• There are no items in your cart

BS 855:1990



The latest, up-to-date edition.

Specification for welded steel boilers for central heating and indirect hot water supply (rated output 44 kW to 3 MW)

Available format(s)

Hardcopy , PDF



Published date


Committees responsible
Section one. General
1.1 Scope
1.2 Definitions
1.3 Performance
1.4 Design pressures and flow temperatures
Section two. Materials and design stresses
2.1 Materials
2.2 Design stress
Section three. Design
3.1 General
3.2 Cylindrical shells subject to internal pressure
3.3 Dished and flanged ends
3.4 Standpipes and branches
3.5 Manhole and sighthole openings
3.6 Stays, stiffeners and supported surfaces
3.7 Tubes and tube plates
3.8 Cylindrical furnaces and combustion chambers
      subject to external pressure
3.9 Fireboxes
Section four. Manufacturer and workmanship
4.1 Pressure parts
4.2 Welding
4.3 Dampers, doors and observation ports
4.4 Ashpits
4.5 Inspection and cleaning holes
4.6 Provisions for mountings, appliances and
4.7 Assembly of boiler
Section five. Mountings and fittings
5.1 Safety valves
5.2 Vent pipes
5.3 Emptying valves or cocks
5.4 Pressure gauges
5.5 Temperature gauges
5.6 Inspector's test gauge connection
5.7 Water-level gauges
5.8 Water-level alarms, fuel cut-outs and fusible
5.9 Connection pipes for water-level fittings
5.10 Feed-water valves
5.11 Blowdown
5.12 Stop valves
Section six. Combustion equipment
6.1 General
6.2 Solid fuel firing
6.3 Liquid fuel firing
6.4 Gas firing
Section seven. Automatic controls and electrical
7.1 Automatic controls for steam and hot water boilers
Section eight. Inspection and marking
8.1 Inspection
8.2 Hydraulic test
8.3 Marking
A. Installation provisions
B. Electrical installation
C. Categories of boilers
D. Information to be supplied by the manufacturer
E. Information to be supplied by the purchaser
1. Design pressures, flow temperatures and outputs
2. Design stress f
3. Minimum thickness of shells subject to internal
4. Values of z for welded longitudinal seams
5. Tapped opening: minimum thickness of plate
6. Values of constant K5
7. Weld attachments
8. Number of bar stays in vertical boilers
9. Minimum thickness of plain tubes subject to
      internal or external pressure
10. Minimum thickness of cylindrical shells subject
      to external pressure
11. Dimensions of manholes and inspection holes
12. Tapping sizes for safety valves
13. Sizes of safety valves (open vented systems only)
14. Tapping sizes for vent pipes
15. Minimum open vent pipe sizes
1. Maximum diameter of unreinforced openings
2. Compensation of welded branches or standpipes
3. Compensated set-through branches
4. Typical method of attachment of ash drop-out tube
5. Fillet-welded studded connections
6. Typical methods of welding manhole frame and
      compensating plates
7. Typical dished ends
8. Shape factor
9. Opening in ends
10. Limits of reinforcement
11. Flanges
12. Angle rings
13. Set-trough branches up to 150 mm o.d. branch
14. Set-in branches: full penetration connections
15. Set-through branches
16. Typical screwed connections
17. Welding details for compensated openings in flat
      end plates
18. Typical arrangement of end plates on single
      furnace economic boilers
19. Access openings for wet-back boilers
20. Attachment of unflanged flat end plates to
      cylindrical shells
21. Attachment of dished or flat flanged end plates
      to cylindrical shells and furnaces
22. Typical arrangement of end plates on multitubular
23. Bar stays
24. Attachment of longitudinal bar stays
25. Plate stays
26. Plus-welded firebox or water-leg stays
27. Detail of mild steel anchor stays
28. Attachment of dished or flat flanged end plates
      to cylindrical shells
29. Attachment of flanged end plates to shell: ends
      thicker than shell
30. Attachment of flanged flat end plates to shell:
      shell thicker than ends
31. Attachment of end plates to reversal chamber of
      firebox wrapper plates
32. Typical details for all-welded gusset stays
33. Attachment between flat plates
34. Attachment of stay tubes to tube plates
35. Effective length L between centres of substantial
      support for fireboxes of vertical boilers
36. Stiffener for horizontal furnaces
37. Typical plate preparation for butt-welded
      longitudinal and circumferential seams
38. Attachment of plain tubes to tube plates
39. Fusion-welded oval manhole frames
40. Detail of furnace joints
41. Attachment of fireboxes to shells
42. Firehole mouthpieces and access openings
43. Welding of fluepipes
44. Fusion welds of cross tubes
45. Typical methods of fitting welded girders to
      welded combustion chambers and fireboxes
46. Butt-welded studded connections
47. Diagrammatic arrangement of water level and high
      steam pressure automatic controls and cut-outs for
      boilers fired with oil or gas complying with
      section six
48. Diagrammatic arrangement of water level and high
      steam pressure automatic controls and cuts-out
      for boilers fired with solid fuel complying with
      section six
49. Heating system categories

Requirements for the design and construction including materials, workmanship, inspection, testing and marking of boilers for use with solid, gaseous and liquid fuels.

Supersedes BS 855(1976) & 87/76507 DC (06/2004) Reviewed and confirmed by BSI, October 2012. (09/2012)
British Standards Institution

1.1.1 This British Standard specifies requirements for the design and construction including materials, workmanship, inspection, testing and marking of welded steel boilers for central heating and indirect hot water supply for which the classification of design pressures, flow temperatures and outputs are given in table 1.

1.1.2 This standard applies to boilers for hot water or low pressure steam (see table 1), with rated heat output between 44 kW and 3 MW and for use with one or more of the following fuels:

  1. smokeless solid fuels, e.g. furnace coke, low temperature coke or anthracite;
  2. bituminous coal fired by means of mechanical stokers;
  3. gaseous fuels of the 2nd and 3rd families (see BS 4947);

and for rated heat output between 300 kW and 3 MW when used with liquid fuels of the classes specified in BS 2869.

This standard also applies to hot water boilers pressurized by steam.

NOTE. The titles of the publications referred to in this standard are listed on page 89.

BS 845-1:1987 Methods for assessing thermal performance of boilers for steam, hot water and high temperature heat transfer fluids Concise procedure
BS 749:1969 Specification for underfeed stokers
BS 3643-1:1981 ISO metric screw threads Principles and basic data
BS 1971:1969 Specification for corrugated furnaces for shell boilers
BS 1387:1985 Specification for screwed and socketed steel tubes and tubulars and for plain end steel tubes suitable for welding or for screwing to BS 21 pipe threads
BS 759-1:1984 Valves, gauges and other safety fittings for application to boilers and to piping installations for and in connection with boilers Specification for valves, mountings and fittings
BS 7190:1989 Method for assessing thermal performance of low temperature hot water boilers using a test rig
BS 6759-1:1984 Safety valves Specification for safety valves for steam and hot water
BS 3602-1:1987 Specification for steel pipes and tubes for pressure purposes: carbon and carbon manganese steel with specified elevated temperature properties Specification for seamless and electric resistance welded including induction welded tubes
BS 4870-4:1988 Specification for approval testing of welding procedures Specification for automatic fusion welding of metallic materials, including welding operator approval
BS 499-1:1991 Welding terms and symbols Glossary for welding, brazing and thermal cutting
BS 5410-2:1978 Code of practice for oil firing Installations of 45 kW and above output capacity for space heating, hot water and steam supply services
BS 4504-1:1969 Circular flanges for pipes, valves and fittings (PN designated) Ferrous
BS 2869:1983 Specification for fuel oils for oil engines and burners for non-marine use

View more information
Excluding VAT

Access your standards online with a subscription


  • Simple online access to standards, technical information and regulations.

  • Critical updates of standards and customisable alerts and notifications.

  • Multi-user online standards collection: secure, flexible and cost effective.