5. Making sure that the network is safe and easy to operate and maintain

Safety is extremely important in steam systems as steam owing to its pressure and high temperature can be hazardous if not handled property.

While effective drainage of condensate from the distribution network can help to prevent water hammer, there are other aspects that should also be considered to make the steam system safe.

5.1 Ensure ergonomics during design and installation of steam systems:

Our observations indicate that key issues in the steam distribution network are often due to poor ergonomics which hamper visibility, accessibility and usability, Often in plants we find that analog / digital displays are installed where they are not easily visible, not enough space is provided to access equipment or accessories for maintenance and critical accessories like isolation valves are located in hard to reach places. Such issues severely hamper plant personnel from being able to run the system in a safe, efficient and reliable manner.

While installing steam pipelines and accessories care should be taken to ensure the following:

Visibility:

Diagnostic displays like pressure gauges, temperature gauges, digital displays, etc. should always be installed in such a manner that they are easily visible to the operator at all times.

Accessibility:

While designing the system and installing pipelines and accessories care should be taken to factor in space required for personnel and tools for maintenance / repair, e.g. Pressure Reducing Stations, Pressure Reducing Valves, Control Valves, On-off Valves, distribution traps should be located at ground level. Working platforms should be provided to enable safe and easy access if accessories are located at a height.

Usability:

Key accessories which require frequent operations or operations during an emergency, like isolation valves should always be located at working height (see Illustration alongside).

Provide steam distribution lines with expansion loops:

Metal pipes, when subjected to temperature variations, expand or contract longitudinally and around their circumference. The lines are subjected to very high temperatures when steam is charged in the lines, causing them to heat up and expand. Similarly when steam to the pipeline is shut off, the lines cool down and contract. If there is no provision to allow for free expansion to occur, excessive stresses in the lines can result in damage or displacement.

Expansion loops accommodate and effectively direct free expansion of the lines. The expansion / contractions are controlled effectively to prevent excessive stresses in the line.

The recommended installation for expansion loops is illustrated below.

The expansion loop is located at the center of two anchor points. The guide supports are placed at a distance of 750 mm from the expansion loop. The length of pipe between a guide and anchor support should be supported by a rest support depending on the pipe span.

Provide isolation valves at strategic locations in the network
Steam systems should be provided with isolation valves to meet three key requirements:

Flexibility in process operations:

Enabling the plant to shut off steam to equipment, processes and sections when not in use.

Ease of maintenance:

Leak proof isolation to enable easy and safe maintenance in the plant at a device, equipment or process block level.

Safety:

Enabling isolation and quick shut down of specific equipment or sections within the plant in case of emergencies, thereby preventing incidents / further harm to personnel and equipment.

Several types of valves available for isolation. However, piston valves are the best choice for steam and condensate applications (see the comparison table below).

Isolation valves in the steam system should be provided at the following key locations :

• Main steam stop valve at the boiler outlet
• Header side of the steam supply line from the boiler to the main header
• Header side of the steam supply line from the main header to sections in the plant / production blocks
• Al the battery limits of the plant/production block (this is required in case more than one production block / section is catered to by the same main line)
• Steam branch lines to the individual process equipment (where more than one equipment is supplied steam from the same branch line, an isolation should also be provided for each equipment at the connection point of the equipment)
• Isolation for pipeline accessories like steam traps and control valves to facilitate maintenance

Provide safety valves at strategic locations in the network

Safety valves are an essential component of steam systems and are provided in the network to prevent potentially hazardous incidents involving personnel or plant equipment.

Process equipment, steam pipelines and accessories are designed to safely handle a specific pressure. Pressure build-up in the steam system beyond the design pressure of the equipment, pipelines or accessories, can cause failure. Safety valves installed in the system automatically operate to relieve the pressure, preventing accidents.

Safety valves should be installed at any location in the steam system where pressure build-up could pose a risk to personnel and the plant.

Below are some key areas where safety valves should be installed:

• On the boiler.
• On steam headers within the boiler house and process blocks.
• As part of the pressure reducing station.
• On process equipment like reactors to relieve pressure within the equipment, and on process equipment with large steam spaces like autoclaves.
• Regular testing of the safety valves should also be carried out to ensure that they are functioning property.

Safety valve outlets should be routed to a safe location

In the event of a pressure build-up in the system, safety valves operate and vent steam.
Safety valve outlets should always be routed to a safe location, to prevent accidental contact of vent steam with plant personnel.

Provide main line steam traps with diffusers

Thermodynamic traps discharge large quantities of hot condensate intermittently. When these traps are left open to discharge to the atmosphere they pose a safety hazard as hot condensate is discharged as a blast.

A diffuser is a compact unit designed to be fitted at the outlet of the thermodynamic steam trap discharging to the atmosphere. It dampens the velocity of condensate discharge, thereby eliminating the blast of condensate making it safer for plant personnel in the vicinity.

The diffuser also addresses other problems associated with the blast discharge from thermodynamic traps like noise and erosion of the ground.

Carry out flexibility analysis or stress analysis of steam pipelines especially high pressure pipelines and superheated steam pipelines

Steam pipelines can be subjected to high pressures and temperatures resulting in stresses/moments and expansion movements.
Stress analysis helps to predict the stress and expansion movement that would occur in the cold and actual running conditions (pressure and temperature conditions).
Types of supports are then defined to ensure that these forces and moments are within limits to ensure safe steam distribution.