New Developments in High Pressure
Equipment Design Features
Mechanical Equipment Manager â€“ Saipem
The urea synthesis environment represents one of the most aggressive media for materials in the
chemical industry and therefore the continuous improvement on
- design details
- metallurgical requirements
- production solutions
- inspection and maintenance criteria
is the basis for the development of solutions towards a corrosion controlled Snamprogetti Urea
Technology. The failure of some Strippers, at the beginning of this decade, boosted the need to find
an immediate and appropriate solution.
The main issue was identified in increasing the control on all elements that constitute the core of
technology application to HP equipment through a â€śwell established urea technology teamâ€ť with
specific skills on process, engineering, inspection including after sales assistance. In this framework
the End Userâ€™s support is having a base role in focusing the topic developing areas for increasing
The results, achieved through this approach, can be listed as follows:
- Updating of qualification procedure for the manufacture of high pressure urea equipment
- Synergy with manufacturers
- Effectiveness in the application of SPC.CR.UR.510 rev. 3 from 2003 up to now
- Improvement with new engineering and production solutions
- Development of new technology (OmegabondÂ® tubes) as result of upgrading of
Snamprogetti titanium stripper technology
- â€śAfter Sale Assistanceâ€ť to the End Users as essential component for continuous
improvement of the technology.
UPDATING OF QUALIFICATION PROCEDURE FOR THE MANUFACTURE OF HIGH
PRESSURE UREA EQUIPMENT
Considering that HP equipment plays a crucial role in reliability of the urea plant, Snamprogetti
decided to issue a more stringent qualification procedure (SPC.CR.UR.519 rev. 1 dated 2005) for
manufacturers of HP equipment. The aim is to ensure that manufacturers understand the criticality
of each production step for the complete success of the technology.
The novelties related to introduction of the new qualification procedure are relevant to
Simulation of design and production process applicable for the selected equipment
Detailed construction drawings.
Welding data book (WPS-PQR) for all the weld joints in contact with the process fluid.
Purchase of all materials and consumables required to prepare qualification test coupons
(QTC), in accordance with the following table, included in the scope of work. QTC welding
activities need to be witnessed by Saipem specialists.
H.P. Urea Equipment
Material Coupons Requirement
(A) (B) (C) (D)
(A1) (C) (D)
(A/A1) Tube to tube sheet welds â€“ Tubes to tube sheet protrusion 5 mm
Tube to tube sheet welds â€“ Tubes to tube sheet protrusion 17 mm
Liner butt weld joint using GTAW or SMAW process.
Liner weld seam joint on buttering layer using GTAW or SMAW process.
140 mm Min.
200 mm Min.
BASE PLATE (C.S.)
BASE PLATE (C.S.)
BASE PLATE (C.S.)
Preparation of all samples and specimens for the corrosion test and metallographic analysis as
per the applicable revision of the General Specification SPC.CR.UR.510. All tests have to be
performed and certified by an independent laboratory previously approved by Saipem.
Ensuring a dedicated after sale service organization
The result is a deep control of manufacturerâ€™s capability in engineering, material purchasing,
manufacturing and inspection from the beginning of the qualification procedure, sharing with
manufacturers all intrinsic criticalities of the complete production. This approach results in a
mandatory vendor list with high production quality either when Saipem is EPC Contractor or when
its role is Technology Licensor.
SYNERGY WITH MANUFACTURERS
Manufacturing and supplying HP equipment for urea technology requires a clear understanding that
production has a crucial role in the final success of the technology. This is the reason why
Saipem/Snamprogetti has developed a continuous relationship with his few qualified manufacturers
to ensure the achievement of the highest quality and the soundness application of all
Saipem/Snamprogetti requirements not only during engineering and materials purchasing phases
but also during production. This approach can be summarized as follows:
- Synergy between Saipem and his qualified manufacturers increasing the awareness of the
crucial role of production as the main component for the final success of the technology
- Sharing with qualified manufacturers the importance of dedicating a team in terms of
engineering and production assuring the continuous improvement also at work shop
- Ensuring a continuous presence of Saipem Inspectors at work shop with the aim, in relation
to each internal production capabilities, of driving and monitoring the production solutions
towards the optimum final results.
EFFECTIVENESS OF SPC.CR.UR.510 REV.3
One of the main issues, integral part of new approach on urea technology, was the evaluation of the
actual applicability of the latest revision of the general specification "Austenitic stainless steels for
urea plant high pressure section" (dated 2003) and the response of the market following the new
material requirements. Attention has been particularly given to:
140 mm Min.
200 mm Min.
BASE PLATE (C.S.)
- availability of materials
- feedback from manufacturers on all requirements related to the essential variables of the
accepted welding processes
- tube to tube sheet weld production mock-up
- laboratories feedback
The rev. 3 of the above mentioned specification was in general well accepted by urea equipment
and piping manufacturers. Although the chemical and metallurgical requirements have been made
more stringent compared to the revision 2, no particular problems have been reported about the
availability of any of the products required for the construction of the urea plant. So far the
deviations that have been requested by manufacturers and agreed by Saipem/Snamprogetti have
been comparatively few and limited to particular circumstances and to some minor components of
the urea plant, mainly forgings. The producers/manufacturers of 25Cr22Ni2Mo did not find
difficulties in producing materials according to revision 3 with the required characteristics.
Manufacturersâ€™ feedback on essential variables of welding procedure qualification was positive and,
in the spirit of partnership, Saipem/Snamprogetti accepted some modifications to match production
The introduction of tube to tube sheet weld production mock-up at three different times of
production was considered, by manufacturers, as three very important milestones allowing an
important direct quality feedback on welds, filler metal and base metals applied.
Revision 3 was also easily adopted by the laboratories approved by Saipem/Snamprogetti to
perform the required tests. The metallurgical examinations posed no problems of execution or
interpretation as they reflect the normal laboratory practice in examining austenitic stainless steels.
More specifically, the classification of the austenitic microstructures based on the ASTM A262
Practice A (step, dual or ditch) proved to be particularly helpful in discriminating between
acceptable and non-acceptable materials, including the 25.22.2 super austenitic alloy for which this
practice was not originally intended. Following the six yearsâ€™ experience (2003 - 2009) in the
application of revision 3 and the feedback received, a new revision is now planned, and it will
include an even better determination of the chemical composition limits based on the type of semi
finished product, whilst most of the other material requirements will be confirmed.
NEW SOLUTIONS ON HP EQUIPMENT PRODUCTION
The target of the continuous improvement and the feed back received from End Users are the basis
of new developments:
The baffle materials in Carbamate Condenser have been changed from Carbon Steel into
Stainless Steel, since a corrosion phenomenon was observed in few cases, as a cause of water
contamination in Carbamate Condenser shell side.
Hereafter a figure of a Carbon Steel baffle near the U bends, in which the hole enlargement and
the corrosion pattern on the baffle is visible
Future standardization of leakage system. Four weep holes for each lining barrel, two weep
holes for each petal and crown and two for each nozzle greater than DN 6 inches will be the
Improvement of weep hole design in terms of safety during plugsâ€™ screwing/unscrewing or
dechoking procedure (strength welds and antirotation system for weep hole). Some
examples are shown in figure 2.
New joint design between lining plates (min. root distance) in 25Cr22Ni2Mo to allow the
deposit of two opposite root weld beads to ensure full fusion of lining corner with buttering
assuring an increased adherence of lining with buttering.
Sampling of coupons for corrosion test for all materials in contact with process fluid
attended by Saipem inspectors.
Testing of all tube sheets, after weld overlay, with high sensitive ultrasonic inspection.
Pre-machining of Carbon Steel heads to minimize the gap between base material and lining
plates to reduce the risk of stress on lining welds after hydro test.
Optimization of welding process through the use of programmable automatic orbital GTAW
machine for tube-tube sheet weld joint.
Introduction of automatic GTAW for last 25Cr22Ni2Mo weld overlay deposit on Stripper
bottom tubesheet with tight interpass temperature control, has allowed a weld deposit with
superior corrosion resistance.
Excellent performances of GTAW are related to:
â€˘ Low heat input
â€˘ Least change in the chemical composition from wire to deposit
â€˘ Better control of weld pool
Modification of hold down grid and coupling area between ferrule and tube for
OmegabondÂ® and Titanium Stripper
Review of manufacturer material purchase specifications in order to ensure the compliance
with process requirements.
Adoption for Carbamate Condenser of a proper dummy shell in order to avoid any damage
on tube bundle during shop handling and any distortion during final welds of tube sheets to
channel and permit a preliminary helium test on tube to tube sheet welds.
Introduction of water jet cut technology for internals in order to avoid HAZ on cut edge.
NEW DEVELOPMENTS OF TECHNOLOGY
In urea plants the environment is very aggressive and stainless steel is exposed to corrosion and
erosion fluids that have to be managed by acting on operating parameters, adding proper quantity of
passivation air, adopting great care in welding materials and generally during critical equipment
The needs driving the development of new solutions and construction processes can be identified
and summarized in:
â€˘ Flexibility of the plant
â€˘ Increase output via more aggressive process conditions
â€˘ Elimination of air passivation system for the Stripper
Snamprogetti's efforts toward the above mentioned objectives led to the development of the Ti/Zr
extrusion-bonded tubes (OmegabondÂ®) advanced tubing solution as result of the cooperation with
ATI Wah Chang. The starting basis is Snamprogettiâ€™s experience in more than 80 titanium strippers
whose life existing factor was represented by the internal tube erosion.
This new tubing technology involves multiple pure metals and bonding technologies and
incorporates extrusion-bonding production processes.
The benefits to urea Producers can be identified in
â€˘ Enabling urea plants to run at higher efficiency
â€˘ Elimination of passivation air in the bottom of the stripper
â€˘ Operation of units at a higher temperature boosting plant capacity and optimizing energy
702 Zirconium and Ti Grade 3
Ti Grade 3 Outer Tubing
702 Zirconium Inner Tubing
AFTER SALE ASSISTANCE
With a background of fifty years in Urea plant technology, Saipem is able to offer its Customers
qualified services and assistance regarding the corrosion problems and general maintenance during
the life of the plant, especially related to the high pressure equipments.
This service can be carried out at site to support the End User during the scheduled shut down of the
plant or from headquarter to support and assist the End User on the several aspects of the equipment
manufacturing (procurement, inspection, repair).
The constant contact between Saipem, qualified high pressure equipment manufacturers and Urea
plant End Users has created a positive synergy able to monitor and manage the â€śproblemsâ€ť during
the life of the equipment. This synergy helps in transferring the experiences into the design and
equipment manufacturing, with the final purpose of improving the quality of the equipment.
Experience feedback is essential to enhance the technology and design of high pressure equipment.
Although high criticality of urea process due to fluidsâ€™ typology the strategy, carried out during last
years and related to:
development of new production solutions
synergy with qualified manufacturers
guarantees very high confidence on final results of manufacturing HP equipment ensuring high
resistance against corrosions/erosions.
The final success is completed with a proper operation and maintenance of the plants provided by