Drilling and completion valves: choke manifolds and frac trees

1. Why drilling duty punishes valves

Choke manifolds, frac trees and well test packages run valves at high pressure in sand-laden flow. Proppant and formation sand act as an abrasive slurry against seats, gates and trim. Plant valves often hold steady duty for years; completion valves work hard for weeks.

The campaign pattern matters as much as the pressure itself. Equipment works intensely, then is flushed, stacked and stored for months. In storage, lubricant dries, seals take a set and corrosion starts quietly. Crews then expect the same valve to pass a seat test at rig-up.

Much of this work is offshore, where access adds cost and delay. The boundary is set out in topside versus subsea: where injection maintenance applies offshore.

2. How these valves fail

Three patterns dominate: passing seats, seized movement and external leaks. One reference point is a risk-based valve integrity study of upstream and midstream sites, published by Valve World. It reports 61 per cent of failures as passing and 28 per cent as seized. Distributions vary by population, and sand service shifts the balance toward erosion.

A closed choke that keeps passing flow suggests a seat fault, not a confirmed one. Bubbles, hiss and downstream pressure rise are screening evidence only. Confirmation needs a seat-leak test under agreed conditions. Options include pressure decay across the closed valve, double block and bleed monitoring, or a witnessed leak test.

Passing has several distinct causes, and each sets a different repair path. Common causes include erosion of the sealing surfaces, embedded debris, dried compound and trapped cavity pressure. The last one is explained in cavity pressure in ball valves.

3. What injection can and cannot reach

In-service injection is not universally possible on this equipment, so check the gates first. Valves built with injection points are designed to be maintained in service. Many drilling and completion valves carry no fittings at all.

1. The valve must have injection fittings in good, usable condition.
2. The valve design and the service must suit injection.
3. Site rules and the permit-to-work must allow work on live equipment.
4. OEM documentation, where it exists, sets limits and warranty terms.

Where the gates pass, treatment earns its place. Cleaner softens old compound and deposits, lubricant restores movement, and sealant films a sound seat. The method is covered in valve sealant injection, and high-pressure work suits an air-operated injection gun. Inject controlled amounts within equipment and fitting ratings. Watch the pressure response, and stop when pressure climbs without progress.

Injection cannot replace metal that sand has removed. Emergency isolation of a valve by body fill is a specialised and higher-risk procedure, performed by trained specialists, assessed case by case.

4. Care between campaigns

Most maintenance happens between campaigns, not during them. After flow stops, the package is recovered, cleaned and prepared for storage. A short, disciplined routine protects the next job.

1. Clean bodies and cavities of sand, salt and residual fluid.
2. Cycle every valve through full travel to feel for tight spots.
3. Lubricate through the fittings on valves that have them.
4. Record any valve that was stiff or passing in service.
5. Re-test seats before the next rig-up, not after it.

Dry, covered storage with protected fittings prevents corrosion and seal set. Valves left dry through long storage often seize, and the belief that a valve needs no care is examined in the maintenance-free valve myth. A condition survey turns the routine into a planned programme; our valve survey service records every valve and defect.

5. Treat, repair or replace

The choice between treatment, repair and replacement rests on the seat metal. If inspection shows erosion has cut the sealing faces, replacement is the honest endpoint. No compound restores removed metal.

When the metal is sound, the fault is often contamination or dried compound. Cleaning and lubrication, followed by a seat-leak test, recover many such valves. This is often the least intrusive path. A valve that stays stiff or passing after treatment needs workshop assessment, not another dose.

Compare the cost of treatment and testing against a replacement trim, and the campaign schedule against delivery time. Comparable high-pressure field results, with no client names, appear in our case studies.