FMC inspect wall thickness

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SUBJECT: Inspection of FMC - Chiksan Flexible Pipe PAGES: 3
This inspection procedure is applicable for choke and kill lines supplied by FMC.
FMC was contacted and the following information obtained.
A) First, to confirm equipment is FMC:

- FMC is stamped on back of hammer union nuts
- A name plate is (was) installed on one elbow of each loop
- A 7 digit part no. is stamped into each piece, beginning with a 31... or 32...
B) Inspection of Long Sweep Elbow

The FMC Chicksan "Operating and Maintenance Instructions" state that "Longsweep swivel
joints which exhibit a loss of wall thickness exceeding 20% at any point must be taken out of service.
Wall thickness may be measured using visual, sonic or mechanical means."

- The majority of erosion occurs on the outside wall of the bends.
- To determine the original wall thickness in the field, it can be determined by wall thickness on
the side of the bend. Then 80% of this measured side wall thickness is the minimum allowable.
Note that this method assumes that there has been no significant side wall reduction.
- The best method to determine minimum allowable wall thickness is to contact FMC, Fluid
Control Div. at Stephenville Texas, Fax (713) 965-8286. Mr. Paul Crawford will need to
know:

- Working Pressure
- Figure No. of the Union
- Long or Short Elbow
- H2S or Standard Service

C) Inspection of pipe wall thickness:

- Are the lines H2S service or standard?
For H2S service one material type is to be used:
- 100,000 psi tensile strength material is used with 80,000 psi yield.
- Hardness will be less than Rc 22, or BHN 235 on the Brinell scale

For standard Service two material types are to be used:
- 120,000 psi tensile strength material is used with 100,000 psi yield.
or
- 130,000 psi tensile strength material is used with 110,000 psi yield.
- Both materials will have hardness greater than Rc 22, or BHN 235 on the
Brinell scale
- Determining material allowable stress level
A method to assist in determining yield strength is to take the Brinnel hardness of the
material. As a rule of thumb:

BHN x 500 = Tensile strength
From the tensile strength we can determine the yield of the material we are working
with. If the lines are H2S service there is no choice of material strength.

The allowable stress which FMC uses is, 2/3 yield, or
- for 80,000 psi this = 53,330 psi allowable stress
- for 100,000 psi this = 66,660 psi " "
- for 110,000 psi this = 73,330 psi " "
- Calculating minimum wall thickness:
FMC uses the following equation, ANSI B31.3, Chapter IX, paragraph K304.1.2,
equation 34a:
T= Wall thickness, in

T = (D / 2) [1 - e-(1.155xP / S)] D= pipe OD, inches
P= pressure, psi
S= Max. allowable stress, in psi.

RESULTS OF CALCULATIONS FOR MINIMUM PIPE WALL THICKNESS:
Note: These wall thickness are based on no additional thickness allowed for future corrosion
and that the maximum WP is 10,000 psi.

H2S service material with 80,000 psi yield:
3" nominal pipe, min wall = .339"
2" nominal pipe, min wall = .230"

Standard service material with 100,000 psi yield:
3" nominal pipe, min wall = .278"
2" nominal pipe, min wall = .188"

Standard service material with 110,000 psi yield:
3" nominal pipe, min wall = .254"
2" nominal pipe, min wall = .172"

EXAMPLE CALCULATION:
3" nominal pipe with an OD of 3.50" and at 10,000 psi WP with no corrosion allowance:
T= Wall thickness, in
D= 3.50"
P= 10,000 psi
S= 53,3300 psi

T = (3.5"/2) [1 - e-(11,550/53,330)]
T = 1.75 [1 - e-.2166] = 1.75 x (1-.805)
T = .339" is minimum wall thickness for 10M w.p. rating.