Mississippi Administrative Code
Title 11 - Mississippi Department of Environmental Quality
Part 5 - Underground Storage Tank Regulations
Chapter 2 - Mississippi Commission on Environmental Quality Underground Storage Tanks Regulations Technical Standards and Corrective Action Requirements for Owners and Operators of Underground Storage Tanks (UST) (Adopted March 22, 1989; Amended August 25, 2011, Last Amended August 23, 2018)
Appendix 11-5-2-280.1 - GUIDELINES FOR THE EVALUATION OF UNDERGROUND STORAGE TANK CATHODIC PROTECTION SYSTEMS
Section 11-5-2-280.1-5 - INSTALLATION/REPAIR OF CATHODIC PROTECTION SYSTEMS
Section 11-5-2-280.1-5-5.1.4 - Metallic Piping Repair/Installation
Provided below are some general observations that are commonly applicable to questions that arise when attempting to meet the corrosion protection requirements on metallic piping and other metallic components of a typical UST system.
Protected Components - Any metallic component of the piping system, including all metallic nipples, ells, tees, couplings, unions, ball valves, etc. must be protected from corrosion if they are in contact with the soil and/or water. Corrosion protection may be accomplished by either a) isolating the component in question from contact with the soil and/or water or b) coating/wrapping with a suitable dielectric material and cathodic protection. Any isolation boot or containment sump designed to isolate the metallic component from contact with the soil must also prevent water from contacting the component in question in order to eliminate the need for cathodic protection. If the metallic component in question is cathodically protected, it must also be coated/wrapped with a suitable dielectric material if it was installed after December 22, 1988.
Unprotected Components - Metallic components of the UST system that do not require corrosion protection include: tank vent lines; any type of tank riser pipe; tank hold down straps; remote tank fill lines and submersible turbine pump (STP) heads. Although the pump head "routinely contains product", it is not required to meet the corrosion protection requirements and may be in contact with the soil or submerged in water without the need for cathodic protection. However, the pump head should remain visible (not buried) so that any obvious corrosion problems or leaks that may be present can be observed and appropriate action taken to prevent or repair any leaks.
Repair - Some confusion exists over whether or not metallic piping that has failed can be repaired or must be replaced. "Repaired" as related to steel pipe involves the replacement of the section of pipe that has failed. The entire run of steel piping does not have to be replaced but the repair must consist of replacement of the section of pipe that has failed. Only steel pipe that is factory coated with a dielectric material (fusion bonded epoxy) can be used to replace the failed section of pipe regardless of whether the existing pipe is galvanized or coated steel. Under no circumstances is it allowable to install galvanized piping when it is intended to serve as a product transfer line. Because of the complexities that may be involved in the cathodic protection of galvanized steel piping, a corrosion expert must evaluate and/or conduct the cathodic protection survey after the repair.
Electrical Continuity - Dielectric unions are normally not installed if the piping is protected by an impressed current system. It is essential that all metallic piping that is part of the UST system is bonded to the negative circuit of the impressed current system if it is buried. It is normally desirable to electrically isolate any metallic portion of the UST system that is not buried or submerged in water from that portion that is buried/submerged.
Electrical Isolation - If metallic piping is galvanically protected, it is critical that effective electrical isolation is provided. Failure to isolate the protected piping will result in premature failure of the sacrificial anodes. Isolation can be difficult to achieve where cathodically protected piping is present under dispensers that have shear valves present. This is due to the requirement that the shear valve must be properly anchored to the island form. Particular care should be exercised in these instances to assure proper isolation. If possible, the dielectric union should be installed below the shear valve so that anchoring does not cause a continuity problem.
Screw Joints - Particular care should be taken when dealing with metallic piping that is mechanically coupled with threaded screw joints. Any threaded joint in a metallic piping material can serve as a break in the electrical continuity of the piping system. It has been established that threaded couple pipe joints can develop enough electrical resistivity over time to effectively isolate each section of a piping system. For obvious reasons, this is highly undesirable in a cathodic protection system and you should ensure that electrical continuity is present between any sections of piping that are intended to be protected. Jumper wires or welding may be necessary across each pipe couple in order to assure electrical continuity between each section of piping.
Flex Connectors - Any metallic flexible connector (including stainless steel) that is utilized on a piping system must be protected from corrosion. The flex connector may be isolated from contact with soil/water or cathodically protected. If the flex connector is cathodically protected, it must also be coated/wrapped with a dielectric material if it was installed after December 22, 1988.
Containment Sumps - If metallic components of a piping system are installed in a containment sump, the sump must be maintained dry. If a sump contains water and you are unable to keep the water out, the metallic components must be protected from corrosion. The metallic components may be protected by installing appropriate isolation boots (in the case of flex connectors) or sacrificial anodes. If cathodic protection is necessary, the sump may or may not be filled with clean sand to a depth adequate to bury the anode. Burial of the anode may help prevent an oxidation film from forming on the anode (and causing passivation) in the event that standing water is not always present in the sump. In either case, it is critical that the anode be installed within the containment sump. Do not place the anode outside of the sump.
"Mixed" Piping - In those instances where fiberglass reinforced plastic or flexible piping is connected to an existing metallic pipe (e.g. to extend a fueling island), a cathodic protection test station or access to the soil where the two dissimilar materials are joined must be provided. This is necessary to effectively test the adequacy of cathodic protection operating on the metallic piping.
