Pipeline CP Coating Breakdown Factors (Again)
Pipeline CP Coating Breakdown Factors (Again)
(OP)
Working on a pipeline coated with 2.5 mm 3-layer polypropylene (nothing outstanding about it).
Using RP-F103 Table A.1 and a 3-layer FBE/PP coating I get:
a=0.1x10E-2
b=0.003*10E-2
giving
fcm = a +0.5*b*T = 0.1x10E-2 + (0.5*0.003x10E-2*25)
fcm = 0.001375
and
fcf = a + b*T
fcf = 0.1x10E-2 + 0.003x10E-2*25
fcf = 0.00175
If I do the calculations to ISO 15589-2, however, I get
fcm = 0.0075
fcf = 0.01
So the coating breakdown factors under ISO 15589 are an order of magnitude higher than those under RP-F103 (and a lot closer to what I would expect).
Is there simply an error in Tables A.1 and / or A.2 of RP-F103 or am I missing something?
Using RP-F103 Table A.1 and a 3-layer FBE/PP coating I get:
a=0.1x10E-2
b=0.003*10E-2
giving
fcm = a +0.5*b*T = 0.1x10E-2 + (0.5*0.003x10E-2*25)
fcm = 0.001375
and
fcf = a + b*T
fcf = 0.1x10E-2 + 0.003x10E-2*25
fcf = 0.00175
If I do the calculations to ISO 15589-2, however, I get
fcm = 0.0075
fcf = 0.01
So the coating breakdown factors under ISO 15589 are an order of magnitude higher than those under RP-F103 (and a lot closer to what I would expect).
Is there simply an error in Tables A.1 and / or A.2 of RP-F103 or am I missing something?





RE: Pipeline CP Coating Breakdown Factors (Again)
It's all down to the black art of CP and how lucky do you feel with each standard
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Pipeline CP Coating Breakdown Factors (Again)
DNV would have you believe a couple of old aluminium takeaway food trays somewhere in the Barents Sea and a couple of beer cans in the Serpentine would protect a 2 km flowline in the North Sea!
Compromise I'm taking is to use the worst case of DNV and ISO coating breakdown factors and plug those into the calculations. A bit mix'n'match, I admit, but I rather tend to believe six (twelve for spacing limits) 10 kg anodes are needed for a 1.8 km 8-inch pipe than one 5 kg anode!
Then, of course, I have to assume half the anodes will fall off or become disconnected in service or be pulled off when the flowline is trenched. Don't believe the latter will happen? In the mid 90s a certain offshore construction contractor trenched a pipeline and due to under-specification of the anode attachment bolts ended up pulling all the anodes to one end of the line!
M-503 doesn't really come into it - that's for subsea structures, painted, with attendant coating breakdown factors based on both water absorption by, and mechanical damage to, the paint.
RE: Pipeline CP Coating Breakdown Factors (Again)
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Pipeline CP Coating Breakdown Factors (Again)
RP-F103:
For 3-layer polypropylene anti-corrison coating (CDS 3) and 300 mm long IMPU field joint coatings (3D system) 25 year design life I get:
fcm = 1.375E-3 for the line pipe
fcm = 0.01375 for the FJC
For a 25 mA/m2 maintenance current density this gives an anode net mass requirement of 15.2 kg.
According to ISO 15589-2 the corresponding mean coating breakdown factor for both line pipe and FJCs is 0.0075 (~5.5 x higher than RP-F013. With a maintenance current density of 20 mA/m2 (80% of RP-F103 value and pipeline is buried so 20 mA/m2 used per ISO 15589-2 recommendation) the net anode mass required is 43.4 kg.
Moreover, due to the very low CBFs under RP-F103 I get an attenuation separation of 1.8+ km using RP-F103 values in the RP-F103 method, compared with ~124 m using the ISO values in the RP-F103 (pick and mix problems acknowledged here).
The ISO values for mass still seem quite low, but the attenuation separation at about 10 pipe joints seems much more in line with what I would expect.
Comments anyone?
RE: Pipeline CP Coating Breakdown Factors (Again)
RE: Pipeline CP Coating Breakdown Factors (Again)
Looking at the ISO 15590-2 attenuation, it would appear to be simply confirming that you can achieve protection at the point L in much the same way as 5.6 of F103.
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04