Expand the table for the selected steel grade
Values calculated using Barlow's formula (P = 2St/D), assuming 75% of the material's yield strength. The data is for reference only and serves as a guide for material selection. Final verification should be carried out as part of design calculations in accordance with the applicable standards (e.g. EN 13480, ASME B31.3).
How to use the working pressure table
The table lists the maximum working pressure of seamless stainless steel pipes and tubes at room temperature (15–25 °C). Each section corresponds to one steel grade - from austenitic 1.4307 (TP304L) and 1.4404 (TP316L), through super-austenitic 1.4547 (S31254), to duplex 1.4462 (S312803/S32205) and the nickel alloys 2.4858 (N08825) and 2.4856 (N06625).
To find the right value, select the steel grade, then read the row matching your outside diameter (OD) and wall thickness (WT). The table covers diameters from 6.00 mm up to 457.20 mm (DN450), grouped into sections corresponding to typical DN sizes. Values are given in both psi and bar. By default the table shows dimensions in millimetres and pressure in bar - you can switch to inches or psi in the toolbar.
Barlow's formula - what the values mean
The table is based on Barlow's formula, which describes the maximum internal pressure a thin-walled cylindrical pipe can withstand:
P = 2 · S · t / D
where P is the hydrostatic test pressure, S is the allowable hoop stress in the wall material, t is the wall thickness, and D is the outside diameter. The values in the table were calculated taking S as 75% of the yield strength (Rp0.2) of the given steel grade, which is a typical safety factor for hydrostatic tests.
Barlow's formula assumes a thin wall (D/t > 20). For pipes with a higher thickness-to-diameter ratio, Lamé's formula is more accurate, but for typical sanitary, installation and process piping Barlow gives a conservative, safe result.
Stainless steel grades - which one to choose
1.4307 (TP304L) and 1.4404 (TP316L) - standard austenitic
The most commonly used stainless pipe grades. 1.4307 is the low-carbon version of 1.4301 (304) steel - resistant to general corrosion, well suited to water, dairy and sanitary installations. 1.4404 (TP316L) contains molybdenum, making it resistant to chlorides - the choice for marine, swimming-pool and chemical-industry installations. For both grades the yield strength is typically 220 MPa, hence the similar pressure values in the table.
1.4547 (S31254) - super-austenitic
An alloy with elevated chromium, nickel and molybdenum content (PREN > 40). Used in seawater-cooled heat exchangers, flue-gas desulphurisation plants and processes with high chloride concentrations. It withstands about 40% higher pressures than 1.4404 for the same pipe geometry.
1.4539 (N08904) - acid-resistant austenitic
High-nickel (24–26% Ni) with copper, resistant to reducing acids - sulphuric, phosphoric, acetic. Frequently chosen in the paper, oil and pharmaceutical industries. Its yield strength is close to TP316L, so the pressure values are similar - but the advantage of 1.4539 lies in corrosion resistance, not mechanical strength.
1.4462 (S31803/S32205) - duplex
Duplex stainless steel with a ferritic-austenitic structure. It combines high mechanical strength (Rp0.2 ≈ 450 MPa, twice that of the austenitics) with good resistance to pitting and stress corrosion. That is why in the pressure table 1.4462 pipes withstand roughly 2× more than 1.4307 at identical dimensions. Used in the oil and gas industry, seawater desalination, and chemical tanks.
2.4858 (N08825) and 2.4856 (N06625) - nickel alloys
Nickel-based alloys (Incoloy 825 and Inconel 625) - they exceed the capabilities of stainless steels in extreme conditions: high temperatures, strong acids, reducing-oxidising environments. 2.4856 (Inconel 625) has the highest strength of the grades offered, hence the highest working pressure values appear in the table. Used in aerospace, nuclear power and chlorine-related installations.
Limitations of the reference data
The values in the table are for reference and do not replace a full design calculation. Before using a pipe in a real installation, consider:
- Corrosion allowance - in aggressive environments, 1–3 mm is subtracted from the wall thickness before it is entered into the formula. The values in the table are for nominal thickness with no allowance.
- Operating temperature - rising temperature reduces the allowable stresses. For TP304L operating at 400 °C, the allowable pressure drops by about 30%. The table is calculated for 15–25 °C.
- Welds and joints - welded pipes have a lower weld joint efficiency factor (typically 0.85–1.0). Seamless pipes do not have this limitation, but bends, flanges and tees require separate analysis.
- Cyclic loading - pulsating or surging pressure requires material fatigue to be taken into account, which Barlow's formula does not cover.
- Design codes - regulated installations (PED 2014/68/EU, ASME B31.3, EN 13480) have their own calculation methodologies and allowable-stress tables that account for all the factors above.
For critical applications we recommend consulting the pipe manufacturer's data sheet and the relevant industry standard. The tabulated values work well for preliminary sizing and comparing grades, but they do not replace a piping design prepared by a qualified engineer.
Frequently asked questions
What is the difference between 1.4307 and 1.4404?
1.4307 (TP304L) and 1.4404 (TP316L) are both low-carbon austenitic stainless steels. The main difference is the presence of molybdenum (2–3%) in 1.4404, which significantly increases resistance to pitting corrosion in chloride environments (seawater, swimming pools, salts). Mechanical strength and working pressure values are similar, but 1.4404 is chosen where resistance matters, and 1.4307 as the more economical option for drinking water, milk or food.
Why does duplex steel 1.4462 withstand higher pressures?
Duplex steel 1.4462 has a yield strength of about 450 MPa, more than twice that of the austenitic 1.4307 or 1.4404 (220 MPa). This results from its mixed ferritic-austenitic structure, in which the phases strengthen each other. At the same pipe geometry, duplex will therefore hold twice the internal pressure.
Do these values apply to welded pipes?
Not directly. The table applies to seamless pipes, which have no strength reduction in the weld area. For longitudinally welded pipes, multiply the value of P by the weld joint efficiency factor (E), which is usually 0.85–1.0 depending on the level of weld inspection and the standard.
What is Barlow's formula?
Barlow's formula is a simplified equation determining the internal pressure a thin-walled cylindrical pipe can withstand: P = 2·S·t/D. Where P is the pressure, S is the allowable hoop stress of the material, t is the wall thickness, and D is the outside diameter. It is used in approximate piping calculations and as the basis in many standards. For thick-walled pipes (D/t < 20), Lamé's formula is more precise.
Does the pressure change with temperature?
Yes - significantly. The yield strength of steel decreases as temperature rises. For TP304L operating at 200 °C, the allowable pressure drops by about 15%, at 400 °C by about 30%, and at 600 °C by more than half. The table gives values for 15–25 °C. For operation at higher temperatures, use the allowable-stress tables in the standards (e.g. ASME B31.3 Table A-1 or EN 13480-3 Annex H).
How do I select the wall thickness for a required pressure?
Rearranging the formula: t = P·D / (2·S). For a given pressure P and diameter D, taking S from the material data sheet (75% of the grade's yield strength), you calculate the minimum wall thickness. Add the corrosion allowance (usually 1–3 mm) and the negative thickness tolerance (usually 12.5% per ASTM or EN). Then choose the nearest standard thickness from the catalogue (Schedule or EN series).
Why do some pipe sizes differ by fractions of a millimetre?
The stainless pipe market combines two dimensional traditions: American (inches, e.g. 1/2", 3/4", 1") and metric (mm). That is why adjacent sizes such as 25.00 mm and 25.40 mm (i.e. 1") or 19.05 mm (3/4") next to 20.00 mm appear in the table. This is not an error - these are two genuine standards used in parallel, depending on the origin of the design standard (ASTM/ASME vs EN/DIN/PN). The same applies to larger sizes: 60.00 mm next to 60.30 mm (2") or 219.10 mm (8" per ASME) next to 200.00 mm.
What is the difference between working pressure and burst pressure?
Working pressure is the safe continuous operating pressure with the safety factor included (in the table - 75% of yield strength). Burst pressure is the theoretical pressure that causes the pipe to rupture - usually 3–4× higher than the working pressure. The table gives the working pressure, i.e. the value to which the pipe can be safely loaded under normal operating conditions.
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