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Development of Heavy Steel Forgings for Nuclear Energy

Equipments

G K Pillai,

Chairman cum Managing Director

Heavy Engineering Corporation Ltd.

Ranchi

Abstract

In view of the governments decision, to set up a number of nuclear power plants, in collaboration with western

countries, Indian companies needed to upgrade the existing level of technological processes to meet the demand for

high quality steel forgings. Till date, only a few countries in the world have the technical knowhow and the facilities

for making the forgings. Due to the stringent quality requirements of the nuclear grade steels, a very high order of

technological processes for making clean steel, forging, heat treatment, machining and testing is required.To develop the capability within our country, Heavy Engineering Corporation Ltd, Ranchi, a Public Sector Unit,

under the Ministry of Heavy Industries & Public Enterprises, took the lead in developing the processes required to

manufacture a 25MT Shell forging, from a 120MT ingot. This paper deals with the various innovative technological

practices developed and established in the Foundry Forge Plant (FFP) of HEC Ltd

Introduction

The steel forgings in a nuclear reactor are continuously exposed to nuclear radiation, high temperature and pressure.

To withstand these effects, steel grades with high toughness requirements and very low levels of impurities are

required to make the forgings. Also, the forging processes involve upsetting of heavy Ingots, punching, mandrel

forging, ring rolling and drawing. To ensure the required steel quality, it is essential to control the levels of

impurities like Phosphorous, Sulphur, Hydrogen, Arsenic, Copper, and Cobalt etc, much below the levels presently

achieved. Only a few countries like, Japan, S Korea, Italy, France have the facilities to supply such forgings. In

India, some forge shops are making smaller items such as Nozzles but these are made from imported ingots/blanks.

HEC Ltd, Ranchi, though primarily set up to meet the demand of Steel and Mining sectors, has decided to enter the

high tech sector of making forgings for nuclear power equipments. It has unique facilities for steel making, forging,

heat treatment, machining and testing in one location. Though the requirements are very stringent and the

equipments were required to be utilized at their optimum levels, HECL has ventured to develop the processes for

making heavy ingots upto 120 MT and forgings weighing about 25 MT,

Product range of Foundry Forge Plant (FFP) and production facilities

FFP supplies castings and forgings for various equipments for Steel, Mining and General Engineering sectors,

besides Main BG Crankshafts for 16 cylinder engines for Railways and some special items for shipyards, space and

defence sectors. The heaviest of the forgings, such as Main Shaft for Crusher, weighed about 50MT, forged from a

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87T ingot. The quality requirements include tests for chemistry, mechanical tests at room temperature and ultrasonic

tests.

The main production equipment are:

Primary steel making units: Electric Arc Furnaces 30T Capacity- 2 nos.,10T Capacity- 1 no.

Secondary Steel making units: Vacuum Arc Degassing Furnace 60T Capacity- 1 no., Ladle Furnace- 1 no. and

Stream degassing Unit 90T Capacity- 1 no

Hydraulic Presses: 6000T Capacity- 1 no., 2650T Capacity- 1 no., 1650T Capacity- 1 no. and 1000T Capacity- 1

no.

Development of Shell Forging weighing about 25T for BARC by HEC

1) Description of ForgingSupply size: 3000mm length (approx.) and 400 mm thick

Material grade: Low-Carbon, Chrome-Moly-Vanadium steel, with very low levels of impurities

Heat Treatment: Quench and temper

Mechanical tests, along Axial, Tangential and Normal directions for Tensile tests at Room Temperature and at

3500C, establishing Ductile Brittle Transition Temperature(Tko), determination of Nil Ductility Transition

Temperature(Pellini Drop Weight Test)

Non Destructive Examination (Ultrasonic and Magnetic Particle tests)

2) Challenges in manufacturing of the Shell ForgingFor making the shell forging, a black forging of size about 3500mm ht. was required to be forged from a 120T

ingot. The following technological constraints were identified in manufacturing of the forging.

a) Capacity constraints in making 120T of steel melt and chemistry with very low levels of impurities, gases

and inclusions.

b) Capacity constraints in upsetting of 90T forged block in the 6000T press.

c) Effective Quality Heat Treatment ( Water quench and Tempering) to ensure uniform properties in all three

directions and across the thickness

d) Machining of the shell forging, to meet the requirements for perpendicularity within 0.1mm and

concentricity of all diameters within 0.05mm with respect to the inside diameter

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3) Technological solutions and the risks encountereda) Impurities in the raw materials, deleterious to low temperature impact properties during service were

controlled through

revision of quality standards for steel scrap

revision of quality standards for fluxes, ferro alloys and argon

Special scrap, with very low levels of impurities, was procured from Bokaro Steel plant and alloying

additions such as metallic Chromium, metallic Manganese with low levels of Arsenic and Phosphorous were

used for making the steel.

b) Fig. 1 schematically shows the route followed for realizing 120T of fully refined metal for pouring the

ingot. Through meticulous planning, monitoring and coordination, our Engineers succeeded in

synchronizing the bath chemistry of 5 melts, latter matching the chemistry of refined metal in

Vacuum Arc Degassing Furnace (VAD) and Ladle Furnace (LF).

managing the logistics of hot metal handling and the risky operation of hot metal holding of the 1st

batch of refined metal in LF for 12 hours.

control of exogenous inclusions while handling of the metal from 6 refractory lined ladles and

achieving the cleanliness even after such long holding

c) In order to control the hydrogen in the steel to a level of less than 1ppm, a Package Boiler exclusively for

the vacuum degassing unit was installed to achieve very low vacuum levels . Further, controls at every

stage of processing were implemented, to reduce hydrogen input in to the metal.

d) Fig 2 schematically shows the route followed for forging and further processing. Through section hot

working, in the 6000T press was a key operation in achieving isotropic properties of the product. The

capacity constraint on this account was resolved by

design, manufacture and use of a Rotating Table for partial upsetting of the heavy forged block,

through successive rotations

e) FFP has gas fired furnaces for heat treating such big forgings. However, to ensure uniform metallurgical

and mechanical properties and satisfy the ultrasonic requirements, we have

developed a heat treatment technology

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carried out the heat treatment in a specially installed Electric Pit Furnace.( 3500mm dia X 8000mm

depth)

f) To achieve the strict dimensional tolerances, the forging was machined, using

CNC Vertical Turning and Boring Machine, for finish machining

CNC Horizontal Boring Machine, for locating the nozzle location and slicing of Test piece rings

from the job.

4) Production of Shell forgingThe various stages of manufacturing, starting from Preliminary refining in 30T EAF, till final despatch of the

forging are shown in the following process charts and photographs.

PROCESS FLOW CHART FOR INGOT MAKING

Fig. 1

Steel Making in 2 Batches

Very High Purity

Scrap

Alloying Additions

High Purity Metallic

Materials

Transfer of Metal to

LF

120 Ton

Ingot

Pouring under

Vacuum

Secondary Refining

and degassing in 60T

VAD

Secondary Refiningand degassing in 60T

VAD

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Primary Refining of Steel in 30T EAF Secondary Refinement in 60T VAD

Stripping of 120T Ingot from mould

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PROCESS FLOW CHART FORGING AND FURTHER PROCESSING

Fig. 2

Ingot for Forging

Forging operation in

6000T Press

Preliminary H/T

Rough Machining

Quality H/T

(Quench & Temper)

Machining

Testing

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Holding of 120T Ingot for Pin Forming Forging of Ingot into block

Block Forging for Upsetting Upsetting of Block

Upsetting of Block on rotating table

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Punching Operation

Ring Rolling on Mandrel Drawing on water cooled taper mandrel

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Step Forging Finished Shell Forging

Set up for Ultrasonic testing Despatch of Finish Machined Forging

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5) Quality of the Forgings Developed for nuclear sectora) Control of Impurities

Table 1- Impurities

Fig.3 Level of impurities in a number of melts

b) Distribution of different elements in a number of melts

Fig.4

Copper < 0.05%

Phosphorus < 0.006%

Sulphur < 0.004%

Hydrogen < 1.5 ppm

Other impurity

elements< 100 ppm

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

Ni Mn Si Cu

0.000

0.002

0.004

0.006

0.008

0.010

0.012

P S Sn Al As Sb

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c)

Homogeneity of Properties

Fig.5 - Yield Strength (MPa) at Room Temperature

Fig.6 - Impact Energy at 15 deg. C

0

100

200

300

400

500

600

700

0 0.25 0.5 0.75 1

Fraction of Section Thickness

Y

ieldStrength(MPa)

100

150

200

250

300

0 0.25 0.5 0.75 1

Fraction of Section Thickness

ImpactEnergy(Joule

s/Cm

2)

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d) Low temperature properties

Fig.7 - Low temperature Impact Energy

Other products of HECL for Strategic Sectors

HEC has made significant contributions to the defence and space sectors also, besides its core strength areas of steel

and mining sectors. Some equipment and components HEC has manufactured for the Defence and Space Sectors

are:

Space and Atomic Energy Sectors

High tech heavy duty structural

Mobile Launch Pedestal

Folding cum Vertically Repositionable Platform (FCVRP)

Horizontal Sliding Door

Heavy Duty Overhead Cranes

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Special Purpose CNC machine tools

Development of Special grade steel (15CDV6)

10 Ton Hammer Head Tower Crane installed at the top of Umbilical Tower of 80 M Height

400 TON crane at ISRO / SHAR (Installed at 46 M Ht in Solid Stage Assembly Building of GSLV

Mk-III Project at SHAR to facilitate Assembly of Launch Vehicle.)

6 AXIS, CNC Vertical Turning & Boring machine for ISRO

Design and manufacture of Magnet Pole Caps and other components of Super Conducting Cyclotron

Magnet (K-500) for Variable Energy Cyclotron Centre, Kolkata

Defence Sector-Army & Navy

Indian Mountain Gun (MK-II)

Gun Barrel

Forged Armour Plates

Turret Casting for T72 Tank

Fabricated Hull & Turret for MBT Arjun

Marine Diesel Engine Block

Stern Gear Systems for INS RANA

Rudder Stock Assembly

Propeller Shaft Assembly

Defence Sector-Ordnance Factories:

Deep Boring CNC Machine (10 M) for IOF, Kanpur

Horizontal Boring Machine for Naval Dockyard, Vishakhapatnam.

Rolling Mill Equipment for Metal & Steel Factory, Ichapur

Gun Barrel Drilling Machine

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Manufacturing plan for nuclear grade steel forgings in 2010-11

Besides this forging, HEC has also manufactured and supplied other forgings such as Rings, Flanges, Covers, and

Plates to the nuclear energy sector.

Recently, NPCIL placed an order for manufacture and supply of Tube Sheet, Nozzle and Cover forgings, as per

material grade 20MnMoNi55. The first ingot for making the nozzles is scheduled for casting in Nov.2010. We are

aiming to complete the supply by 3rd quarter of 2011. Also, seeing the demand for Shells of diameter beyond

2500mm and Dish end forgings, we are going ahead with upgrading our facilities for the manufacture and supply of

these forgings.

The Heavy Machine Building Plant of HECL, has excellent facilities for machining and weld fabrication of large

structures/assemblies. We propose to further upgrade the welding processes and facilities to conform to the

requirements of nuclear pressure vessel fabrication in order to take up manufacture of equipments for nuclear power

plants.

Conclusion:

The results achieved showed that we had established the technological processes for achieving the required quality

levels of steel forgings for nuclear power plant equipment. HEC understands that much bigger sizes of forgings are

required for the commercial power plants. But, the Engineers in HEC are confident of taking up bigger challenges

and help the country in import substitution. We are in the process of collaborating with established manufacturers,

for upgradation of our facilities, to meet the demand for heavy steel forgings required for Pressurizer vessels, Steam

Generators and Reactor Vessels.

I take this opportunity in acknowledging the invaluable guidance and support provided by Sri R.S. Yadav, AD,

RPG,BARC and his team of Engineers Sri R.N.Sen and Vivek Srivastav, in helping us in identifying the

improvements in the processes, making a comprehensive manufacturing and quality assurance plan, upgradation of

the testing processes and facilities and meticulous follow up of the processes. They have been a huge source of

strength in overcoming various hurdles faced during development of the processes.