Alatas Safe Load Indicator Upgrade – Offshore Pedestal Crane

Intro

Alatas completed an upgrade to a PAT Kruger Load Moment Limiter (LML) on an Offshore Liebherr Pedestal Crane, which was facing obsolescence.

Alatas’ own Safe Load Indicator (SLI) was installed as part of the upgrade, along with all required sensors, cables, and junction boxes. The Alatas SLI was able to not only provide equivalent functionality to the obsolete LML but also add additional functionality such as:

• Sensor and System Configuration through the Cab Screen
• Freely Configurable Slew Sector Limitation
• Hydraulic Limit Interface for crane motion limitation
• Cab Screen Display of Crane Equipment Manuals and Connection Schematics Display
• Full Lift and Event Data Logging on a cyclic buffer

As a result, the safe operation of the crane has been restored and modernized, introducing the latest safety features. Due to the standard design utilized in the SLI, any repairs required down the line can be resolved using readily available components, greatly reducing the risk of extended downtime. Furthermore, potential upgrades to the crane’s control system have been made more accessible due to the modular design of Alatas’ Crane Management System (CMS).

BACKGROUND

Alatas was approached by a client regarding a Load Moment Limiter (LML) system which was facing obsolescence.

The LML, supplied with the Liebherr RL pedestal crane during the initial build/installation in 1998, was a PAT Kruger LML of type DS 350. Sensors connected to this LML include a single channel 4-20mA Load Pin, and an Angle Sensor bolted to the side of the boom. The Operator Display Unit in the crane cabin displayed all measured data using analog dials and LED lights. Functions provided by this system were as follows:

• Crane Radius Indication (m)
• Actual Load Indication (To)
• Permissible Load (To)
• Utilization (%)
• Indication of Prewarning(90%SWL) and Overload(110%SWL)
• Sea State and Rope Reeving Selection

The client requested an upgrade to this LML, ensuring that all existing functions were replicated, including additional functionality of a Slew Sector Limitation and Hydraulic Limit Interface. The Slew Sector Limitation was requested to reinforce protection to a newly installed Communication tower on the platform, and several fuel storage tanks on the top deck.

ALATAS’ SOLUTION

The solution for this system’s requirements was Alatas’ own Safe Load Indicator, fully designed, engineered, and tested in-house. The Alatas Safe Load Indicator (ALSLI) is a modular product in Alatas’ range of System Upgrades, which as standard comes with a dual channel Load Pin, and Boom Angle Sensor. In this application, the optional Add-Ons for Slew Sector Limitation, and Hydraulic Interface were also selected to meet the client’s requirements.

Due to the standardized design of the ALSLI, the existing 4-20mA Load Pin was able to be re-utilized, reducing immediate upgrade costs to the client. Since all calibration and configuration of the system is possible through the ALSLI Cab Screen, this section of the system can be upgraded at a later date, with no requirement for a laptop/software change on-site.

For the Slew Sector Limitation, a bespoke bracket was designed to gear into the crane’s internal slew gear teeth. The geared bracket translates the rotation of the crane to the rotation of the Slew Encoder’s shaft, used to track rotational position by the ALSLI. A proximity switch also attached to this bespoke bracket enables position checking of the encoder every time the crane is brought back to its boom rest. Utilizing these two sensors to check drift increases the Safety Level of the design.

For the Hydraulic Limitation Interface, the ALSLI had to have interlock access to several of the crane’s motions including Luff Up/Down, and Slew CW/CCW. The engineered solution utilized included two separate approaches.

For Slew motion prevention, the existing Slew limit switch functionality could be interfaced with. Since the crane does not have a main slip ring, passing power up from the platform, the crane cannot slew greater than 270deg from its home position. For this reason, there is an existing set of slew limit switches. The ALSLI relays were connected between the existing slew limit switches and the main control panel. When the relays are switched OFF, the main control panel activates the same functionality as when the limit switch is reached, preventing further motion in that direction.

For Luffing motion prevention, two of the ALSLI’s relays were installed between the main crane control panel and the Luffing DCV solenoids. When the relays are OFF, the solenoids for the selected direction cannot be activated by the crane control system.

Prior to completion of SLI’s Installation and Commissioning, Alatas provided training for the Crane Operator and relevant technicians to assist with continued use and maintenance of the Alatas SLI after our technicians had de-mobilized

Job Scope

• Disconnection and Removal of existing LML (PAT Kruger) equipment
• Operator Display
• Angle Sensor
• LML Control Panel
• Obsolete Junction Boxes and Cables
• Install and connect the new SLI (Alatas) equipment
• Cab Screen/HMI
• Dual Channel Boom Angle Sensor
• Slew Encoder & Proximity Switch (using bespoke bracketry)
• SLI Control Panel
• Running of new cables
• Calibration, configuration, and commissioning
• Calibrate Boom Angle Sensor, test Radius
• Calibrate Slew Encoder and proximity switch, and test the slew angle after rotations
• Calibrate Load Pin using waterbag, test in increments
• Configure Slew Sector Limits, test hydraulic limit interface

Alatas Safe Load Indicator Upgrade – Offshore Pedestal Crane Gallery