Alloy T41 / Durehete vs BMG AT-41

Apr 11, 2017 | Technical Blogs

In August 2012, Broder Metals Group Ltd became the exclusive stockholder and distributor for High Temperature Bolting Alloy T41 round bar material developed by PRD Fasteners Ltd. The material is extensively used for turbine and process plant fasteners and for boiler support rods in coal fired power plants around the world.

This blog is one of a series that provides an overview of the history of the product while later ones will provide details about the product, both for internal technical information for our sales staff, and as general information for any interested outsider.

The material, PRD-AT41or identified by its’ specification BS EN 10269:1999: 20CrMoVTiB4-10, and Material number 1.7729, was originally developed in the mid 2000’s because PRD Fasteners was losing customer satisfaction by having to rely on the unpredictable availability of the equivalent Alloy T41 material from the Tata / Firth Rixson distribution partnership, known as Durehete 1055.

Durehete 1055 is a 1Cr1Mo3/4V tempered martensitic material with added Titanium and Boron. Durehete 1055 was first developed in the 1960s to operate at the UK’s normal boiler steam conditions of 565o C, although early materials suffered from inadequate creep ductility. Creep failure of high temperature bolting is generally related to inadequate long-term ductility under displacement controlled loading conditions (for example, stress relaxation after repeated bolt tightening).

Introduction of tighter standards led to improvement in material reliability. One significant area of work was around the relative impact of impurities which can cause grain boundary embitterment, and which lead to the development (based by work by BL King 1980) of the “R” parameter. The R parameter, which is always reported for PRD-AT41 is:

R = P+2.43(As)+3.57(Sn)+8.16(Sb)+ 0.13(Cu)

Note: There is no mandated value of the R parameter in BS EN 10269, but generally it is deemed that R should be less than or equal to 0.1 as a low R value is felt to have a beneficial effect on creep rupture ductility.

With these improvements, the material became extensively used in coal fired power stations around the world.

Unfortunately, one recurring criticism surrounded the lack of availability of sufficient Durehete 1055 bar stock in sizes fastener manufacturers required to fulfil power station requirements. In 2006 PRD Fasteners decided that they needed to develop a material source they could rely upon in order to preserve their reputation amongst end users of their fasteners. Working with a major European mill and independent test houses, they sourced a material that could be offered to the market as a reliably available alternative to Durehete 1055. PRD Fasteners labelled the material PRD AT41.

In 2007 PRD Fasteners asked EON Power Technology to assess whether PRD AT41 was a technically valid alternative to Durehete 1055.

The project examined the metallographic properties, chemical analysis and hardness of PRD AT41 in depth, and the final report (PT/07/LH979/R), dated September 2007, concluded that the material should be accepted as suitable for use for the manufacture of high temperature fasteners, and listed PRD AT41 as a Group 6 material in TECH/PROC/014 Part 1 Issue 2.1 March 2004 (Tech Proc for replacement of high temperature fasteners). In developing and seeking end user approval for the material, significant testing and additional specification requirements were built into the PRD Fasteners product, beyond those of Durehete 1055.

Since 2007, PRD Fasteners has sold some 350 tonnes of material into the power generation customers, including Drax Power Station (Western Europe’s second largest coal fired power plant).

In 2011, Broder Metals Group, through its’ subsidiary AI Materials Ltd, was asked to source Durehete 1055 by customers in Australia and Singapore. Coming across the same supply problems as PRD Fasteners had found, PRD’s AT41 was offered instead and Broder Metals Group effectively found a new market.

When, in mid-2012 PRD Fasteners asked Broder Metals Group to consider taking over the stock management and distribution of this material in order to allow PRD Fasteners to concentrate on their core business of fastener manufacture, Broder Metals Group saw the advantage in adding the material to its’ fastener product range of Alloy 286/660, Alloy 718, 304 & 316 High Tensile Stainless etc. The attraction of being able to offer AT41 on a reliable basis to its’ extensive fastener manufacturer customer base was also important. It was readily apparent that an agreement was in the interests of both parties and Broder Metals Group purchased the stock held by PRD Fasteners. This stock plus some purchased directly from the mill to fill “holes” in stock size coverage is held at Broder Metals Group’s new warehouse facility in Sheffield.

Broder Metals Group is free, under the agreement, to sell the bar anywhere in the world and to anyone that wishes to purchase it.

It is Broder Metals Group’s intention to maintain a full range of sizes and an average stock level of about 160 tonnes to offer an immediately available and reliable material source. Broder Metal Group’s trademark service level of same/next day despatch applies to this material, as well as every other material in its’ product range.

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