Frequently Asked Questions (FAQ)

Corrosion Resistant Alloys > Technical Resources > Frequently Asked Questions (FAQ)

Technical FAQs

What does it mean to "meet NACE"?

We are often asked if a material “meets NACE.” In this instance, NACE refers to a document titled NACE MR0175 that was first issued in 1975 by the National Association of Corrosion Engineers, now known as NACE International. NACE MR0175, is titled Petroleum and natural gas industries — Materials for use in H2S-containing environments in oil and gas production. It was issued as a recommendation of threshold limits of H2S above which precautions against environmental cracking are considered necessary. In 2003, MR0175 was adopted by ISO and designated as ISO 15156.

NACE MR0175/ISO 15156 addresses the resistance of materials to environmental cracking that can be caused by H2S. It does not address loss of material by general corrosion or localized corrosion such as pitting or crevice corrosion. It is also not a material specification, in that it does not address minimum mechanical properties, manufacturing processes or quality control requirements such as microstructure and non-destructive examination.

For more information on this topic, please refer to the white paper we’ve provided, What is NACE MR0175/ISO 15156?.

What is galvanic corrosion and is it something that needs to be considered?

Galvanic corrosion occurs when two dissimilar metals are in contact in the presence of an electrolyte. The difference in electro potential of the metals results in a galvanic reaction similar to that in a battery. Because dissimilar metals are often in contact in oil and gas production equipment, galvanic corrosion is a valid concern. Examples of this include mixed tubing strings, CRA tubing or liners in contact with steel casing, nickel alloy accessories in conjunction with stainless tube, etc. For more information on this topic, please refer to the white paper we’ve provided, Galvanic Corrosion.

What is a PREN number? 

PREN stands for Pitting Resistance Equivalent Number. It provides a relative comparison of the resistance of alloys to localized corrosion based upon their chemical composition. Various empirical formulas have been developed for calculation of the PREN. NACE MR0175 requires use of the following the equation:

PREN = CR% + 3.3 x (Mo% + 0.5 x W%) + 16 x N%

To calculate a PREN number using this calculator

What are the standard API OCTG pipe ranges? (R1, R2, R3)

Range 1
Range 2
Range 3
Casing & Tubing Total Range Length, inclusive 16′ – 25′ 25′ – 34′ 34′ – 48′
Maximum permissible variation on 100% on each quantity of 18 t per order item 5′
Pup Joints Length* 2′ ; 3′ ; 4′ ; 6′ ; 8′ ; 10′ ; 12′
Tolerance +/- 0.25
Coupling Stock By agreement
*2′ pup joints may be furnished up to 3′ long by agreement between manufacturer and purchaser, lengths other than those listed may be furnished by agreement between manufacturer and purchaser.

What completion equipment can be manufactured from cold worked nickel alloy tubes?

Cold worked nickel alloy tubes can be used for most any equipment that can be machined from or a tube with 2-3/8*’ to 10-3/4” OD and wall thickness less than 1.35 inches. This includes many downhole components such as polished bore receptacles (PBR), tie back receptacles (TBR), seal bores, extensions, mandrels, blast joints, flow couplings, and shroud casing components within the packer. Cold worked nickel tubes are particularly beneficial for long length parts with a large OD and thin wall. Historically, precipitation hardened (PH)( nickel bars, such as 718 and 925, have been used for such components since those alloys are often readily available from distributors. However with our JIT mill, we can now provide custom near net shape tubes quick enough to reduce the overall manufacturing time and cost of the components. The cold worked nickel alloys may also provide additional metallurgical benefits including higher toughness and hydrogen embrittlement resistance.

For more on this topic, click here to watch a video on downhole completion equipment manufactured with corrosion resistant alloys.

What are the main advantages of using cold worked nickel alloy tubes versus PH bar for the manufacture of downhole completion tools?

Manufacturing downhole completion equipment from cold worked nickel alloy tubes such as CRA 2550E can improve technical performance and quality, improve delivery, improve or maintain standard costs, and reduce risk exposure.

CRA’s cold worked nickel alloy tubes made from CRA 2550E are available in lengths up to 70 feet (21.34 meters) allowing for longer integral part lengths and is a proven metallurgy in downhole production environments. 2550 is an ISO Group 4 alloy approved by NACE and is API 5CRA compliant. It’s mechanical and corrosion properties are comparable to PH bar, and often times even an upgrade. It is capable of being produced to very precise dimensions.

CRA can manufacture cold worked nickel alloy tubes on our mill on a just-in-time basis. Lead times can be as quick as a few days. There is also minimal post mill machining required when you start with a tube rather than bar, positively impacting the overall delivery of the completed part to the customer.

CRA can manufacture cold worked nickel alloy tubes to exact lengths and quantities on our mill, reducing drops and the need for over ordering. Starting with a tube as opposed to a bar also reduces the need to turn, bore, hone, etc. which in turn reduces material waste and machine time, and cost as a result.

In terms of risk reduction, CRA 2550E cold worked nickel alloy tubes are less susceptible to hydrogen embrittlement than PH bar stock, and have pitting and corrosion resistance comparable to 625+ and 725.

For more detail on this topic, please see this video on downhole completion equipment manufactured with corrosion resistant alloys here.

How do Corrosion Resistant Alloys get their strength?

Corrosion Resistant Alloys fall in to two categories; heat treated alloys and cold worked (or cold hardened) alloys. The heat treated alloys are strengthened by either a quench and temper process or a precipitation heat treatment. Martensitic Stainless steels such as 13Cr-L80 are quench and tempered, while nickel alloys such as 718 and 925 are precipitation heat treated. Duplex Stainless steels such as 25Cr and Solid Solution nickel base alloys like G3 and CRA 2550E are cold worked alloys. To see more information on these alloys and others please click here.

What are the various methods of manufacturing cold working (or cold hardened) tube?

There are two primary methods for producing cold worked tube; pilgering and drawing. There are other methods of cold working, but they have limited history in the upstream oil and gas industry where high yield strength material is typically required. Pilgering involves forging the material between a mandrel on the inside of the tube and a pair of rotating dies on the outside. Drawing involves pulling the tube through a tapered die with a mandrel inside the tube such that the material is squeezed between the tapered die and mandrel. To see more about our JIT manufacturing process please click here.

When are corrosion resistant alloys required?

Corrosion resistant alloys should be considered anytime there is the potential presence of water, particularly when combined with CO2, H2S or chlorides.

What are the key factors taken into account when deciding which CRA material to use?

For oil and gas production the following should be considered:

  • Production Environment: short-term & long-term

    • Water cut, bubble point, velocity, pH, & chlorides.
    • Partial Pressures of H2S & CO2
    • Reservoir souring
    • BHT & surface or mud-line temperatures
    • BHP & FTP
    • Contaminants – organic acids
    • Desired project life
  • Annular Environment: short-term & long-term

    • Chlorides – types of clear brines – NaCl, NaBr2, ZnBr2
    • pH, oxygen scavenger, corrosion inhibitor, & biocide
    • Effect of acid gas leaks up the annulus
  • Workover:

    • Acidizing, clear brines without inhibitor & oxygen scavenger, & mixing with sour gases during flow back.
    • Flow back through subsea equipment
    • Shut in conditions
  • Failure:

    • The cost of a quality material design never exceeds the cost of a failure.

Additional FAQs

When was CRA founded?

Corrosion Resistant Alloys, LLC (CRA) was founded on March 1st, 2002 in the energy hub of Houston, Texas. Since CRA was founded, it has evolved from purely a distributor, to a distributor with mill manufacturing capabilities, and lastly to the just-in-time job shop mill manufacturer that it is today. Throughout our journey, CRA has found the niche that affords the industry and their customers the most value. Today, CRA has customers, offices, and representation in both the Western and Eastern Hemisphere. We continue to focus on enhancing our ability to serve our customers and the industry as we look into the future.

How did CRA’s JIT mill manufacturing model come about?

Corrosion Resistant Alloys, LLC (CRA) started as a distributor of high alloy tubulars to the upstream oil and gas industry. Since our founding, CRA has targeted the quick delivery CRA tubular market. However, the way in which we support this market has evolved to better meet the needs of our customers.

CRA has had the opportunity to see the inefficiencies of distribution firsthand. At one point we had the largest CRA tubular inventory in the world, and we constantly struggled to accurately forecast future demands due to cycles in the industry, nickel price fluctuations, and constant specification changes.

Mills typically quote long lead times with the goal of standardizing production and filling capacity, creating the need for operators and service companies to order material for projects months or years in advance. Often times, these orders are placed before the well has finished final engineering, leaving customers with very little flexibility in the event there is an unexpected change. From the time of order placement to the actual need date, we have seen everything from project cancellations to change in well design, to revised deliveries, and a long list of other obstacles. The non-standard quantities, specifications, lengths, and tolerances are often disruptive to the standard mills. When the mills are pressured to accommodate such business for their good customers it creates pressure on their ability to maintain reliable deliveries to their other customers. No one wins in this scenario. CRA’s model alleviates pressure on the standard mills needing to accommodate this business.

The primary purpose of distribution is to service companies that do not have time to wait for material from the mill. Distributors mitigate their risk by stocking standard items. As a result specialized and customer sizes, are rarely available from inventory.

This is where CRA’s just-in-time job shop mill manufacturing model was born. CRA can provide you the exact material size and specification you need, in the exact quantities you need it, in as quick as a few days.

For more information on the JIT advantage click here or the JIT process click here.

What is CRA’s core focus?

CRA’s core focus is just-in-time job shop mill manufacturing of high quality corrosion resistant alloy tubulars. This approach is uniquely tailored to provide non-standard quantities, dimensions, specifications, deliveries, and lengths of OCTG and downhole equipment material that other mills and distribution often cannot offer. CRA’s manufactured products are delivered in a quick as a few days, reducing costs and risks of project delays and eliminating the need for excessive inventories. Manufacturing parts using cold worked tubes, rather than bar, minimizes additional machining costs and lead times and offers technical advantages. CRA combines just in time mill manufacturing with extensive global industry experience to find creative value offerings on every project.

To see more about the products and services CRA is able to provide, please visit our products and services page here.

What is CRA’s manufacturing process?

CRA’s finished tubes are manufactured by traditional methods. The material starts off as an ingot or continuous cast billet. It is then hot worked to achieve a sound wrought structure and converted to a hollow tube shell by hot working or trepanning. The choice of which process route to use is dependent upon several variables including quantity and customer delivery need. The tube shells are annealed to obtain the required microstructure, cold pilgered to the achieve finish size and mechanical properties, straightened, non-destructive/destructive/visual testing, and then final cutting/inspection/marking.

For more information on our just-in-time mill manufacturing process, please click here.

What are typical manufacturing lead times?

Standard OCTG mill lead times can range from 20 to 50+ weeks while bar mill orders can range from 8 to 50+ weeks. Alternatively, CRA’s just in time job shop mill can deliver manufactured tubing and pipe in as quick as a few days. This affords customers more time in the design and engineering phase, helps them mobilize quicker, and reduces costs and risks of project delays. It also eliminates excessive inventory buildups and frees up capital for other opportunities.

To learn more about our JIT process, please click here.

Where are the manufacturing facilities located?

CRA’s operational cold finishing pilger mill is located in Canton, OH in the United States. This mill was manufactured by Mannesmann-Meer in 1967, purchased by CRA in 2008 and is the largest operational cold finishing pilger mill in the Western Hemisphere. It has a size range of 2-7/8″ to 10-3/4″ OD, a max output length of 70’+, and a production capacity of 350,000 lbs/month.

CRA owns two additional cold finishing pilger mills currently being stored in Houston, Texas with plans to be operational in Q3 of 2023. Our new facility currently under construction in Brenham, TX will expand our capabilities, streamline processes, and tripling existing capacities.

Does CRA stock material and if so, what are the typical range of sizes and grades?

Through PipeSearch, CRA has access to over $2 billion in cra OCTG worldwide ranging from 13 Chrome to Duplex Stainless Steel and Nickel Alloy grades in sizes 2-3/8″ – 10-3/4″OD.

To contact us regarding a specific need, please click here.

What are the future plans for CRA?

We will continue to advance our just in time mill manufacturing capabilities to enhance our vision of being the fastest, most reliable, quality provider of corrosion resistant alloy tubulars in the world. Most significantly, this includes a new facility currently under construction in Brenham, TX that will house our additional cold pilger mills and help expand our capabilities. Phase One is expected to be completed in Q3 of 2023. This new facility will streamline processes and triple existing capacities. It is also our goal to expand into other industries such as aerospace, nuclear, refining, defense, and downstream oil and gas. The future looks bright for CRA!