What is ASTM A691 5CR Pipe?

ASTM A691 5CR is a chrome-moly alloy grade for electric fusion welded pipe. The 5CR designation means 5% chromium content paired with 0.5% molybdenum. This chemical composition resists oxidation and sulfidation at high temperatures far better than standard carbon steel or lower chrome grades. The chromium forms a protective oxide layer on the pipe surface. This layer prevents scaling when the pipe faces temperatures above 500°C. Molybdenum provides creep strength. The pipe maintains its shape under load at elevated temperatures instead of slowly deforming.

We supply this grade for refinery heater piping, catalytic reformer circuits and high-temperature process lines. When 2.25CR or 3CR cannot handle the service conditions, 5CR becomes the preferred choice.

Chemical Composition of ASTM A691 5CR Pipe

The 5CR composition gives the pipe its high-temperature capabilities. Here is the chemical composition of the alloy:

Designation C Mn P S Si Cr Mo
ASTM A691 5Cr 0.15 0.30-0.60 0.025 0.025 0.5 4.00-6.00 0.45-0.65

Applications of ASTM A691 5CR Pipe

The 5CR grade is used in 2 major industries that operate at elevated temperatures and need good oxidation resistance.

Refinery Heaters

Fired heaters in refineries push temperatures past what 2.25CR can handle. The tubes and transfer lines face direct radiant heat from burners. Scale formation becomes a major problem at these temperatures. The 5% chromium content keeps the oxide layer intact. We supply heater outlet piping and convection section tubing for crude units and vacuum units.

Chemical Plants

High-temperature hydrocarbon service demands material that will not scale or lose strength over time. Catalytic reformers and hydrotreaters operate in this range. The 5CR grade handles hydrogen-rich environments at elevated temperatures. Process piping between reactors and heat exchangers often specifies this material.

Frequently Asked Questions

  • What is the advantage of 5CR over 2.25CR?

    Higher chromium means better protection against oxidation and sulfidation. At temperatures above 593°C (1100°F), the 2.25CR grade starts to scale faster and the oxide layer breaks down. With 5CR, you get roughly double the chromium content. This keeps the protective layer stable at higher temperatures. If your service runs between 593°C and 649°C, 5CR is the safer choice. Below 593°C, 2.25CR usually does the job and costs less.