COOLING WATER INJECTION SKIDS BASED ON GE STUDY-HABSHAN
HOT TAP CALCULATION
COMPANY
: ABU DHABI GAS INDUSTRIES LTD (GASCO)
EPC CONTRACTOR : BABCOCK BORSIG SERVICE
ENGINEERING
CONSULTANT
: TEBODIN MIDDLE EAST LTD
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Table of Contents
1. INTRODUCTION
2. SCOPE
3. DEFINITION AND ABBERVIATIONS
3.1 Definitions
4. REFERENCE DOCUMENTS
4.1 Codes and standarads
4.2 Project Specific Document
4.3 Company DGS
5. HOT TAP LIMITATION
5.1 Process Fluid
5.2 Pipe Material
ANNEXURE-A : 6” X 1/2" HOT-TAP (WT-6.8MM)
6. INTRODUCTION
7. MAXIMUM TEMPERATURE OF THE PIPE WALL
8. TEMPERATURE DERATING METHOD
9. VELOCITY CONSIDERATIONS
10. LOADING
11. CONFIGURATION REQUIREMENTS
11.1 General
11.2 Area Replacement
12. STRENGTH TEST PRESSURE
13. CONCLUSION AND RECOMMENDATION
ATTACHMENT-1 : PIPING LAYOUT
ATTACHMENT-2 : UT REPORT
ATTACHMENT-3: WELDING PROCEDURE SPECIFICATIONS PARAMETERS
ATTACHMENT-3: WELDING TEMPERATURE OF PIPE WALL
ATTACHMENT-3: HOT TAP SAFE TEST PRESSURE RATIO
23
24
25
1.
INTRODUCTION
Abu Dhabi Gas Industries Ltd. (GASCO) owns and operates Habshan Plant Located in the
In the western region of the emirate of Abu Dhabi which is situated 150 Kms south of Abu
Dhabi city. The plant elevation is 64 meters of jebel Dhanna Datum and approx. 25
kilometers from the coast. Habshan cooling water system is divided into three units,
Namely Habshan-0; 1 & 2.
GASCO- Habshan has been facing the problem of brass tube failure in lube oil coolers &
carbon steel tube failures in water chillers and in order out the problem , a study was
carried out by GE.
As a recommendation from GE study, GASCO intends three chemical injection packages for
each cooling water expansion drum 66-V-501 located in Habshan-0, and 66-V-701 located in
Habshan –II . These packages are corrosion inhibitor injection package, Biocide injection
package and Oil dispersant injection package .
GASCO awarded the project to M/s Babcock Borsig Service on EPC basis to meet the
objective of this project.
M/s. Babcock Borsig Service has awarded detail engineering part of the project to Tebodin
middle east Ltd.(TME) as a subcontractor to Babcock.
2. SCOPE
Under this project six (6) hot tapping connections are required as tabulated below. The hot
tap shall be carried out based on approved document “Method Statement for Hot Tapping”
(HBT/E-040449-MS-1300-009). The calculation enclosed in appendix-A is applicable to
TP-03, TP-04 & TP-05, Where the actual wall thickness of the run pipe (6” NPS) is 6.8mm as
measured by UT.
For TP-09,TP-10 & TP-11 same calculations are applicable , since the wall thickness is 6.9mm
as measured by UT and all other parameters are identical.
Tie-in
TP-03
TP-04
TP-05
Hot Tap
6”X1/2”
6”X1/2”
6”X1/2”
Service
Cooling water
Cooling water
Cooling water
Table-1
Header(Existing)Line no
66-3501-L-6”
66-3501-L-6”
66-3501-L-6”
Branch (new) Line no
66-xxxx-CH-1/2”-13450-N
66-xxxx-CH-1/2”-13450-N
66-xxxx-CH-1/2”-13450-N
TP-09
TP-10
TP-11
6”X1/2”
6”X1/2”
6”X1/2”
Cooling water
Cooling water
Cooling water
66-0709-CWS-6”
66-0709-CWS-6”
66-0709-CWS-6”
66-xxxx-CH-1/2”-13450-N
66-xxxx-CH-1/2”-13450-N
66-xxxx-CH-1/2”-13450-N
This report gives the outline for hot tap design calculations to arrive the maximum
operating pressure and other design guidelines to be considered while carrying out hot
tapping works on the operating cooling water lines.
The Design calculation for hot tapping shall be include the following considerations:
●
Process Data / Limitations
● Pipe
Data / welding suitability
● Pressure, Temperature
and Velocity considerations
● Loading
3.
DEFINITIONS AND ABBREVIATIONS
3.1
Definitions
COMPANY
Abu Dhabi Gas Industries ltd (GASCO)
PURCHASER/EPC/
BABCOCK BORSIG SERVICE
CONTRACTOR
ENGINEERING
TEBODIN MIDDLE EAST LTD (TME)
CONSULTANT
VENDOR
VENDOR of Equipment, including Sub-vendors(s) appointed by
VENDOR to carry out part or all the work
4. REFERENCE DOCUMENTS
4.1 Codes and Standards
ASME B31.3
- Process piping
ASME Sec VIII
- Boiler and pressure Vessel Code
DEP 31.38.60.10-Gen - Hot-Tapping on pipelines, Piping and equipment
4.2 Project Specific Document
HBT/E-0400449-MS-1300-009 - Method Statement for Hot Tapping
02-A0-xxxx
- Utility Flow Diagram UNIT-66 cooling water System
02-A0-xxxx
- Piping Plan Area 60-22
4.3 Company DGS
DGS-1300-100
- Design General Specification for piping Tie-ins
HBT/E-SP-XXX
- Piping Material Specification
5. HOT TAP LIMITATION
5.1 Process Fluid
According to DGS-1300-100 Section 8.3.2. Hot tapping shall only be performed under the
following conditions:
● The
contained process fluids shall remain stable when subjected to the high metal
Temperature during welding
● The
process fluids remain stable when it comes in contact with air during drilling and
Perforation operations
● There
shall be no decomposition or chemical reaction between components of the
Contained fluid (explosive, ignition, exothermic reaction)
● There
shall be no chemical reaction between the fluid and the hot contained wall
(Burning, stress, corrosion, embrittlement).
These requirements lead to a number of situations in which welding operations are prohibited on
equipment which contains:
• Mixtures of gases or vapours within their flammable range or which may become flammable as a
result of heat input in welding operations
• Substances which may undergo reaction or decomposition leading to dangerous increase in
pressure. Explosion or attack on metal. In this context, attention is drawn to the possibility that
under certain conditions of concentration, temperature and pressure, acetylene and other
unsaturated hydrocarbons may decompose explosively, initiated by a welding hot spot
• Oxygen-enriched atmospheres in the presence of hydrocarbons which may be present either in the
atmosphere or deposited on the interior surface of equipment or pipe
• Compressed air in the presence of hydrocarbons which may be present either in the air or
deposited on interior surfaces of equipment or pipe
• Gaseous mixtures in which the partial pressure of hydrogen exceeds 700kPa(g), except where
evidence from tests has demonstrated that this can be done safely .
In addition, welding operation is prohibited on piping which contains hazardous subs conditions,
as listed below. If any of these substances are known to be present within the piping , even in small
quantities, investigations should be made on the stability of the fluid at the pipe wall temperature.
The relevant substances/conditions included:
• Acetylene
• Acetonitrile
• Butadiene
• Caustic soda
• Chlorine
• Compressed air (Pressure is excess of 3000 kPa(g))
• Ethylene
• Ethylene oxide
• Rich/lean DEAIMEA
• HP steam (pressure in excess of 329 kg/cm2 g)
• Hydrogen
• Hydrogen sulphide
• Hydrofluoric acid
• Oxygen
• Propane
• Propane oxide
• Sulphuric acid
• Toxic substances
Conditions:
• Vacuum conditions
• Dissolved hydrogen in the pipe wall (e.g. due to service history)
• Pyrophoric scale deposits
Note:
1. The above list is not exhaustive, but gives an indication only.
2. The fluid under consideration is Cooling Water and does not involve any of the above
Substances.
3. Vacuum conditions are not envisaged during welding.
5.2 Pipe Material
Fitting and branch material shall be of a type and grade compatible with the material of the run-pipe
to be hot-tapped.
Hot-Tap welding should not normally be performed on materials which require post-weld heat
treatment (PWHT). However, if stress relieving or post-weld heat treatment is required, a specialist
shall be consulted to access whether it is in fact feasible to make the specific hot-tapping operation
with post-weld heat treatment. (Stress-relieving may be required when a material is susceptible to
stress corrosion cracking and post-weld heat treatment may be specified by the design code when
the wall thickness is greater than a certain limit).
Welding operations shall not be performed if the actual wall thickness of the run-pipe, as determined
by ultrasonic testing, is less than 4.8mm.
Welding shall not be performed on lined, clad or special internally coated pipe.
ANNEXURE-A: 6" X 112" HOT-TAP (WT-6.8MM)
6. INTRODUCTION
The following design data of the existing 6" cooling water line (66-3501-L-6") has been considered
for hot tap design calculation at TP-03. The tie- in location is at the area 60-22(Refer attachment-1) .
Pipe Material
-
API 5L Gr.B
Service
-
Cooling Water
Wall Thickness (H)
-
6.8 mm (Refer attachment-2)
MAOP (Max. Al lowable Operating Pressure) - 6 bar g
MNOP (Max. Normal Operating Pressure)
- 6 bar g
Expected arrival Pressure at Tie-in point
- 6 bar g (To be confirmed by COMPANY)
Max. Design Temperature
- 87 °C
Max. Operating Temperature
- 45 °C
7. MAXIMUM TEMPERATURE OF THE PIPE WALL
The maximum temperature of the inside of the pipe wall attained during welding may be derived
from the actual wall thickness of the pipe (ta) and the expected heat input (HI) from the
following equation:
HI = K V * A
S
Where:
HI = heat input (Joules per mm)
K = net facto( = 0.85 for butt welds, and = 0.57 (=213 x 0.85) for fillet welds.
v = voltage (volts)
A = current (amperes)
S = travel speed (mm/s)
For a specific hot-tap. the permitted ranges of voltages. current and welding speed are defined in
the Welding Procedure Specification (WPSl or method statement. The actual or mid-range valves can
be considered.
The heat input during the Root pass, 1 st butterin9 and 2nd buttering are calculated using the
current , voltage and travel speed values derived from the WPS parameter provided by
CONTRACTOR (Refer attachment-3) and are tabulaled below in Table-A1 :
HI = K V*A
S
HI = 0.57 22.5*90
1.76
HI = 659.57 J/mm
Table-A1: Heat Input for NPS 6" X 1/2" Hot Tap
Pass
1) Root Pass
2) Buttering
3) Buttering
Current
Voltage(V)
90
90
90
22.5
22.5
22.5
Travel
speed(mm/s)
1.75
1.75
1.75
RA heat input
(j/mm)
659.57
659.57
659.57
From the heat input vs wall thickness graph. The welding temperature of the pipe wall (i.e. The
maximum temperature of the inside of the pipe wall attained during welding) is determined for the
preheat case with initial pipe wall temperature of 25 °C. (Refer Attachment-4 of this document which is
a copy of Appendix-12 of OGS-1300-OO1).
The actual run pipe (ON 6' existing header) wall thickness is 6.8 mm. As confirmed by UT (Refer
attachment-2). From the graph in attachment-4, the inner pipe wall temperatures, the penetration
depths, reduced wall thicknesses during the critical welding passes are calculated and tabulated
below in Table-A2 :
Table-A2
Pass
1) Root Pass
2) Buttering
3) Buttering
Max.inner wall
temperature(oc)
Penetration depth`u’ (mm)
Reduced wall
thickness `t’ (mm)
420
350
272
1.61
1.30
1.08
5.19
5.50
5.72
Post pass
thickness *
(mm)
8.8
10.8
12.8
• Assume conservative estimate of 2mm thickness each pass.
As per Section 6.3.3.3 of DGS·1300·100, for general safety reasons:
1) During the hot tap welding, the pressure of fluid inside the run pipe shall not exceed the
maximum allowable pressure. The maximum allowable pressure during welding operation is calculated
by the Temperature Derating Method.
2) At any time during the hot tap operation, the pressure of fluid inside the run pipe shall not
exceed the maximum working pressure of the hot tap equipment. The maximum normal
operating pressure (MNOP) of the Cooling water line is 6 bar (g) (To be confirmed by
COMPANY). Thus the hot tap equipment rating should be higher than 6 bar (g).
8 . TEMPERATURE DERATING METHOD
The allowable pressure is given by the equation:
P = 2t SEWT
(D-2tY)
Where
(as per ASME B31 .3)
P = Max. Allowable operating pressure during welding operation in N/mm2
S = 137.89 N/mm2 for API5L Gr.B@8rC
D = Outside diameter of the run pipe = 168.28 mm
w = Weld joint strength reduction factor = 1.00 (at temp. 510 D C and below)
y = Coefficient from table 304.1.1 of ASME 831 .3 = 0.4
t = Reduced wall thickness, (H-u) = 5.19 mm
E = Quality Factor from Table A-1A or A-l 8 of ASME 831 .3 = 1.00
T = Temperature Derating Factor is 0.634 (Refer DGS-1300-100, Sec 8.3.3.3, Table-l)
p = 2 x 5.1 9 x 137.89 x 1.00 x 1.00 x 0.634
168.28 - (2 x 5.1 9 x 0.4)
= 5.53 N/mm2
= 55.3 bar (9) > 6 bar (g)
Hence calculated maximum allowable operating pressure is 55.3 bar (g) whereas the expected
arrival pressure at the hot tap point is 6 bar (g)
"THE OPERATING PRESSURE OF THE EXISTING MAIN PIPE IS ACCEPT A8LE FOR HOT TAPPING
OPERATION".
9. VELOCITY CONSIDERATIONS
The suggested maximum and minimum velocity for liquid flow is 1.75 m/sec and 0.5 m/s
respectively.
Max. Flow Rate, Q = AV
Q= π x (d1)2 x V
4
Where, di = inside diameter of 6" run pipe = 0.1547 m
V= 1.75 m1sec
Q =
3.14x(0.1547)2 x1 .75
4
= 0.0329 ml/s = 118.44 ml /h
Min. Flow Rate. Q = AV
Q= π x (d1)2 x V
4
Where, di = inside diameter of 6" run pipe = 0.1547 m
v = 0.5 m/sec
Q= 3.14x(O.1547)2 xO.5 = O. 0094m3/s = 33.84m3/h
4
The flow corresponding to the minimum velocity of O.5m/sec shall at least be maintained during hot
lapping. COMPANY shall ensure the minimum velocity of 0.5 m/sec (0 = 33.84 m3 /h) during
welding.
10. LOADING
The hot-tap branch will be installed at 900 to the axis of the run pipe. The hot lap machine shall be
properly and adequately supported such that weight of the hot-tap isolation valve and the drilling unit
(hot-tap machine) etc. shall not cause any twisting of the run pipe. Also the operation shall be such as
not to cause any buckling of the pipe wall at the base of the branch.
11 . CONFIGURATION REQUIREMENTS
11.1 General
Care shall be taken during hot tapping to ensure the following:
• The separation of the attachment fillet welds from existing circumferential welds shall be at
least one run pipe diameter (i.e. 6" or 168.3 mm) and in no case shall be less than 150 mm.
• Interference with the longitudinal weld seam of the run pipe shall be avoided
• The chosen location in the run pipe shall be checked and verified as suitable for the hot tap
connect ion, taking into consideration factors such as diameter and ovality, remaining (existing) pipe
wall thickness, internal I external corrosion, defects in the pipe wall like internal deposits, soundness
of adjacent welds, weld seam locations etc.
11.2 Area Replacement
A run pipe having a branch connection is weakend by the opening made in it. The branch
connection must reinforce the opening and restore the original strength of the run pipe. 11 is the
intent of this document that these integrally reinforced branch outlet fitting and the deposited weld
metal used to attach the fitting to run pipes contain all the reinforcement required by the
applicable piping codes without the addiction of saddles or pads.
As the proposed hoi tap is 6" x 1/2" socklet , area replacement calculation are not required in this
case.
12. STRENGTH TEST PRESSURE
The general testing procedures to be followed shall be:
1. The hot-tap valve before installing on the branch shall be body and leak tested as per the
direction of the company.
2. Testing of the branch connection, with the valve installed and in the open position. to
demonstrate leak tightness and strength. Duration should be at least 30 minutes.
3. Leak testing of the drilling machine mounted on the valve (with valve closed) for duration of 5
minutes.
The hot tap valve shall have a pressure test applied to the seats and body. During the test, this
pressure acts as an external pressure on the run pipe. In order to avoid buckling of run pipe. as per
c1ause 8.8 .1 of DGS-13~loo. for set on branch connections, the strength test pressure shall be as per
Appendices 15 of DGS-1300-1 00.
PT = Test pressure in the branch pipe
PA = Actual Pressure in the run pipe = 6 bar g (To be confirmed by COMPANY)
F = Ratio of actual operating stress level in the wall of the run pipe to the material Specific minimum
yield strength (SMYS)
S = Stress Value
S = [ P (D-2tY) ] /2tEW
S = [ 6x (168.28-2x 6.8 x 0 .4) ] / (2 x 6.8 x 1.0x 1.0)
= 71.84 bar (g)
= 1042 psi
F = 1042/35000 = 0.0297
It is assumed that F = 0.5 for more conservative result.
0= Outside diameter of the run pipe = 168.28 mm
d = Out Side diameter of the branch pipe = 21 .34 mm
t = Actual thickness of the run pipe = 6.8 mm
As per Appendix 15 of DGS-1300-100 (copy enclosed as Attachment -5) for .
d / D=0.13
D/ t = 24.75
F = 0.5
PT I PA = 1.625
Hence PT = 1.625 x 6 = 9.75 bar (g)
This pressure the run pipe can withstand without buckling. Hence the test pressure for the branch
connection shall not exceed 9.75 bar (g).
13. CONCLUSION AND RECOMMENDATION
• The tabulated values of voltage. current and travel speed listed in Table-A 1 are provided by the
CONTRACTOR and shall be maintained during the welding of the branch fitting.
• Flow rate during the welding shall be Q = 33.84 ml/h to maintain minimum velocity of 0.5m/sec
• The Maximum test pressure for the branch connect ion shall be 9.75 bar (g) and the testing
medium shall be water.
• Before starting the hot lap operation the CONTRACTOR shall f ill the hot tap procedure check
list (Appendix 17 of DGS-1300-1OO) and shall get approval from COMPANY.
• For General Safety Precaution for hot lap the CONTRACTOR shall refer to Section 7.4 of DGS-1300100
• The document includes only one set of calculation for the HOT -TAP operation and shall be
applicable for all six (6) connections (Refer Table-1). Since the calculation parameters are
identical.