Prior work showed that the Ni-Cr-Mo alloys UNS N06058 and UNS N06059 can be reliably explosion clad to carbon steel and are fully compliant with ASME Code. Additionally, corrosion tests in hydrochloric and sulfuric acid, in "green death solution" and further mechanical tests according to SA 265 (Nickel and Nickel-Base Alloy-Clad Steel Plate) have been conducted.

To fabricate equipment such as pressure vessels, explosion cladding is followed by shell and head forming. If requested by the codes, a post weld heat treatment may also be mandatory. After this sequence, the clad bond zone layer has been investigated with respect to mechanical properties and corrosion resistance.

Therefore, best practices for explosive cladding and head forming were identified and evidence was provided that the explosive cladding process does not affect the above-mentioned properties of Ni-Cr-Mo materials. The effect of the post weld heat treatment on the corrosion properties in hydrochloric and sulfuric acid was also investigated and differences between alloy UNS N06058 and alloy UNS N06059 could be detected.

Classification of the used clad materials and motivation for explosion clad trials

The alloys used as clad material for this study are members of the so-called "C-family". It consists of Ni-Cr-Mo alloys, which are known for combining the corrosion resistance of Ni-Cr alloys in oxidizing media with corrosion resistance of Ni-Mo alloys in reducing media. As a result, these materials have proven to be extremely durable in a wide range of highly aggressive media. The development of these materials started in the 1930s with Alloy C. This alloy showed remarkable corrosion resistance in a wide spread of media, low sensitivity for pitting or crevice corrosion and virtual immunity to chloride induced stress corrosion cracking1-2.

With these properties, the alloy was well suited for applications in the chemical process industry, oil refining equipment, petrochemical equipment and many more applications in highly aggressive media. With the increasing demands in these application fields, new alloys needed to be explored by using new production processes such as the VOD (vacuum oxygen decarburization). Thus, purer materials could be produced leading to the development of alloys like UNS N06022 and UNS N10276 (nominal compositions see Table 1). These new materials were characterized by lower contents in carbon and silicon resulting from the new production-methods. By that, the binding of chromium in carbides could be decreased and the chromium content in the microstructural matrix was elevated. This resulted in a positive effect on corrosion resistance1-2 .

This content is only available via PDF.
You can access this article if you purchase or spend a download.