Predicting LNG Loading Arms Structural Bearings Condition

Abstract

Abstract The scope of this technical paper is to present existing methodology of predicting structural bearings condition of LNG Loading Arms in ADNOC LNG through a systematic monitoring system (LNG Loading Arms Verticality Check) included into maintenance periodic routines in order to maintain operational reliability, optimize plant availability. Few years back, ADNOC LNG experienced abnormal structural bearings noise along with leaning issue of two LNG Loading Arms, culminating with one Loading Arm becoming immovable. Despite the fact that the structural bearings are designed for entire life span of Loading Arm, it was recommended by OEM to replace all three structural bearings (slew, luff and apex), activity which was performed with significant resources and cost impact. A systematic monitoring approach to monitor the verticality of mobile arms was adopted into the ADNOC LNG Preventive Maintenance Program associated with LNG Loading Arms. The technical paper is presenting the methodology and best practices to trend and benchmark wear-and-tear process experienced in the LNG Loading Arms structural bearings. LNG Loading Arms - Verticality Check utilized a combination of GPS, conventional surveying and electronic techniques for the rapid acquisition coordination data required for the monitoring approach. Several detailed verticality check surveys were conducted for four LNG Loading Arms by determining coordinates (plan and height) from a network of GPS observations connecting newly constructed reference control points as the basis of a 3D network. The monitoring procedure was designed to trend the existing targets coordinates (installed on the LNG Loading Arms - "bull-eyes") and compared with the As-New structural bearing condition and LNG Loading Arms operating behavior, keeping in account the verticality deviation causes attributed to several factors (Loading Arms positioning errors, structural bearing clearance, other mechanical structural distortion, etc.). Each of the Loading Arms were found to be out of verticality along the virtual critical axis, but still within the calculated acceptable limits. Current maintenance practice on monitoring the Loading Arms verticality check is a powerful systematic tool for better assessment of structural bearings condition in ADNOC LNG - Das Island plant, methodology which can be implemented within other facilities using transfer arms.