The Problem

Corrosion at pipe supports is one of the leading causes of process piping failures. It is the beam supports and saddle clamps that have historically caused the majority of problems. These have the following undesirable features in common:

• Crevices – the formation of a crevice at the pipe surface.
• Water Entrapment – water is trapped and held in contact with the pipe surface.
• Poor Inspectability and Maintainability – virtually impossible to paint or otherwise maintain; visual and/or NDT inspection are often difficult.
• Galvanic Couples – even when both the pipe and support are steel, the metallurgical differences can still provide enough potential difference to drive a corrosion cell.

The Corrosion Mechanism:

1. Water is trapped.
2. The paint system fails (atmospheric coatings soften in immersion service).
3. Corrosion is initiated.
4. Corrosion undercuts paint film.
5. Crevice corrosion starts.
6. Pipe fails.

Nu-Bolt™ and I-Rod® have been specified on thousands of offshore production platforms since 1987. They simply and economically address the root cause of crevice corrosion by:

• Eliminating crevices.
• Eliminating water entrapment.
• Eliminating metal-to-metal contact.
• Allowing for ease of inspection and maintenance.
• Providing complete support to the piping system.

Designed by corrosion engineers, the Nu-Bolt assembly combines the half round I-Rod support with a modified pipe U-Bolt. A variety of corrosion resistant treatments provide reliable, long term service in the severe operating environments associated with offshore oil and gas production and coastal process facilities.

Polyshrink is applied over the shank of the U-Bolt to protect the paint system during installation. Polyshrink is not designed to protect the U-Bolt. The material is a cross linked, high-compressive-strength, UV Stable polyolefin. It can remain in service in temperatures up to 230 °F (110 °C).

Coatings - The Bolt itself is available in 316 SS, or carbon steel with one of two coatings: Hot-Dip Galvanize, or SermaGard®. SermaGard is a corrosion resistant coating reliable in even the most harsh offshore conditions.

Half Round I-Rod Support - The standard I-Rod material works extremely well for most process piping conditions. In situations with extreme operating temperatures, Deepwater can substitute the more resistant I-Rod HT material. Deepwater has also begun to offer PEEK material for environments that prove too severe for either (though these instances are rather rare).

I-Rod®

I-Rod® is a high-strength thermoplastic rod in a half round configuration. I-Rod is inserted so the round surface interfaces with the pipe.

The half round profile:

• Minimizes contact crevice, and thus eliminates moisture retention.
• Provides a standoff between the pipe and support, and thus:
  - Insulates electrically.
  - Improves maintainability.
  - Improves inspectability.

The high-strength thermoplastic material also:

• Provides excellent compressive strength.
• Is UV stable.
• Has a low friction coefficient, which assists in pipe fitting when used as a beam dressing, and reduces coating damage during new construction.

When used independently as a beam dressing, I-Rod® is typically supplied in 5’ and 10’ lengths.

• Half-round shape:  The I-Rod's half-round shape minimizes contact between the pipe and the support, eliminating the crevice. Keeping water out keeps corrosion at bay.
   
• Maintenance:  The Nu-bolt assembly also provides an electrically isolated stand-off between the pipe and the supporting beam or saddle clamp. This allows for easy maintenance and inspection, while preventing galvanic corrosion between dissimilar metals (the pipe and support).
   
• Durability:  I-Rod also has excellent compressive strength and a very low friction coefficient. Some Nu-bolts have been in continuous operation since 1989 with no reported failures. See the 13-year study on one of the the first platforms to specify I-Rod for all of the structure's pipe supports.

I-Rod Specifications (Standard High Impact Thermoplastic)
 

To assist our customers, we have put together answers to the most frequently asked questions regarding I-Rod pipe support systems.

The photos below were recorded during a routine topside inspection of an offshore structure that was installed in 1989. This was the first offshore structure where the I-Rod system was specified for new construction. The total added cost of this system was less than $10,000. The photos demonstrate the success of the system, which has subsequently been used on thousands of offshore structures.