Severe and mixed chemical service: flue gas desulphurisation, pulp and paper bleaching, pharmaceutical and fine chemical reactors, pickling and acid handling, and waste incineration. Its combination of chromium and molybdenum resists pitting, crevice attack and chloride stress corrosion cracking in streams that alternate between oxidising and reducing.

The C-series alloys contain both chromium and molybdenum, so they cope with oxidising and reducing conditions and with mixed chemistry. The B-series is nickel-molybdenum with little chromium, which makes it outstanding in hydrochloric and other reducing acids but poor wherever oxidising species such as ferric ions or dissolved oxygen are present.

Because 316 fails in the intended service. In chlorides, hot mineral acids, hypochlorite and mixed process streams, 316 suffers pitting, crevice corrosion and chloride stress corrosion cracking. Hastelloy resists all three. It costs many times more, so it is specified where the cheaper alloy has a demonstrated failure mode, not as an upgrade.

Yes, and welded fabrication is normal for vessels and piping, usually by TIG or MIG with matching filler. C-276 in particular was developed to be weldable without post-weld heat treatment, retaining corrosion resistance in the as-welded condition, which is a significant practical advantage over earlier alloys that sensitised at the weld.

Frequently, and it is how much of the material is actually used. A corrosion-resistant layer is deposited on a carbon or low-alloy steel substrate, giving the corrosion performance of the alloy at a fraction of the cost for a thick-walled vessel. Overlay thickness and dilution control are the critical variables.

With difficulty, like the rest of the nickel alloys. It work-hardens rapidly, is gummy, conducts heat poorly and is abrasive, so tool life is short. Rigid setups, sharp positive-rake tooling, low surface speeds, heavy constant feeds and flood coolant are needed, and interrupted or dwelling cuts should be avoided entirely.

Plate, sheet, round and flat bar, pipe, tube, fittings and welding consumables, most commonly in C-276. Availability thins quickly outside the reference grades, and lead times on less common alloys and sections can be long, so material availability is worth confirming early in a project rather than at procurement.