Personnel working near pipelines can be subject to electrical hazards such as lightning, AC fault current/voltage, and steady-state AC induction. "Ground mats" have typically been used at above ground pipeline structures where these hazards exist, but past designs do not provide adequate protection against lightning conditions.

DEI now offers an 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 new, affordable Solid-State Decoupler (SSD) line for use in conjunction with the Gradient Control Mat (GCM).

Features & Characteristics

• Low cost design.
• Galvanized steel grid, using 3" x 3" squares.
• Low inductance design limits step and touch potentials due to lightning.
• Decoupling the mat offers long life and improved CP on the pipeline.
• Data available on design life and supplemental anodes.

1.  Gradient Control Mat (4’ x 8’): Order #GCM4-8. Specify quantity.

2.  Anodes Required: Order from supplier of choice per Table 2 and Section 2.1 and 2.2 of the Correng Report referenced in this web page.

3.  Decoupler: For most applications, the SSD model suggested is SSD-2/2-1.2-75 which blocks ±2.0 volts (hence, polarity is not an issue when installing), has a 1.2 kA fault current rating at 30 cycles, and a 75 kA lightning current rating (4x10 µsec). Decouplers with higher AC fault and lightning current ratings are also available - See the SSD web page. Specify model number and quantity.

For large station mats, it is suggested that connections to the gradient control mat be made at the incoming and outgoing pipelines. Other pipe segments within a station may also need to be referenced to ground through additional decouplers.

4.  Thermit Welding Molds:

(a) For mechanically and electrically bonding adjacent mat sections together (0.135” to 0.135” diameter galvanized steel wire), order “MOLD-135” and “WELD-135-15” (20/pack; industry standard #15 CP cartridge). Specify quantity of each. It is recommended that mats be joined approximately every 18 inches (450 mm).

(b) For bonding the #6 AWG decoupler and anode leads to the 0.135” diameter galvanized steel wire of the mat, order “MOLD-6” and “WELD-6-25”(20/pack; industry standard #25 CP cartridge). Specify quantity of each. The life of either of the above molds is estimated at 50 welds nominal, 100 welds maximum.

c) All thermit welded decoupler and anode leads to the mat, plus all thermit welded connections to join adjacent mats, should be completely sealed. A recommended sealant is the Denso LT tape available in 4" wide x 25' long rolls, available from DEI or the distributor of choice. About a 2" length of this tape is required to seal each connection. Other user provided equivalent sealants may also be used.

5.  SSD Decoupler Mounting Options:

(a) Banding may be utilized as illustrated in Figure 2. The banding is to be purchased by the user. Contact DEI for banding material sources. This mounting option requires that leads be run from one decoupler bus to the pipeline and from the other decoupler bus to the mat. Two leads to each bus are recommended for a total of four leads. Order two of #MTL-6-12 for 12”(300mm) leads or two of #MTL-6-36 for 36”(900mm) leads. Two sets of leads are provided with either model number; hence, one of either model ordered will provide two leads. #6 AWG copper leads are furnished with terminals attached to one end (plus nuts, bolts, washers, for securing to the SSD bus) with the other lead end unfinished. Order the mold and weld metal in Item 4(b) for welding the leads to the mat. The user is responsible for the lead connection to the pipeline. (Custom molds can be acquired for welding the leads to the pipeline upon request provided the pipe diameter is given and it is specified whether the weld is to a vertical pipe wall or on the top side of a horizontal pipe.) All leads should be cut to the shortest possible length during installation to minimize touch potential.

(b) Attachment via pin brazing M8 studs to a steel pipe is illustrated in Figure 3. The user must have the required pin brazing equipment and consumable items (i.e., the M8-1.25 threaded studs with a 16mm threaded section furnished with two washers and a locknut and ceramic ferrules). Equipment and studs are available from several manufacturers - contact DEI for assistance if required. The desirability of this option is that it virtually eliminates the inductance of one lead connection because one SSD terminal is directly connected to the pipe via the pin brazed stud. For each decoupler installed using pin brazed stud mounting, order one #HCN-M8 (the Hex Coupling Nut plus M8 bolt and washers required) plus one set of leads, #MTL-6-12 for 12” (300mm) leads or #MTL-6-36 for 36”(900mm) leads.

Ordering Information Checklist:

1) Gradient control Mat: GCM4-8
2) Decoupler: Model SSD-2/2-1.2-75 unless other model selected.
3) Thermit Welding Molds/Charges:
• For joining adjacent mats:
- MOLD-135
- WELD-135-15 (20/pack)
• For joining anode and decoupler leads to mat:
- MOLD-6
- WELD-6-25 (20/pack)
• Decoupler Mounting Options:
- Leads: MTL-12 or MTL-36
- Banding: Material by others
- Pin Brazing: Equipment/studs/ceramic ferules by others. Order HCN-M8 kit from DEI.

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.

Solution: DEI now offers an 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 new, 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