By Othman Soliman — Solids Control & Drilling-Waste specialist, 26+ yrs (GCC & MENA). Last reviewed .
Agitators keep the mud uniform and the barite in suspension — when they fail, solids settle, weight varies and barite is lost. This is the deep reference: sizing and coverage, impeller and shaft mechanics, the seal/gearbox/bearing drivetrain, and the electrical failures of continuously running motors. See the visual failure gallery.
Where it sits: in the active and reserve compartments, working with mud guns to keep solids suspended and properties uniform across the tank system. Under-sized or worn, they leave the dead zones and barite sag that show up as mud-weight problems and lost volume.
Agitators keep the mud — and especially the barite — in suspension across the tank. Check pumping capacity, active liquid volume, rheology, tank geometry, impeller clearance and placement. Nominal turnover does not prove whole-tank suspension; verify density uniformity and settled beds.
Agitator duty inadequate for the tank and fluid
Mechanism
Required circulation depends on active volume, tank geometry, fluid rheology, solids loading, impeller geometry, speed and placement. Inadequate pumping capacity or coverage leaves weakly circulated zones.
Shows as
Settled beds and barite sag away from the impeller; weight stratification.
Detect / inspect
Check OEM pumping capacity and power at actual rheology and operating level, geometry, placement and coverage; inspect beds and density at multiple locations.
Consequence downstream
Lost volume, mud-weight variation, barite loss.
Correction
Verify OEM pumping capacity and drivetrain limits for the actual duty; adjust impeller, speed, clearance, placement or number of units, then confirm whole-tank uniformity in the field.
Too few agitators / poor placement (coverage gaps)
Mechanism
Spacing and number must cover the whole compartment; gaps between units settle out.
Shows as
Dead corners and mid-tank settling.
Detect / inspect
Map coverage across the compartment; inspect for beds between units.
Consequence downstream
Settling and barite sag in the gaps.
Correction
Add/relocate agitators for full coverage; supplement with mud guns.
Wrong impeller type / pitch for the duty
Mechanism
Impeller design sets flow pattern (axial vs radial). The wrong type gives poor suspension or excessive shear/foam.
Shows as
Poor suspension or unwanted shear/foam.
Detect / inspect
Check impeller type/pitch vs the suspension duty.
Consequence downstream
Settling or fluid-quality problems.
Correction
Select impeller type/pitch for suspension; match to the mud and tank.
Mounting / structure not rigid enough
Mechanism
A weak mount lets the agitator shaft whip, stressing seals, bearings and the gearbox.
Check mount rigidity and alignment; watch for shaft movement.
Consequence downstream
Mechanical failures and downtime.
Correction
Stiffen/repair the mount; align the drive; eliminate shaft whirl.
Mechanical failures
The drivetrain — impeller, shaft, bearings, seals, gearbox — under continuous abrasive immersion. These are the failures that take an agitator offline.
Impeller / blade wear and erosion
Mechanism
Abrasive mud erodes impeller blades, cutting the flow they produce.
Non-rated gear, poor bonding or water ingress in the tank area.
Shows as
Non-Ex devices, earth faults after wash-down.
Detect / inspect
Verify Ex rating, bonding, enclosure IP.
Consequence downstream
Safety risk and electrical outages.
Correction
Use rated gear; maintain bonding and seals; control wash-down.
Design & operating targets
Suspension: barite and solids kept suspended across the whole compartment — no settled beds.
Sizing: impeller pumping capacity and power verified for actual rheology, solids loading, tank geometry and operating levels; horsepower and density alone are insufficient.
Coverage: number and placement (plus mud guns) leave no dead zones.
Drivetrain: rigid mount, true shaft, sound seals, gearbox and bearings.
Impeller: correct type/pitch for suspension without excessive shear/foam.
Field inspection checklist — agitators & impellers
Suspension: no settled beds or barite sag; mud weight consistent top-to-bottom.
Coverage: agitators sized, numbered and placed for the whole compartment; mud guns supplementing.
Impeller: correct type, not worn; producing the intended flow.
Shaft/mount: rigid mount, true shaft, no whirl or vibration.
Seals: intact; gear oil clean and uncontaminated.
Gearbox/bearings: no abnormal noise, heat or vibration; lubrication maintained.
Motor: healthy (megger/current), overloads set, Ex rating and bonding intact, enclosures sealed.
This reference describes failure modes and engineering principles in general terms. Corrective actions must be matched to your actual equipment, fluid, formation and procedures, and carried out under the relevant rig and safety standards.
Grounded in standard solids-control and mud-mixing practice and field references (drilling-fluid handbooks; agitator OEM guidance). SC DrillTech is independent and vendor-neutral.
Take it further
Tools and references built from the same field experience as this page — independent and vendor-neutral.
New here? Start with the book. Field Secrets — 262-page field manual, 54 chapters. Get the book →
Is your barite staying in suspension — or sitting in the tank bottom?
Investigate fluid rheology, solids properties and residence time alongside agitator sizing, coverage and condition; agitation alone does not establish the cause of barite sag. An independent evaluation maps the dead zones and matches the agitation to the mud you're actually running.
The 10 Solids-Control Numbers Every Engineer Must Track — what to measure, the formula, the field target and the red flag. Grounded in API RP 13B-1, RP 13C, EPA 40 CFR 435 & OSPAR.
Enter your email to access the guide. We will not add you to a mailing list. Privacy policy.
