Gradient Control Mat Decoupling
Gradient control mats are installed around above ground pipeline structures to protect workers from potentially hazardous voltages that can be present on cathodically protected pipelines. Pipeline voltages can result from the following conditions:
- Induced AC voltage
- An AC fault in improperly grounded electrical equipment
- A lightning strike directly to or adjacent to the pipeline
The effectiveness of a gradient control mat is determined by the step potential and the touch potential that it allows for the voltage sources described. Unfortunately, no known manufacturer has provided any technical data on the effectiveness of their mat in limiting step and touch potentials. Additionally, single conductor mats such as the spiral configuration type, have been found completely ineffective in limiting step and touch potentials from lightning to safe levels.
DEI offers the engineered Gradient Control Mat (GCM) to address lightning and AC fault current conditions, backed by analysis from experts in lightning protection and with a full review by Correng Consulting of the cathodic protection guidelines of this mat design. Step and touch potentials are now limited with the DEI grid-type mat, in a much lower cost design. DEI also recommends decoupling gradient control mats to improve CP on the pipeline, and offers the affordable Solid-State Decoupler (SSD) line for use in conjunction with the Gradient Control Mat.
A decoupling device such as the SSD is recommended for use in conjunction with the gradient control mat as it allows for several distinct advantages including:
- The galvanic potential of the mat material becomes irrelevant
- Pipeline CP readings can be taken in the vicinity of the mat
- Any interaction with the pipeline CP system is eliminated
- The life of the anodes used to protect the mat is significantly increased