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newSchoolWorks.com › VoTechWorks › Manufacturing & Marine › Shipbuilding / Marine Fabrication › Marine Outfitting: Systems Installation and Interior Fabrication › Lesson 3
MFG-SHIP13-06 · Lesson 3 · 14 clock hours · theory

Pipe System Fundamentals and Material Identification

Objective. The student identifies common shipboard pipe materials, schedule ratings, and end-preparation methods, and correctly selects pipe and fitting specifications from a piping class schedule for three given service systems.

Why Pipe Material Selection Matters on a Ship

A shipboard piping system is not a single network — it is a collection of separate systems, each carrying a fluid at a specific pressure, temperature, and corrosivity. Seawater corrodes carbon steel rapidly. Diesel fuel requires materials that resist swelling and degradation. Potable water must meet sanitary standards. Selecting the wrong pipe material or pressure rating is a safety and structural failure waiting to happen, and it violates the rules of the classification society (such as ABS) that certifies the vessel. Your job in marine outfitting begins with understanding what the pipe is made of, how thick its wall is, and how it connects to the next section.

Common Shipboard Pipe Materials

Carbon Steel is the workhorse of shipboard piping. It is strong, weldable, and relatively inexpensive. It is used for fuel lines, compressed air, hydraulic lines, and many general-purpose services. Carbon steel corrodes in the presence of saltwater and moisture, so it is typically coated, galvanized, or kept away from seawater service. ASTM A53 and A106 are common grades you will encounter.

Stainless Steel (typically 316L in marine environments) offers excellent corrosion resistance and is used where hygiene or corrosion is a primary concern — potable water distribution and some exhaust or chemical lines. It is more expensive and requires specific filler metals when welded to avoid sensitization.

Copper-Nickel (Cu-Ni) alloy — most often 90/10 (90% copper, 10% nickel) or 70/30 — is the standard material for seawater cooling and fire-suppression systems. It resists biofouling and the erosive, corrosive attack of flowing saltwater far better than carbon steel. Cu-Ni is joined by brazing, special welding procedures, or mechanical fittings. Never use carbon steel tools on Cu-Ni without cleaning them first; iron contamination causes rapid corrosion.

CPVC (Chlorinated Polyvinyl Chloride) is a thermoplastic approved for certain low-pressure, moderate-temperature services aboard vessels, including potable water and some seawater lines in pleasure craft and small commercial vessels. It is lightweight and corrosion-proof but is not approved for high-pressure or high-temperature service, and it is brittle when cold. Cuts are made with a fine-tooth saw or pipe cutter; ends are joined with solvent cement.

Schedule Ratings and Wall Thickness

The word "schedule" refers to wall thickness relative to the pipe's outside diameter (OD). For a given nominal pipe size (NPS), the OD is fixed regardless of schedule. Increasing the schedule number means a thicker wall and therefore a higher pressure rating and smaller inside diameter (ID).

The key reference for carbon and alloy steel pipe dimensions is ASME B36.10M (Welded and Seamless Wrought Steel Pipe). For stainless steel, refer to ASME B36.19M. These tables list NPS, OD, and wall thickness for every schedule. In the hands-on activity, you will measure actual samples and compare your readings to those tables. A well-calibrated vernier caliper is your tool; always measure the OD at the pipe end and the wall at a freshly cut cross-section.

Piping Class Schedules

Shipyards and naval architects create a piping class schedule (sometimes called a piping specification) for each vessel. This document assigns every service system a pipe class code. Each code spells out the allowable pipe material, schedule, fitting type, flange rating, gasket material, and bolt specification. You do not select these from memory — you look them up. Reading the piping class schedule correctly is a core job skill. For example, a seawater cooling system might be assigned Class SW-1: Cu-Ni 90/10 pipe, 150-lb ANSI flanges, neoprene gaskets, and stainless bolts. A diesel fuel line might be Class DF-1: Schedule 80 carbon steel, threaded or socket-weld fittings, and spiral-wound metallic gaskets.

End Preparation and Joining Methods

How pipe ends are prepared determines how they are joined:

P&ID Symbols

A Piping and Instrumentation Diagram (P&ID) is a schematic that shows every pipe, valve, instrument, and piece of equipment in a system using standardized symbols. The ISA-5.1 standard governs instrument symbology; ISO 10628 and common shipyard drawing conventions govern pipe and valve symbols. You must be able to identify at minimum: gate valve, globe valve, check valve, ball valve, strainer, pressure gauge, expansion loop, flanged joint, screwed joint, and reducer. Reading a P&ID incorrectly during installation can result in a valve installed backward or a strainer placed on the wrong line — failures that can disable a ship system.

Safety Points

Key terms10

Nominal Pipe Size (NPS)A standardized dimensioning system for pipe in which the nominal size is a reference number, not an exact measurement; for NPS 14 and larger, the NPS equals the actual outside diameter in inches, but for smaller sizes the NPS does not equal either OD or ID.
Schedule (pipe)A series of wall-thickness designations for a given pipe OD; a higher schedule number means a thicker wall, smaller bore, and higher allowable pressure. Common schedules are 40, 80, 160, and XXH.
Piping Class ScheduleA vessel-specific specification document that assigns every service system a class code defining allowable pipe material, schedule, fitting type, flange rating, gasket, and bolt specification.
Copper-Nickel (Cu-Ni)A copper-based alloy (typically 90/10 or 70/30 copper-to-nickel ratio) used extensively in marine seawater piping for its excellent resistance to saltwater corrosion and biofouling.
CPVCChlorinated polyvinyl chloride; a thermoplastic pipe material approved for certain low-pressure, moderate-temperature shipboard services such as potable water; joined with solvent cement.
P&ID (Piping and Instrumentation Diagram)A schematic drawing using standardized symbols (governed by ISA-5.1 and related standards) to show all pipes, valves, instruments, and equipment in a system and how they interconnect.
ASME B36.10MThe ASME standard that tabulates outside diameters and wall thicknesses for welded and seamless wrought carbon and alloy steel pipe across all schedule designations.
Flange Pressure ClassA rating (e.g., 150, 300, 600) assigned to pipe flanges per ANSI/ASME B16.5 that defines the maximum allowable pressure and temperature the flanged joint can safely handle.
Bevel (end preparation)An angled cut machined or ground on a pipe end to create a groove profile that allows full-penetration butt welds; the angle and root face must match the applicable WPS.
NPT (National Pipe Taper)The US standard for tapered pipe threads used on threaded pipe ends and fittings; the taper creates a mechanical seal when assembled with thread sealant or PTFE tape.

Worked examples4

1. You measure the outside diameter of a carbon steel pipe sample with a vernier caliper and read 2.375 inches. Your ASME B36.10M table shows NPS 2 has an OD of 2.375 in., Schedule 40 wall thickness of 0.154 in., and Schedule 80 wall thickness of 0.218 in. You also measure the wall thickness at the cut end and read 0.218 in. What is the NPS and schedule of this pipe?
  1. Step 1 — Identify the NPS: Look up 2.375 in. in the OD column of ASME B36.10M. The table shows OD = 2.375 in. corresponds to NPS 2.
  2. Step 2 — Identify the schedule: Compare your measured wall (0.218 in.) to the table values for NPS 2. Schedule 40 wall = 0.154 in.; Schedule 80 wall = 0.218 in. Your measurement matches Schedule 80.
  3. Step 3 — Confirm: OD matches NPS 2 regardless of schedule (OD does not change with schedule). Wall matches Sch 80. Both data points are consistent.
Answer: This is NPS 2, Schedule 80 carbon steel pipe.
2. A piping class schedule assigns seawater cooling lines a pipe class of 90/10 Cu-Ni with 150-lb raised-face flanges. A technician proposes substituting Schedule 40 carbon steel because it is in stock. Calculate the wall thickness of NPS 3 Schedule 40 carbon steel (OD = 3.500 in., wall = 0.216 in.) and explain why the substitution is not acceptable regardless of wall thickness.
  1. Step 1 — Wall thickness of NPS 3 Sch 40: Wall = 0.216 in. (from ASME B36.10M). This is a factual lookup, no arithmetic needed.
  2. Step 2 — Evaluate the substitution on material grounds: Seawater is highly corrosive to carbon steel. Carbon steel will corrode rapidly from both inside (saltwater flow) and outside (bilge moisture/salt spray), leading to pitting, wall loss, and eventual failure — a flooding risk.
  3. Step 3 — Evaluate on specification grounds: The vessel's piping class schedule mandates Cu-Ni for this service. Deviating from the specification without engineering and classification-society approval violates the vessel's approved drawings and potentially its ABS class certificate.
  4. Step 4 — Conclusion: The substitution is not acceptable. Material, not only wall thickness, must match the piping class schedule for the service.
Answer: NPS 3 Sch 40 wall = 0.216 in., but carbon steel cannot substitute for Cu-Ni in seawater service because it will corrode rapidly and the substitution violates the approved piping class specification.
3. A vernier caliper reads 1.315 inches OD on a pipe sample. Using ASME B36.10M, which NPS does this correspond to? If the wall measures 0.133 in., what schedule is it?
  1. Step 1 — Look up OD 1.315 in. in ASME B36.10M OD column: 1.315 in. OD corresponds to NPS 1.
  2. Step 2 — Compare wall 0.133 in. to table values for NPS 1: Schedule 40 wall = 0.133 in. (standard). Schedule 80 wall = 0.179 in.
  3. Step 3 — The measured wall of 0.133 in. matches Schedule 40.
Answer: This pipe is NPS 1, Schedule 40.
4. A fitting end is cut square and the pipe end is also cut square with no bevel. A shipfitter says the joint can be butt-welded. A senior fitter says it must be socket-welded or the end must be re-prepped. Who is correct and why?
  1. Step 1 — Recall end preparation rules: A full-penetration butt weld requires a beveled end (typically a 37.5° bevel with a root face) so the welder can achieve fusion through the full pipe wall. A square-cut plain end does not provide the groove geometry needed.
  2. Step 2 — Evaluate the senior fitter's statement: A square-cut plain end is correct for socket-weld fittings (the pipe slips into the socket) or for mechanical couplings. For butt welding, the end must be beveled per the applicable WPS.
  3. Step 3 — Conclusion: The senior fitter is correct. The square-cut end must either be re-prepped with a bevel for butt welding or the joint design must be changed to a socket-weld fitting.
Answer: The senior fitter is correct. A square-cut plain end is not acceptable for butt welding; it must be beveled per the WPS, or a socket-weld fitting must be used instead.

The math in this lesson1

Learners match caliper OD and wall readings to ASME B36.10M tables to identify NPS and schedule.
N-Q.3
Brush up in the math halls at newSchoolWorks.com:
In class: Hands-on material station: students examine labeled samples of carbon steel (Schedule 40 and 80), stainless, copper-nickel, and CPVC pipe; they record nominal pipe size, outside diameter measured with calipers, and wall thickness, then compare measured values to ASME B36.10 nominal data in a reference table. · Piping class schedule exercise: using a simplified shipboard piping specification sheet, each student selects the correct pipe class, gasket type, and bolt specification for five different service systems (seawater cooling, potable water, diesel fuel, bilge, and compressed air) and defends choices in a brief class discussion. · P&ID symbol quiz: students receive a blank P&ID fragment and must label 15 standard symbols (gate valve, check valve, strainer, pressure gauge, expansion loop, flanged joint, screwed joint, reducer) using an ISA/ISO reference sheet, then compare to answer key.
Materials: Pipe sample kit (various materials and schedules), vernier calipers, ASME B36.10 nominal pipe size table (reference excerpt), simplified shipboard piping class schedule handout, P&ID symbol reference sheet, ISA-5.1 symbol standard excerpt
Check: Material identification worksheet and P&ID symbol quiz combined score must reach 80%; calipers reading checked by instructor for correct technique before worksheet is accepted.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

NCCER Shipfitting — Piping Systems
1. For a given nominal pipe size (NPS), what happens to the outside diameter (OD) as the schedule number increases?
NCCER Shipfitting — Material Identification
2. Which pipe material is the standard choice for shipboard seawater cooling lines due to its resistance to saltwater corrosion and biofouling?
NCCER Shipfitting — Blueprint Reading and Measurement
3. A technician measures an NPS 4 carbon steel pipe and reads an OD of 4.500 in. and a wall of 0.237 in. Using ASME B36.10M values (NPS 4 OD = 4.500 in., Sch 40 wall = 0.237 in., Sch 80 wall = 0.337 in.), what is the pipe schedule?
NCCER Shipfitting — Piping Systems
4. A shipboard piping class schedule specifies Schedule 80 carbon steel with threaded NPT fittings for the diesel fuel service. A fitter wants to use Schedule 40 carbon steel instead because it is available. What is the primary reason this substitution is not acceptable without engineering approval?
NCCER Shipfitting — Safety
5. When working with CPVC pipe and solvent cement in a confined space aboard a vessel, which combination of PPE and precaution is most important?
NCCER Shipfitting — Blueprint Reading
6. On a P&ID, a symbol showing two triangles pointing toward each other at their tips, positioned in a pipe line, most commonly represents which component?
NCCER Shipfitting — Piping Systems
7. A piping class schedule lists the potable water system as requiring 316L stainless steel pipe with 150-lb raised-face flanges and EPDM gaskets. A worker substitutes standard carbon steel flanges with ring-type-joint (RTJ) faces because they are rated Class 300. Why is this substitution incorrect?
NCCER Shipfitting — Material Identification
8. Which ASME standard is the primary reference for outside diameters and wall thicknesses of carbon and alloy steel pipe?
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