CLASS PROGRAMME

Approval of manufacturers
DNV-CP-0351 Edition September 2021

Manufacture of heat treated products - heat

treatment workshop

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DNV AS
FOREWORD

DNV class programmes contain procedural and technical requirements including acceptance
criteria for obtaining and retaining certificates for objects and organisations related to
classification.

© DNV AS September 2021

Any comments may be sent by e-mail to rules@dnv.com

This service document has been prepared based on available knowledge, technology and/or information at the time of issuance of this
document. The use of this document by other parties than DNV is at the user's sole risk. DNV does not accept any liability or responsibility
for loss or damages resulting from any use of this document.
CHANGES – CURRENT

Changes - current
This document supersedes the May 2016 edition of DNVGL-CP-0351.
The numbering and/or title of items containing changes is highlighted in red.

Changes September 2021

Topic Reference Description

Rebranding to DNV All This document has been revised due to the rebranding of DNV
GL to DNV. The following have been updated: the company
name, material and certificate designations, and references to
other documents in the DNV portfolio. Some of the documents
referred to may not yet have been rebranded. If so, please see
the relevant DNV GL document. No technical content has been
changed.

Editorial corrections
In addition to the above stated changes, editorial corrections may have been made.

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CONTENTS

Contents
Changes – current.................................................................................................. 3

Section 1 General.................................................................................................... 5
1 Objective..............................................................................................5
2 Scope and application..........................................................................5
3 Request for approval........................................................................... 6
4 References........................................................................................... 6

Section 2 Documentation requirements.................................................................. 7

1 Incoming material and order documentation.......................................7
2 Identification and traceability............................................................. 7
3 Heat treatment furnaces......................................................................7
4 Procedures and records....................................................................... 7
5 Quenching and cooling process and media.......................................... 8
6 Case hardening.................................................................................... 8
7 Nitriding hardening (with/without carburizing).................................. 8
8 Induction hardening............................................................................ 9
9 Welding................................................................................................9
10 Weld repairs...................................................................................... 9
11 Other records, test facilities and procedures..................................... 9

Section 3 Approval testing.................................................................................... 10

1 Test products and testing scope........................................................ 10
2 Testing requirements.........................................................................11

Appendix A Approval coverage............................................................................. 14

1 Approval coverage of heat treatment processes, material types
and grades............................................................................................14

Appendix B Approval scope...................................................................................16

1 Approval scope, major approval requirements and certification
scope.................................................................................................... 16

Changes – historic................................................................................................ 17

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SECTION 1 GENERAL

Section 1
1 Objective
The objective of this class programme (CP) is to provide a description for which the Society bases its
approval of manufacturers intending to deliver heat treated or surface hardened products in accordance with
DNV-RU-SHIP Pt.2 or other applicable standards provided by the Society.

2 Scope and application

This programme is applicable for approval of manufacturers for:
— heat treated products
— surface hardened products
as referred in the Society’s rules and standards. For a description of general requirements, conditions and
procedures related to the approval, please refer to DNV-CP-0346 which shall be applied in combination with
this programme. The corresponding class programmes for the specific products shall also apply.
The approval will typically cover:
— an independent heat treatment company
— a manufacturer (e.g. foundry) in-house heat treatment facility
— a heat treatment sub-contractor
The corresponding requirements are given in App.B.
The programme is applicable for the approval of manufacturers for one or more of the heat treatments:
— normalizing or normalizing + tempering
1
— quenching and tempering
— solution heat treatment without quenching
1)
— solution heat treatment with quenching
— tempering (e.g. malleable cast iron)
— stress relieving heat treatment
— soft annealing (spheroidize annealing)
— recrystallization annealing
— diffusion annealing/homogenizing annealing
— coarse grain annealing
— precipitation hardening
— case hardening
— nitriding
— induction hardening.
Some heat treatment processes may qualify other processes as indicated in App.A. Note that for any other
process to be qualified in addition to the tested one, the heat treatment documentation and specifications,
see Sec.2, shall be submitted and accepted by the Society.
Guidance note:
Other processes than those listed may be approved subject to case-by-case consideration. Adjusted scope of documentation and
testing may be required as relevant.

---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e---
Surface hardening by mechanical process such as shot peening is not covered by this approval programme.

1
Approval is limited to quenching media and quenching method.

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 Section 1
3 Request for approval
The manufacturer shall indicate the application which approval is requested. For this a list or table shall be
given, including at least:
— applicable heat treatment types (see App.A)
— reference to applicable material types and grades according to the Society’s rules and standards, (e.g.
DNV-RU-SHIP Pt.2 Ch.2 Sec.8 [2]) for the applicable chemical composition, mechanical properties and
heat treatment, or subject to agreement, reference to other recognised standards
— type of products and manufacturing method (e.g. castings, forgings, rolled products etc.)
— range of applicable product sizes (dimensions, maximum thickness and weight).

4 References
Table 1 List of references

No. Reference Title

1 ASTM E 112 Standard test method for determining average grain size

2 ASTM E562 Standard test method for determining volume fraction by systematic manual point count

3 ISO 643 Steels – micrographic determination of the apparent grain size

Standard test method for conducting temperature uniformity surveys of furnaces used to heat treat
4 ASTM A991
steel products

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SECTION 2 DOCUMENTATION REQUIREMENTS

Section 2
1 Incoming material and order documentation
Manufacturer’s requirements for and handling of order documentation and incoming material in terms of:
— a list of suppliers for starting material and a copy of their approval certificate
— handling of incoming material
— handling of incoming material certificates and verification of material identification
— specifications for chemical composition and procedure for validation of composition
— if relevant; specifications for hardenability
— documentation of heat treatment condition of incoming products (if applicable)
— specifications for and verification of surface condition of incoming products
— specification for/order information related to heat treatment, e.g. customer or manufacturers’ specification
— if relevant; order information and drawings indicating areas which shall (and shall not) be subjected to
surface hardening
— specification for/order information related to properties to be achieved (mechanical, surface, dimensions)
and methods for verification and reporting.

2 Identification and traceability

Procedures for identification and traceability (i.e. ensuring full traceability of the products and test samples at
all times).

3 Heat treatment furnaces

The following information shall be submitted:
— type of furnace and dimensions, ID numbers
— heating source
— maximum operating temperature
— furnace control; manual or automatic. For automatic control; own system or commercial. Description of
the furnace control system
— working zone; dimension and sketch of working zone
— furnace atmosphere (media): vacuum, low/medium/normal pressure, inert gas
— type of thermocouples
— sketch indicating the positions of thermocouples, and including position of contact thermocouples (i.e.
connected to the products, where applicable)
— accuracy, calibration status and calibration certificates of temperature control devices, i.e. thermocouples
and recorders.

4 Procedures and records

This shall give all relevant details including but not necessarily restricted to:
— applied heat treatment process
— heat treatment specifications with respect to:
— heat treatment procedures, specifying temperatures (start, holding, stop cooling/quenching), holding
and soaking times (thickness dependencies), heating rates, and cooling or quenching rates, time
between quenching and tempering, etc.
— any re-heat treatment procedure to be given, if applicable
— method for cleaning after heat treatment.

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The following reports and record shall be submitted:

Section 2
— furnace temperature uniformity test report with records, particularly indicating the effective working zone
with respect to the lowest locations towards furnace floor and nearest location to furnace door. ASTM
A991 or other equivalent standard should be used
— furnace loading and unloading procedure and plan, i.e. including at least loading method, hot or cold
loading/unloading, number and arrangement of products, distance between products, maximum loading
2
mass, etc. . Example loading maps indicating the positions of the products(s) in the furnace shall be
submitted
— example records of representative actual heat treatments indicating temperature-time course.

5 Quenching and cooling process and media

The following information shall be submitted:
— type of cooling or quenching media
— type of process, separate or integrated process
— type of cooling/quenching (e.g. in air, fan, submerging in media, spraying, etc.)
— for basins/tanks: number and dimensions, media, agitation method, equipment for temperature
monitoring
— for spraying: velocity, type and size of nozzles etc.
The following procedures shall be submitted:
— furnace unloading procedure, i.e. describing method of unloading, max time for removal from furnace to
start quenching, e.g. entry in quench tank
— for quenching media:
— control of circulation/agitation
3
— control and monitoring of temperature
— maintenance, control and renewal of media
— holding time (calculation of, control of and recording of holding time, e.g. related to product thickness
and mass).

6 Case hardening
Additional procedures, specifications and methods for:
— monitoring of furnace atmosphere and composition
— hardening process (direct, single or double hardening)
— protection of surfaces not to be hardened
— tempering.

7 Nitriding hardening (with/without carburizing)

Additionally, facilities (type and capacity), procedures, specifications and methods for:
— gas nitriding
— bath nitriding
— ion nitriding.

2
Loading on furnace floor without distance pieces or loading in bucket is in general not permitted unless
otherwise agreed
3
Cooling media temperature shall normally be maintained below 50°C for the whole cooling process.

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 Section 2
8 Induction hardening
Facilities (type and capacity), procedures, specifications and methods for:
— induction process, including quenching after heating
— inductors/induction coil.

9 Welding
The following information shall be submitted both for weld repair and for production welding:
— description of the welding:
— equipment
— qualifications of welders and welding supervisors. Welders certificates shall be submitted
— welding procedure specifications (WPS)
— the welding shall be qualified by welding procedure tests. Reports on welding procedure qualification
tests (WPQR).
Unless otherwise agreed with the Society, the scope of the welding procedure tests shall comply with
DNV-RU-SHIP Pt.2 Ch.4 Sec.5, and documented as described in the approval of welding workshop (WWA)
programme DNV-CP-0352.

10 Weld repairs
In addition to [4], the welding procedure specification (WPS) shall also include:
— extent and depths allowed for weld repair
— preparation of groove before welding
— non-destructive testing before and after welding
— surface preparation after welding
— heat treatment after welding
— reference to manufacturer’s procedure for the maintenance of records of weld repairs.

11 Other records, test facilities and procedures

The following shall be submitted:
— visual inspection: relevant templates for recording, and a few records of previously performed visual
inspections of same or similar products
— details and description of relevant in-house testing facilities and calibration details, test procedures and
qualification of testing personnel
— NDT procedures, equipment for NDT including calibration details, and qualification of personnel for NDT
— information about and procedures for important manufacturing and testing routines, such as cutting and
macrographic inspection of products etc.

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SECTION 3 APPROVAL TESTING

Section 3
1 Test products and testing scope

1.1 General
The test products shall be selected so that the intended approval scope as outlined in Sec.1 is covered.
Unless otherwise specified herein, the sampling, testing procedures and acceptance criteria shall comply with
the relevant requirements of the DNV rules.
Starting material for approval testing, e.g. semi-finished steel products, shall be produced at works approved
by the Society.

1.2 Extent of approval testing

Qualification by approval testing is required for each:
— heat treatment process (delivery condition, condition of supply) as indicated in App.A
— material type, group or grade as indicated in App.A
— some material grades may also cover other grades as indicated in App.A
— product type/manufacturing method (castings, forgings, rolled products etc.)
— maximum dimension for which approval testing is performed.
The allowable range of heat treatment temperature shall be proposed, agreed and qualified by the
temperature(s) used for the approval testing.
Thickness dependency of holding and soaking time shall either be qualified by testing, or proposed based
on documented and established industry practice. If manufacturer intend to change the holding and soaking
time to other parameters than that established during the verification, new approval is required.

1.3 Selection and position of the test samples

Sampling shall be done in accordance with the Society's rules and in accordance with the relevant approval
programme for the material/product being qualified, unless otherwise agreed. In absence of clear rule
requirements, sampling positions may be proposed by the manufacturer and then agreed on case by case
basis.
Additionally, the following test specimens are required. Test specimens shall be prepared from a sample
product of dimensions representative for the maximum product size, for:
— tensile and impact test:
— for thickness or diameter up to maximum 50 mm, the axis shall be at the mid-thickness or the centre
of the cross section
— for all delivery conditions except QT: For thickness or diameter greater than 50 mm, the axis shall be
at one quarter thickness (mid-radius) below any heat treated surface
— for delivery condition QT: For thickness or diameter greater than 50 mm, the axis shall be at one
quarter thickness (mid-radius) or 80 mm, whichever is less, below any heat treated surface
— microstructure: near surface, at ¼ thickness, at mid thickness, and at tensile/impact test position if
different from these
— hardness: at or near surface, at ¼ thickness, at mid thickness, and at tensile/impact test position if
different from these.
Test samples shall be taken out in final heat treatment delivery condition and shall not be subjected to any
separate heat treatment.

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 Section 3
2 Testing requirements

2.1 General
For all processes and products as given in [1.2], extent of testing, methods, evaluation and requirements
for the product shall be as given in the DNV rules and the corresponding AoM programme for the material/
product being qualified, unless otherwise stated herein.

2.2 Temperature uniformity survey of furnaces

An extensive temperature uniformity survey (TUS) of heat treatment furnaces is required in order to assure
uniform temperature and reliable control and checking of temperature. TUS shall be carried out with agreed
procedure and witnessed by the Society's representative at least once.
Calibration of furnaces shall at least include:
— temperature shall be measured using contact thermocouples on sample products located at each corner
and of the center of the working zone
— temperature shall be measured at typical holding temperature for the products (in the upper range of
applicable holding temperatures)
— holding time: minimum 30 minutes
— recording interval: minimum one recording per two minutes
— typical tolerances are: +/- 14°C at or above 800°C and +/- 10°C below 800°C.
Temperature shall be monitored by recorders with resolution sufficient to clearly define all aspects of the
heating, holding and cooling process. From the recording of the temperatures of the contact thermocouples,
a comparison shall be made with the records of the furnace thermocouples. The chart of time and
temperature showing the output from contact thermocouples and furnace control thermocouples shall be
submitted.
Temperature uniformity determined according to the methods described in ASTM A 991 or equivalent
standard is acceptable.
TUS shall be carried out at least annually and TUS report shall be presented to the Society's surveyor on
request. The periodical TUS may be carried out by the heat treatment company. Evidence of furnace surveys
and calibration shall be provided.

2.3 Qualification of alternative heat treatment processes (as relevant)

Heat treatment processes not in line with common industry practice shall be qualified, e.g. a normalizing
process being different from common practice with respect holding time at soaking temperature. Common
industry practice is in this respect considered as the practice specified by nationally or internationally
recognized standards or reference books. Approval may be given when found to be equivalent or better than
normally accepted processes.
Note:
Such approval is applicable for the process, not the product. The final delivery condition of a "product" shall always follow the
requirements of DNV rules. E.g. hull structural steel castings shall be delivered in the conditions given in DNV-RU-SHIP Pt.2 Ch.2
Sec.8 [2.3].

---e-n-d---o-f---n-o-t-e---
Test scope for qualification of alternative heat treatment processes shall be agreed with the Society. It may
typically include:
— to be qualified with thickest product for approval, or alternatively a heat sink/sample product of same
thickness and composition, using heaviest furnace loading and/or most dense packed loading to be used
for production

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— contact thermocouples shall be placed both on the surface of the product extremities, and in a hole drilled

Section 3
into the mid-thickness position of the sacrificial product/heat sink, and the temperatures recorded
— furnace atmosphere temperature shall be measured and recorded in parallel
— readings from the contact thermocouples shall be compared with the temperature records from the
furnace atmosphere, and plotted on the same graph for comparison
— temperatures shall be monitored by a recorder with resolution sufficient to clearly define all aspects of the
heating, holding and cooling process
— allowable soaking temperature range is typically -10°C and +30°C.

2.4 Heat treatment sensitivity study, QT condition (as relevant)

For candidate alloys where quenching and tempering parameters are not standardised or established, a
heat treatment sensitivity study is required. The same applies for non-standard quenching and tempering
processes.
A heat treatment sensitivity study simulating production conditions shall be applied in order to check the
candidate material’s sensitivity to deviations from a target (optimum) heat treatment specification. It is thus
essential that the target (optimum) heat treatment is performed in a manner simulating realistic conditions
for production. Extent of testing to qualify heat treatment sensitivity study may be proposed and should be
agreed in advance.
As an alternative to new 'heat treatment sensitivity study' during approval process, manufacturer may submit
existing data from their previous studies for consideration by DNV and based on evaluation a complete or
partial exception may be granted from this requirement.
Unless otherwise agreed or required, the following heat treatment conditions apply:

Table 1 Variables for temperature sensitivity study

Time at austenitisation
Austenitisation temperature Tempering temperature Tempering time
temperature

Specified temperature -30°C Specified time Specified temperature -15 °C Specified time

Specified temperature +30°C Specified time Specified temperature +15 °C Specified time

Specified temperature 120% of specified time Specified temperature 120% of specified time

Specified temperature 80% of specified time Specified temperature 80% of specified time

2.5 Jominy end quench test, when required by purchaser (as relevant)
For quenched and tempered steels as well as case hardening steels (e.g. 16MnCr5, 20MnCr5, 18CrNiMo7-6
and equivalent), the hardenability shall, when required by the purchaser, be determined and reported using
Jominy end quench test. Testing shall be performed according to ASTM A255 or an equivalent standard.
The applied test method and obtained test results shall be reported.

2.6 Additional testing for case hardened products including gear

transmissions (as relevant)
The applicable minimum methods and requirements to be fulfilled in addition to this programme are indicated
in DNV-CP-0247 and in DNV-RU-SHIP Pt.4 Ch.4. Further requirements for qualification of case hardening of
gear transmission parts may be required by the Society.

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 Section 3
2.7 Additional testing for nitrided products with or without carburizing (as
relevant)
A coupon following the entire nitriding process shall be tested and documented with respect to:
— case depth (to 400 HV)
— white layer thickness (to be as specified, or < 0.025 mm)
— core properties.

2.8 Additional testing for induction hardened products (as relevant)

A coupon with the same profile as the actual product following the entire induction hardening process shall be
tested and documented with respect to:
— hardness contour
— hardness contour at pitch diameter (for gears)
— hardness contour at tooth root (for gears)
— material microstructure at surface and through the hardened depth.

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APPENDIX A APPROVAL COVERAGE

Appendix A
1 Approval coverage of heat treatment processes, material types
and grades
Table 1 Approval coverage related to material types and grades given by DNV-RU-SHIP Pt.2 Ch.2

Heat treatment
process subjected Material grade tested Approval coverage
to approval testing

C and C-Mn steel grade All C and C-Mn steel grades

Alloy steel grade All alloy steel grades

Heat treatment without All stainless steel grades of same type (e.g. austenitic, duplex,
Stainless steel grade
surface hardening martensitic, ferritic, etc.)

Cast iron grades All cast iron grades

Non-iron metallic grade All non-iron metallic grades of same type (e.g. bronze)

Heat treatment with Covers only the material grade and the surface hardening process
-
surface hardening subjected to approval testing

Table 2 Approval coverage related to heat treatment process as per DNV-RU-SHIP Pt.2 Ch.2

Heat treatment process 1, 2)

Heat treatment process qualified in addition to the tested heat treatment
subjected to approval testing

Normalizing, normalizing and

Soft annealing, tempering, stress relieving
tempering

Quenching and tempering Quenching, tempering, stress relieving

Solution heat treatment

Soft annealing, tempering, stress relieving
without quenching

Solution heat treatment with

Solution heat treatment without quenching, soft annealing, tempering, stress relieving
quenching

Tempering Stress relieving

Stress relieving heat treatment -

Soft annealing (spheroidize

Tempering, stress relieving
annealing)

Recrystallization annealing Tempering, stress relieving

Diffusion annealing,
Tempering, stress relieving
homogenization annealing

Coarse grain annealing Tempering, stress relieving

Precipitation hardening Tempering, stress relieving

Case hardening -

Nitriding -

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 Heat treatment process

Appendix A
1, 2)
Heat treatment process qualified in addition to the tested heat treatment
subjected to approval testing

Induction hardening -

1) On condition that the heat treatment workshop provides sufficient evidence about their knowledge and capability
(ref. documentation requirements given by Sec.2) of listed heat treatment processes
2) Additional processes not listed in this column may be accepted by the Society, e.g. taking into consideration
the heat treatment parameters (temperature, quenching, complexity, material types, etc.) In such cases, the
manufacturer shall apply for extended coverage and obtain acceptance before start of testing

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APPENDIX B APPROVAL SCOPE

Appendix B
1 Approval scope, major approval requirements and certification
scope
Table 1 The manufacturers may typically be approved within the following scopes

Certification of
Approval 1)
Approval is required for materials/products by Guidance note:
scope:
manufacturer (W-certificate)

Material Furnace calibration (furnace

manufacturers Limited to grade/products uniformity test), HT procedure
in-house heat — Each furnace mentioned in the AoM verification and process
treatment certificate qualification as relevant, may be
facility performed simultaneously

Furnace calibration (furnace

Heat
— Each furnace uniformity test), HT procedure
treatment
— Each heat treatment sub- Not allowed verification and process
sub-
contractor qualification as relevant, may be
contractor
performed simultaneously

— Each furnace
— Per product/material group:
— Limited to grade/products
— casting and forging group — Material shall be provided from
group mentioned in the
— pipes and fitting group DNV approved manufacturer(s)
Independent AoM certificate
Heat — plate and section group — Furnace calibration (furnace
— Original material
treatment — surface hardened products uniformity test), HT procedure
certificates for semi-
company except parts for gears verification and process
finished products shall
— surface hardened parts for qualification as relevant, may
be attached to material/
gears be performed simultaneously
product certificates
— non-ferrous group
— other/miscellaneous group

1) For full details, see the approval programme requirements.

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CHANGES – HISTORIC

Changes – historic
May 2016 edition
This is a new document.

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