Background
With the development of new
and deeper water offshore locations, and the increasing H2S levels of both
newer and older reservoirs, special considerations have arisen for material
selection relative to sulfide stress cracking (SSC). Many of these completions
are operating in water depths that subject materials to combinations of low
temperatures down to 5 C and dynamic loading. As higher H2S partial pressures
are being encountered from new and existing reservoirs, unresolved questions
are being asked regarding resistance to SSC of many commonly used materials.
In some cases, industry guidelines as found in NACE MR0175/ISO 15156 have
been developed through consensus without verification by testing or evaluation.
Mostly, the concerns are for
commonly utilized materials (up to 110 ksi SMYS) such as high strength steels,
modified 13Cr, and for materials like 17-4 PH SS, 316 SS, and Monel 400 (and
super austenitics/duplex stainless steels, as well). These later materials
are widely used in sweet service, but have not been evaluated for SSC limits
to the same degree as newer alloys included in NACE MR0175/ISO 15156 standard.
However, as H2S partial pressures increase, tendencies for SSC will likely
increase, but experience with the development of the new MR0175/ISO 15156
standard has shown that little data has been available from which to develop
SSC limits over a range of H2S partial pressure and pH (See Fig. 1), and temperature. Therefore,
the current limitations for use of these alloys found in MR0175 / ISO15156
may be overly restrictive. Additionally, it may not take into account the
range of conditions for deep water applications and dynamic designs.
Problems
Evaluation
and selection of materials for sour oil and gas service essentially started
in the 1950’s, accelerated in the 1970’s with concerns for deep sour wells,
and again in the 1980-90’s with North Sea applications. However, much of this
effort has been directed at characterizing the behavior of materials used
in onshore wellhead components and downhole tubulars where service temperatures
were primarily higher than ambient temperature. In this work, it was found
that the susceptibility to SSC generally decreased with increasing temperature
over the range of around room temperature to over 125 C. Many of these studies
utilize standard test methods conducted at 24 C which seemed to be an appropriate
“reasonable worst case” for this type of service.
In
limited studies, it was also learned that susceptibility to SSC is actually
higher at a temperature somewhat below room temperature. However, there
is only inadequate data on SSC of commonly used materials at temperatures
below 24 C to develop SSC limits.
Furthermore,
evaluations for SSC have been primarily been conducted under conditions of
static load (stress), with threshold stresses determined under this simple
loading condition. This type of analysis is fine for designs that are based
on primarily static loading. However, many companies utilizing offshore components
such as risers and flow lines are using dynamic designs to achieve production
from deeper water locations. The role of dynamic loading on threshold behavior
has not been adequately examined to provide a rigorous design basis for dynamic
designs.
Based
on the abovementioned considerations, three topics for testing and evaluation
have been assembled in this JIP proposal. Work is planned to start 1stQ
2005 and arrangements for contracts and funding are currently being made.
Program Description
InterCorr
is pleased to announce that it has developed a new flexible joint industry
program (JIP) format for evaluation of the abovementioned topics. Under this
new effort, InterCorr has identified specific focused studies on these topics
related to SSC. Each topic will be funded by multiclient support and each
will have a fixed scope of work and deliverables which can be completed within
a one-year project period (calendar year 2005 running from 1st
Quarter through 4th Quarter 2005). Sponsors will have the ability
to fund any or all projects identified below.
The
three JIP projects identified for completion in FY 2005 are defined as follows:
·
Evaluation of SSC limits per NACE MR0175/ISO
15156 for commonly used materials: 17-4 PH, AISI 316 SS, and Monel K500; included
balloting of resultant limits.
·
SSC of carbon steel and modified 13Cr
materials at low subsea temperatures vs. commonly used room temperature tests.
·
Evaluation of Cyclic (Non-Fatigue) Loading
on SSC Behavior of carbon steel and modified 13Cr materials vs. commonly used
static load tests.
A
special feature of this program is an option for the sponsors to have additional
tests conducted under similar conditions on a proprietary and preferred price
basis.
Alloy
selection will focus on generics with alloys selected based on minimum composition
and maximum strength considerations for maximum utility of the data.
The
details of the three experimental programs proposed for 2005 and funding levels
for each are given below.
Project 2005-A – Evaluation of SSC Resistance of “Sweet”
Materials in H2S Environments for Development of Ballot Guidelines in MR0175/ISO
15156
The
development of MR0175/ISO 15156 has indicated that there is little H2S data
on commonly used sweet service materials. This project will provide an engineering
data base on 17-4 PH SS, 316 SS, and Monel 400 (and other materials such as
superaustenitics as the funding level allows). It will include H2S partial
pressure, pH and temperature as variables. The data will be collated and formatted
for balloting of exposure limits for these materials.
Experimental Program Details.
Materials: 3 conditions: 17-4 PH SS, 316 SS, Monel K500
(all per NACE MR0175/ISO 15156)
Heats: 3 heats of each material will be
selected in the upper range of sour service hardness.
H2S Partial Pressures: 1 condition
per material (in the proposed range 3.4 to 10 kPa H2S at pH 4.5 for 17-4 PH;
100 to 350 kPa at pH 3.5 for 316 and & Monel K500).
Solution pH: See above (3.5
to 4.5).
Chloride Content: 1 condition (5 to 15
percent).
Temperatures: 3 conditions
(23 C to 125 C) as may be required to define performance.
Stress Levels: 1 per
condition with triplicate specimens at 90 percent actual yield strength.
Additional Conditions: In order to
properly assess SSC limits an additional three conditions (H2S, pH, and/or
chloride) will be utilized as required.
Total number of tests: 81 tests.
Method: NACE TM0177 Method A
Data presentation: tabular
data; threshold plots (stress versus time to failure). Ballot items for MR0175/ISO
15156 will be prepared for sponsor review.
Estimated Budget: $54,000. If additional
sponsorship is obtained, additional materials beyond the initial three will
be included as the funding and sponsor interests permits.
Project 2005-B – Appraisal of SSC at Low Temperature
This study will focus on the development of
engineering data to support the use of common materials in subsea applications.
It will utilize standard test methodologies and assessment of threshold stresses
and KISSC at specific levels of H2S concentration, pH and temperature.
Materials of greatest interest are high strength steels and modified
13Cr alloys used for casing, risers and flow lines. However, the data may
have implications for other materials and applications in subsea applications.
Experimental Program Details.
Materials:
4 conditions (API T-95 Type I; AISI 4130-40 (HRC 22max.) 13Cr
L-80; and Modified 13Cr-110.
H2S partial pressure:
1 condition for each material type (100 kPa for steels and 10 kPa for Modified
13Cr)
Solution pH:
1 condition for each material type (3.0 for steels and 3.5 for 13Cr)
Chloride content: 1 condition (5 to 15 percent NaCl)
Test Temperatures:
2 conditions (5 C, 23 C)
Test Methods:
NACE TM0177 Method A and Method D
Stress Conditions:
5 conditions - 2 applied tensile stresses per condition (90 percent actual
yield stress; second stress condition to be selected to be the same stress
or lower depending on results at 90 percent) for tension tests; 3 wedge loaded
DCB specimens.
Total number of tests:
40 tests.
Data Presentation:
Tabular data; stress versus time-to- failure for tension specimens; KISSC
for DCB specimens.
Program Budget:
$36,000
Project 2005-C – Evaluation of Cyclic (Non-Fatigue) Loading
on SSC Behavior
This
project will assess the impact of cyclic stresses on the threshold for SSC
of a selected group of materials including a high strength steel, and a modified
13Cr alloy. It will document and provide engineering data to assess dynamic
designs where hydrogen charging is obtained from H2S corrosion. Such results
may also provide insights into the effects of hydrogen charging from external
cathodic protection under dynamic loading conditions, as well.
Experimental Program Details:
Materials: 2 conditions: API T-95 Type 1 and Modified
13Cr-110 completion steels
H2S Partial Pressures:
1 condition (100 kPa for steels and 10 kPa for Modified 13Cr)
Solution pH:
1 condition (3.0 for steels and 3.5 for Modified 13Cr)
Chloride Content: 1 condition (5 percent
NaCl)
Temperatures:
2 conditions (40 F, 75 F)
Stress Conditions:
3 tests SSR Cyclic load + 10% of mean stress; 250 cycles maximum; where
mean stress is to be 90 percent of actual yield or lower as needed to characterize
materials and the impact of cyclic load (For example: 90, 80, or 70 percent
of actual yield strength depending on initial results).
Total number of tests: 24
tests (duplicate tests at each condition).
Test Method:
NACE TM0198 slow strain rate specimen
Data Presentation:
tabular data; threshold plots (stress versus time to failure)
Program Budget:
$30,000
Program
Benefits
The initial benefit of this new flexible
JIP format is that participating companies will pay only a portion of the
total cost of these projects. The program will set specific one year goals
for funding and deliverables and the final scope of the work will be reviewed
and approved by the companies that participate. All reporting will
be paperless providing data in electronic format and a secure JIP website
which will be used to archive the program data and deliverables for easy access
by participating companies.
Additionally,
InterCorr will utilize the secure website to develop any ballot items for
MR0175/ISO 15156. This will include the use of an online forum for reviewing
ballot items that may results from this program.
Sponsors
may fund individual and multiple projects. To build further consensus and
support, each sponsor will have an option to conduct a designated number of
tests within certain parameters on a proprietary and preferred price basis
at extra cost, if they choose. Furthermore, the results from this program
will be held in confidence among the sponsoring companies for a period of
at least two years from their release to the program sponsors or until approval
is given from the sponsors to release the data for purposes of NACE ballot
preparation or industry standards initiatives.
Companies
desiring to join the program after the 1st quarter 2005 will have
to pay 15 percent higher fees than those paid by the original program sponsors.
This arrangement gives the initial program sponsors maximum leveraging of
their sponsorship fee. Sponsors can utilize year end FY 2004 or FY 2005 funding
to participate in this program.
Budget
The
budget for each of these projects has been formulated is summarized below:
·
Project
2005-A (17-4 PH, 316 SS & Monel 400; Evaluation for MR0175/ISO 15156)
$54,000 total ($9,000 per company)
·
Project
2005-B (Influence of low temperature on SSC)
$36,000 total ($6,000 per company)
·
Project
2005-C (Evaluation of Cyclic loading on SSC)
$30,000 total ($5,000 per company)
·
Optional Project Addendum for Interested
Sponsors (This fee will cover a limited number of additional tests conducted
by InterCorr on a proprietary basis under same conditions used in this program;
the number of tests will depend on the conditions selected. These will
be performed at 15 percent less than normal commercial rates). $5,000
per company
Per company fee for participation
in all three projects (Projects 2005 A-C) is $20,000 (or $25,000 including
the Optional Project Addendum). The fees will be payable in two installments
at the start (in either 4thQ 2004 or 1stQ 2005) and
completion of the projects (4thQ 2005).
The
cost of participation in these tasks is based on the participation of by six
(6) interested companies and includes costs associated for testing, engineering,
program management and administration, and reporting. If additional companies agree to participate
additional scope may be added to particular projects, with the approval of
the existing sponsors.
The
scope of the additional studies will be determined by the specific funding
level available and needs of the sponsoring group.
Alternatively, greater shared costs may be considered (with the approval of
the sponsors) to accomplish the project deliverables of specific tasks should
less than six companies agree to participate.
Background & Experience
InterCorr
International, Inc. is one of the foremost corrosion and materials testing
and research organizations. It has over 20 years of experience with evaluation
of materials in H2S environments for upstream and downstream petroleum applications.
It has over 1000 clients in 40 countries, worldwide.
This
program will involve Dr. Russell D. Kane, InterCorr Vice President, as the
program manager. He has extensive experience with evaluation of materials
for sour service applications and development of the NACE MR0175 document.
Dr. Kane is currently a member of the NACE TG 299 Oversight Committee for
the new NACE MR0175/ISO 15156 International Standard. Dr. Kane will be assisted
by the engineering and laboratory staff of InterCorr.
Action
Input for this program has
been received from prospective sponsors resulting from the initial solicitation
submitted earlier this year. Arrangements for contracts and funding currently
underway for this program planned for initiation in 1st Quarter
2005.
Those interested to obtain
more information, discuss the details of this program, or review a participation
agreement, please contact Dr. R.D. Kane or Dr. Julio Maldonado at +1 (281)
444-2282 or by email at: rkane@intercorr.com
or jmaldonado@ntercorr.com.
Figure
1 - SSC domains as a function of pH and H2S partial pressure.
