A water treatment project operator contacted us after commissioning failures on a set of RO high-pressure pumps. The shafts on two units had developed circumferential cracking within a short period of initial startup. The factory's position was fatigue from pressure cycling. The recommended fix was a shaft replacement with the same specification.

We requested the full material traceability package before agreeing to any course of action.

What the heat treatment record showed

The heat treatment record for the duplex stainless steel (2205 / UNS S31803) shaft forgings showed a solution annealing temperature at the lower boundary of the acceptable range for the alloy. Not outside specification. At the boundary. Combined with a rapid quench cycle documented in the production records, the microstructure was at risk of sigma phase precipitation in the heat-affected zone of the interference fit with the impeller stack.

Why it would not have been caught

Sigma phase embrittlement in duplex stainless is not detectable by standard MT or PT inspection. It requires metallographic examination of a cross-section. The factory's incoming inspection would not have caught it. Standard production NDE would not have caught it.

What we recommended

• Destructive metallographic testing of one shaft from the failed units
• Review of all heat treatment records across the batch
• If sigma phase confirmed: replacement shafts with full material certification and independent heat treatment verification

The testing confirmed the hypothesis. The replacement specification included an independent heat treatment witness requirement.

What this means at procurement

Buying the cheapest duplex shaft forgings in China is straightforward. Buying them with confidence requires knowing what to look for in the heat treatment records before they leave the shop. Solution annealing temperature, hold time, and quench medium must all be specified, witnessed, and recorded — not just within range, but at the centre of the acceptable range.

What we do

Meritus Technology specifies and witnesses heat treatment on duplex, super duplex, and high-alloy forgings sourced from Chinese mills and forging shops. If you have RO or high-pressure pump procurement coming up, we are happy to discuss what we look for.

Contact: sales@meritustech.com · +86 134 8206 1802 · www.meritustech.com