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

Current through June 25, 2024
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.