Schedule 80 Pipe Pressure Rating, Price And Properties Sheets

Schedule 80 is a wall thickness class, not a material and not a pressure rating. It tells you how thick the pipe wall is at a given nominal pipe size: the outside diameter stays the same across all schedules, while the wall gets thicker and the bore gets smaller as the schedule number rises. That single fact explains almost everything else about Schedule 80 - why it holds more pressure than Schedule 40, why it weighs more, why it costs more, and why it is the schedule most codes expect when a pipe end is threaded.

 

This guide gives you the numbers: wall thickness, inside diameter and weight for every size from 1/8 in to 12 in NPS, maximum allowable working pressures for carbon steel, stainless steel, duplex, super duplex and PVC, the equation behind those pressures, how temperature derates them, indicative prices, and the standards that govern what you actually receive. All pressure figures are calculated with the ASME B31.3 thin wall hoop stress equation and are for estimating; your engineer of record must confirm them against the code edition and the mill certificate for the heat you buy.

Schedule 80 has a wall about 35 percent thicker than Schedule 40 at 1/2 in NPS and about 55 percent thicker at 8 in NPS, at the same outside diameter. It carries roughly 20 to 40 percent more pressure, weighs 28 to 52 percent more, and has a smaller bore. Choose it for threaded ends, higher pressure, external mechanical loads or corrosion allowance. Choose Schedule 40 where the line is fully welded, pressure is moderate and flow capacity or cost matters more.

Quick Reference: Schedule 80 pipe at a glance

 

What Does "Schedule 80" Mean in Pipe Specification?

Schedule 80 is a wall thickness designation. It fixes the wall thickness for a given nominal pipe size while leaving the outside diameter unchanged, so the pressure capability rises and the bore shrinks.

The word schedule in pipe terminology refers to wall thickness. It comes from a classification system developed by ANSI and ASME in which the schedule number approximates the ratio of internal service pressure to allowable material stress:

Schedule Number is approximately (P / S) x 1000, where P is the internal service pressure in psi and S is the allowable material stress in psi.

 

That relation is the origin of the numbers, not a design equation, and it is only approximate. In modern practice each schedule is simply a fixed wall thickness per NPS, published in ASME B36.10M for carbon and alloy steel and ASME B36.19M for stainless steel. Three rules hold across every schedule:

• The outside diameter is set by nominal pipe size and is identical for Schedule 10, 40, 80, 160 and XXS.

• Wall thickness increases as the schedule number increases.

• Inside diameter decreases as the wall thickens, so flow area and flow capacity fall.

Those three rules are why a Schedule 80 pipe fits the same flanges, the same butt weld fittings and the same hangers as a Schedule 40 pipe of the same NPS, yet carries a very different pressure rating and a different flow rate. If you only remember one thing, remember that schedule is a wall thickness code, and wall thickness plus allowable stress is what determines pressure.

 

What Are the Exact Dimensions and Wall Thicknesses of Schedule 80 Pipe?

Schedule 80 wall runs from 0.095 in at 1/8 in NPS to 0.688 in at 12 in NPS, with the outside diameter fixed by NPS throughout. The two tables below are reproduced unchanged from the published dimension charts and cover the full size range plus a direct Schedule 40 comparison.

Schedule 80 Pipe Dimensions - Full Size Range

The weight column is the value most often needed on site and in freight quotes, because support spacing, crane lifts and shipping cost are all driven by mass per foot rather than by length. For a deeper look at what that mass means structurally, see How much weight a Schedule 80 steel pipe can support and the companion page on Schedule 80 steel pipe dimensions and weight.

Schedule 80 vs Schedule 40 - Wall Thickness Comparison

The wall advantage of Schedule 80 over Schedule 40 grows with pipe size. At 1/2 in NPS the wall is 35 percent thicker and the weight 28 percent higher; at 8 in NPS the wall is 55 percent thicker and the weight 52 percent higher. That divergence matters when you are budgeting a large diameter carbon steel line, because the extra steel is paid for twice - once in material and once in supports and freight.

If you are deciding between the two schedules on a stainless line, the dedicated comparison difference between Schedule 40 and 80 stainless steel pipe covers the stainless specific arguments, including the 80S designation used in B36.19M.

 

How Do You Calculate the Pressure Rating of Schedule 80 Pipe?

Maximum allowable working pressure comes from the hoop stress equation P = 2 x S x t / D. Pressure depends on three variables only - wall thickness, outside diameter and allowable stress - and schedule controls just one of them.

 

The governing relation for a thin wall cylinder, in the form used by ASME B31.3, is:

P = (2 x S x t) / D, where P is internal pressure in psi, S is the allowable stress of the material at the operating temperature in psi, t is wall thickness in inches and D is outside diameter in inches.

Worked example, 1/2 in NPS Schedule 80 in ASTM A106 Grade B at room temperature. From the dimension table, OD is 0.840 in and wall is 0.147 in; the allowable stress is 15,000 psi. Substituting:

1. 2 x S x t = 2 x 15,000 x 0.147 = 4,410

2. Divide by D: 4,410 / 0.840 = 5,250 psi

3. That is the maximum allowable working pressure before any corrosion, erosion or threading allowance is taken, and before the wall thickness tolerance is considered.

Three corrections turn that calculation into a real design. First, ASME B31.3 adds a Y coefficient and a weld joint factor E to the equation, so the code form is not identical to the simple hoop stress form used here. Second, the code minimum required thickness is the pressure design thickness plus corrosion and erosion allowance plus mechanical allowance, and a threaded end is a mechanical allowance. Third, the delivered wall may be up to 12.5 percent below nominal, so you buy nominal wall = required thickness / 0.875. The simple equation above is therefore a screening tool, not a code calculation.

Data note on allowable stress. The pressure tables in this guide use the allowable stress values published with the original charts: 15,000 psi for A106 Grade B and 16,700 psi for 304L and 316L at room temperature. ASME B31.3 Table A-1, ASME B31.1 and ASME BPVC Section II Part D do not always list the same value for the same grade, and B31.3 has revised several carbon steel values between editions. Always take S from the edition you are designing to and record that edition on the calculation sheet.

 

What Pressure Can Carbon Steel Schedule 80 Pipe Handle?

ASTM A106 Grade B Schedule 80 ranges from about 5,250 psi at 1/2 in NPS down to about 1,739 psi at 8 in NPS. Pressure falls with size because OD grows faster than wall thickness.

Carbon Steel Schedule 80 Pipe Pressure Ratings (A106 Grade B, 70 F)

The downward trend with size surprises people who assume a bigger pipe is a stronger pipe. It is not: hoop stress is proportional to diameter, so as OD increases at a roughly constant wall, the pressure that produces the same stress in the wall falls. A 1/2 in NPS line rated at 5,250 psi becomes a 8 in NPS line rated at 1,739 psi even though the wall has more than tripled in absolute terms.

These figures are at room temperature and exclude all allowances. For elevated temperature work, and for the strength and load arguments that sit alongside pressure, see Schedule 80 steel pipe strength and our seamless and welded steel pipe range.

What Pressure Can Stainless Steel Schedule 80 Pipe Handle?

Stainless and duplex grades outperform A106 Grade B at room temperature, not the reverse. 304L and 316L reach about 3,063 psi at 2 in NPS and super duplex 2507 reaches about 5,061 psi, against roughly 2,752 psi for A106 Grade B.

Stainless Steel Schedule 80 Pipe Pressure Ratings

On the allowable stress basis used in these charts, austenitic stainless grades carry a higher listed allowable stress at room temperature than A106 Grade B - 16,700 psi for 304L and 316L against 15,000 psi - so at identical size and schedule their calculated MAWP is higher, not lower. The ranking then follows allowable stress: 304L and 316L at 16,700 psi, 316H and 321 at 18,800 psi, duplex 2205 at 22,100 psi and super duplex 2507 at 27,600 psi. Where the ordering reverses is at elevated temperature, because austenitic grades hold their allowable stress far better than carbon steel as temperature rises.

Grade selection should still be driven by the fluid rather than by the pressure table. If the line carries chlorides, compare Inconel 625 against 316L or weigh duplex 2205 against super duplex 2507 before committing to a wall thickness. JN Alloy supplies Schedule 80 stainless through the stainless steel pipe range, including 316L, 321 and 347.

 

How Does Temperature Reduce the Pressure Rating?

Allowable stress falls as temperature rises, and the pressure rating falls in direct proportion. A106 Grade B retains about 78 percent of its room temperature allowable stress at 600 F, so its pressure rating drops by the same proportion.

 

Effect of Temperature on Allowable Stress

Because pressure is directly proportional to S in the hoop stress equation, any percentage reduction in allowable stress is the same percentage reduction in rating. Take the 2 in NPS A106 Grade B example: the room temperature rating is about 2,752 psi. At 400 F the allowable stress drops to about 14,400 psi, a 4 percent reduction, and the rating falls to roughly 2,644 psi. At 600 F the retained fraction is about 78 percent and the rating falls with it.

Two practical cautions follow. A106 Grade B is a carbon steel specification intended for service up to roughly 425 C (800 F); above that, chrome moly grades such as ASTM A335 P11, P22 or P91 are normally required for creep resistance. And at the top of its range the tabulated values become sensitive to the code edition, so the 800 F column in particular should be confirmed against the edition you are designing to before it is used in a calculation.

What Are the Pressure Ratings for Schedule 80 PVC Pipe?

Schedule 80 PVC is rated 850 psi at 1/2 in NPS falling to 280 psi at 6 in NPS at 73 F, and retains only about 30 percent of that at 140 F. It is a low temperature, low pressure, chemically resistant option, not a substitute for steel.

PVC Schedule 80 Pressure Ratings

The temperature sensitivity of PVC is far steeper than that of any metal. A 1/2 in NPS line rated 850 psi at 73 F is rated about 255 psi at 140 F, and PVC softens well before the temperatures at which carbon steel is still comfortably within its allowable stress. PVC Schedule 80 is therefore used for chemical drainage, irrigation, low pressure process lines and corrosive services where metal would be attacked, and it is never used for steam, compressed air at pressure, or hot hydrocarbon service.

What Mechanical Properties Do Schedule 80 Pipe Materials Have?

Tensile strength ranges from 415 MPa for A106 Grade B to 830 MPa for Inconel 625, while yield strength ranges from 170 MPa for 304L and 316L to 550 MPa for super duplex 2507. Yield, not tensile, is what governs how a pipe behaves under pressure.

Mechanical Properties - Common Schedule 80 Pipe Materials

Pressure design works from allowable stress, which is derived from yield and tensile strength with a code safety factor, so a higher yield generally translates into a higher rating. That is the whole reason super duplex 2507 sits at the top of the pressure table while 304L sits near the bottom despite being a perfectly good pipe material. The trade is cost and fabricability: yield strength of 550 MPa comes with a material price several times that of 316L and a narrower welding window.

Note also that elongation and hardness matter as much as strength when the line will be bent, formed or welded. The 25 percent minimum elongation of the duplex grades is markedly lower than the 35 percent of 304L, which is why duplex needs more care in bending and forming. If your design cycles rather than holds steady pressure, pair this table with steel pipe lifespan under repeated loading.

Which Physical Properties Matter Most When Choosing Schedule 80 Pipe?

Thermal expansion and thermal conductivity drive most real-world pipe problems. PVC expands about four times more than steel per degree, which is why plastic lines need expansion loops that steel lines do not.

Physical Properties Comparison

Three of these rows decide most design arguments. Thermal expansion determines whether you need expansion loops, offsets or bellows: at roughly 54 x 10^-6 per degree C, PVC moves about four times as much as carbon steel and about three and a half times as much as 316L. Thermal conductivity determines how quickly the line heats and cools, and therefore how severe the thermal shock and the weld heat affected zone will be: stainless conducts at about a third of the rate of carbon steel. Elastic modulus determines stiffness and therefore support spacing and the natural frequency of the line, which is what governs vibration problems.

Density is the one that surprises estimators. Because 316L is slightly denser than carbon steel at 7.98 against 7.85 g/cm3, a stainless line of identical dimensions weighs marginally more than the carbon steel equivalent - but the duplex grades are slightly lighter again at 7.80. PVC at 1.40 g/cm3 is roughly a fifth of the mass, which is the main reason it is chosen for long runs where support cost dominates.

How Much Does Schedule 80 Pipe Cost per Foot?

Indicative Schedule 80 pricing runs from about $2 per foot for PVC up to about $1,650 per foot for super duplex 2507 at 6 in NPS. Price rises steeply with both size and alloy content, and size dominates.

The figures below are indicative mill or distributor ranges for budgeting only. Pipe prices move with nickel, chromium and molybdenum markets, with energy cost, with order quantity and with certification requirements, so treat them as order of magnitude guidance and request a live quotation for procurement.

Carbon Steel Schedule 80 Pipe Price (ASTM A106 Grade B, Seamless)

Stainless Steel Schedule 80 Pipe Price (ASTM A312, Seamless)

PVC Schedule 80 Pipe Price

What actually drives the price of a Schedule 80 pipe order

A useful sanity check: at 6 in NPS the carbon steel range is roughly $75 to $120 per foot, 316L is roughly $370 to $570, and super duplex 2507 is roughly $1,100 to $1,650. That is an order of magnitude between carbon steel and a high alloy at the same size and schedule, which is why grade selection - not schedule selection - is almost always the bigger commercial decision. For live pricing on the high alloy end, see nickel alloy pipe and alloy pipes.

 Should You Choose Schedule 40 or Schedule 80 Pipe?

Choose Schedule 40 for welded or flanged lines at moderate pressure where flow and cost matter. Choose Schedule 80 for threaded ends, higher pressure, external loads, or where you need corrosion allowance.

Schedule 40 vs Schedule 80 - Selection Matrix

Two of the nine decision factors are effectively mandatory rather than optional. If the line will be threaded, Schedule 80 is the practical minimum because cutting an NPT thread removes real wall. If the owner specification or the applicable code calls for Schedule 80 in hazardous service, the decision is made for you. Everything else in the matrix is a trade between pressure capability, bore, weight and money.

The counter-argument to Schedule 80 is flow. At 4 in NPS you give up about 0.2 in of bore, which reduces flow area by roughly 14 percent at the same velocity, or raises pressure drop materially at the same flow. On a long transfer line that penalty is paid every hour of operation, while the extra pressure capability may never be used. If you need the wall but also need the bore, the usual answer is to move up one NPS at Schedule 40 rather than staying at Schedule 80.

Which Standards and Codes Govern Schedule 80 Pipe?

Three layers apply: the product specification that defines the material, the dimensional standard that defines wall thickness, and the pressure code that governs design. Naming all three on the purchase order is what prevents a wrong delivery.

Applicable Standards and Codes by Material

The most common procurement error is ordering to a dimensional standard without a product specification, or the reverse. ASME B36.10M and B36.19M give you wall thickness and weight but say nothing about chemistry, mechanical properties or testing; ASTM A106, A312, A790, B622 and B444 give you chemistry and properties but no dimensions. You need both, plus the pressure code that the line is designed to. If you are unsure what a specification actually covers, what ASTM A312 means and A312 versus A358 explain the most frequently confused pair.

Fittings and connections bring their own dimensional standards into the same order. Butt weld fittings are covered by ASME B16.9, forged socket weld and threaded fittings by ASME B16.11, flanges by ASME B16.5, and small bore connections by pipe nipples and swage nipples.

How Does Wall Thickness Affect Corrosion Life?

A thicker wall buys time, not resistance. It increases the corrosion allowance available before the pipe reaches minimum required thickness, but it does not change the corrosion rate - only a better alloy does that.

Corrosion Resistance by Material

Read that table as two separate decisions. The columns on general corrosion, chloride pitting and stress corrosion cracking tell you whether the alloy survives the fluid at all: carbon steel needs coating or inhibition, 304 pits above roughly 200 ppm chloride, 316L is limited to about 1,000 ppm and remains susceptible to chloride stress corrosion cracking, duplex 2205 pushes toward 5,000 ppm and resists cracking, and super duplex 2507 plus the nickel alloys handle full seawater and acid service. The wall thickness then decides how many years of the surviving corrosion rate you have purchased.

That is why the rule of thumb is to fix the alloy first and the schedule second. Doubling wall on 304 in seawater buys perhaps a few years; moving to duplex pipe or to super duplex S32750 changes the corrosion rate itself. For seawater specifically, which alloy to use for seawater piping and the S32750 desalination guide go further, and for acid duty see nickel alloy pipe selection by acid type.

What Manufacturing Tolerances Apply to Schedule 80 Wall Thickness?

Delivered wall may be up to 12.5 percent below the nominal value in the dimension tables. Design on minimum wall, and order the nominal thickness that still clears the requirement after the tolerance.

Tolerances and allowances that reduce the wall you actually have

Working through those numbers explains the Schedule 80 default for threaded pipe more precisely than any rule of thumb. A 1 in Schedule 40 wall of 0.133 in, reduced by the 12.5 percent tolerance to about 0.116 in, and then reduced by a 0.070 in thread depth, leaves roughly 0.046 in - far too little. The same calculation on Schedule 80 starts at 0.179 in, tolerances to about 0.157 in, and leaves roughly 0.087 in. That is the arithmetic behind the code requirement.

Threaded connections also introduce the fittings question. Where the design calls for threaded joints, threaded flanges and forged pipe fittings are normally specified alongside, and the assembly should be seal welded or inspected per the owner specification where the service is hazardous.

Which Schedule 80 Material Suits Corrosive or Seawater Service?

Match the alloy to the fluid first. 316L covers mild chemical duty; duplex 2205 covers brackish and moderate chloride service; super duplex 2507, Hastelloy C276 and Inconel 625 cover seawater, acid and sour service.\

Schedule 80 material selection by service

The high alloy end of that table is worth reading twice, because it is where the pressure tables and the corrosion tables point in different directions. Super duplex 2507 gives the highest MAWP of the metallic grades listed here and is markedly cheaper than a nickel alloy, so it wins wherever the chloride load is high but the chemistry is not aggressively reducing. Once hydrochloric or sulphuric acid enters the picture, Hastelloy C276 becomes the reference grade - see the Hastelloy C276 hub and the dedicated acid service guide. Where both are live candidates, C276 against Inconel 625 sets out the trade.

Offshore and subsea lines add sour service qualification on top of corrosion, which is covered separately in how to select nickel alloy pipe for offshore oil and gas and the best alloy for offshore pipelines.

What Are the Practical Limits of Schedule 80 Pipe?

Schedule 80 is not a universal upgrade. It costs more, flows less, weighs more, and it does nothing for corrosion chemistry or for temperatures beyond the base material.

• Smaller bore. At 4 in NPS you lose about 0.2 in of ID against Schedule 40, roughly 14 percent of flow area, which raises pressure drop at constant flow.

• More weight. Up to 52 percent heavier per foot at 8 in NPS, which propagates into support design, labour and freight.

• Higher cost. You pay for the extra steel twice: once in material and once in handling.

• No help with corrosion chemistry. Wall thickness is a time allowance, not resistance. A grade change is the fix for pitting, crevice attack or stress corrosion cracking.

• Still bounded by the base material. Schedule 80 PVC is still limited to about 60 C, and Schedule 80 A106 is still limited to about 425 C. The schedule does not extend either ceiling.

• Not a substitute for a proper code calculation. The pressure tables here use the simple hoop stress form and exclude corrosion, erosion, threading and tolerance allowances.

• Threaded joints remain the weak point. Even at Schedule 80, a threaded connection is the most likely leak path in a hazardous service line; welding is the better detail wherever the design allows it.

How Do You Specify and Buy Schedule 80 Pipe?

1. Fix the design envelope first. Record design pressure, design temperature, fluid composition, chloride content, flow velocity and whether the line will be threaded or welded. Every later decision is derived from these six values.

2. Pick the nominal pipe size from flow, not from pressure. Size the bore for the required flow rate and allowable pressure drop. Because Schedule 80 has a smaller ID than Schedule 40 at the same NPS, check that the reduced bore still delivers the duty.

3. Choose the material grade from the fluid, not from the schedule. Wall thickness is not corrosion protection. Select the grade from the fluid chemistry and temperature first - see the corrosion and material selection tables in this guide - then choose the schedule.

4. Look up allowable stress S at design temperature. Take S from the table of the code edition you are designing to (ASME B31.3 Table A-1 for process piping, B31.1 for power piping). Do not reuse the room temperature value at elevated temperature.

5. Calculate the pressure design thickness. Use the governing code equation. For the thin wall form used throughout this guide, P = 2 x S x t / D; rearranged, t = P x D / (2 x S). ASME B31.3 adds the Y coefficient and the weld joint factor E.

6. Add corrosion, erosion and mechanical allowances. Minimum required thickness = pressure design thickness + corrosion and erosion allowance + mechanical allowance (thread depth or groove depth). Threading a 1 in NPT end removes about 0.070 in of wall.

7. Order against nominal wall plus mill tolerance. Because the delivered wall may be up to 12.5 percent under nominal, order the schedule whose minimum wall still exceeds the required thickness. Divide the required thickness by 0.875 to get the nominal to buy.

8. Specify the standard, the class and the documentation. State the product specification (ASTM A106, A312, A790, B622 or B444), the dimensional standard (ASME B36.10M or B36.19M), the schedule, the NPS range, the length, and the inspection documents (EN 10204 3.1 or 3.2, PMI, hydrostatic test) on the purchase order.

Frequently Asked Questions

 What is the pressure rating of 2 inch Schedule 80 carbon steel pipe (A106 Grade B)?

For ASTM A106 Grade B seamless pipe at 2 inch NPS, the Schedule 80 wall is 0.218 in and the OD is 2.375 in. With an allowable stress of 15,000 psi at room temperature, the hoop stress equation gives P = 2 x 15,000 x 0.218 / 2.375, which is about 2,752 psi. At 400 F the allowable stress falls to about 14,400 psi and the rating drops to about 2,644 psi.

What is the pressure rating of 2 inch Schedule 80 stainless steel pipe (316L)?

For ASTM A312 TP316L at 2 inch NPS Schedule 80, the allowable stress at 70 F is 16,700 psi, giving a MAWP of about 3,063 psi. That is higher than A106 Grade B at the same size and schedule, because 316L has a higher listed allowable stress at room temperature.

What is the pressure rating of Schedule 80 PVC pipe?

At 73 F, Schedule 80 PVC ratings run from 850 psi at 1/2 in NPS down to 280 psi at 6 in NPS. At 140 F the rating is roughly 30 percent of the room temperature value, so 1/2 in NPS falls to about 255 psi. PVC Schedule 80 is not suitable for steam or high temperature service.

Is Schedule 80 pipe always stronger than Schedule 40?

Yes at the same nominal pipe size. Schedule 80 always has a thicker wall, which gives a higher pressure rating, greater resistance to external loads and more material available as corrosion allowance. The OD is identical between schedules; only wall thickness and ID differ.

Why is Schedule 80 required for threaded pipe connections?

Cutting an NPT thread removes wall material. A 1 in NPT thread has 11.5 threads per inch per ASME B1.20.1, a pitch of 0.08696 in and a thread depth of about 0.070 in. Schedule 40 at 1 in NPS has a 0.133 in wall, leaving only about 0.063 in under the thread root. Schedule 80 has a 0.179 in wall, leaving about 0.109 in - a materially better margin. ASME B31.1 and B31.3 require Schedule 80 or heavier for threaded metallic pipe.

How much heavier is Schedule 80 compared with Schedule 40?

At small sizes from 1/2 in to 1 in NPS, Schedule 80 is about 25 to 35 percent heavier per foot. At 6 in to 8 in NPS the difference grows to 50 to 55 percent. That extra mass affects pipe support design, installation labour and freight.

What is the inside diameter of 4 inch Schedule 80 pipe?

The OD of 4 in NPS pipe is always 4.500 in regardless of schedule. Schedule 80 wall is 0.337 in, so the ID is 4.500 minus 2 x 0.337, which is 3.826 in. Schedule 40 at the same size has an ID of 4.026 in, about 0.2 in larger.

Can Schedule 80 stainless steel pipe be used for high temperature steam service?

Yes with the right grade. For steam up to about 750 F, stabilised grades such as 321 or 347 are preferred over 304 and 316 to avoid sensitisation. The pressure rating must be recalculated at the operating temperature, and ASME B31.1 governs power and steam piping rather than B31.3.

How do you calculate the pressure rating of Schedule 80 pipe?

Use the hoop stress relation P = 2 x S x t / D, where S is the allowable stress at design temperature, t is the wall thickness and D is the outside diameter. For 1/2 in NPS A106 Grade B: 2 x 15,000 x 0.147 / 0.840 = 5,250 psi, which matches the pressure chart in this guide.

Does the OD change between Schedule 40 and Schedule 80?

No. Outer diameter is fixed by nominal pipe size and is identical for every schedule at that NPS. This is why fittings, flanges, hangers and supports are interchangeable between schedules, while the bore and the pressure capability are not.

What wall thickness tolerance applies to Schedule 80 pipe?

The delivered wall may be up to 12.5 percent below the nominal value in the dimension tables. Designers should therefore calculate with the minimum wall rather than the nominal wall, and order a nominal thickness of at least the required thickness divided by 0.875.

Is Schedule 80 available in stainless steel and nickel alloys?

Yes. Schedule 80 (often written 80S for stainless) is produced in 304L, 316L, 316H, 321, 347, 904L, 254 SMO, duplex 2205, super duplex 2507 and the nickel alloys covered by ASTM B622 and B444. JN Alloy stocks stainless and nickel alloy pipe through the stainless steel pipe and nickel alloy pipe ranges.

Which is better for seawater service: 316L, duplex 2205 or super duplex 2507?

316L is marginal in ambient seawater and is generally limited to about 1,000 ppm chloride; duplex 2205 raises that to roughly 5,000 ppm and resists chloride stress corrosion cracking; super duplex 2507 is rated for continuous seawater service. For a full comparison see the guide to alloy selection for seawater piping.

Why do allowable stress values differ between websites?

Because different codes and different editions use different bases. ASME B31.3 Table A-1, ASME B31.1 and ASME BPVC Section II Part D do not always list the same value for the same grade, and B31.3 has revised several carbon steel values between editions. Always take S from the edition of the code you are designing to, and state that edition on the calculation sheet.

What is the difference between Schedule 80 and Schedule 80S?

Schedule 80S is the stainless steel designation used in ASME B36.19M. The wall thicknesses in B36.19M match the B36.10M Schedule 80 values for most sizes, so the two are functionally interchangeable in procurement, but the S suffix signals that the stainless dimensional standard governs.

Does Schedule 80 pipe cost much more than Schedule 40?

The price premium tracks the extra steel. At small sizes the wall is about 35 percent thicker and weight about 28 percent higher, so expect a similar order of premium on material; at 8 in NPS the weight penalty reaches 52 percent. Price per foot also rises steeply with NPS and with alloy content.

Can Schedule 80 pipe be welded?

Yes. Metallic Schedule 80 pipe is routinely butt welded to ASME B16.9 fittings or socket welded to ASME B16.11 forged fittings. Schedule 40 is more common where the line is fully welded and pressure is moderate, because the thinner wall costs less and gives a larger bore.

What is the maximum temperature for carbon steel Schedule 80 pipe?

ASTM A106 covers seamless carbon steel pipe for service up to about 425 C (800 F). Above that temperature chrome moly grades such as ASTM A335 P11, P22 or P91 are normally required for creep resistance. The allowable stress falls steadily with temperature, so the pressure rating must be derated as well.

How does wall thickness affect corrosion life?

A thicker wall gives a larger corrosion allowance, so a pipe that loses a fixed amount of wall per year lasts proportionally longer before it reaches the minimum required thickness. It does not change the corrosion rate itself. Upgrading the alloy is usually more effective than simply adding wall.

What documentation should accompany a Schedule 80 pipe order?

Ask for the mill test certificate to EN 10204 3.1 as a minimum, or 3.2 where third party witness is required. For alloy pipe add positive material identification, hydrostatic or nondestructive test records, and heat number traceability linking each length to its certificate.

Does JN Alloy supply Schedule 80 pipe in Hastelloy and Inconel?

Yes. Hastelloy C276 to ASTM B622 and Inconel 625 to ASTM B444 are supplied in Schedule 80 and heavier, with EN 10204 certification. These are specified where the fluid is too aggressive for stainless steel - see the Hastelloy C276 hub and the Inconel 625 guide for service envelopes.