ASME B31.1 / B31.3 & MSS SP-69
Affects elastic modulus and allowable stress at temperature
Calcium silicate: 8-14 | Mineral wool: 6-10 | Fiberglass: 3-6
Industry practice: 0.1" or L/240. Drainage lines may require tighter limits.
Fraction of yield strength for gravity bending. Typical: 0.33 (1/3 SMYS)
Understand pipe support design, span tables, support types, thermal movement, and beam theory for piping
Pipe support span is calculated as the lesser of two criteria: (1) stress-based span where bending stress from M = wL²/8 must not exceed a fraction of yield strength (typically 0.33×SMYS at temperature), and (2) deflection-based span where midspan sag from δ = 5wL⁴/(384EI) must stay within limits (typically 0.1 inch). The governing maximum span is the smaller of the two values.
MSS SP-69 (Manufacturers Standardization Society Standard Practice 69) provides recommended pipe support spacing tables for standard weight pipe. It covers NPS 1 through 36 for gas and water-filled service. These tabulated values assume simple supports with no insulation and serve as quick-reference guidelines that should be verified against project-specific stress and deflection calculations per ASME B31.1 or B31.3.
Natural frequency must exceed 4 Hz to avoid resonance with rotating equipment vibration (compressors, pumps, engines typically excite at 4-60 Hz). The fundamental frequency is calculated as fn = (π/2) × √(EIg/wL⁴) for simply supported spans. If fn falls below 4 Hz, shorten the span or add intermediate supports.
Total distributed load includes: pipe weight (from ASME B36.10M tables), fluid contents weight (water at 62.4 lb/ft³, oil at ~53 lb/ft³, or gas), insulation weight based on thickness and density, cladding/jacketing weight, and concentrated loads from valves or fittings. Wind loads for outdoor installations are combined with gravity loads using SRSS (square root of sum of squares) for orthogonal load combination.
The typical allowable deflection for pipe support spans is 0.1 inches (2.5 mm) for most process piping applications. Some specifications use L/240 (span length divided by 240) as an alternative criterion. For large-diameter pipelines or less critical services, up to 0.25 inches may be acceptable. The deflection limit often governs over stress for large-diameter, thin-wall pipe.