What is ASTM a691 grade 9cr pipe?
The American Society for Testing and Materials has specifications for metallic pipes. The specifications denote the mechanical, physical and chemical properties of the pipes. There are different metallic compositions used to make piping products. The ASTM A691 Grade 9CR Pipe is such a specification for chromium molybdenum alloy metals that perform at high temperatures and pressures.
What are the classes of a691 grade 9cr alloy steel efw pipes?
The pipes of any particular specification can be further divided into grades based on the compositional difference. The grades are then classified under different classes based on their heat treatment methods. The ASTM A691 Grade 9CR Alloy Steel EFW Pipes have over 25 different classes starting from class 10 and running up to class 73.
There are normalized, quenched, tempered, precipitation heat-treated, and stress-relieved classes. The  ASTM A691 9CR EFW Steel Pipes get their different mechanical abilities and hardnesses based on the heat treatment. So the different classes can perform differently with their ductility and hardness based on their heat treatment, although they all have the same chemical composition.
ASTM a691 9cr vs 2-1/4cr pipe
Even though the specification mandates a chromium and molybdenum mixture in the composition, the ratios differ from grade to grade. The ASTM A691 9CR Pipe has 9% chromium and 1% molybdenum in the composition. But the 2-¼ cr pipes have only ⅖% chromium. This makes the ASTM A691 9CR Alloy Steel EFW Pipes stronger and harder. The latter has 241 HB hardness. Both grades have the same tensile strength ranging from 515MPa and the same minimum yield strength of 310MPa.
Why a691 9cr chrome moly pipes suitable for high-pressure service?
Chrome moly pipes are meant for high-pressure and high-temperature services. However, their diameters make a difference in the production mechanism. The diameters range from ⅜ inches to 36 inches. The pipes below 12 inches in diameter can be cold drawn from a single billet of the metal. The cold-drawn A691 9cr chrome moly pipes can withstand much pressure without leaking. However, the ones larger than 12 inches in diameter are made from hot rolled pressure quality plates through electric fusion welding.
The welded pipes have relatively less strength at the welded joints. The ASTM A691 GRADE 9 CR Alloy Steel Pipes that are larger in diameter don’t perform as high as the small diameter pipes, when it comes to high pressure because of the welded joint.
Which filler metals are used to weld ASTM a691 9cr efw steel pipes?
Filler metals are used to make sure that the welded groove does not make the welded point weaker in the Alloy Steel A691 9CR EFW Pipes. So the choice of filler metal is always as equal in strength as the base metal, or slightly stronger than the base metal. For the chrome moly pipes, any filler metal that is equal or stronger can be used. The Alloy Steel A691 9 Cr Welded Pipes can be welded with other alloys or nickel.
What is ASTM a691 grade 9 cr alloy steel pipes galvanized process?
The galvanization process is done by coating a metal or alloy with another metal that is less reactive and acts as a barrier to oxide formation and corrosion. The ASTM A691 GRADE 9 CR Alloy Steel Pipes are dipped into a hydrolysis chamber where the galvanizing metal is electrostatically dissolved into the liquid and then precipitated on the surface of the base metal.
