FAQ Group: Boiler Testing

As we are coming out of lockdown, several members are getting back to running their locomotives. Please remember to check your boiler paperwork to ensure it is still in date.

If you need a boiler test please contact one of the boiler examiners beforehand to agree a date and time. Do not turn up expecting them to drop what they are doing to test your boiler. If you do not have the contact details please contact the secretary (lindanic@sky.com or 07761960788) and she will book it for you.

There are 4 different types of examination, these are relevant to all boilers (16mm to 7 ¼”).

A shell test – This is a one-off test carried out on all new boilers to twice working pressure. If you have purchased a professionally built boiler it should come with a certificate, this will need to be presented to the boiler examiner and there will be no need for them to do another shell test unless you have modified the boiler.

If you built the boiler yourself the boiler must not have any fittings in place  and all bushes plugged. One bush is used to connect the test gear which requires ¼ BSP or 3/8”x 26tpi male threads. While the examiners have some adapters, you should check with them before the test.

A Written Scheme of Examination – This is completed for new boilers or boilers of purchased engines new to the Society. A copy of the Written Scheme is sent to the Southern Federation of Model Engineers as part of the club’s insurance scheme.

A Hydraulic Test – Required every 4 years, (for steel boilers every 2 years after the test at 4 years) the boiler is filled with water and pressurised to

1 ½ times working pressure with all fittings in place except the safety valve/s. One bush is used to connect the test gear which requires ¼ BSP or 3/8”x 26tpi male threads. While the examiners have some adapters, you should check with them before the test.

The pressure gauge can be left in place providing the scale is sufficient to take the test pressure. Otherwise the pressure gauge has to be removed to be hydraulically calibrated and the siphon blanked off.

A Steam Test – A steam test certificate is valid for up to 14 months at the examiner’s discretion, (the examiner will complete the retest date on the certificate depending on a number of circumstances. (e.g. the hydraulic test runs out before the steam test).

The pressure gauge must be removed and presented for separate hydraulic testing/calibrating before the steam test.

There must be at least 2 means of adding water to the boiler successfully demonstrated as part of the test.

The safety valve/s must open at the working pressure and must prevent the boiler pressure exceeding the working pressure plus 10% with the blower fully open and a full fire burning.

These are guidelines, please feel free to ask the boiler examiner for more information.

If you are planning to build a new boiler please talk to a boiler examiner before starting to ensure that it will meet current standards.

LPG Tanks A reminder that gas tanks need a safety check at not greater than four yearly intervals.

The boiler inspectors are:

Ian Spencer                   Stu Davidson                 Brian Nicholls                          Eddie Gibbons               Gordon Bullard

• Ian Spencer  
• Stuart Davidson
• Eddie Gibbons  
• Brian Nicholls
• Gordon Bullard

DESIGN VERIFICATION

Before construction, the boiler examiner must see the proposed drawings to confirm that the design and materials are acceptable.

SHELL TEST

Boilers constructed by the owner will need to undergo a shell test. A new boiler has this initial test at twice the declared ‘working pressure’. It must be stripped of all cladding and fittings, and all but one of the bushes must be plugged. 

The test pressure will be increased in stages to prevent unnecessary distortion of the annealed copper. The test pressure will be maintained for a minimum of 10 minutes to allow thorough examination of all soldered joints.

Leaks from blanking plugs must be rectified and the test repeated, but any leak from a joint will constitute a fail. Minor distortion between stays will (at the tester’s discretion) be acceptable, but excessive bulging will constitute a fail. The boiler will then be drained into a jug to measure its capacity.

HYDRAULIC TEST (Every Four Years)

Brass fittings must be removed to check for dezincification, but cladding and bronze fittings may (if the owner prefers) be left in si’tu. All fittings except the safety valve are then to be attached.

The test pressure of 1.5 times the declared ‘working pressure’ will be applied in a single stage, and it will be maintained for a minimum of 10 minutes. The tester may require the cladding to be removed if the boiler fails to hold the test pressure.

Any leaks from the fittings must be rectified. 

STEAM TEST (Annually to a maximum of 14 months)

This is performed with the boiler installed in the model and fully operational. No stripping or preparation is required.

The test includes:
Cold examination to be performed prior to steaming the boilerPressure guage to be removed and calibrated against master gauge, then refitted if satisfactory

Boiler to be steamed at maximum firing rate. At maximum rate the working pressure must be maintained through the action of the safety valve.

Pressure must not rise beyond +10% of the working pressure with the engine stopped. Firing rate to be maintained to the examiners satisfaction Gauge glass operation to be verifiedIf fitted, water pump must be seen to be operating No evidence of leaks should be seen 

Refillable Gas TanksRefillable Gas Tanks up to 450cc capacity (tanks above this capacity are not acceptable).
Design Verification:

Before construction, the boiler examiner must see the proposed drawings to confirm that the design and materials are acceptable.

HYDRAULIC TEST  (Every Four Years)

Larger tanks require this periodic test.

The test pressure depends on the fuel mix being used, but is generally:
• 220 psig for plain butane (Blue Calor gas or lighter fuel).
• 380 psig for propane butane mixes up to 40% propane (Camping gas etc).

All but one of the bushes must be plugged, and the test pump, which has a 1/8” BSP male outlet, will be connected to the remaining bush. The boiler examiner must witness the tank being filled with water to ensure the minimum of air remains within.

The test pressure will be increased in stages to prevent unnecessary distortion of the annealed copper. The test pressure will be maintained for a minimum of 10 minutes to allow thorough examination of all soldered joints.

Leaks from blanking plugs must be rectified and the test repeated, but any leak from a joint will constitute a fail.

Minor distortion between stays will (at the tester’s discretion) be acceptable, but excessive bulging will constitute a fail.

Commercial tanks are supplied with a certificate that satisfies this test for the first four years.

GAS TEST (Every Year)

No preparation is required. The tank must have all fittings attached, and be filled with its normal fuel. It is immersed in slightly warm water to check for leaks.

If fitted, the pressure gauge should not be immersed. Any leaks must be rectified.

The owner should regularly check any stop valves to ensure they don’t leak when turned off. The tank must not be stored with gas in it if any leaks are detected (no matter how small they are).

INTRODUCTION  

With effect from 1 January 2006, revised procedures covering the testing and certification of boilers came into effect.  This guidance note highlights the salient points of these procedures but it does not cover every detail.  The full procedures are available for inspection at the Track and it is the responsibility of members who construct or operate boilers to familiarise themselves with the requirements.

SCOPE

The procedures as set out below are applicable to copper boilers up to and including 500 bar litres.To obtain the capacity of a boiler the working pressure in bars is multiplied by the volume in litres – e.g. a boiler working at 5 bars with a volume of 4 litres has a capacity of 20 bar litres.  (1 bar = 14.5 p.s.i.   1 litre = 1.76 pints) 

FREQUENCY OF TESTS 

Under the new procedures the following tests are required:-Hydraulic Test:  On a new boiler and subsequently every 4 years

Cold Visual Inspection:  On a new boiler and subsequently annually

Steam Test:  On a new boiler and subsequently annually (there is no period of grace beyond the expiry date on the certificate)

COMMERCIALLY BUILT BOILERS 

Where a member has purchased a new boiler which has been manufactured and hydraulically tested by a recognised commercial manufacturer, the manufacturer’s certificate for a hydraulic test to twice the working pressure will be acceptable as proof that the structure of the boiler has satisfied the requirements for the hydraulic test. 

A visual examination, a hydraulic test with fittings in place to 1-1/2 times working pressure and a steam test will still be required before the boiler can be certified for use.  Boilers built commercially after 31 May 2002 and not having a CE mark shall not be tested. 

DESIGN

When a boiler has been built to a published design no further verification of design calculations will be required.  The member will be required to submit drawings and calculations to prove adequate margins of safety if;

• The boiler is not to a published design 
• The boiler incorporates changes to a published design
• The working pressure has been increased above that shown on the published drawings
• No working pressure is shown on the published drawings

The regulations also specify other design features which shall be applied to new construction :-

•  A boiler shall have at least 2 independent means of water feed e.g. axle pump, hand pump, 2 injectors. However feed requirements for boilers under 3 bar litres can be via a Goodall valve or the capacity of the gas tank must be such that the fuel must run out before the boiler is empty of water (below the lower nut on the water guage glass).
• Valve spindles shall be captive on new boilers from 1 Jan 2011 – a TSMEE requirement.
• Water gauges shall be independent of any other fittings ( e.g. not taken from the manifold )
• Pressure gauges should have a full scale reading at least 30% above Working Pressure.
• Pressure guages must be marked with a red line at the maximum working pressure

CONSTRUCTION 

All prospective builders must contact the boiler testers before beginning construction to agree possible requirements and the testers shall be given the opportunity of examining a boiler at least twice during its construction.  This is to facilitate the inspection of joints which may not be visible when the boiler is complete. The frequency of intermediate examinations will be agreed during initial discussions.  

 VISUAL EXAMINATION

Boilers will be subject to a visual examination with all fittings in place.  A boiler will be examined visually prior to each hydraulic test.  Subsequent annual visual examinations will take place prior to steam tests annually. The examination will check for defects such as: Mechanical damage;   Wasting;   Loose fittings;   Inoperable valves;   Evidence of leaks.

 HYDRAULIC TESTING

 A new boiler must be hydraulically tested to twice its working pressure.  The initial hydraulic examination must be undertaken without cladding or lagging in place. 

Subsequent hydraulic tests are required at intervals not exceeding 4 years.  The subsequent tests are to one and a half times the working pressure and may be conducted with lagging and cladding in place. 

As part of the hydraulic test procedure the pressure gauge will be tested against the certificated test gauge.  The boiler’s pressure gauge must be accurate at the working pressure. The gauge must be clearly ‘red lined’ at the maximum working pressure.

The test pressure must be sustained for at least 10 mins. and any loss of pressure must be accounted for.

BOILER IDENTIFICATION 

At the satisfactory completion of the initial hydraulic test a boiler will be allocated an identification number.  This number to be stamped on the boiler in a location where it will be visible when the boiler is in use.

STEAM TEST

 A steam test will be conducted on a boiler when new, then annually.  The examination will include verification of the following :-

• Correct operation of at least two independent feed systems
• Operation of safety valves at correct pressure
• Ensuring blower is not capable of raising boiler pressure by more than Working Pressure + 10%
• Correct operation of gauge glass(es)
• Correct operation of pressure gauge. 

STRUCTURAL REPAIRS

When a boiler has been subject to structural repair or modification it will be considered as a new boiler for testing procedures.
 

 EXAMINERS’ AUTHORITY

The regulations permit the examiner to vary the test requirements where he considers this to be appropriate. 

It would be appreciated if members give notice to the boiler inspectors when tests are required.