ASME B36.10M & B36.19M Pipe Schedule & Dimensions: Complete Engineering Guide

Converting Nominal Pipe Size (NPS) and Schedule into OD, wall $t$, ID, and linear weight is daily plant work. Confusing NPS with OD, or STD with Sch 40, drives procurement errors and field fit-up failures. High-pressure line classes often call Schedule 160 — a thick wall that is easy to mis-order if the MTO only says “extra heavy.”

Look up NPS ½–24 schedules (including Sch 160) in the Pipe Schedule & Dimension calculator — start from the common NPS 6 Sch 160 or NPS 4 Sch 160 SpecRoute.

Quick Summary (TL;DR)

• Takeaway: NPS is a tag, not OD. Use catalog OD and schedule $t$; flow uses $ID = OD - 2t$; pressure design uses $OD$.
• Governing relation: Plain-end CS mass $W_m = 0.0246615 \cdot t \cdot (OD - t)$ ($\text{kg/m}$, $\rho = 7{,}850\text{ kg/m}^3$).
• Code / basis: ASME B36.10M (CS/alloy) and B36.19M (S-schedules); STD ≠ Sch 40 above NPS 10.

Pipe schedule dimensions in the field

ASME B36.10M vs ASME B36.19M

• ASME B36.10M: Wrought welded and seamless carbon and alloy steel pipe.
• ASME B36.19M: Stainless steel pipe with S-suffix schedules (5S, 10S, 40S, 80S).

Worked example — NPS 8 Schedule 80 dimensions

Given Parameters

• Nominal Size: NPS 8 (DN 200)
• Schedule: Schedule 80 (XS)
• Material: ASTM A106 Gr. B ($\rho = 7,850\text{ kg/m}^3$)
• Fluid: Water @ 20°C ($\rho_w = 998\text{ kg/m}^3$)

Open the same row in FEK: Pipe Schedule & Dimension (NPS 8 · Sch 80).

Step 1 — Table lookup (B36.10M)

$OD = 219.08\text{ mm } (8.625\text{ in})$ $t = 12.70\text{ mm } (0.500\text{ in})$

Step 2 — Inside diameter

$ID = 219.08 - 2(12.70) = 193.68\text{ mm } (7.625\text{ in})$

Step 3 — Flow area

$A_{\text{flow}} = \frac{\pi \cdot (193.68)^2}{4} = 29,461\text{ mm}^2 = 0.02946\text{ m}^2$

Step 4 — Empty pipe weight

$W_{\text{pipe}} = 0.0246615 \times 12.70 \times (219.08 - 12.70) = 64.64\text{ kg/m } (43.43\text{ lb/ft})$

Step 5 — Water-filled weight (rack loading)

• Water weight: $W_{\text{water}} = 0.02946 \times 998 = 29.40\text{ kg/m}$
• Total weight: $W_{\text{total}} = 64.64 + 29.40 = 94.04\text{ kg/m } (63.19\text{ lb/ft})$

Procurement & engineering traps

Trap 1 — STD/XS vs Sch 40/80 Divergence

STD and Sch 40 match only for NPS 1/8 through NPS 10. Example NPS 12:

Ordering NPS 12 STD when the line class requires Sch 40 delivers an under-designed spool.

Trap 2 — B36.19M Sch 40S vs B36.10M Sch 40

For $\text{NPS} \le 12$, Sch 40 and Sch 40S walls match. At $\text{NPS} \ge 14$, Sch 40S is capped at $9.53\text{ mm}$ while B36.10M Sch 40 continues to grow (NPS 16 Sch 40 = $12.70\text{ mm}$).

Trap 3 — “Schedule 160 pipe” vs XS / XXS

Schedule 160 is a B36.10M wall class — thicker than Sch 80 / XS on common sizes. It is not the same tag as XXS. Example FEK rows (carbon screening):

OD is unchanged by schedule (NPS 6 OD = 168.28 mm). Ordering Sch 80 when the class needs Sch 160 understates wall and weight.

Interactive tool CTA

Frequently Asked Questions (FAQ)

Q1. What is Schedule 160 pipe?

Schedule 160 is a thick B36.10M wall designation used on higher-pressure carbon/alloy lines. Example: NPS 6 Sch 160 → OD 168.28 mm, $t$ 18.26 mm, ID 131.76 mm, $W_m \approx 67.56\text{ kg/m}$ in FEK. Open the live row: 6-inch-sch-160.

Q2. Why is NPS 4 OD 114.3 mm, not 101.6 mm?

Historical NPS tags reflect nominal internal capacity, not OD. Only at NPS 14+ does NPS equal OD in inches.

Q3. Should I use OD or ID for velocity vs pressure calculations?

• Velocity ($v = Q / A$): Inside Diameter ($ID$).
• ASME B31.3 Pressure Design & Insulation: Outside Diameter ($OD$).

Q4. What is the standard mill under-tolerance for pipe?

ASTM A106 / A53 / A312 typically allow $-12.5\%$ on nominal wall. Minimum delivered wall can be $0.875 \times t$ — always account for this in pressure design.

Q5. Why do some websites list STD = Sch 40 for NPS 12?

That is a common internet shortcut and wrong for NPS 12+. FEK and B36.10M keep STD and Sch 40 as separate walls above NPS 10 — verify the schedule tag on the MTO, not a blog table that merges them.