Pressure Control Group
Engineering
Surface Treatment
Specification
Application Tungsten CarbideCobalt High Velocity
Oxy Fuel (HVOF)
Spray Hardfacing
Substrate Low Alloy Steels
This document contains proprietary and confidential information
which belongs to National-Oilwell Varco, L.P., its affiliates or
subsidiaries (all collectively referred to hereinafter as "NOV"). It is
loaned for limited purposes only and remains the property of NOV.
Reproduction, in whole or in part, or use of this design or
distribution of this information to others is not permitted without the
express written consent of NOV. This document is to be returned to
NOV upon request and in any event upon completion of the use for
which it was loaned. This document and the information contained
and represented herein is the copyrighted property of NOV.
National Oilwell Varco 2014
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NOV PCG Form EF-004 Rev 1
National Oilwell Varco
Rig Solutions
Pressure Control Group
6390 N. Eldridge Parkway
Houston TX 77041
Phone +1 (832) 424-6000
DOCUMENT NUMBER
REV
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REVISION HISTORY
Rev
06/01/2020
Date
(mm/dd/yyyy)
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NOV PCG Form EF-004 Rev 1
New Release
Rajan
Varughese
Matt
Rahimi
Rajan
Varughese
Revision Description
Authored
Checked Approved
Document number
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Page
TABLE OF CONTENTS
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PAGE
1
SCOPE
4
2
REFERENCED DOCUMENTS
4
3
BASE MATERIAL PREPERATION
4
4
POWDER
5
5
HVOF APPLICATION
5
6
QUALIFICATION TEST COUPON (QTC)
6
7
QTC TESTING
6
8
NON-DESTRUCTIVE TESTING
7
9
REWORK AND DEVIATIONS
7
10 CERTIFICATION
7
11 TRACEABILITY
8
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SCOPE
1.1
This Surface Treatment specification covers High Velocity Oxy Fuel (HVOF)
application of 86WC-10Co-4Cr Tungsten Carbide hard-facing in Cobalt matrix.
1.2
This specification is intended solely for Tungsten Carbide with cobalt matrix hardfacing coating on low alloy steels (Alloying elements 5%).
1.3
Units in the U.S. Customary System (e.g. °F, psi, ft-lbs) are the required values.
Metric units (e.g. °C, MPa, J) are for reference only.
REFERENCED DOCUMENTS
2.1
NACE MR0175
2.2
ASTM E1920, E2109, E384, C633, E18, E10
2.3
API 6A, API 16A
Note: Industry standards shall be latest edition at the time of use, unless year or revision level is
specifically referenced
3
BASE MATERIAL PREPERATION
3.1
The base metal (substrate) shall be provided in the fully heat-treated condition
specified by the applicable NOV material specification. After application of the
HVOF coating, further heat treatment (such as austenitizing, quenching or
tempering) shall not be performed.
3.2
The area to be sprayed shall be:
3.3
3.2.1
Liquid Penetrant inspected per SOP 8.002 (Rig Doc. 100311859) prior
to application of the HVOF coating. Acceptance criteria shall be per
elastomer seal requirements.
3.2.2
Solvent cleaned and grit blasted prior to spraying to form an adequate
anchor pattern and to remove any oil and contaminants from the
surface.
When parts are re-worked, parts shall have all the previous coating removed and
shall be suitably undercut, surface cleaned and blasted for HVOF application.
Note The maximum thickness this HVOF coating can be sprayed on is 0.020
inches (0.508 mm). The maximum finished thickness is 0.012 inches (0.305 mm).
3.4
Blasted parts shall be immediately wrapped to protect the surface from
contamination.
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3.5
All efforts shall be made to spray parts as soon as possible after blasting.
3.6
A metal bond coat (MBC) may be utilized to build up the substrate up to 0.030
inches in thickness. If MBC is used, it shall be applied to the QTCs as well.
POWDER
4.1
The powder used shall have the following nominal composition range:
Tungsten carbide (%)
Cobalt (%)
Chromium (%)
Balance (%)
83.5 - 87.0
9.0 - 11.5
3.0 - 5.0
1.0 max
Note: Balance will typically include Fe, Ni and O 2.
4.1.1
5
Any other powder compositions shall be submitted for approval prior to
application to PCG Metallurgy.
4.2
The HVOF application shall be capable of producing a hardness of greater than or
equal to 940 HV.
4.3
Powder shall be stored in a secured area and protected from excessive humidity.
4.4
Sieve analysis per ASTM B214 or equivalent procedure shall be performed and
reported on each lot of powder.
HVOF APPLICATION
5.1
Parts shall be sprayed in accordance with a NOV PCG approved procedure.
Written approval shall be obtained prior to application.
5.2
The following parameters, at a minimum, shall be monitored and maintained at
optimal levels prior to and during the spray process by an automated process
5.2.1
Fuel mixture
5.2.2
Gas mixture
5.2.3
Nozzle Pressure
5.3
Work piece shall be preheated to a minimum of 150°F (65°C) and a maximum of
350°F (176°C) prior to spray application.
5.4
HVOF shall be robotically applied. Robot and part rotation shall be synchronized
in order to permit uniform application of the coating.
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5.5
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HVOF spray process shall be conducted in a fully enclosed area to prevent
contamination.
QUALIFICATION TEST COUPON (QTC)
6.1
6.2
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A set of buttons of 1
powder used.
and at least
shall be sprayed per lot of
6.1.1
The number of buttons shall be enough to perform all testing required
in section 7.
6.1.2
Three buttons will be required for adhesion testing.
The QTCs shall be:
6.2.1
Same or similar hardness and composition to the parts they qualify.
Typically, hardness should be within +/- 10 HBN points from the range
specified for the material on which the coating is being applied, and the
substrate should be in the same family of materials (i.e. low alloy
steels).
6.2.2
Produced in a moving (rotating) fixture to represent the speed of the
part being spayed.
QTC TESTING
7.1
All QTC testing shall be performed by an ISO 17025:2005 accredited laboratory.
7.1.1
Laboratory shall have specific accreditations for ASTM C633, ASTM
E1920, ASTM E2109, and ASTM E384.
7.2
The specimen for metallographic evaluation and hardness testing shall be
prepared per ASTM E1920.
7.3
Ten Vickers hardness punches shall be performed per ASTM E384 using a
maximum 500g load. The Knoop method shall not be allowed. Use Figure 1
below as a guide for location of hardness indentations.
Figure 1
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HV hardness test location guide. Not to scale.
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7.4
7.5
7.6
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7.3.1
Average of ten microhardness tests shall be greater than or equal to
940HV and the hardness values shall have a standard deviation of less
than or equal to 200 HV.
7.3.2
A photo record of the hardness indentations shall be provided with the
Lab Report.
Porosity in the HVOF layer shall be examined per ASTM E2109, Method B.
7.4.1
The acceptance criteria shall be an average area of porosity less than
or equal to 2.0%.
7.4.2
The photo record of at least two of the fields of view shall be provided
on the Lab Report.
Adhesion testing shall be performed per ASTM C633.
7.5.1
No substitutes for ASTM C633 method shall be accepted.
7.5.2
Three buttons shall be tested per part number per lot of powder used.
7.5.3
Acceptance criteria for adhesion strength is 11,000 psi (75.8 MPa)
minimum average.
7.5.4
Report percentage of cohesive and adhesive failure.
7.5.5
Localized fracture in a coating which exceeds 10,500 psi is acceptable.
Failure to meet the minimum requirements of this section constitutes a rejection of
all parts sprayed with the same lot of powder.
NON-DESTRUCTIVE TESTING
9
8.1
All parts shall be dye penetrant (PT) tested on the HVOF coating and base metal
interface after finish grinding/machining per the latest revision of NOV SOP 8.002.
8.2
Acceptance criteria shall be per the metal to metal seal criteria.
REWORK AND DEVIATIONS
9.1
10
Any deviations from this specification or rework of parts shall be permitted only
upon prior written approval from NOV. NOV PCG Engineering shall be the final
authority on any deviations.
CERTIFICATION
10.1 A data book shall be provided to NOV with each shipment.
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10.2 The following information shall be provided with each data book.
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10.2.1
Purchase order number
10.2.2
Part number
10.2.3
Lot number and MTR of the powder used
10.2.4
Results of Vickers Microhardness per Section 7.3 including a photo of
the hardness indentations
10.2.5
Results of Porosity per Section 7.4 including photos of the fields of
view
10.2.6
Results of Adhesion testing per Section 7.5
10.2.7
Final NDE results per section 8
TRACEABILITY
11.1 All traceability and traceability markings required by the drawing and/or PO shall
be maintained throughout the application process.
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NOV PCG Form EF-004 Rev 1