The Simple Pressure Vessels (Safety) Regulations 2016 No. 1092

Regulation 4(1)

SCHEDULE 1 Essential Safety Requirements

PART 1 Materials

1.  Materials used in the manufacture of a vessel must be selected according to the intended use of the vessel and in accordance with paragraphs 2 to 9.

Pressurised parts

2.  The materials used for manufacturing the pressurised parts of the vessel must be—

(a) capable of being welded;

(b) ductile and tough, so that a rupture at minimum working temperature does not give rise to either fragmentation or brittle-type fracture;

(c) not adversely affected by ageing.

3.  For steel vessels, the material must in addition meet the requirements set out in paragraph 5 and, for aluminium or aluminium alloy vessels, those set out in paragraph 6.

4.  The materials must be accompanied by an inspection slip as defined in paragraph 21(b) of Schedule 2, drawn up by the producer of the materials.

Steel vessels

5.  Non-alloy quality steels must meet the following requirements—

(a) they must be non-effervescent and supplied after normalisation treatment, or in an equivalent state;

(b) the content per product of carbon must be less than 0.25% and that of sulphur and phosphorous must each be less than 0.05%

(c) they must have the following mechanical properties per product—

(i) the maximum tensile strength _{Rm, max} must be less than 580 N/mm^2;

(ii) the elongation after fracture must be:

if test pieces are taken parallel to the direction of rolling:

thickness ≥ 3 mm:	A	≥ 22%,
thickness < 3 mm:	A 80 mm	≥ 17%,

or, if test pieces are taken perpendicular to the direction of rolling:

thickness ≥ 3 mm:	A	≥ 20%,
thickness < 3 mm:	A80 mm	≥15%,

(iii) the average bending rupture energy (KCV) for three longitudinal test pieces at minimum working temperature must not be less than 35 J/cm². Not more than one of the three figures may be less than 35 J/cm², with a minimum of 25 J/cm². In the case of steels intended to be used in the manufacture of vessels the minimum working temperature of which is lower than - 10°C and the wall thickness of which exceeds 5 mm, this property must be checked.

Aluminium vessels

6.—(1) Non-alloy aluminium must have an aluminium content of at least 99.5% and the alloys referred to in regulation 2(1)(b) (interpretation) must display adequate resistance to intercrystalline corrosion at maximum working temperature.

(2) Moreover, these materials must satisfy the following requirements—

(a) they must by supplied in an annealed state;

(b) they must have the following mechanical characteristics per product—

(i) the maximum tensile strength R_{m, max} must be no more than 350 N/mm²,

(ii) the elongation after fracture must be—

(aa) A ≥ 16% if the test piece is taken parallel to the direction of rolling;

(bb) A ≥ 14% if the test piece is taken perpendicular to the direction of rolling.

Welding materials

7.  The welding materials used to manufacture the welds on or of the vessel must be appropriate to and compatible with the materials to be welded.

Accessories contributing to the strength of the vessel

8.—(1) Accessories contributing to the strength of the vessel (for example bolts and nuts) must be made—

(a) of a material specified in paragraphs 2 to 6; or

(b) of other kinds of steel, aluminium or an appropriate aluminium alloy compatible with materials used for the manufacture of pressurised parts.

(2) The materials referred to in sub-paragraph (1)(b) must, at minimum working temperature, have an appropriate elongation after fracture and bending rupture energy.

Non-pressurised parts

9.  All unpressurised parts of welded vessels must be of materials which are compatible with that of the components to which they are welded.

Symbols

10.  In this Part—

(a) “A” means elongation after fracture () in %;

(b) “A_{80 mm}” means elongation after fracture () in %;

(c) “KCV” means bending rupture energy in J/cm²

(d) “R_{m, max}” means maximum tensile strength in N/mm²

PART 2 Vessel Design

11.—(1) A manufacturer must, when designing a vessel, define the use to which it will be put, and select—

(a) the minimum working temperature T_min;

(b) the maximum working temperature T_max; and

(c) the maximum working pressure PS.

(2) Where a minimum working temperature exceeding - 10°C is selected, the qualities required of the materials must be satisfied at - 10°C.

12.  A manufacturer must also take account of the following provisions—

(a) it must be possible to inspect the inside of vessels;

(b) it must be possible to drain the vessels;

(c) the mechanical qualities must be maintained throughout the period of use of the vessel for the intended purpose;

(d) the vessels must, bearing in mind their prescribed use, be adequately protected against corrosion.

13.  A manufacturer must take account of the fact that under the conditions of use envisaged—

(a) the vessels must not be subjected to stress likely to impair their safety in use;

(b) internal pressure must not permanently exceed the maximum working pressure PS. However, it may momentarily do so by up to 10%.

14.  Circumferential and longitudinal seams must be made using full penetration welds or welds of equivalent effectiveness and convex ends, other than hemispherical ones, must have a cylindrical edge.

Wall thickness

15.—(1) If the product of PS x V is not more than 3 000 bar.L, the manufacturer must select one of the methods described in paragraphs 16 (calculation method) and 17 (experimental method) for determining vessel wall thickness.

(2) If the product of PS x V is more than 3 000 bar.L, or if the maximum working temperature exceeds 100°C, such thickness must be determined by the method described in paragraph 16 (calculation method).

(3) The actual wall thickness of the cylindrical section and ends must, however, be not less than 2 mm in the case of steel vessels and not less than 3 mm in the case of aluminium or aluminium alloy vessels.

Calculation method

16.—(1) The minimum thickness of pressurised parts must be calculated having regard to the intensity of the stresses and to the following provisions—

(a) the calculation pressure to be taken into account must not be less than the maximum working pressure PS selected;

(b) the permissible general membrane stress must not exceed the lower of the values 0.6 R_eT or 0.3 R_m and the manufacturer must use the R_eT and R_m minimum values guaranteed by the producer of the material in order to determine the permissible stress.

(2) Where the cylindrical portion of the vessel has one or more longitudinal welds made using a non-automatic welding process, the thickness calculated as referred to in sub-paragraph (1) must be multiplied by the coefficient 1.15.

(3) In this paragraph—

(a) “R_eT” means the yield strength in N/mm², which is the value at the maximum working temperature T_max of any of the following—

(i) the upper yield point R_eH in N/mm², for a material with both a lower and an upper yield point;

(ii) the 0.2% proof strength R_p0.2 in N/mm²;

(iii) the 1.0% proof strength R_p1.0 in N/mm², in the case of non-alloy aluminium;

(b) “R_m” means tensile strength in N/mm².

Experimental method

17.  Wall thickness must be so determined as to enable the vessels to resist at ambient temperature a pressure equal to at least five times the maximum working pressure, with a permanent circumferential deformation factor of no more than 1%.

PART 3 Manufacturing processes

18.  Vessels must be constructed and subjected to production checks in accordance with Parts 2, 3 or 4 of Schedule 2.

Preparation of the component parts

19.  Preparation of the component parts (for example forming and chamfering) must not give rise to surface defects or cracks or changes in the mechanical characteristics likely to be detrimental to the safety of the vessels.

Welds on pressurised parts

20.  The characteristics of welds and adjacent zones must be similar to those of the welded materials and must be free of any surface or internal defects detrimental to the safety of the vessels.

21.—(1) Welds must be performed by qualified welders or operators possessing the appropriate level of competence, in accordance with approved welding processes.

(2) In sub-paragraph (1)—

(a) “qualified” means qualified by means of tests carried out by a notified body; and

(b) “approved” means approved by a notified body.

22.  The manufacturer must also, during manufacture, ensure consistent weld quality by conducting appropriate tests using adequate procedures. These tests must be the subject of a report.

Putting into service of the vessels

23.  Vessels must be accompanied by the instructions and safety information.