process (pressing a U-shaped pipe between two semi-circular dies to form an O-shaped pipe, welding the pipe closed and circumferentially expanding it to obtain a highly circular shape) for the conduction of liquid and gaseous hydrocarbons These materials have been developed with specific chemical and mechanical properties, such as mechanical strength, weldability, ductility, resistance to corrosion and hydrogen embrittlement, by adding microalloying elements, such as niobium, vanadium and titanium[15,16]. Materials Research corrosion product films for all regions of the WJ (BM, WM and HAZ) and the BM alone depend on the solution pH, H2S concentration and steel microstructure; for example, a severe attack in the HAZ was evidenced, which indicates the effect of the microstructure on the corrosion attack mechanism

Materials

Weight loss tests

Results and Discussion

Conclusions