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Alloy T41 / 20CrMoVTiB4-10 / 1.7729

Steel for Power Plant High Temperature Bolt applications

Alloy T41 / 20CrMoVTiB4-10 / 1.7729

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 details about the product, both for internal technical information for our sales staff, and as general information for any interested outsider.  A previous blog has discussed the history of the product.

A full document (including all information released as blogs) is available as a PDF, providing in depth the material’s chemical, mechanical and metallographic properties is available on request – please email mike.andrews@broder-metals-group.com for a free copy.

Material specification

PRD AT41 bar is produced in a German mill via the ingot cast route in accordance with PRD Data Sheet DH/28/1 revision 3 (3-09/2007) and process specifications PFC 7729 SDS rev 5+, PFC 7729 BGS rev 5+ and PFC 7729 GFM rev 1+. Ingot cast material tends to produce a finer grain structure, which in turn provides better creep properties than continuous cast (concast) material.

The material is heat treated in accordance with BSEN 10269:1999; 20CrMoVTiB4-10 with appropriate sub-critical annealing, hardening and tempering cycles according to the diameter of the material. Every bar is subject to spectroscope analysis, and every bar is Circograph and Ultrasonically tested to DIN EN 10308 03/12 CLASS 4.  The werkstoffe number is 1.7729.

Independent microstructural examination from one longitudinal section across the full cross-sectional width of the bar product is carried out and reported as standard for each cast of material.

Grain size testing to ASTM-E 112 with acceptance limits of size 5 or finer is also reported as standard for each cast.

PRD-AT41, and the fasteners manufactured out of it, was approved by EON in September 2007 for use on high temperature steam turbine plant. Full details of the testing process and acceptance results can be found in the EON Power Technology Report No PT/LH979/R.

The extensive proving trials and the maintained testing regimes via independent test houses, means that the material meets or exceeds the following industry standard specifications:

  • CEGB GDCD TD2 ISS2
  • CEGB 0259604/82 (T41)
  • GEC Turbine Generators Ltd Specification 30/227 ISS 10/83
  • BS 1506 681-820
  • BS 4882 B16A
  • Siemens AG Specification TLV 9185 01
  • BSEN 10269 1999 Material Number 1.7729
  • Durehete 1055
  • PFC 7729 SDS revision 5
  • PFC 7729 BGS revision 5
  • PFC 7729 GFM revision 1

Finally, in addition to meeting the standard requirements of material of this type, e.g. BE EN 10269: 1999 and 1999+A1:2006 (Steels and nickel alloys for fasteners with specified elevated and/or low temperature properties) the following information is supplied as standard on all Mill or Broder Metals Group’s own EN 10204 3.1 certificates (either / both supplied at the request of the customer):

  1. Values of Sb (Antimony) and R – normally the Sb value is not reported unless specifically requested, but without which the value of R cannot be independently checked.
  2. Grain size (which is ASTM 5 or finer)
  3. The results of the independent microstructural examination on each cast.

Material Application

The material is ideal for high room- and elevated-temperature fasteners, has good creep, notch and relaxation resistance up to 570o C, and is comparable to low alloy steel turbine casting materials in terms of its thermal expansion coefficients.

These properties make the material ideal for use for turbine and process plant fasteners and for boiler support rods and is increasingly being considered for all power generation plant, in addition to its’ traditional use in coal-fired power stations.

Testing Regime

100% of bars are hardness tested, and the hardest & softest bars are selected for full mechanical testing and must meet the following requirements in the longitudinal direction:

100% of bars are spectroscope analysed and results compared against the relevant standard.

100% of bars are Circograph tested and Ultrasonically tested to DIN EN 10308.03/02 Class 4.

All material is delivered fully identified and batch traceable, along with mill or Broder Metals Group EN 10204 3.1 certification at customer’s request. All certification shows manufacturing process number, chemical analysis, mechanical properties, non-destructive testing results, heat treatment, grain size and microstructural examination details.

Additional testing can be carried out to satisfy critical requirements at independent test houses as required.

Contact

To discuss the properties of PRD-AT41 or to seek supply opportunities, please contact Broder Metals Group on ++44 (0) 114 232 9241 or email: sales@broder-metals-group.com

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Alloy T41 / 20CrMoVTiB4-10 / 1.7729

Steel for Power Plant High Temperature Bolt applications

Alloy T41 / 20CrMoVTiB4-10 / 1.7729

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.

A full document (including all information released as blogs) is available as a PDF, providing in depth the material’s chemical, mechanical and metallographic properties is available on request – please email mike.andrews@broder-metals-group.com for a free copy.

History

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 (see details below) 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.

Contact

To discuss the properties of PRD-AT41 or to seek supply opportunities, please contact Broder Metals Group on ++44 (0) 114 232 9241 or email: sales@broder-metals-group.com

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Is Pricing an Art?

Question arose within Broder Metals Group after we had maintained our policy of replacement pricing, and as prices for stock such as Alloy 718, Alloy 625 and Alloy 286/660 are going down, we reduced our prices.

I was surprised at the internal debate. Should we make extra margin by keeping prices high? Should we average our stock prices? Should we price each receipt on a cost plus basis and have prices jumping around. However, we stuck to our policy – when stock prices are going up we need to make sure we recover enough cash to pay for higher priced replacement stocks. On the reverse, we need less cash to replenish stocks when stock prices are falling so we can help our customers.

The fact that we had a debate was interesting though, and set me wondering.

The Economist’s view would be that what we paid for stock is irrelevant. There is only a market price, and we should sell at the market price. However, how do we determine the market price? What our customers tell us? Or what other suppliers tell us? Take our PRD-AT41(the enhanced version of durehete 1055). As soon as we took in tour 163 tonnes of stock, the main UK competitor slashed their market price according to our major customers – well they had either been ripping off those customers for years or our customers though it might be a good idea to benefit from the extra competition. We believe our customers obviously (well those with whom we have a long standing relationship and they know our offer is based on honesty).

But, what do we do when we cannot set prices using replacement costing – for example when we price our manufacture of bespoke flanges and fittings in grades such as duplex / super duplex and titanium? Here we have a good idea what the cost is going to be, but the market price is what will be determined between us and our customer. So our negotiation determines the price offered – and our customer can decide whether the price is economic, and we can determine whether the return we will get justifies the risk we will take in buying the material & manufacturing the product – ah, but subject of another blog!

Comments welcomed on how others set prices.

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