Selecting the Best Piping Supports in Oil and Gas

In my 20 years of designing piping systems for offshore platforms and onshore refineries, I have seen how a single poorly selected support can shut down an entire facility. I remember a project where a rigid shoe support was mistakenly installed instead of a variable spring hanger on a high-temperature steam line. Within three weeks, the thermal expansion forced the pipe upward, overloading a pump nozzle and causing a major hydrocarbon leak. That incident drove home a fundamental truth: piping supports are not passive steel brackets; they are dynamic structural elements that dictate the safety of the entire plant.

Selecting the correct support requires a deep understanding of thermal displacement, static weight distribution, and dynamic forces. In this guide, I will share my field-tested insights into classifying, designing, and installing these critical components to ensure your piping systems remain safe, compliant, and highly reliable.

Designing Piping Supports in Oil and Gas

When designing piping systems, we classify supports into three primary functional categories: rigid, elastic (spring), and dynamic. Each category serves a specific purpose in managing the forces exerted by the piping system on surrounding structures and equipment.

1. Rigid Supports

Rigid supports prevent movement in specific directions without allowing any deflection. They are the most common supports used to carry deadweight loads.

• Anchors: Restrain all six degrees of freedom (three translational and three rotational). They are used to split piping systems into independent thermal expansion sections.
• Guides: Restrain lateral movement while allowing axial sliding. These are essential for preventing buckling in long pipe runs.
• Shoes: Metal attachments welded or clamped to the bottom of the pipe. They elevate insulated pipes above structural steel to prevent insulation damage and allow sliding.

2. Elastic (Spring) Supports

When a piping system undergoes significant vertical thermal expansion, rigid supports can cause massive thermal stresses or lift off completely. In these scenarios, we use spring supports.

• Variable Spring Hangers: The supporting force varies with the spring deflection. They are typically used when vertical movement is moderate (under 50 millimeters) and the load variation is acceptable.
• Constant Spring Hangers: These maintain a constant supporting force throughout the entire travel range. They are mandatory for critical piping connected to strain-sensitive equipment like steam turbines or compressors.

3. Dynamic Supports

Dynamic supports protect piping systems from sudden, transient loads such as water hammer, steam hammer, wind, and seismic events.

• Snubbers: Hydraulic or mechanical devices that allow slow thermal movement but lock up instantly during rapid dynamic events to restrain the pipe.
• Sway Braces: Spring-loaded devices that provide an opposing force to control steady-state vibration.

Thermal Expansion and Spring Rate Calculations

To calculate the thermal expansion of a carbon steel pipe, we use the linear expansion formula:

dL = L * alpha * dT

Where:
– dL is the total thermal expansion in millimeters.
– L is the length of the pipe run in meters.
– alpha is the mean coefficient of thermal expansion for the material (for carbon steel, this is approximately 0.012 millimeters per meter per degree Celsius).
– dT is the difference between the operating temperature and the ambient installation temperature in degrees Celsius.

For a 100-meter run of carbon steel pipe operating at 250 degrees Celsius with an installation temperature of 20 degrees Celsius, the expansion is:
dL = 100 * 0.012 * (250 – 20) = 276 millimeters.
Managing this 276 millimeters of movement requires a carefully engineered combination of expansion loops, guides, and spring hangers.

The spring rate (K) is determined by dividing the operating load (F) by the thermal travel (x):

K = F / x

According to ASME B31.3, the variability of a variable spring hanger must not exceed 25 percent. Variability is calculated as:
Variability = (Operating Load – Preset Load) / Operating Load * 100
If the variability exceeds 25 percent, a constant spring hanger must be specified instead to prevent excessive load transfer to adjacent equipment.

Installing Piping Supports in Oil and Gas

Proper installation is just as critical as correct design. If a support is installed incorrectly, the stress profile of the entire piping system changes, which can lead to catastrophic failures. Use this checklist during your next field walkdown to ensure compliance with MSS SP-89.

Field Case Study: Real-World Application

I highly recommend performing a dynamic modal analysis during the design phase for any piping system connected to reciprocating machinery. Relying solely on static stress analysis often leads to under-designed support systems that fail under real-world dynamic loads.

Frequently Asked Engineering Questions