With sustainability such a hot topic, it’s little wonder so much attention has been given to highly visible and energy hungry items; but in many instances, invisible energy leaks such as steam are taking a toll. Hans de Kegel of AVT Reliability suggests businesses take a planned approach to help save energy and money.
In steam systems, a 3mm orifice under a pressure of 7bar (100psi) can result in the loss of 25 tonnes of steam every year.
If leaks continue to be ignored, not only can the drop in system pressure lead to lower operating efficiency, but over time the corrosive power of steam can cause equipment failure, resulting in expensive repairs or even replacement.
There is also the risk of accident and potential liability. The Health & Safety Executive’s Pressure Systems Safety Regulations 2000 aims to prevent serious injury resulting from the failure of a pressure system or one of its component parts.
This includes stringent guidelines covering the use of materials, the application of safety devices and the need for a suitable maintenance program, which is perhaps the lynchpin of this whole subject.
Planned maintenance can go a long way towards eliminating the damage caused by leaks, but at present there is no commonly accepted standard practice.
This may be because leaks haven’t been given the focus and attention they deserve, or because steam leaks can occur in a variety of locations, including valve stems, pressure regulators and connection flanges pipe joints, adding to the complexities of detection.
One of the most common locations for leaks is in a steam trap, an essential component of any system. Because of their critical importance, it’s worth exploring in more detail.
There are three basic types of steam trap – all classified by ISO 6704:1982:
- Thermostatic traps react to changes in steam temperature, and will pass condensate when lower temperatures are reached.
- Mechanical traps – which include float and bucket traps – sense and respond to changes in the difference in density between steam and condensate.
- Thermodynamic (disc, impulse and labyrinth) traps are operated by changes in fluid dynamics and rely partly on the formation of flash steam from condensate.
Combined with other variations – including continuous flow, intermittent or fixed – it’s clear that a broad spread of technology exists, each presenting unique challenges in terms of diagnosis and maintenance.
Surveys test and document the operational status of steam traps, utilising both ultrasound and temperature differentials, and create a comprehensive trap inventory including location, type, and application engineering. Survey reports also include a full economic analysis to determine ROI, as well as recommendations for specific improvements.
Typically, industry takes three broad approaches to aid accurate diagnosis of steam trap leaks, each of which can be highly effective in the right conditions:
- Visual inspection – the use of a testing-tee arrangement, test cock, or an inline sight glass for reviewing the steam trap discharge to the atmosphere can accurately determine: blow-by steam or a failed open condition; severe steam leakage; improper installation; under-sizing; incorrect type, and incorrect installation practice. This demands an in-depth understanding of the difference between flash steam and blow-by steam, but can expose the technician to the potential and damaging release of hot steam. Though a relatively low-cost option, even visual inspections involve a small additional cost associated with installing the components that permit online visual testing.
- Thermal measurement – the pressure/temperature relationships of steam means that temperature measurements can be extremely helpful in establishing existing steam system pressures, while thermal tests include infrared thermography, contact thermal recorders (thermocouples), and infrared point radiometers (pyrometers). Each has unique pros and cons.
- Acoustic/ultrasonic inspection – providing a versatile and accurate steam system diagnostic tool, ultrasound devices are a simple method of testing steam trap stations and are extremely accurate in detecting the distinctive high frequency noises made during the proper operation of a steam trap.
The sensitivity of most high frequency monitoring equipment allows the testing person to hear not only completely failed steam traps (blowing steam), but even leaking steam from a trap in operation.
Knowing what to look for – and listen to – and what subtle variations mean will significantly reduce the chances of misdiagnosis, and so the experience of the technician is therefore critical.
The range of traps available, coupled with the sheer size of many steam operations and the complexities of detection, mean that it is not uncommon for leaks to be missed or misdiagnosed.
This may lead to faulty traps being left in operation and/or functioning traps being replaced. The net result is the same: more lost energy and more unnecessary expense on energy waste.
While undertaking any form of survey is good, a best practice approach may be to take a preventative rather than cure approach. Key to this is the introduction of a planned programme with a clearly defined schedule of steam trap survey routes – ideally on a quarterly basis.