Optimization of a Welding Procedure for Making Critical Aluminum Welds on the LBNF Absorber Core Block

TL;DR

This paper details the optimization of a welding procedure for aluminum core blocks in the LBNF Absorber, focusing on minimizing tungsten inclusions through parameter adjustments like electrode size and pre-heating.

Contribution

It presents a fine-tuning of existing welding procedures to improve weld quality and reduce tungsten inclusions in critical aluminum welds for accelerator components.

Findings

Larger electrodes with pre-heating reduce tungsten inclusions.

Pre-heating and electrode size significantly impact weld quality.

Most welds passed ASME B31.3 inspection despite not meeting all standards.

Abstract

The LBNF Absorber consists of thirteen 6061-T6 aluminum core blocks. The core blocks are water cooled with de-ionized (DI) water which becomes radioactive during beam operations. The cooling water flows through gun-drilled channels in the core blocks. A weld quality optimization was performed to produce National Aeronautical Standard 1514 Class I quality welds on the aluminum core blocks. This was not successful in all cases. An existing Gas Tungsten Arc Welding Procedure Specification was fine tuned to minimize, in most cases, and eliminate detect-able tungsten inclusions in the welds. All the weld coupons, however passed welding inspection as per the piping code: ASME B31.3 Normal Fluid Service. Tungsten electrode diameter, type, and manufacturer were varied. Some of the samples were pre-heated and others were not. It was observed that larger diameter electrodes, 5/32 in., with pre-heated joints resulted in welds with the least number of tungsten inclusions. It is hypothesized that thinner electrodes breakdown easily and get lodged into the weld pool during the welding process. This breakdown is further enhanced by the large temperature differential between the un-preheated sample and the hot electrode.