For OCTG factories, pipe finishing plants, oil service operators, Boyu Petro’s fully rotational bucking units (YNJQ400 / YNJQ590 series) deliver accurate make-up & break-out torque up to 205 kN.m for casing, tubing and premium downhole tools. Torque deviation, loss of torque output and unstable torque curves are the top downtime causes for bucking equipment. This article shares standardized maintenance workflows and step-by-step torque fault diagnosis solutions based on 30 years of Boyu petroleum machinery manufacturing experience.
1. Why Torque Stability Is Critical for Bucking Units
1) Bucking units are core equipment for API standard pipe threaded connection makeup. Consistent, calibrated torque directly determines well integrity and premium thread qualification:
2) Under-torque: Loose couplings, medium leakage, well safety hazards
3) Over-torque: Thread deformation, pipe body damage, massive scrap loss
4) Torque reading drift: Unqualified torque-turn records, failed third-party API inspection
Boyu YNJQ series bucking units adopt 6+6 synchronized hydraulic cylinder clamping system, Siemens S7-1200 PLC real-time torque acquisition and Italian-made synchronizers to guarantee ±0.5% torque precision. However, improper daily maintenance will quickly trigger torque failures and shorten equipment service life.
2. Standard Tiered Routine Maintenance to Prevent Torque Failures
Regular maintenance eliminates 80% of torque malfunctions before they occur. Boyu Petro divides maintenance into daily, weekly and monthly standards for all bucking unit models.
2.1 Daily Shift Maintenance (15 mins before startup)
1. Hydraulic system inspection
1} Check hydraulic oil level, eliminate external oil leaks on cylinders, hoses and valve blocks; low oil level leads to insufficient system pressure and torque loss
2) Remove mud, pipe filings and thread compound residue on power tong, backup tong jaws and dies to avoid slipping during clamping
2.Control system check
1) Verify PLC industrial computer torque sensor signal connection, tighten loose wiring plugs; poor contact causes inaccurate torque display
2) Test emergency stop and torque limit interlock function
3.Mechanical lubrication
Grease jaw rollers, rotary bearing and floating backup tong sliding rails to reduce clamping friction fluctuation
2. Weekly Preventive Maintenance
1) Hydraulic filter cleaning: Clean suction & return oil filters to prevent oil contamination that abrades hydraulic pumps and reduces output pressure
2) Clamping component inspection: Check jaw die wear, rotate or replace non-marking dies if grooves appear; worn dies cause pipe slip and torque loss
3) Torque calibration test: Run standard calibration pipe joint to verify torque reading error; re-calibrate if deviation exceeds ±2%
4) Bleed air from hydraulic circuits: Air trapped in cylinders creates torque fluctuation and unstable rotation torque curves
2. Monthly Deep Maintenance
1) Full hydraulic oil replacement: Replace 46# anti-wear hydraulic oil every 3 months under heavy-duty continuous operation
2) Disassemble 6 synchronized hydraulic cylinders, replace aging sealing rings; internal cylinder leakage is a major hidden torque failure risk
3) Siemens PLC system self-test: Check load cell torque sensor zero drift, back up torque recipe parameters
4) Inspect frequency converter and speed control system; unstable rotation speed leads to abnormal torque spikes
3. Top 6 Common Bucking Unit Torque Failures & Step-by-Step Solutions
Combined with after-sales service cases of Boyu YNJQ400, YNJQ590 fully rotational bucking units, we sort out the most frequent torque faults and targeted troubleshooting steps.
Fault 1: Machine cannot reach rated maximum torque (max output far below 205 kN.m)
Root Causes
1) Hydraulic system pressure loss: damaged relief valve, oil pipe leakage, clogged filter
2) Hydraulic cylinder seal aging, internal leakage of power tong cylinders
3) Jaw dies severely worn, pipe slips during makeup
4) Pump wear leads to insufficient flow supply
Solutions
1) Adjust relief valve pressure to standard 20MPa; replace stuck or leaking relief valve
2) Tighten all hydraulic fitting joints, replace cracked high-pressure hoses
3) Disassemble 6 synchronized hydraulic cylinders, replace all worn O-rings and oil seals
4) Rotate or replace clamping dies; adjust jaw opening clearance to match pipe OD
5) Clean oil filters, top up qualified hydraulic oil to standard liquid level
Fault 2: Torque reading inaccurate, large deviation between display and actual torque
Root Causes
1) Torque load cell sensor calibration drift
2) Loose sensor wiring, poor signal transmission
30 Hydraulic oil mixed with air, pressure fluctuates in real time
4) PLC torque parameter recipe lost or modified incorrectly
Solutions
1) Re-perform full torque calibration with standard test pipe joints following Boyu operation manual
2) Reconnect and lock all sensor aviation plugs, repair damaged signal cables
3) Bleed air from each hydraulic cylinder and main hydraulic circuit
4) Restore factory torque parameters, save dedicated recipes for different pipe sizes (casing / tubing / premium OCTG)
Fault 3: Abnormal torque spikes during makeup, thread damage occurs frequently
Root Causes
1) Pipe center misalignment, backup tong floating adjustment failure
2) Excessive dirt or thread compound residue on threads & dies
3) Synchronizer malfunction, asynchronous clamping of 6 hydraulic cylinders
Solutions
1) Adjust the unit’s eccentricity offset function (0–200mm horizontal offset) to center pipe automatically; repair stuck floating backup tong
2) Fully clean dies, pipe couplings and pipe body before clamping
3) Inspect Italian-made hydraulic synchronizer, replace damaged synchronizer if clamping cylinders move out of sync
4) Fault 4: Torque suddenly drops to zero during make-up/break-out rotation
Root Causes
1) Hydraulic pump sudden failure or power supply interruption
2) Torque limit interlock triggered by system overpressure
3) Main solenoid valve stuck, hydraulic circuit cut off
Solutions
1) Check power cabinet circuit, restart PLC and hydraulic power unit
2) Reset torque limit parameters on 15" industrial touch screen, clear system fault codes
3) Disassemble and clean directional solenoid valves, replace stuck valve spools
Fault 5: Unstable torque curve, fluctuating torque value during continuous rotation
Root Causes
1) Contaminated, emulsified hydraulic oil with water or metal debris
2) Loose foundation anchor bolts, machine vibration during operation
3) Frequency converter speed regulation failure, unstable rotation speed
Solutions
1) Drain all contaminated hydraulic oil, clean the fuel tank and install new filters before refilling new oil
2) Tighten all equipment foundation bolts, add anti-vibration pads for heavy-load workpieces
3) Run frequency converter self-diagnosis, adjust automatic speed control parameters
4) Fault 6: Backup tong slips, torque fails to build up when breaking out couplings
Root Causes
1) Backup tong jaw dies worn unevenly
2) Backup tong hydraulic cylinder insufficient clamping force
3) Floating center adjustment mechanism stuck
Solutions
1) Flip dies 180° or install new non-marking dies for chrome premium threads
2) Check backup tong hydraulic pressure, repair cylinder internal leakage
3) Lubricate floating slide rails, clear mud and rust blocking the automatic centering mechanism
4. Safety Rules During Bucking Unit Maintenance & Troubleshooting
1) Lockout-tagout (LOTO) mandatory: Cut off all power and hydraulic pressure before any disassembly or inspection to prevent accidental rotation injury
2) Do not replace hydraulic components with non-OEM spare parts; Boyu original seals, sensors and synchronizers guarantee torque accuracy
3) Record all maintenance and fault repair logs, track component wear cycles to arrange pre-replacement of vulnerable parts
4) For premium thread pipe processing, only use factory-specified non-marking dies to avoid pipe surface damage caused by improper maintenance
5. Boyu Petro After-Sales Technical Support for Bucking Unit Torque Faults
As a professional bucking unit manufacturer with 30+ years of oilfield equipment R&D and production, Boyu Petro provides full lifecycle maintenance support for all YNJQ series bucking machines:
1.Free online one-on-one technical troubleshooting via video call 24/7
2.Global fast delivery of original spare parts: torque sensors, hydraulic cylinders, synchronizers, jaw dies and PLC modules
3.On-site maintenance and calibration service for overseas production lines and oil service yards
4.Customized maintenance training for operator and maintenance teams to reduce long-term equipment failure rate
If you encounter persistent torque failure that cannot be solved by basic troubleshooting, contact our technical team at boyu@boyu-petro.com with your bucking unit model and fault description for professional remote guidance.
