A 3-1/16" 10K choke & kill manifold, eight gate valves, and the trim swap that bought it five more years of sour service.

The transporter rolled in on a Tuesday afternoon. A 3-1/16" 10,000 psi choke & kill manifold from ADNOC Offshore — Lower Zakum platform, sour-service trim, painted ADNOC red — sat strapped to the trailer with a stamped tag that said the API 16C 5-year recert was due in 27 days. It came in alongside a BOP stack from the same platform that we recerted in parallel; this is the choke and kill side of that intake.

The customer brief was tight and honest: full API 16C 5-year recertification per the standard, NACE MR0175 / ISO 15156 compliance, hydrostatic shell test at 1.5× working pressure, function test on every valve and choke, and a clean FAT pack the operator could hand to ADNOC HSE without a single yellow tag. The deadline was Lower Zakum's next workover slot. Twenty-eight days. Eight gate valves and two chokes. Every body, every stem, every stud — on the bench.

API 16C is unambiguous on this. A 5-year recert is not a clean-and-paint exercise; it is a full strip, NDT pass, hydrotest hold and FAT certification — and on a sour-service stack, the trim must be NACE MR0175 / ISO 15156 compliant from seat to packing to bolting. The operator's ask was correct. The inspection just told us how much trim was actually coming out of the boxes.

Twenty-eight days, end to end. We stripped all 8 gate valves and both chokes down to bare bodies, sent every metallic part through MPI + UT + hardness verification per NACE MR0175 (≤ 22 HRC ceiling), replaced every seat in the stack with Inconel-625-clad NACE-trim seats, swapped every stem packing to HNBR + FKM back-up, replaced both choke trim sets with OEM dimensional kits, and pulled all 64 body studs to put ASTM A193 B7M / 2HM sour-service bolting back in. Every body went through a hydrostatic shell test at 1.5× WP — 15,000 psi held for 30 minutes — and every valve got a function-cycle test on the closed-loop rig before it went into the FAT pack.

The bodies themselves — AISI 4130 alloy steel forgings, 10K class — passed UT and MPI with no rejectable indications. That was the easy part. The harder part was the stem-packing chamber on two of the gate valves: chloride pitting deep enough that we re-machined the chamber 0.15 mm under and fitted oversize HNBR seals to rebuild the seal land cleanly. That work is in the spec table at /05.

On a sour-service recert what matters most is what is NOT in the trim. No standard B7 studs. No NBR seals. No plain carbon-steel seat inserts. You don't pass API 16C by hitting numbers — you pass it by having nothing in the assembly that violates NACE.— Omar Al Maktoum · Lead Valve Technician · Jebel Ali

Every API 16C 5-year recert we run goes through the same four phases. The clock varies with what the bodies and trim hand us; the phase names don't change. This one ran clean to the day.

Below is the abridged checklist from SOP-OG-018, the procedure we use for every API 16C 5-year recert in the Jebel Ali bay. The full document runs 41 lines; this is the subset that was ticked off on this manifold, in order.

Below is what the as-found survey returned against OEM and API 16C tolerance, and what the rebuild handed back. Four findings would have failed an API 16C audit on the spot — all four are highlighted, all four were corrected in Phase 03.

On day 28, the ADNOC vendor rep walked the FAT pack on the bench and signed every page live. The manifold left Jebel Ali on day 29, low-loaded back to the Lower Zakum deployment yard, and was scheduled for redeployment on the next workover slot. The recert stamp on the spool reads valid through February 2031. NACE MR0175 / ISO 15156 compliance is certified on every wetted metallic part and every elastomer in the assembly. The 58-page FAT pack is on file at the operator's document control.