Piping design.
From diagram to detail.

01 / SYSTEM SELECTION

Start with the service.

These requirements can overlap. Hygienic design does not remove the need to check pressure integrity, and a pressure-compliant line is not automatically hygienic.

02 / DIMENSIONAL REFERENCE

NPS, DN, OD and Schedule.

NPS and DN are nominal designations. Use the actual inside diameter for flow calculations. OD means outside diameter; wall thickness is t. A Schedule specifies a dimensional series, not a pressure rating.

Source: HT PIPE, B36.19 dimensional table (accessed 27 September 2026). *IDs calculated as OD − 2t from the displayed nominal dimensions; manufacturing tolerances are excluded.

For the sizes shown, 40S and 80S wall dimensions also match Schedule 40 and 80. Do not extend that equivalence to every size. Specify the required dimensional standard and material specification on procurement documents.

Pipe wall selection still requires design pressure and temperature, allowable stress, applicable joint factors, allowances and manufacturing tolerances. A size table cannot establish allowable operating pressure.

03 / PRODUCT-CONTACT SYSTEMS

Tube size is a different language.

An inch-based hygienic tube is designated by its actual OD. A 2-inch tube has a 50.80 mm OD; NPS 2 pipe has a 60.3 mm OD. Their fittings are not interchangeable.

Source: Alfa Laval, Tubes and Fittings, “Hygienic Tube Information,” PDF page 9 (accessed 27 September 2026). Converted from inches using 25.4 mm/in; ID = OD − 2t. Other dimensional series use different sizes.

Design for cleaning and inspection

• Arrange drainage and avoid stagnant branches, crevices and product traps.
• Specify product-contact finish and weld acceptance; inspect internal weld condition and alignment.
• Select seals for the product, cleaning chemicals and temperature. Check the complete clamp assembly rating.
• Validate CIP (clean-in-place) time, temperature, chemistry and hydraulic conditions for the actual circuit. A chosen velocity alone does not prove cleaning effectiveness.

Hygienic design framework: EHEDG guidelines, including Doc. 8, Hygienic Design Principles. Use the applicable project edition and product requirements.

04 / QUICK CALCULATIONS

Calculate with the bore.

Inside diameter and mean velocity

Use Dᵢ in m, Q in m³/s, A in m² and v in m/s. Convert m³/h to m³/s by dividing by 3600. For gas, Q must be the volume flow at local operating pressure and temperature, not an unconverted normal or standard volume flow.

Pressure loss in a constant-bore line

For steady, fully developed, single-phase incompressible flow: Δp is friction and local loss in Pa; L is straight length (m); fᴅ is the Darcy friction factor; K represents local loss coefficients; ρ is density (kg/m³); μ is dynamic viscosity (Pa·s). Use coefficients appropriate to the fittings and their reference velocity.

For fully developed laminar flow in a circular pipe, fᴅ = 64/Re. Turbulent flow requires a suitable correlation or Moody chart using Reynolds number and relative roughness. Elevation, equipment losses and changes in velocity must also enter the system energy balance. Compressible gas, two-phase flow and non-Newtonian foods require an appropriate model.

Thermal movement

α is the mean thermal expansion coefficient (1/K); L is length (m); ΔT is temperature change (K). This gives free thermal expansion, not restraint force or nozzle load. Check flexibility and support behavior for the actual system.

05 / DESIGN WORKFLOW

Turn the P&ID into an installation.

1. Establish inputs. Review the P&ID revision, line list, piping classes, design conditions and equipment nozzle data. Resolve discrepancies before routing.
2. Place equipment and maintenance envelopes. Reserve space for motor removal, filter withdrawal, valve operation, lifting and access.
3. Route each line. Maintain tags, connectivity, specified size and material. Coordinate drains, vents, instruments, flow direction and required slopes.
4. Review mechanical behavior. Coordinate weight, thermal movement, support locations, vibration and allowable equipment nozzle loads. Do not pull misaligned pipework into position with flange bolts.
5. Check interfaces. Verify flange facing, rating, gasket and bolting; account for insulation, weld access, support structure and installation sequence.
6. Release coordinated documents. Update drawings, isometrics where required, BOM/MTO, support details and inspection requirements. Capture installed changes in the as-built record.

Practical background: at Tamkar Gas, my work included 3D modeling and detailing of gas-compression packages from supplied P&IDs and engineering requirements, with piping routing, component integration, collision checks, manufacturing drawings and BOMs.

06 / BEFORE RELEASE

Check the whole system.

• Service and materials: establish design conditions, fluid compatibility, corrosion allowance and material traceability.
• Pressure integrity: check pipe, fittings, valves, flanges, seals and instruments as a connected assembly. Schedule, PN and Class are different designations.
• Fabrication: define welding requirements, tolerances, inspection access and acceptance criteria.
• Operation: check accessibility, drain/vent arrangements, trapped pressure, isolation and maintenance removal paths.
• Hygiene: review drainage, welds, seals and cleaning coverage where the line contacts product.
• Testing: establish the approved test procedure, medium, pressure, temperature, boundaries and component limits from the governing code and project conditions. Do not apply one fixed test multiplier to all services.

07 / SOURCE MAP

Keep each reference in its role.

• ASME B31.3 — process-piping design and construction framework.
• ASME B36.19 dimensional reference — selected stainless pipe sizes, as tabulated by HT PIPE; confirm against the project edition before procurement.
• ASME B16.5 — pipe flanges and flanged fittings; use the applicable material and temperature ratings.
• Alfa Laval tubing catalogue — manufacturer dimensional data for the inch OD tube examples.
• EHEDG — hygienic design guidance and assessment methods.

Source pages checked 27 September 2026. Supplier tables are quick references, not controlled copies of standards. Formulas are elementary geometric, continuity, Darcy–Weisbach and thermal-expansion relations with assumptions stated above. This chapter does not assign a universal design-code edition, wall thickness or test pressure.