Introduction

Wireless Instruments in Hazardous Location

This article examines the impact of implementing wireless instruments in hazardous location or harsh corrosive environment.

Corrosion causes damage across connections and contacts
  • Client

    Control Systems Engineer

  • Services

    Measuring instruments

  • Technologies

    Wireless

  • Dates

    04/12/2017

Description

Oil & gas, petrochemicals, chemicals and other process industries often face the problems of electrical downtime, total disruption of electrical service, erratic behaviour of instrumentation system, input/output (I/O) cards loss in DCS and ESD systems, increased resistance across the connection and contactor results in false data transmission through the instrument data cable to the system, due to open or intermittent connection of the power cable or instrument data cable.

Wet, salt-mist, dirty, dust contaminated or corrosive vapours containing and saliferous plant environment increase the risk of corrosion and chemical vapours attack on the metals used in wire terminal connections, switches, and contactors.

Wiring connection has been also affected due to creep corrosion and metallic dendrites causes, due to the reaction of corrosive vapours with the metal of connector at high or variable humid condition.

Effects of corrosion on wiring systems

All instruments wiring system or cable infrastructure have a tendency to undergo a chemical corrosive reaction with different industrial reactive gases/vapours (sulphur, chlorine, etc), and its elemental compound (sulphide, chloride, etc). The harsh corrosion reactive plant environment requires detailed engineering design of appropriate corrosion control measure to avoid unnecessary electrical downtime, planned/unplanned maintenances and inspections costs, due to corrosion induced failures of instrumentation and control systems. The effects of humidity and temperature are also a major impact on the rate of corrosion and chemical attack on the metals of the instruments wiring system.

Typical corrosion related issues found in wiring system as shown in Fig.1, during inspections in corrosion reactive harsh environment, includes:

  • Incorrect or damaged cable gland
  • Damaged cables
  • Corroded terminals, switches, and contactors
  • Corrosion occurs across the connection and contactors result in increased resistance, and
  • Corrosion fatigue failure of terminals.

Fig 1. The picture shows the corroded wiring terminals and damaged cable caused by long-term corrosion effects.

Instruments wiring system or cables infrastructure affected by short/long-term exposure to corrosion reactive display a variety of typical behaviour patterns are following as:

  • Electrical shutdown or total disruption of electrical services, due to short/open circuits
  • Unexplained loss of input/output section of decaying of operational circuit
  • Input/output (I/O) cards loss in DCS and PLC, data reading and transmission problems, and erratic behaviour occurs, etc
  • All the terminals, leads, switches and electrical contractors, become corroded and reduce the conductivity of the metals
  • The connection of the data/power cables inside the junction boxes located on the field and marshalling or system cabinets located in local equipment/control rooms are affected, due to which resistance increases across the connection and contactors, results in false data transmission through the cable to the system, and
  • In the presence of harsh corrosive environment and vibration assist in the formation of corrosion fatigue cracks in the terminals leads, thus leading to wiring system failures.

Additionally, non-corrosion related stress in wiring infrastructure may also impact the measurement quality including crushed cables, excessive length, mechanical fatigue, poor gladding, cable routing complexity, routing between moving components, supporting the weight, grounding, etc.

Traditional Vs. Alternative approaches

Traditional Approach

The simplest method to prevent, minimize or control the risk of corrosion and chemical vapours attack in corrosion reactive harsh environment are:

  1. To keep instrumentation systems out of the area altogether; and
  2. To make the area less hazardous or less reactive with controlled humid and temperature through process improvements.

But when instruments must be required to install in corrosion reactive harsh areas(such as waste gas treatment and sulphur handling area etc.), then all the instrument wiring system or cable infrastructure such as instruments and multi-core home run cables, main and intermediate junction boxes, conduits, main and branch cable trays, termination racks, cable tray supports, panels and enclosures, multi-cable transit (MCTs), and system or marshalling cabinets must be safely installed and maintained to the pertinent or suboptimal standards to prevent deterioration process of metals used in instrument wiring system.

The expense of protecting and installing of instrument wiring systems or cable infrastructure can significantly add to capital expenditures and requires an additional operational maintenance cost of preventing, minimising or controlling the rate of corrosion to ensure that the protection level is being maintained.

Alternative Approach

An alternative method uses wireless instrumentation systems instead of traditional wired instruments. Wireless infrastructure is the new possibility to avoid these entire instruments wiring system related problems, expenses, corrosion-related inspections and planned/unplanned maintenances.

Oil & gas companies and operators are increasingly looking for the new ways to make existing processes more efficient by eliminating waste and reducing fixed costs and hassles associated with installing, altering, or expanding wired infrastructure. These include instrument wiring systems or cable infrastructure and labour costs as well as lost time and productivity. Additionally, whereas a wired system can require substantial changes to infrastructure, wireless instrumentation can dramatically cut costs in instrument wiring systems throughout the project life cycle, including increased data-gathering flexibility, as well as allow for easier future expansion.

Significant impacts of wireless instruments

Implementation of wireless instruments to oil & gas, petrochemicals, chemicals and other process industries provides various effective characteristics such as robustness, real-time fast response, reduce time-consuming installation process, remove wiring infrastructure and lower power consumption. It has been observed significant impacts of implementation in wireless instruments over wired instruments in unclassified areas of the process plant, hazardous location or harsh corrosion reactive environment. Wireless instruments can be viewed from engineering/design and construction/fabrication point of view. These are major impact areas, not only for clients but also for EPCs, other contractors, and vendors.

Engineering/Design Impacts

Application of the wireless instrumentation in process plant is having many positive impacts on project engineering such as lower installation costs, quicker installation time, faster commissioning, more efficient change order management, removal of requirements for power supplies and protection barriers with unique power replaceable battery packs, increase system/vendor compatibility, device and system compatibility, removal of redundant equipment, ease of self- or remote-diagnosis and faster or real-time responses. In addition, extension of plant systems and moving or adding I/O points during construction would be easier without the need for unit or application downtime Implementation of wireless instrumentation may reduce project engineering/design costs through:

  • Reduced materials weight (instrument wiring system or cable infrastructure)
  • Reduced system design-time requirements
  • Reduced change request and change order management
  • Less piping and electrical work for cable routing
  • No 3D modelling for cable tray routing, trays and supports, location and design of junction boxes, and local panels, conduits, sleeves, etc
  • Less time and effort for installing cable infrastructure such as instruments and multi-core, home-run cables, main and intermediate junction boxes, conduits, main and branch cable trays, termination racks, cable tray supports, panels and enclosures, multiple cable transits (MCTs) and system or marshalling cabinets, and
  • Less material consideration based on area classification and protection.

Wireless instruments can be configured and reconfigured without being exposed and/or connected to test terminal leads in hazardous or harsh corrosive/reactive environments.

Deliverable/Document Impacts

Implementation of wireless instrumentation in the harsh corrosive environment also creates impacts on the engineering/design documents and construction/fabrication deliverables. The engineering/design documentation effort can also considerably reduce by reducing requirements for:

  • Cable schedule, cable schematic diagram, cable philosophy diagram and logic diagram
  • Junction box loading
  • Loop/segment diagrams
  • Wiring connection schedule, wiring reports (intermediate and main junction box, marshalling and shield bar reports)
  • Design index (database for wiring system detail) and specification sheet for cable/junction box
  • Cable electrical detail and junction box standard installation detail drawing
  • Enclosure and equipment room layout drawing
  • Cable tray routing plan and cable tray support detail drawing
  • Multiple cable transit (MCTs) layout drawing, and
  • Documents related to effecting devising for corrosion control.

Conclusion

Authors have concluded that wireless instrumentation is a cost-effective solution for corrosive plant environment. They provide inexpensive, easy-to-install measurements in unclassified areas, and can also be implemented in hazardous locations and harsh, corrosive and reactive environments. Along with the savings described above, advantages in hazardous or corrosive/reactive harsh environments include eliminating hazardous area-rated or chemical/corrosion-resistant conduits, wiring and junction boxes, as well as the need for corrosion control measures or breakdown costs due to corrosion induced failures.

About the Authors

Sheikh Rafik Manihar Ahmed, Control Systems Engineer and Innovation Catalyst; Kuleesha Mahajan, Area Lead for Control Systems Engineer; and Arun Garg, Control Systems Engineer. All are working at Fluor Daniel in New Delhi.

Captions:

Fig 1. The picture shows the corroded wiring terminals and damaged cable caused by long-term corrosion effects.

Pix 2: Corrosion damage wires in harsh environment.

Pix 3: An example of wireless instruments. Photo credit: ABB

Author

Arun Garg,

Arun Garg, Control Systems Engineer

Related