# ASME B31.8 Pipeline Design Pressure Calculator

> Source: https://netray.co/tools/asme-b31-8-pipeline-design-pressure-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Calculate the design pressure of steel gas pipe from OD, wall thickness, SMYS, design factor, joint factor and temperature factor.

## Category

industry-templates

## Industry

Oil and Gas Equipment

## Audience

- Pipeline engineer
- Design engineer
- Estimator
- Quality engineer

## Tool

**Kind:** calculator

**Inputs:**

#### Outside diameter

**Key:** od

**Type:** number

**Default:** 12.75

**Min:** 0.5

**Step:** 0.125

**Unit:** in

**Help:** Nominal OD, for example 12.75 for NPS 12.

#### Nominal wall thickness

**Key:** wall

**Type:** number

**Default:** 0.375

**Min:** 0.05

**Step:** 0.001

**Unit:** in

**Help:** Use nominal wall, and subtract corrosion allowance first if your design requires it.

#### Pipe grade (SMYS)

**Key:** smys

**Type:** select

**Default:** 52000

**Options:**

##### Grade B, 35,000 psi

**Value:** 35000

##### X42, 42,000 psi

**Value:** 42000

##### X52, 52,000 psi

**Value:** 52000

##### X60, 60,000 psi

**Value:** 60000

##### X65, 65,000 psi

**Value:** 65000

##### X70, 70,000 psi

**Value:** 70000

##### X80, 80,000 psi

**Value:** 80000

#### Design factor F (class location)

**Key:** f

**Type:** select

**Default:** 0.72

**Options:**

##### Class 1, Division 1: 0.80

**Value:** 0.8

##### Class 1, Division 2: 0.72

**Value:** 0.72

##### Class 2: 0.60

**Value:** 0.6

##### Class 3: 0.50

**Value:** 0.5

##### Class 4: 0.40

**Value:** 0.4

#### Longitudinal joint factor E

**Key:** e

**Type:** select

**Default:** 1

**Options:**

##### Seamless, ERW, SAW, 1.00

**Value:** 1

##### Furnace butt weld, 0.60

**Value:** 0.6

#### Temperature derating factor T

**Key:** t

**Type:** select

**Default:** 1

**Options:**

##### 250 F or below, 1.000

**Value:** 1

##### 300 F, 0.967

**Value:** 0.967

##### 350 F, 0.933

**Value:** 0.933

##### 400 F, 0.900

**Value:** 0.9

##### 450 F, 0.867

**Value:** 0.867

**Outputs:**

#### Design pressure

**Key:** p_psi

**Expr:** 2 * smys * wall / od * f * e * t

**Format:** number

**Primary:** true

**Description:** Design pressure in psig from the B31.8 formula.

#### Design pressure (bar)

**Key:** p_bar

**Expr:** p_psi * 0.0689476

**Format:** decimal

#### Design pressure (MPa)

**Key:** p_mpa

**Expr:** p_psi * 0.00689476

**Format:** decimal

#### Hoop stress at design pressure, % of SMYS

**Key:** smys_pct

**Expr:** f * e * t * 100

**Format:** percent

**Description:** Allowed fraction of SMYS used at the design pressure.

#### Diameter to wall ratio

**Key:** dt

**Expr:** od / wall

**Format:** decimal

**Description:** D/t. Very high or very low values need extra design review.

**Chart:**

#### Design pressure vs wall thickness

**Type:** line

**X:** wall

**From:** 0.15

**To:** 0.75

**Steps:** 25

**Series:**

- p_psi

**Disclaimer:** Screening calculation for the basic hoop stress design formula. It does not cover longitudinal stress, thermal expansion, external loads, fittings, valves or the supplementary rules in the code. Final design must be by a qualified engineer using the current edition of ASME B31.8.

## Content

**Intro:** For steel gas pipelines, ASME B31.8 sets the design pressure from the pipe diameter, wall thickness and strength, reduced by a design factor that depends on how many buildings are near the line. This calculator applies that formula and shows the answer in psig, bar and MPa.

**Sections:**

#### How to use the calculator

**Body:** Enter the pipe OD and nominal wall, pick the API 5L grade for the specified minimum yield strength, then choose the design factor for the class location, the longitudinal joint factor and the temperature factor. The result is the design pressure from the hoop stress equation. The chart sweeps wall thickness so you can see how much extra pressure capability each wall step gives, which helps when you compare schedules or plate suppliers.

#### The formula and factors

**Body:** The design pressure is P = (2 S t / D) x F x E x T, where S is the specified minimum yield strength, t is the nominal wall thickness, D is the outside diameter, F is the design factor, E is the longitudinal joint factor and T is the temperature derating factor. Higher class locations have lower design factors because more people live near the line. Temperature above 250 F reduces the allowable pressure.

**Bullets:**

- Class 1 Division 1 is 0.80, Division 2 is 0.72.
- Class 2 is 0.60, Class 3 is 0.50 and Class 4 is 0.40.
- Use the factors for the code edition your project is bound to.

#### Worked example

**Body:** Take 12.75 inch OD, 0.375 inch wall, X52 with a Class 1 Division 2 location, E of 1 and T of 1. Then P = 2 x 52,000 x 0.375 / 12.75 x 0.72 = about 2,202 psig. In that case the hoop stress at the design pressure is 72 percent of SMYS. If the same line passes through a Class 3 area, F drops to 0.50 and the design pressure falls to about 1,529 psig.

#### Common mistakes

**Body:** Common mistakes include using actual mill yield instead of the specified minimum, forgetting to deduct corrosion or erosion allowance from the wall, applying the wrong class location factor, and treating the result as the test or relief pressure. Test pressure, relief setting and operating limits are separate calculations governed by their own rules. Hydrostatic test pressure is not the same as design pressure.

**Cta:** If you want pipe design data and test records checked against purchase and receiving data in your ERP, we can scope that with you.

**Faq:**

#### Is design pressure the same as MAOP?

**Answer:** Not always. The maximum allowable operating pressure is set by the pipeline operator and the regulations in force, using design pressure, test pressure and history. This calculator only returns the design pressure from the hoop stress formula.

#### Which wall thickness should I enter?

**Answer:** Use the nominal wall thickness, reduced by any corrosion or erosion allowance that your design basis requires. Some jurisdictions also require a mill tolerance reduction for certain checks, so follow the project design basis.

#### Can I use this for liquid lines under B31.4?

**Answer:** ASME B31.4 uses a related hoop stress formula with different design factors and rules. Do not reuse the B31.8 factors for liquid pipelines. Check the correct code and its design factor table.

#### Why does temperature change the result?

**Answer:** At higher temperatures the strength of steel falls, so B31.8 applies a derating factor T. At 250 F and below the factor is 1.0. The factor values in the dropdown are for orientation, confirm them against the code edition.

## Search terms

ASME B31.8 design pressure formula, pipeline MAOP calculator, Barlow formula pipeline calculator, B31.8 design factor class location, pipe design pressure from wall thickness, hoop stress SMYS percentage, gas pipeline design pressure calculation, API 5L X52 design pressure

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