Testing Requirements in the Boiler House
The following test routines are required by the UK HSE (Health and Safety Executive) for a manned boiler house.
External chambers (float or probe type controls)
1. Blow through of the chambers is required, using the sequencing purge valves to remove any
2. Separately, the first and second low alarms are tested.
1. Lower the actual boiler water level to the 1st low (by evaporation), and then blow down to the 2nd low.
The main reason for this weekly test is to ensure that the alarm is given, and at the correct level, when the level drops slowly in the boiler (because floats could stick).
2. A high alarm is usually tested weekly.
Direct mounted level controls with internal protection tubes
A daily test is still required, but this means dropping the actual level, unless test facilities are incorporated. The time involved and the loss of heat, water and treatment chemicals means that this is only really practical in smaller boilers.
The UK regulations for supervision state that, for ‘standard’ (for example, non-self-monitoring, high integrity) controls there must be a trained boiler attendant on site at all times that the boiler is operating.
Testing requirements in the unmanned boiler house
In many countries and in all types of industries, there is a need or desire to run steam boiler plant unattended. This has led to the development of special, high integrity ‘self-monitoring’ level alarms, and controls for increased safety in the event of low water conditions.
For externally mounted float controls, automatic sequencing valves are required, plus a control system which will then carry out automatic sequenced blowdown of the external chambers and electrical testing of the externally mounted boiler level controls (Figure 3.20.2).
Automatic test system for direct mounted float type level controls
With probe type, high integrity, self-monitoring level controls, the ‘self-checking’ facility is carried out via the probe and its associated controller, so a further, special control system is not required. The latest conductivity systems which incorporate a high integrity self-monitoring feature, will check for faults continuously, and electronically.
Faults can include the build-up of scale or dirt on the probe and also any moisture leakage into the probe. If such a fault is detected, the control system will initiate an alarm and cause the boiler to safely shut down.
The main user advantage of these special low water level alarms is not only increased safety but also that daily testing is not necessary. This means that there is little point in fitting high integrity probe controls in external chambers, where it would still be necessary to blow through the chambers, on a daily basis, to remove any sludge.
Probe type, high integrity, self-monitoring low water level alarms are therefore fitted in internal protection tubes.
The manual weekly test must still be carried out under UK regulations. In Germany, where approved probe-type high integrity self-monitoring low water alarms are fitted, the interval between manual tests is 6 months.
Under the UK regulations, if high integrity self-monitoring systems are fitted, supervision requirements are reduced to the need to have someone available to respond to any alarm and call for further assistance. An adequately trained security guard or porter could be considered suitable.
When the low water level alarm systems are housed in external chambers they will require manually blowing down and testing, and this must be carried out at least once per day. In these cases a trained boiler attendant must be on site whenever the boiler is operating including during ‘silent hours’ (nights and weekends).
The trained boiler attendant need not be permanently situated in the boiler house but must be able to respond immediately to the level alarms.
When high integrity self-monitoring low level alarms are mounted in the boiler shell, since they are automatically self-testing, they only require a full operational test by a trained boiler attendant once per week.
When standard low level alarms (floats or probes) are fitted in external chambers, automatic sequencing valves have to be fitted in order for the alarm system to be deemed self-monitoring. A trained boiler attendant need not be on site at all times and another person (watchman or porter) can be put in charge of the boiler instead, as part of his duties during the silent hours.
This person should always be ready to respond correctly to the boiler alarms, shutting down the boiler if necessary. Thus, depending on the type of installation there are two possible types of supervision: A trained boiler attendant (or technician), who must be fully conversant with the operation of the boiler and its controls; or an individual such as a watchman who, although not a fully trained boiler attendant, must be familiar with the alarm protocol and know the procedure for shutting down the boiler.
Testing steam boiler control systems
Any boiler regulations will emphasise that regular testing of any boiler control system, particularly with respect to the water level, is an important requirement. All testing should be carried out with the water in the visible region of the water level gauge.
All testing should be carried out by a trained boiler attendant. In the case of level devices mounted in chambers with manual sequencing valves, testing involves operating the sequencing valves at least once per day to lower the water in each chamber and to test the operation of the water level control, and the controls/alarms at first and second low levels. Similarly for traditional (non-self-monitoring) low water level alarms mounted directly in the boiler, the trained boiler attendant must lower the actual boiler water level every day in order to test these alarms.
However, for high integrity self-monitoring controls mounted directly in the boiler, there is no need for daily testing.
For all types of level control system there is a weekly test to be carried out, and this involves isolating the feedwater supply, lowering the water by evaporation to first low level and blowing down to second low level. This weekly test is a full functional test of the system’s ability to cope with actual boiler water level change.
It is recommended that all tests be properly logged in a boiler house log book, for which the Engineering Manager is responsible.
Footnote: These basic notes are based on UK boiler house practice, rules, and regulations. These regulations vary around the world, some examples follow: