Designing Connectors for the Harshest Environments
Applications that routinely experience harsh-environment conditions require connector solutions with the appropriate materials, shells, contacts, ingress protection rating, standards compliance, and assembly features.
By Steve Smashey, President, SOS Engineering, Inc.; Mike Conte, General Manager, SOS Engineering, Inc.; and Randy Cameron, Director, Technical Services, Inova Geophysical
Designing connector solutions for the harshest environment conditions is no easy task. Harsh-environment applications command a wide range of design requirements that must be met to ensure reliable performance over time. Harsh-environment connectors are available in a broad array of shell styles, shapes, and sizes with different materials and assembly types to meet these various application demands. Many harsh-environment connectors even surpass the specifications required for military applications, including those used for oil and gas exploration, recovery, and refining. However, all harsh-environment connectors start by combining heavy-duty materials and a rugged design with highly reliable contacts, durable shells, and a robust assembly.
Oil, Gas, and Petrochemical Applications
Whether used on offshore oil rigs or on land, connectors designed into oil and gas equipment must withstand rugged environmental conditions, including extreme temperatures, high pressure, shock, vibration, moisture, dust, dirt, and other contaminants. For oil and gas exploration, recovery, and refining applications, connectors must be rated to withstand the following environmental conditions:
- Saltwater depths up to 30 meters
- Freshwater depths up to 125 meters for 24 hours (mated)
- Freshwater depths up to 5 meters for 24 hours (unmated)
- Operating temperatures extending from -55°C to +70°C
If designed correctly to meet these specifications, connectors will have an ingress protection rating of IP67 or IP68. If these specifications are not met, contact failures can cause costly damage to capital equipment and even loss of life. Below are several key design considerations that ensure connectors meet harsh environment standards.
High-quality electrical contacts (i.e., pins and sockets) are the foundation of any high-performance connector. Electrical contacts play a vital role in the integrity and reliability of signal transmissions, and especially so in harsh environments like oil and gas exploration, recovery, and refining equipment. Robust contacts leverage high-quality materials and terminations to meet rugged application requirements.
Higher quality materials produce higher quality contacts. Copper alloys are typically sourced for sockets used in commercial applications. For harsh environments, copper alloys are commonly used for their high resistance to corrosion. Leaded-nickel-copper and beryllium copper are also ideal materials for rugged contacts due to their tensile strength and durability.
Pin carriers are often made out of Valox 412E thermoplastic polyester resin. This is a semi-crystalline material based on polybutylene terephthalate (PBT). Valox 412E combines high mechanical, thermal, and electrical properties with very good chemical resistance to a variety of chemicals, including aliphatic hydrocarbons, petrol, oils, greases, dilute acids and bases, detergents, and most aqueous salt solutions.
Plating materials are also vital to the performance characteristics of a connector contact. Materials are chosen for several performance characteristics, including corrosion resistance, electrical conductivity, thermal conductivity, solderability, wear resistance, operational life, and infrared reflectance (IR). For harsh environments, heavy gold plating of at least 50 micro inches is typically required. This plating meets MIL-G-45204 plating specifications for corrosion resistance from mud, dirt, moisture, salt spray, and other contaminants. Gold also provides excellent electrical conductivity, thermal conductivity, solderability, wear resistance, and operational life, and thicker gold plating increases the number of mating cycles. Gold-plated contacts are used in many harsh-environment applications to maintain low contact resistance over time because gold is resistant to oxidation.
Selective gold plating has become a very cost-effective way to plate electrical contacts because it uses less gold without reducing the functionality of the contact. Selective gold plating is often used for commercial applications, as are other plating materials, including silver, copper, nickel, and tin.
To further protect contacts, a non-corrosive stainless-steel hood is often used and typically implements a rounded lead-in to ensure proper male pin alignment.
After plating, contacts ruggedized for harsh environments should be selectively textured to improve bonding with the rubber during the overmolding process. Selectively texturing a contact before bonding removes impurities and creates a rough surface to ensure proper adhesion and significantly increase the strength of the bond, which is especially important for contacts used in harsh environments.
Harsh-environment connector designs must ensure that moisture and other contaminants cannot seep into the interior of the contact along the path where the overmold material adheres to the metal contact. Silicone is typically used as the primary sealing compound. One special technique is to bond the contacts in neoprene high-performance rubber, which offers excellent moisture and heat resistance up to 70°C. Silicone rubber is widely used and can often be used as one- or two-part polymers with fillers to improve properties or reduce cost. Silicone rubber is generally non-reactive, stable, and resistant to extreme environments and temperatures extending from -55°C to 70°C while still maintaining its useful properties.
For the most demanding applications, like oil and gas exploration, recovery, and refining, a two-shot overmolding procedure is often used to deliver a higher level of rigidity and sealing, and ensure that the connector is water- resistant to depths of up to 125 meters for 24 hours when mated and to depths of up to five meters for 24 hours when unmated.
Ruggedized Connector Shells
Connector shells can be made out of a wide range of materials to meet application requirements such as durability, weight, corrosion resistance, and cost. Depending on these requirements, thermoplastic housings and die-cast metal shells may be used to withstand demanding conditions. Durable thermoplastic housings are lighter and more cost-effective than metal housings. They are also corrosion-resistant and thus don’t require a protective coating.
Metal housings are more rigid and will hold their shape better under greater forces than even the toughest plastic housings. Metal housings also offer higher thermal resistance. Aluminum 6061-T6 is often used for the shell material in oil, gas, and petrochemical applications. To protect from corrosion, a Type II Class 1 sulfuric acid anodizing is used to coat these aluminum connector shells with a minimum thickness of 0.4mm (10 microns).
A cable grommet is a tube or ring made of rubber, plastic, or metal, through which an electrical cable passes. These grommets seal cable connections so water cannot seep into the back end of the connector.
Applications that routinely experience harsh-environment conditions, like shock, vibration, dirt, dust, moisture, and high pressure, require connector solutions with the appropriate materials, shells, contacts, ingress protection rating, standards compliance, and assembly. There are many design factors that go into the development of harsh-environment connectivity solutions. From the contacts to the shell, all connector elements must provide rugged, durable performance to meet the demands of the application. In harsh-environment applications like oil and gas exploration, recovery, and refining equipment, only the highest quality designs, materials, and processes can ensure long-term connector performance and operation.
For more information, visit SOS Engineering online.