4.Identify the applicable code framework for LPG piping systems under the 2018 International Fuel Gas Code (IFGC) and distinguish when the International Plumbing Code (IPC) governs non-flammable gas piping.
5.Apply the jurisdictional limits for LPG systems, including container placement, pressure regulation, and the ½ PSI (14-inch water column) threshold that separates low-pressure from high-pressure design.
6.Calculate pipe sizing using the longest-run method and the branch-length method for LPG vapor systems.
7.Specify correct materials, joint types, and installation requirements for LPG piping, including steel, copper, and corrugated stainless steel tubing (CSST).
8.Recognize the master plumber’s legal responsibility for permits, inspections, and safety compliance under the Texas State Board of Plumbing Examiners rules.
1.1 Scope and Code Hierarchy
LPG (liquefied petroleum gas) piping installation is governed by the 2018 International Fuel Gas Code (IFGC), which is adopted by reference in the Texas Master Plumber exam. The 2018 International Plumbing Code (IPC) applies only to non-flammable medical gas and similar systems; LPG is exclusively a fuel gas matter.
The code hierarchy for LPG work is:
IFGC Chapter 1 – Administration; permits and inspections.
IFGC Chapter 2 – Definitions.
IFGC Chapter 3 – General regulations (odorization, appliance connections).
IFGC Chapter 5 – Chimneys and vents (not typically LPG-specific but relevant for appliance venting).
IFGC Chapter 6 – Specific appliance requirements.
IFGC Chapter 7 – Gaseous hydrogen (not LPG).
IFGC Chapter 8 – Referenced standards.
The Texas Plumbing License Law (Texas Occupations Code, Chapter 1301) and Board Rules (Texas Administrative Code, Title 22, Part 4) require that a master plumber be responsible for the installation, alteration, and repair of gas piping. The master plumber must ensure that all work is performed by licensed individuals and that permits are obtained from the local authority having jurisdiction (AHJ).
1.2 Definitions and Key Terminology
Candidates must be precise with the following terms:
LPG (Liquefied Petroleum Gas): A mixture of propane and butane, stored as a liquid under pressure. For piping design, we assume propane vapor with a specific gravity of approximately 1.5 (heavier than air).
Vapor Pressure: The pressure exerted by the gas above the liquid in a container. For propane at 70°F, this is approximately 110 PSIG; at 100°F, it rises to about 172 PSIG.
First Stage Regulator: Reduces container pressure (up to 250 PSIG) to 10 PSIG.
Second Stage Regulator: Reduces 10 PSIG to appliance pressure (typically 11 inches water column or 0.4 PSI).
Integral Two-Stage Regulator: A single unit performing both functions.
Pressure Drop: The allowable loss in pressure from the point of delivery to the appliance, typically 0.5 inches water column for low-pressure systems.
CSST (Corrugated Stainless Steel Tubing): Flexible gas piping with a plastic jacket, requiring bonding and grounding per manufacturer’s instructions and the National Electrical Code.
Point of Delivery: The outlet of the second-stage regulator or the outlet of the meter (for utility gas). For LPG, this is the outlet of the final pressure regulator.
1.3 Container Location and Regulator Requirements
LPG containers must be located outdoors, at least 10 feet from any building opening (doors, windows, or mechanical ventilation intakes), and 10 feet from any source of ignition. The IFGC references NFPA 58 (Liquefied Petroleum Gas Code) for container installation details.
Key regulatory points:
Containers must not be located under buildings or above-grade decks.
Container valves must be protected from physical damage.
A hydrostatic relief valve must be installed between the container and the first-stage regulator.
The first-stage regulator must be installed outdoors, at the container, with the vent pointing downward to prevent water entry.
Exam Trap: The 10-foot separation is measured from the container’s pressure relief valve discharge to the building opening, not from the container body itself. Many candidates incorrectly measure from the tank shell.
1.4 Pressure Classification and Design Thresholds
The IFGC classifies gas piping systems into two pressure categories:
Low Pressure: Systems operating at 0.5 PSI (14 inches water column) or less.
High Pressure: Systems operating above 0.5 PSI.
For LPG, the standard residential and light commercial design uses a two-stage regulation system:
50.Container pressure (100–250 PSIG) reduced to 10 PSIG by the first-stage regulator.
51.10 PSIG reduced to 11 inches water column (0.4 PSI) by the second-stage regulator.
The piping between the first and second stage is considered high pressure and must be sized for a 1 PSI pressure drop. The piping downstream of the second-stage regulator is low pressure and must be sized for a 0.5 inches water column drop.
Master-Level Responsibility: The master plumber must verify that the second-stage regulator is installed outdoors or in a ventilated enclosure. Indoor installation of a second-stage regulator is prohibited unless it is a listed appliance regulator with a vent limiter.
1.5 Pipe Sizing: The Longest Run Method
The IFGC provides two sizing methods: the longest run method (Table 402.4) and the branch length method (Table 402.4(2)). For LPG, we use the same tables as natural gas, but the specific gravity correction factor must be applied.
Step-by-Step Procedure:
59.Determine the total load in BTUH for each appliance. Use the manufacturer’s input ratings. For standard appliances, use: range/oven 65,000 BTUH, water heater 40,000 BTUH, furnace 100,000 BTUH, dryer 35,000 BTUH.
60.Measure the longest run from the point of delivery (second-stage regulator outlet) to the farthest appliance, including all fittings and equivalent lengths.
61.Apply the specific gravity correction. LPG vapor (propane) has a specific gravity of 1.5. The IFGC tables are based on natural gas (specific gravity 0.60). The correction factor is:
CF = √(0.60 / 1.5) = √0.4 ≈ 0.632
Therefore, for the same pipe size and length, LPG delivers approximately 63% of the capacity of natural gas. Alternatively, you can use the IFGC Table 402.4(1) which provides LPG capacities directly.
64.Select pipe size from the table such that the capacity at the given length exceeds the total load.
Example: A system has a total load of 200,000 BTUH and a longest run of 50 feet. Using the LPG column of the IFGC table, a ½-inch pipe at 50 feet may deliver only 150,000 BTUH, so you would select ¾-inch pipe, which delivers approximately 280,000 BTUH.
Exam Trap: Candidates often forget to include the equivalent length of fittings. A standard rule: add 20% to the measured length for fittings, or use the actual equivalent lengths from Table 402.4 (e.g., a 90° elbow in ¾-inch pipe = 2.5 feet equivalent).
1.6 Pipe Sizing: The Branch Length Method
The branch length method allows for smaller pipe sizes by calculating each branch separately. The procedure:
70.Determine the load for each branch.
71.Measure the length from the point of delivery to the end of that branch (not the farthest appliance).
72.Size each branch independently.
This method is more economical but requires careful documentation. The master plumber must ensure that the pressure drop at the farthest appliance does not exceed the allowable limit.
Field Point: For LPG systems with a single appliance (e.g., a tankless water heater), the branch length method is identical to the longest run method. For multi-appliance systems, the branch method can reduce pipe size by one nominal size in many cases.
1.7 Materials and Joints
The IFGC permits the following materials for LPG piping:
Steel Pipe: ASTM A53 Grade B, black steel, threaded or welded. Minimum wall thickness Schedule 40 for sizes up to 6 inches. Threaded joints must use a pipe thread compound resistant to LPG (do not use Teflon tape on flare fittings).
Copper Tube: Type K or L, with brazed joints (BCuP-5 or BAg-5 filler metal). Solder (soft solder with melting point below 1,000°F) is prohibited for gas piping. Flare fittings are permitted for LPG with a maximum operating pressure of 20 PSIG.
CSST: Must be installed per the manufacturer’s installation instructions and must be bonded to the electrical grounding system. The bonding clamp must be attached to the CSST fitting or the pipe itself, not to the jacket.
Polyethylene (PE) Pipe: Only for underground outdoor use, with a minimum burial depth of 12 inches. PE must not be used indoors or above grade.
Prohibited Materials:
Galvanized steel pipe (interior of the pipe can flake and clog orifices).
Aluminum pipe (corrodes in contact with concrete or dissimilar metals).
Rubber or plastic hose (except listed appliance connectors, maximum 3 feet for residential).
Joint Requirements:
Threaded joints: Minimum 3 threads engaged; use a listed thread compound.
Brazed joints: Must be made by a qualified operator; the joint must be cleaned and fluxed.
Flare joints: Must use a 45° flare, with the flare nut tightened to the manufacturer’s torque specification.
1.8 Installation Requirements and Purging
Piping Support:
Horizontal steel pipe: supports every 8 feet (½ inch and smaller), 10 feet (¾ inch to 1 inch), 12 feet (larger).
Vertical pipe: supports at each floor level, but at least every 15 feet.
CSST: supports every 4 feet for horizontal runs, and every 6 feet for vertical runs, per most manufacturer instructions.
Purging:
After installation and before connection to appliances, the piping must be purged of air. For LPG, this is critical because an air-gas mixture within the flammable range (approximately 2.1% to 9.5% propane in air) can explode.
Purge with LPG vapor to a safe outdoor location. Do not purge indoors.
The master plumber must verify that all appliance valves are closed before purging.
Prohibited Installations:
Gas piping must not be embedded in concrete or masonry (unless cathodically protected and approved).
Piping must not run through ductwork, chimney, or garbage chute.
Piping must not be installed in a hollow wall unless the wall is ventilated or the pipe is protected.
1.9 Pressure Testing and Leak Detection
Before the system is placed in service, the piping must be pressure tested. The IFGC requires:
Low-Pressure Systems (≤ 0.5 PSI): Test at 10 PSIG for a minimum of 30 minutes. No measurable drop is allowed.
High-Pressure Systems (> 0.5 PSI): Test at 1.5 times the maximum operating pressure, but not less than 100 PSIG, for 30 minutes.
Procedure:
110.Isolate the system from the container or regulator.
111.Connect a calibrated test gauge (0–100 PSIG minimum).
112.Pressurize with air or inert gas (nitrogen). Do not use oxygen or flammable gas for the pressure test.
113.After the test, release pressure and connect the appliance.
114.Perform a leak check using a manometer or electronic leak detector. Soapy water (bubble test) is acceptable for threaded joints.
Exam Trap: The test pressure is measured at the highest point of the system. If the system has vertical risers, the gauge reading at the bottom will be higher due to the static head of the test medium. For air, this is negligible, but for water (hydrostatic test), it is significant. The IFGC permits air or inert gas, not water, for gas piping.
1.10 Appliance Connections and Shutoff Valves
Each appliance must have an accessible individual shutoff valve within 6 feet of the appliance. The valve must be a listed gas shutoff valve with a 1/8-inch NPT plugged tap for pressure testing.
Appliance Connectors:
Flexible connectors must be listed (ANSI Z21.24) and limited to 3 feet for residential appliances (6 feet for commercial cooking equipment).
Connectors must not pass through walls, floors, or ceilings.
The connector must be installed so that it does not restrict the appliance’s movement for servicing.
Sediment Traps:
A drip leg (sediment trap) must be installed downstream of the shutoff valve and before the appliance control. The trap must be at least 3 inches long and accessible for cleaning.
Texas Occupations Code Chapter 1301; TAC Title 22, Part 4
1.12 Practical Field Points for the Master Plumber
130.Permit and Inspection: As the responsible licensed master, you must pull the permit before starting work. The AHJ may require a rough-in inspection before covering piping and a final inspection after appliances are connected.
131.Documentation: Keep a copy of the sizing calculations, test results, and manufacturer installation instructions on site. The AHJ has the right to request them.
132.Safety: LPG is heavier than air. In a leak, gas will settle in basements and crawl spaces. Install gas detectors where required by the AHJ, and ensure that all low points are ventilated.
133.Coordination with Other Trades: CSST bonding is often the electrician’s responsibility, but the master plumber must verify that the bonding clamp is installed before the final inspection. If not, the gas piping system is a shock and fire hazard.
134.Existing Systems: When extending an existing LPG system, verify the container size and regulator capacity. A 120-gallon tank may not supply a new high-load appliance. The master plumber must calculate the total connected load and advise the owner if a larger container or a second-stage regulator upgrade is needed.
1.13 Common Exam Traps
Specific Gravity: Do not use natural gas capacities for LPG without applying the correction factor. The exam will often provide a table with both columns; read the heading carefully.
Test Pressure: The 10 PSIG test applies only to low-pressure systems. If the system includes a high-pressure section (between first and second stage), that section must be tested at 100 PSIG minimum.
Solder Prohibition: Soft solder (50/50 or 95/5) is allowed for water piping but never for gas. Brazing requires a filler metal with a melting point above 1,000°F.
Flexible Connectors: The 3-foot limit is for the connector itself, not the total length of CSST. CSST is a piping material, not an appliance connector.
Ventilation of Regulators: A second-stage regulator installed indoors must have its vent piped to the outdoors. A regulator with a vent limiter may be installed indoors only if the AHJ approves.
1.14 Summary
LPG piping installation requires the master plumber to integrate knowledge of the IFGC, NFPA 58, and Texas administrative rules. The critical skills are accurate pipe sizing with specific gravity correction, proper material selection, and rigorous pressure testing. The master plumber’s legal responsibility extends beyond the physical installation to include permitting, inspection coordination, and safety documentation. On the exam, focus on the pressure thresholds, the sizing tables, and the distinction between low-pressure and high-pressure testing requirements.
