8/10/2019 Guideline for Selection of Instrument Tubing And
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Statoil advisory document
Guideline for selection of instrument tubing and clamps for offshore
and onshore plantsTechnical and professional description, TD0101, Final Ver. 1, Valid from 2005-04-18Publisher/follow-up: TEK PE D&V, Hans von der Lippe
Classification: Open
Validity area:
UPN/Norway/All value chain/On- and offshore
1 Introduction.......................................................................................................................................2
1.1 Objective.............................................................................................................................................2
1.2 Warrant ...............................................................................................................................................2
2 Requirements.....................................................................................................................................2
2.1 Location and service ...........................................................................................................................2
2.2 Material selection................................................................................................................................2
2.3 Painting and insulation........................................................................................................................3
2.4 Inspection during operation ................................................................................................................3
3 Definitions..........................................................................................................................................4
4 References..........................................................................................................................................4
App A Table 1 Material selection for instrument tubing and other components ...................................5
8/10/2019 Guideline for Selection of Instrument Tubing And
2/6
Statoil advisory document
Guideline for selection of instrument tubing and clamps for offshore and onshore plants
Technical and professional description TD0101, Final Ver. 1, Valid from 2005-04-18
Validity area: UPN/Norway/All value chain/On- and offshore
Classification: Open Page 2 of 6
1 Introduction
1.1
Objective
The objective with this guideline is to give premises for optimised material selections for instrument
tubing and to avoid corrosion (i.e. crevice corrosion, etc.) between the instrument tubing and clamps
for offshore and onshore installations. It is recommended to use this guideline for new projects and
when performing modification projects onshore and offshore.
1.1.1 Background
This document is produced on the bases of experienced crevice corrosion problems on instrument
tubing at several installations onshore and offshore (i.e. Sleipner, Troll A, Kollsnes gas plant,
Gullfaks), see reference (1).
1.2 Warrant
This document is linked to the following documents:
Operation, maintenance and modifications (AR12) (Statoil group/All locations/On-and offshore)
Norsok M-001 Material Selection (ST061)
Norsok M-501. Surface preparation and protective coating (ST018)
Norsok M-630 Material data sheets for piping (ST071)
Norsok M-650 Qualification of manufacturers of special materials (ST072)
Norsok I-001 Field Instrumentation (ST007)Norsok R-004 Piping and equipment insulation (ST078)
L-SP-200 Piping and valve specification (TR2000)
2 Requirements
2.1 Location and service
Material selection for instrument tubing and other components including instrument clamps for
onshore and offshore installations are listed in table 1 in Appendix. The table consists of two main
groups, i.e. material selection in saliferious marine atmosphere and in non-saliferious atmosphereincluding indoor and dry conditions.
2.2 Material selection
The material selection shown in table 1 is based on Norsok standard M-001 and field experience at
different Statoil installations and should when implemented minimise the risk for corrosion problems
as crevice corrosion, CSCC, etc. The general recommendation is to use type 316 stainless steel tubing
for indoor service and type 6Mo stainless steel or type 25 Cr duplex in external marine and saliferious
environments. All instrument tubing for seawater services shall be in titanium materials.
8/10/2019 Guideline for Selection of Instrument Tubing And
3/6
Statoil advisory document
Guideline for selection of instrument tubing and clamps for offshore and onshore plants
Technical and professional description TD0101, Final Ver. 1, Valid from 2005-04-18
Validity area: UPN/Norway/All value chain/On- and offshore
Classification: Open Page 3 of 6
The material selection using type 6Mo and type 25 Cr duplex stainless steels should be safe for normal
temperature conditions for instrument tubing, but there may be a small risk for initiation of crevices
under long periods with wet and chloride containing conditions at high temperatures and between very
tight and critical crevices. A more extreme but partly relevant reference is the Avesta Handbook (2)
with crevice corrosion test results for type 316 and 6Mo materials in natural seawater at ambient
temperature as well as at 70oC. After 6 months of submerged testing in ambient seawater there was nocrevice corrosion on type 6Mo samples, but severe crevice corrosion on all type 316 samples. At 70 oC,
one of fifteen samples showed initiation of crevices on type 6Mo samples and all type 316 samples had
crevice corrosion . Based on these test results it is concluded that type 6Mo material should be
acceptable for use in marine atmospheric conditions and will be a much more robust material selection
than the standard type 316 stainless steel.
Type 25 Cr duplex material is considered to have same crevice corrosion resistance in marine
environments as type 6Mo material. See also Norsok standard M-001.
Based on experience in Company different material grades can be used for respectively instrument
tubing and for instance manifolds, valves, etc. As crevice corrosion under clamps has been the main
corrosion problem the up-grading of tubing material should solve this corrosion problem without a
need to up-grade material selection for manifolds, valves, etc. However, temperature restrictions for
selected materials shall apply according to table 1.
For seawater service titanium shall be used. Components shall be in material grade Hastelloy C-276.
Service restrictions for titanium will follow guidelines in Norsok standard M-001. Temperature
restriction for Hastelloy C-276 is recommended as maximum 30 oC in chlorinated seawater.
Temperature and environment restrictions for materials not listed in table 1, see Norsok standard
M-001.
Material selection of instrument tubing in other environments not listed in table 1 and services shall be
evaluated especially.
Manufacturers of type 6Mo stainless steel and type 25 Cr duplex tubing shall be qualified in
accordance with Norsok standard M-650.
Non-metallic clamps shall be used if there is a risk for vibrations of instrument tubing.
2.3 Painting and insulation
Painting shall be applied on instrument tubing to be insulated (i.e. heat traced) and in accordance with
Norsok standard M-501. It is recommended to reinforce the painted surfaces under clamps with a
heavy duty mastic coated tape system. Pre-insulated tubing systems may be selected pending approval
by Company.
Non-metallic clamps are preferred when instrument tubing is painted.
2.4 Inspection during operation
Inspection should be planed for and performed on instrument tubing under clamps within three yearsafter completed commissioning at installations. Based on experience the most critical areas should be
8/10/2019 Guideline for Selection of Instrument Tubing And
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Statoil advisory document
Guideline for selection of instrument tubing and clamps for offshore and onshore plants
Technical and professional description TD0101, Final Ver. 1, Valid from 2005-04-18
Validity area: UPN/Norway/All value chain/On- and offshore
Classification: Open Page 4 of 6
selected for visual inspection. If no corrosion is observed, the actual inspection area may be deleted
from the inspection program.
3 Definitions
PRE Pitting Resistance Equivalent.
PRE = % Chromium + 3.3 x % Molybdenum + 16 x % Nitrogen
Type 6Mo Austenitic stainless steel alloys with 6% Mo and PRE>40.
Type 316 Austenitic stainless steel alloys with 17% Cr, 12% Ni, 2.5% Mo
22Cr Duplex Ferritic/austenitic stainless steel alloys with 22% Cr
25Cr Duplex Ferritic/austenitic stainless steel alloys with 25% Cr and PRE >40
Ti grade 2 and grade 5 Titanium alloys
Hastelloy C-276 Nickel base alloy with PRE>40
Operating temperature The temperature in the equipment when the plant operates at steady state
condition, subject to normal variation in operating parameters.
Crevice corrosion Form of localised corrosion caused within crevices in a corrosive mediumPitting corrosion Form of localised corrosion causing sharply defined holes on surfaces in a
corrosive medium.
CSCC Chloride Stress Corrosion Cracking
SSC Sulphide Stress Cracking
4 References
C025-S-0000-J-RE-001, Erfaringsrapport: Anbefalinger av instrumenttubing og klammer,
gyldighetsomrde land og hav, datert 15/7-2002.
Corrosion Handbook, Avesta Sheffield AB, 1994
8/10/2019 Guideline for Selection of Instrument Tubing And
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Statoil advisory document
Guideline for selection of instrument tubing and clamps for offshore and onshore pla
Technical and professional description TD0101, Final Ver. 1, Valid
Validity area: UPN/Norway/All value chain/On- and offshore
Classification: Open
App A Table 1 Material selection for instrument tubing and other components
Atmosphere/
fieldenvironment
Service
(Note i)
Material for
instrumenttubing
Material for other
components i.e.fittings/small
valves.
Maximum
temperature tominimise risk of
external CSCC.
Maximum
temperatureto minimise
risk of
internal
crevice
corrosion
(Note iv)Hydrocarbon
& hydraulic
Type 316 Type 316 Max 60oC(Note iii) N/A
Instrumentair
Type 316 Type 316 Max 60oC(Note iii) N/A
Sea water Titanium grade 2 Titanium grade 2 and 5
Hastalloy C-276
N/A
N/A85
oC
30oC
Indoor and
dry
atmosphere
or
External non-saliferious
atmosphereFresh water Type 316 Type 316 Max 60
oC(Note iii) N/A
Hydrocarbon& hydraulic
Type 6 Mo25 Cr duplex
Type 316Type 6Mo
Hastalloy C-276
Max 60oCfor type 316
Max 110oCfor type 25Cr
Max 120oCfor type 6Mo
N/AN/A
N/A
Instrumentair
Type 6 Mo25 Cr duplex
Type 316Type 6MoHastalloy C-276
Max 60oCfor type 316
Max 110oCfor type 25Cr
Max 120oCfor type 6Mo
N/AN/AN/A
Sea water Titanium grade 2 Titanium grade 2 and 5
Hastalloy C-276
N/A
N/A85
oC
30oC
External and
saliferious
marine
atmosphere
Fresh water Type 6 Mo
25 Cr duplex
Type 316
Type 6MoHastalloy C-276
Max 60 oCfor type 316
Max 110oCfor type 25Cr
Max 120oCfor type 6Mo
N/A
N/AN/A
8/10/2019 Guideline for Selection of Instrument Tubing And
6/6
Statoil advisory document
Guideline for selection of instrument tubing and clamps for offshore and onshore plants
Technical and professional description TD0101, Final Ver. 1, Valid from 2005-04-18
Validity area: UPN/Norway/All value chain/On- and offshore
Classification: Open Page 6 of 6
Notes:
1. See Norsok standard M-001 for sour (H2S /SSC) service restrictions.
2. Optional for use of metal or polymer type clamps.
3.
Maximum operating temperature of 70oC indoor or in sheltered areas for type 316 stainless steel.
Non-insulated systems.
4.
A maximum temperature for risk of initiation of crevice corrosion will apply. Maximum 30oC inchlorinated seawater is recommended.