Technical knowledge
Pipe schedules and wall thickness: choosing the wall that the duty needs
How pipe schedules relate to wall thickness, why schedule number is not a strength measure, how corrosion allowance and mill tolerance affect the choice, and how to specify wall thickness for alloy piping.
What a schedule actually is
Schedules originated as a convenient way to group wall thicknesses. Standard weight, extra strong and double extra strong were later numbered, giving the familiar 40, 80 and 160 designations. For smaller sizes several schedules share the same wall thickness, and for larger sizes the series diverges, so the schedule number alone never tells you the thickness.
How to read it
| Schedule | Relative wall | Typical use |
|---|---|---|
| 5S / 10S | Thin | Low pressure stainless and nickel systems |
| 40 / 40S | Standard | General process |
| 80 / 80S | Heavy | Higher pressure, threaded joints |
| 160 | Very heavy | High pressure small bore |
| XXS | Extra heavy | Special high pressure duty |
Tip The S suffix denotes stainless and nickel alloy wall series, which differ from the carbon steel series at some sizes. Always read the actual wall thickness from the table for your size and schedule.
How to select the wall for alloy piping
- Calculate the minimum wall required by the design code for the design pressure and temperature.
- Add corrosion allowance only where the alloy actually needs it. Nickel alloys and titanium in seawater normally require none.
- Add allowance for threading, grooving or heavy machining where applicable.
- Account for mill tolerance on wall thickness, which is typically a percentage of the nominal wall.
- Confirm availability, since very heavy walls in nickel alloys have long lead times.
Keeping fittings consistent with pipe
Butt weld fittings are made to match the pipe wall so the bore is continuous and the weld is sound. State the schedule or the actual wall thickness on both the pipe and the fitting order, and verify the bore at receipt. A mismatch in bore creates a step that causes turbulence, erosion and poor radiographic results.
Questions about this topic
Is Schedule 80 stronger than Schedule 40?
The wall is thicker, so the pipe carries higher pressure, but schedule is a dimensional designation rather than a strength rating. The allowable pressure also depends on the material and the temperature.
Do nickel alloy pipes need corrosion allowance?
Usually not. In seawater, titanium and nickel alloys are selected precisely because they do not need a corrosion allowance, and the wall is set by pressure and mechanical requirements.
Why does mill tolerance matter?
The delivered wall can be below nominal by a defined percentage. If the design minimum is close to nominal, the tolerance can take the delivered wall below the requirement, so it must be considered at the design stage.
Questions about our products
What products does Hangbo Alloy supply?
Four product families, all available in nickel-based alloys, titanium, duplex and special stainless steel: flanges, butt weld pipe fittings, elbows, and seamless tube and pipe. Flanges cover weld neck, long weld neck, slip-on, blind, socket weld, threaded and lap joint patterns. Fittings and elbows cover concentric and eccentric reducers, equal and reducing tees, caps, stub ends, and 45°, 90° and 180° returns in both long and short radius, plus 3D and 5D bends for piggable lines. Seamless tube and pipe is supplied cold drawn or hot finished from 6 mm to 630 mm outside diameter.
Which alloy grades are available for these products?
More than 90 grades are published in our grade library. The most requested are Inconel 625, 718, 600 and X-750, Hastelloy C-276, C-22 and B-2, Monel 400 and K-500, Incoloy 800H, 825 and 925, duplex 2205 and super duplex 2507, 316L, 904L and 254SMO stainless steel, and titanium Grade 2 and Grade 5. Nickel-based grades can also be supplied with VIM plus ESR double melting where cleanliness or fatigue life is critical.
What sizes, wall thicknesses and pressure classes can you supply?
Flanges run from NPS ½ to NPS 24 to ASME B16.5 and from NPS 26 to NPS 60 to ASME B16.47 Series A or B, in pressure classes 150 through 2500. Butt weld fittings and elbows run from NPS ½ to NPS 48 (DN 15 to DN 1200) in wall thickness Schedule 5S through XXS. Seamless tube and pipe covers 6 mm to 630 mm outside diameter, in random lengths of about 5 to 7 metres or fixed lengths up to 12 metres. Non-standard and intermediate sizes are quoted on request.
Which material and dimensional standards do you work to?
Forged flanges to ASTM B564, B381 and A182 with dimensions to ASME B16.5 and ASME B16.47. Butt weld fittings and elbows to ASTM B366 and A403 with dimensions to ASME B16.9 and MSS SP-43. Seamless tube and pipe to ASTM B444, B423, B622, B163, B167, B861, A312, A213 and A790. Marking follows MSS SP-25 and the applicable product standard. If your project is governed by EN, DIN, JIS or a company specification, send the document and we will confirm equivalence before quoting.
Is there a minimum order quantity?
There is no minimum for standard sizes and grades held in stock, and prototypes, spares and small trial batches are accepted. Made-to-order melts and special forgings carry a minimum weight that depends on the alloy and the route, typically from about 500 kg for special grades.
What inspection and certification is issued with the goods?
Every shipment carries an EN 10204 3.1 mill test certificate quoting the actual chemical and mechanical results for the specific heat lot, together with dimensional records and heat treatment data where applicable. Testing is carried out in house by optical emission spectrometry, tensile, impact and hardness testing, plus ultrasonic and eddy current examination, with hydrostatic pressure and intergranular corrosion testing to ASTM G28 or A262 Practice E where the specification requires it. Third party inspection by SGS or another recognised agency can be arranged, and their report is issued alongside the shipment.
What are typical lead times?
Standard stock items ship within days. Common production grades such as Inconel 625 or duplex 2205 are typically a few weeks. Special chemistries, larger forgings and items that require third party inspection take longer and are quoted individually against the requirement.
How are the products packed for export?
Flanges and fittings receive a rust preventive coating, are individually wrapped and are packed in plywood cases secured with steel banding. Tube ends are capped and bundles are strapped. Packing lists quote heat numbers so every case can be cross-checked against the mill certificate on arrival. We quote EXW, FOB, CFR, CIF and DAP, and mixed-alloy orders can be consolidated into one shipment with a single documentation package.
How do I request a quotation or a sample?
Send the grade or UNS number, the dimensions including schedule or wall thickness, the governing material and dimensional standards, quantity, any heat treatment or NDT scope and the certificate type you need; a drawing is ideal for special flanges and fittings. Email demi@nickel-alloy.com or message us on WhatsApp +86 15618279078 and we normally issue a formal quotation within 24 hours on working days. Samples and previous test reports can be arranged before the first order.
Talk to an engineer
Share your duty conditions and we will shortlist candidate alloys within one working day.