API 6A CRA is a supplement to API 6A that covers a group of high-performance, age-hardened nickel alloys, including Alloy 718, Alloy 725 and Alloy 925, as well as Alloys 716, 935 and 945. From a material supplier's perspective, it covers the most relevant aspects of a metal's properties: production route, chemical composition, mechanical properties, microstructure and test conditions.
Who publishes it?
API is the American Petroleum Institute. Formed in 1919, the trade association promotes safety across the global natural gas and oil industry. One of its main activities is bringing together subject matter experts to develop and maintain standards that cover materials and operational practices.
What does API 6A cover?
API 6A is a large document, over 400 pages, covering all aspects of materials specification for wellhead and Christmas tree equipment. It details the requirements for specific components such as tubing and casing hangers, valve bodies and bonnets, stems, lock screws, flanges, hubs, clamps and connectors, along with identification and marking of components, general dimensional control and operational parameters.
What we supply
We stock a number of these very high-strength nickel alloys, certified to both the relevant API standards (API 6A and API 6A CRA) and NACE (MR0175 / ISO 15156-3). In every case, these alloys develop their high strength through a secondary ageing heat treatment.
How these alloys develop their strength
In all cases, these alloys develop their high strength through a secondary ageing heat treatment. After solution annealing and quenching, they are aged by holding at around 700°C for several hours. This precipitates very fine particles throughout the microstructure, which help to pin grain boundaries in place and thereby strengthen the alloy. The precipitates are created by alloying each grade with small quantities of niobium, titanium and aluminium, which combine with nickel.
The grades we stock
Alloy 718 (UNS N07718, ASTM B637, W.Nr. 2.4668) is perhaps the most widely specified of this family. We stock more than 30 different sizes, from 1/2" to 9" diameter.
Alloy 725 (UNS N07725, ASTM B637) is less widely specified. It is a high-strength variant of Alloy 625, offering comparable strength to Alloy 718, with a higher alloy content, significantly more molybdenum and better pitting corrosion resistance. It is therefore somewhat more expensive. We stock a focused range from 1" to 4" diameter.
Alloy 925 (UNS N09925, ASTM B805) is a relatively younger alloy, the high-strength variant of Alloy 825 and less highly alloyed than both Alloy 725 and Alloy 718. It interests large users as a lower-cost alternative to Alloy 718 where the absolute level of corrosion resistance is not as critical. We hold significant stock of solid bars from 4 1/2" to 9" diameter, used in various oil tool components.