The Pressure Equipment (Safety) Regulations 2016

Calculation method U.K.

5.—(1) As regards pressure containment and other loading aspects—

(a) the allowable stresses for pressure equipment must be limited having regard to reasonably foreseeable failure modes under operating conditions, for which purpose safety factors must be applied to eliminate fully any uncertainty arising out of manufacture, actual operational conditions, stresses, calculation models and the properties and behaviour of the material; and

(b) the calculation methods used must provide sufficient safety margins consistent, where applicable, with the requirements of Part 6.

(2) The requirements set out above may be met by applying one of the following methods, as appropriate, if necessary as a supplement to or in combination with another method—

(a) design by formula;

(b) design by analysis; or

(c) design by fracture mechanics.

(3) As regards resistance—

(a) appropriate design calculations must be used to establish the resistance of the pressure equipment concerned; and in particular—

(i) the calculation pressures must not be less than the maximum allowable pressures and take into account static head and dynamic fluid pressures and the decomposition of unstable fluids;

(ii) where a vessel is separated into individual pressure-containing chambers, the partition wall must be designed on the basis of the highest possible chamber pressure relative to the lowest pressure possible in the adjoining chamber;

(iii) the calculation temperatures must allow for appropriate safety margins;

(iv) the design must take appropriate account of all possible combinations of temperature and pressure which might arise under reasonably foreseeable operating conditions for the equipment;

(v) the maximum stresses and peak stress concentrations must be kept within safe limits;

(vi) the calculation for pressure containment must utilise the values appropriate to the properties of the material, based on documented data, having regard to the provisions set out in Part 4 together with appropriate safety factors; material characteristics to be considered, where applicable, include—

(aa) yield strength, 0.2 % or 1.0 % proof strength as appropriate at calculation temperature;

(bb) tensile strength;

(cc) time-dependent strength, i.e. creep strength;

(dd) fatigue data;

(ee) Young's modulus (modulus of elasticity);

(ff) appropriate amount of plastic strain;

(gg) bending rupture energy;

(hh) fracture toughness.

(vii) appropriate joint factors must be applied to the material properties depending, for example, on the type of non-destructive testing, the materials joined and the operating conditions envisaged;

(viii) the design must take appropriate account of all reasonably foreseeable degradation mechanisms (for example corrosion, creep and fatigue) commensurate with the intended use of the equipment and attention must be drawn, in the instructions referred to in paragraph 30, to particular features of the design which are relevant to the life of the equipment, for example—

(aa) for creep: design hours of operation at specified temperatures;

(bb) for fatigue: design number of cycles at specified stress levels;

(cc) for corrosion: design corrosion allowance.

(4) As regards stability aspects, where the calculated thickness does not allow for adequate structural stability, the necessary measures must be taken to remedy the situation taking into account the risks from transport and handling.