horizontal directional drilling (HDD)

Praveen Kumar on 10th August 2022

What is HDD ?

HDD is a horizontal directional Drilling Process which is make possible to conduct the crossing like reaver, Canal, Bridges, Flyovers, Railway tracks, National highways, All types of Roads, water body, drainages for the pipelines of Water, Gas and Oil etc.

Index of HDD Process

1.0 References
2.0 Design & Engineering
3.0 Pipeline Calculation
4.0 Installation Procedure

1.0 References

SPECIFICATIONS AND CALCULATION:
ASME B 31.8 - Gas Transmission and Distribution Piping Systems
API RP 1102 - Steel Pipelines Crossing Railroads and Highways

2.0 Design & Engineering

The following calculations shall be done and examine the stress imposed on a pipeline during the installation of a horizontal directionally drilled crossing prior to pullback during pullback and post installation to confirm that the pipeline will not fail.

The calculations are based on the following:
• Pipe empty on conveyors
• Pipe full of water on conveyors
• Pipe Pull back- empty/full of water

The following stresses are considered:
• Spanning Stress
• Curvature Stress
• Pulling Forces
• External Pressure

The pipe will be pulled on PIPE & PROFILE DATA BASIS, PIPE WEIGHTS, STRESS ANALYSIS:
• Spanning Stress
• Curvature Stress
• Tensile Stress
• Hoop Stress
• Stress summery

We need to consider the number of segments of HDD based on above parameters and other mandatory requirement of Isolation valves as per alignment sheets etc.

3.0 Pipeline Calculation

We need to calculate the stress calculation as described in the Deutsche standard NEN 3650 and NEN 3651 or equivalent.

The following phases should be analyzed in the pipeline design... process:

Predisposition of the launching catenary:
Before the pulling operation, the pipeline is outside the bore-hole and has a configuration which allows it to enter the hole. During this phase, the only bending moment is due to the curvature of the catenary and the weight. The pipeline should be designed so that it behaves elastically.

Pull-back operation:
In this phase the pipeline will be pulled back through the bore-hole.
The following forces should be considered:

Bending moment due to curvature of the hole;
• Friction force between the pipe and drilling mud including the friction due to extra cables/sleeves attached to the string;
• Friction force inside the hole, at the location where the soil reaction occurs;
• stress due to soil reaction;
• The resultant stress should be calculated and the pipeline designed to behave elastically.

Operating conditions:
• In this phase the loads acting on the pipeline are:
• Bending moment due to curvature of the hole; internal pressure of the gas;
• temperature difference of the line between the pipe-laying and operating conditions;
• dead loads Vertical soil load at the top of the pipe can be calculated for different pipe laying conditions.

The following effects should be combined for the purposes of calculating the resultant stress:

Calculated longitudinal effects on the entire pipeline system;
Calculated effects on the cross-section of the pipeline.
The stress/strain shall not exceed the relevant allowable stress.
The effects of soil load on the cross-section of the pipe may be analyzed. This analysis should be carried out at the deepest point reached in drilling.

4.0 Installation Procedure

After a detailed study of the soil investigation of the River, the following installation method has been formulated to provide a successful installation using horizontal directional drilling.

HDD OPERATION:-
The following details the methodology of Horizontal Directional Drilling (HDD) works.

HDD is a two-stage process. The first stage will consist of drilling a small diameter pilot hole along a designated directional path. The second stage involves enlarging this pilot hole to a diameter that will accommodate the carrier pipe and pulling carrier pipe back into the enlarged hole.

Pilot Hole:-

Rig up shall be done after mobilizing the equipment at drill location. Rig shall be anchored apposite the crossing before start of pilot hole.

The pilot hole shall by drilled with a Horizontal Directional drilling rig, to enter the ground at an angle of entry as per calculation. Pilot hole directional capability is accomplished by using a Drill Bit. The offset creates a steering bias in its direction and plane. If a change in direction is required, the same will be done by pushing drill string so that the direction of bias is the same as desired change in direction. Mechanical cutting action can be achieved by the bit attached to the offset drill string.

The actual path of the pilot hole will be monitored by a state-of-art magnetic guidance system (Drill Bit Locator) . The actual path of the pilot hole is monitored during drilling by taking periodic readings of the inclination and azimuth of the leading edge. These readings, in conjunction with measurements of the distance drilled since the last survey, are used to calculate the horizontal and vertical co-ordinates along the pilot hole relative to the initial entry point on the surface and profile is plotted for the actual path being taken along the proposed alignment. Readings are taken at every joint (normally a drill road length) the track record will help during cable and pipeline damage.
When the bit penetrates the surface at the exit point, the pilot hole is complete.

Reamimg and Pulling

After the completion of pilot hole, depending on the drilled cuttings and actual soil encountered during the pilot hole, combinations of Cutters /Reamers will be used to enlarge the hole.

The Cutter / Reamer will be fixed to the drill string will be rotated and pulled/pushed through the pilot hole. The cutter will cut through the hole with the cutting action of bentonite pumped through the drill string. On completion of first pass other Reamer (sizes may vary as per actual condition) shall be used to enlarge the hole. Cleaning passes as required shall be done depending on the soil conditions encountered. It is to be noted that the passes mentioned in the schedule are tentative and might change as per the soil conditions encountered as per the pilot hole logs. It will be decided at the site to use various combination of down hole tools as per the requirement by the Driller. Also the sizes of Reamers/Cutters and sequences to use these can be varying as per actual site conditions.

Once the cutting passes are complete a non-rotating swivel will be attached to the pull head welded to the pipeline section to prevent tensional stress on the pipeline. The drill string is aligned with the product pipe. An overhead bend will be formed by lifting the product pipe to the correct height to allow smooth entry in the borehole. As the pipeline section is drawn towards the drill rig the pipeline section will be adequately cradled with rolling cradles IUM) to facilitate a stress free line-up with the pre-reamed hole. Product pipe shall be placed on rollers to minimize the friction during pulling.

Bentonite will be pumped during pullback. Bentonite slurry and returns from the drilled hole shall be disposed off either in the river through the small ditch or in the mud pit to be excavated at site. During drilling process check shall be maintained to check the viscosity and mixing of mud shall be controlled as per the soil conditions in countered. Upon reaching rig side, the final reamer and pull back swivel are removed and the pulling head cut from in the product pipe. After completion of pull back, the rig down shall be done and the equipment is demobilized after clearing/cleaning the work area.

Please Enter the Details of HDD Site and Section

Pipe Material Grade

Pipe Outer Diameter in Inch

Pipe Wall Thickness in MM

Assumed Radius of Curvature in Mtr

Section Length in Meter

Entry Angle (8°-20°)

Exit Angle in Degree (5° to 15°)

Minimum Depth of Profile in Meter

Line Design Pressure in Kg/cm.sq

Length of One Drill Pipe in Meter

Weight of Drill Pipe in Kg / Meter

Reamer Weight (Max Considered)

Result of HDD Load Calculation

Client: Not Available

PMC/TPI : Not Available

Contractor: Not Available

Project: Not Available

HDD Location: Not Available

Calculation as per Input given by you
Item Description	Symbol	-	Unit
Pipe Material	-	-	-
Outside Diameter	Do	-	Meter
Inside Diameter	Di	-	Meter
Wall Thickness	T	-	mm
Specified Minimum Yield Strength	SMYS	-	psi
Weight of pipe in Air	Wt	-	Kg/m
Modulus of Elasticity for steel	E	-	N / m2
Radius of Curvature (Assumed)	R	-	Meter
Co-efficient of Drag	d	-	N/m2
Mud Density	dm	-	Kg / m3
Water Density	dw	-	Kg / m3
Density of steel	ds	-	Kg / m3
Proposed Section Length	L	-	Meter
Entry Angle	Q1	-	Deg
Exit Angle	Q2	-	Deg
Maximum Depth of Profile	D	-	Meter
Line Design Pressure	p	-	Kg / M2
Pre-hydrotest Pressure (1.5 X Design Pressure)	Pre-test	-	Kg / M2
Post-hydrotest Pressure (1.5 x Design Pressure)	Post-test	-	Kg / M2
Length of One HDD Machine Drill Pipe	Ld	-	Meter
Weight of HDD Machine Drill Pipe	Wd	-	Kg / Meter
Total weight of used HDD Machine Drill Pipe	tWd	-	Kg
Co-efficient of Friction in Down hole (μ)	f	-	No Unit
Static friction Co-efficient on Roller (μ)	s	-	No Unit
Reamer Weight (Maximum Considered)	Rw	-	Kg

1.0 Cross Section Area of Pipe (As in Meter ²)

(CSa) = Π/4 (Do²-Di²)

(CSa) = Π/4 (Do²-Di²) = CSa Meter²

2.0 MOMENT OF INERTIA (I in Meter⁴)

Moment of Inertia (I) = Π/4 (Do⁴-Di⁴)

I = Π/64 (Do⁴-Di⁴) = I Meter ⁴

3.0 WEIGHT OF ONE DRILL PIPE (W IN KG)

Weight of one Drill Pipe (W) = Ld * Wd

W = Ld * Wd = Wod Kgs

4.0 LOAD CALCULATIONS

4.1 Buoyancy of Steel Pipe in Down Hole (B IN KG/Meter)

B = Π/4 * Do² * dm

B = Π/4 * Do² * dm = B Kgs/Meter

4.2 Total Weight of Steel Pipe in Down Hole : (Wb in Kg/Meter)

Wb = Wt - B

horizontal directional drilling (HDD)

What is HDD ?

Index of HDD Process

1.0 References

2.0 Design & Engineering

3.0 Pipeline Calculation

4.0 Installation Procedure

Please Enter the DATA for HDD Profile Header

Please Enter the Details of HDD Site and Section

Result of HDD Load Calculation

Client: Not Available

PMC/TPI : Not Available

Contractor: Not Available

Project: Not Available

HDD Location: Not Available

1.0 Cross Section Area of Pipe (As in Meter 2)

(CSa) = Π/4 (Do²-Di²)

(CSa) = Π/4 (Do 2-Di 2) = CSa Meter 2

2.0 MOMENT OF INERTIA (I in Meter 4)

Moment of Inertia (I) = Π/4 (Do4-Di4)

I = Π/64 (Do4-Di4) = I Meter 4

3.0 WEIGHT OF ONE DRILL PIPE (W IN KG)

Weight of one Drill Pipe (W) = Ld * Wd

W = Ld * Wd = Wod Kgs

4.0 LOAD CALCULATIONS

4.1 Buoyancy of Steel Pipe in Down Hole (B IN KG/Meter)

B = Π/4 * Do2 * dm

B = Π/4 * Do2 * dm = B Kgs/Meter

4.2 Total Weight of Steel Pipe in Down Hole : (Wb in Kg/Meter)

Wb = Wt - B

Wb = Wt - B = Wb Kg/Meter

4.3 Bending Moment :-( bm in Newton / Meter)

bm = (E * I) / R

bm = (E * I) / R = bm Newton

4.4 Force due to Buoyancy:- (F1 in Newton)

F1 = (f) * (-Wb) * (L) * 9.806

F1 = (f) * (-Wb) * (L) * 9.806 = F1 Newton

4.5 Force due to Curvature:- (F2 in Newton)

F2 = (4 * f * bm) / (∏ / 360 (Q entry * R + Q Exit * R))

F2 = (4 * f * bm) / (Π / 360 * ((Q1 * R) + (Q2 * R)) = F2 Newton

4.6 Force due to Cohesion:- (F3 in Newton)

F3 = d * Π * Do * L

F3 = d * Π * Do * L = F3 Newton

4.7 Pulling Force: (F in Newton)

F = F1 + F2 +F3

F = F1 + F2 +F3 = F Newton

4.8 Total Pulling Load: (in Kg)

tpl = 1.5 * (F + tWd + Rw)

tpl = 1.5 * (F + tWd + Rw) = tpl Ton

5.0 STRESS CALCULATIONS

5.1 Maximum Allowable Stress :- (in N/M 2)

s = 90% of SMYS

s = 90% * SMYS = s Newton / Meter 2

5.2 Bending Stress :- (in N/M 2)

Bs = E * D / 2 * R

Bs = E * Do / 2 * R = Bs Newton / Meter 2

5.3 Tensile Stress :- (in N/M 2)

ts = F * CSa

ts = F * CSa = ts Newton / Meter 2

5.4 Longitudinal Stress during Installation :- (in N/M 2)

Ls = ts + Bs

Ls = ts + Bs = ts Newton / Meter 2

HENCE, PULLING IS SAFE OR NOT

6.0 Stress Calculations During Post Hydrotest:

6.1 Hydrostatic Test Stress :- (in N/M 2)

Bh = Post-Test * Do / 2 * T

Bh = Post-Hydrotest * Do / 2 * T = ts Newton / Meter 2

6.2 FOR Post Installation :-

pi = Bs + Bh

pi = Bs + Bh = pi Newton / Meter 2

7.0 Stress Calculations For Maximum Allowable Stress

S = Allowable Stress for bending

S = s - pi

S = s - pi = pi Newton / Meter 2

8.0 Minimum Allowable Radius of Curvature :- (in Meter)

r = (E * Do) / 2 * S

r = (E * Do) / 2 * S = r Meter

HENCE, The calculated radius is Less or Greater than the proposed radius of curvature.

1.0 Cross Section Area of Pipe (As in Meter ²)

(CSa) = Π/4 (Do²-Di²) = CSa Meter²

2.0 MOMENT OF INERTIA (I in Meter⁴)

Moment of Inertia (I) = Π/4 (Do⁴-Di⁴)

I = Π/64 (Do⁴-Di⁴) = I Meter ⁴

B = Π/4 * Do² * dm

B = Π/4 * Do² * dm = B Kgs/Meter

5.1 Maximum Allowable Stress :- (in N/M²)

s = 90% * SMYS = s Newton / Meter²

5.2 Bending Stress :- (in N/M²)

Bs = E * Do / 2 * R = Bs Newton / Meter²

5.3 Tensile Stress :- (in N/M²)

ts = F * CSa = ts Newton / Meter²

5.4 Longitudinal Stress during Installation :- (in N/M²)

Ls = ts + Bs = ts Newton / Meter²

6.1 Hydrostatic Test Stress :- (in N/M²)

Bh = Post-Hydrotest * Do / 2 * T = ts Newton / Meter²

pi = Bs + Bh = pi Newton / Meter²

S = s - pi = pi Newton / Meter²