What we do · Why it matters · 04
How digesters can fail
Replacing and installing new digesters can crush capital expense budgets.
Our business is to sustain healthy vessels for many decades without wasting resources. Relining and repairing exposed steel shells is a science we have decades of experience with.
Protect the base metal first
The shell is the only part of a digester you cannot replace in an outage. Everything we do is aimed at never weakening it.
Caustic stress corrosion cracking needs three things at the same time: a susceptible material, a caustic environment, and tensile stress. Take away any one of them and the mechanism does not start. A shield takes away the environment — the liquor never reaches the steel — and, unlike weld overlay, it adds nothing back.
Weld overlay removes the environment too, but every pass puts heat into the shell, leaves a fresh heat-affected zone and adds tensile residual stress: one of the three preconditions, laid down deliberately across the whole wall. Arc spray adds no weld metal, no heat and no new stress. The base metal is left exactly as strong as it was.
We do carry out weld overlay where a customer requires it. We also tell them what it means: a vessel that needs inspecting and repairing far more often than a sprayed one.
Our perspective on when weld overlay can help.
Spray vs. weld overlay →Avoid the trigger, not just the damage
Every crack found is a crack ground out, and every excavation takes metal from a wall that has none to spare. Weakening the base metal is the outcome we work hardest to avoid — not by repairing better, but by never triggering the mechanism in the first place.