Online Storage Tank Floor Inspection

Storage Tank Floor Condition Assessment Without Taking Tanks Out of Service
  • Eliminate the high cost of tank downtime
  • Greatly reduce VOC emissions
  • Eliminate the need for temporary product storage
  • No cleaning required (high sludge levels may require mixing)
  • Increase personnel safety by avoiding confined space entry
  • Prioritize tanks for turnaround
  • Extend inspection intervals when using risk-based inspection
  • Gain information on newly-acquired assets with limited documentation

Comprehensive storage tank floor inspection services are provided by Diakont using a robotic crawler dubbed the Stingray, which can be safely deployed while the tanks remain filled and operational. Utilizing a patented combination of non-destructive examination (NDE) sensors housed within an explosion-proof enclosure, Stingray inspection systems supply complete inspection coverage, actually exceeding API 653 inspection requirements.

 

Overview

Above-ground Storage Tank floor inspections are primarily driven by API 653 requirements. Traditional floor inspections are performed manually, requiring storage tanks to be taken out-of-service, cleaned, and degassed to allow workers to enter the confined space. These tank turnarounds create vapor clouds, create unique safety risks, and are extremely costly due to both prepping the tank for human occupation and the opportunity cost of being unavailable for use.

Diakont provides comprehensive storage tank floor inspection services using a robotic crawler called the Stingray, which is safely deployed into above ground storage tanks while they remain filled and operational. Using a combination of non-destructive examination (NDE) sensors housed within an explosion-proof enclosure, Stingray inspection systems supply complete inspection coverage in accordance with API 653 requirements.

Online tank floor inspections can be conducted more often than manual inspections which allows operators to prioritize tanks for turnarounds and extend inspection intervals through risk-based inspections. This inspection technology is also crucial for gaining information on newly-acquired assets with limited documentation.

 

 

Comprehensive NDE Solution

The Stingray system is a robotic crawler-type tool, connected to a control station with an umbilical cable. The robot and umbilical cable are purged and pressurized with dry nitrogen. The system is certified to operate in Class 1, Division 1 environments, where ignitable concentrations of flammable gas or vapors exist under normal operating conditions.

Diakont’s Stingray inspection system is equipped with a patented suite of NDE sensors to assess the storage tank floor integrity. The Stingray provides the two complementary inspection methodologies of MFL and UT that can be run simultaneously. MFL is a robust sensor that can detect anomalies in almost any surface condition and the UT inspection has high accuracy measurement capabilities for characterizing any flaws detected. A higher confidence can also be obtained with detection by both NDE systems.

  • Magnetic flux leakage (MFL) – The Stingray system is equipped with 64 Hall effect MFL sensors. This MFL system has a rotating magnetic assembly that facilitates turning off the magnetic field by cancellation. The Stingray is also equipped with 4 Eddy Current sensors that are used to measure liftoff of sensor housing.
  • Ultrasonic testing (UT) – The Stingray system is outfitted with high accuracy UT sensors to measure floor thickness and assess anomaly size and depth. The UT module has 96 sensors positioned in an array of 4 staggered rows to provide 100% inspection coverage. In addition to measuring the floor plate thickness, the UT sensors are able to determine the thickness of any coating that may be present.

The Stingray system is also equipped with 3D imaging sonar which performs XYZ scans of the tank floor to provide navigation and obstacle avoidance support when tank floor sediment prevents the onboard cameras from receiving clear images.

Control of VOC Vapor Release

Diakont’s Robot Deployment Procedure is designed to keep vapor emissions as low as reasonably achievable. To meet this goal, the hatch is only opened once during the initial launch, and again at the conclusion of the inspection to retrieve the robot. Diakont achieves this by inspecting the tank floor in 24-hour shifts, in order to minimize the time the temporary hatch is in place. Diakont field crews follow the below procedure during the launch:

  • Manway bolts are changed prior to removal of hatch
  • Personnel removing the hatch do so upwind of the manway
  • SCBA is worn by all personnel on tank roof’s containing certain products, and are equipped with personal 4-gas detectors
  • Designated person is on stand-by with an IR Infrared Thermometer Gun to watch for vapor release
  • Once permanent hatch is removed, a flat temporary hatch, outfitted with a sealing gasket, is immediately placed over the opening
  • Stingray and deployment tripod with sealing gasket are lowered just above the flat temporary hatch
  • Flat hatch is removed, and the deployment tripod is immediately lowered over the opening and secured to the manway
  • Tripod hatch is opened, and the robot is lowered into the tank via a manual winch
  • Once the robot is completely below the manway edge, the hatch is closed
  • There is an opening in the center of the tripod hatch, which seals around the umbilical, while at the same time allowing the umbilical to move through the opening without losing seal
Inspection Procedure

Once onsite at the tank facility, Diakont technicians deploy a mobile diagnostic lab to a safe location near the storage tank. Technicians check all grounding, then power on the equipment on the ground for a complete function test and calibration. To verify the Stingray NDE sensor calibration, Diakont technicians use a verification test plate of the same thickness as the storage tank floor (including built-in anomalies in accordance with API 653 standards). After verifying system functionality and sensor calibration, Diakont technicians load the Stingray tool into the deployment tripod. Diakont technicians use a crane to lift the deployment tripod and Stingray tool to the tank roof. Technicians remove the manway and take extra precautions to limit vapor release while lowering the Stingray into the tank.

Diakont technicians lower the Stingray tool to the tank floor and configure the on-board sonar navigation. Diakont technicians then drive the Stingray tool to the edge of the first floor plate and scan the entire tank floor plate by plate. Each plate and the annular ring are scanned using MFL and UT, creating a comprehensive NDE map of the tank floor. Two Diakont technicians operate the Stingray system; a robot operator and an NDE technician. The NDE technician monitors the sensor data in real-time. If any large anomalies are discovered, the technicians can go back and rescan to characterize the defect on location.