Pipe wall thickness issue 2

[09091960]

Hi All
In general buried gas pipe line going pass high consequence areas required to be heavy wall to avoid the risk involvement. Given the pipe line dia 559 mm, wall thickness of 7.92 mm and MAOP of 7322Mpa to safely operating under the above conditions, instead of having the heavy wall can the operator only reduce the MAOP to a certain % from the MAOP to satisfy the conditions? Or else what are the factors effecting to take up a decision under these circumstances. Appreciate if someone gives me proper direction to tackle this issue.

 

[racookpe1978]

How are you going to avoid corrosion and erosion?

You said this was a high risk area? How much risk do you want (your customer want) to take based on years of future liability just to save a few dollars on thick-walled pipe?

 

[msquared48]

I know a of a well publicized situation where the piping used was insufficient, resulting in a very damaging situation.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[ione]

7322Mpa = 73220 bar

Are you sure about the unit?

 

[BigInch]

Looks like kPag to me, or 1000 psig +/-

Reduction of operating pressure is the same as increasing the hoop stress safety factor, each of which is a valid approach to decreasing the risk factor of operating in high consequence and sensitive areas. Other considerations might be extra burial depth, or adding mechanical protection in the form of concrete plates above the pipeline, concrete slabs, etc. Additional measures might also be to increase the patrol observation frequency, from yearly, to monthly, to weekly. Early warning leak detection systems might be another measure, as well as adding remote operated valves, or valves that will close on a particular level, or rate of pressure loss. Fencing and marking of the right-of-way could be another approach. You could propose only one, or all. Which ones and what you finally do may depend on how your regulating authority views the effectiveness of each one. All the above have been used in one location or another to increase the general safety and decrease the risk of operating within high consequence areas.



"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.liv

 

[SNORGY]

If the assumptions 559 mm (22") OD and 7322 kPa (1062 psi) are correct, then even with Grade 359 (API 5LX-52) pipe I arrive at a hoop stress around 72% of SMYS. In Canada, this pipe would be considered the thinnest wall possible before being "special thin wall", and in all but a Class 1 Location (comparable to "low consequence" area), it wouldn't be accepted at the conditions given.

You could reduce MOP.

Regards,

SNORGY.

 

[BigInch]

OK, as far as a solution involving only a reduction of MAOP, you're apparently in AU and I don't know that gas code, but under B31.8 and Title49, a dense city setting, or compressor station would require at the least a reduction to 590, or 737 psig respectively.

"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.liv

 

[brimmer]

I will jump in as well, the short answer to your question is yes can reduce operating pressure, BigInch has essentially nailed it though. I would just add, when I select piping to HCA's, take into account where the pipeline is, is it near heavier areas of population, is it near industrial areas where there will be a lot of ground disturbance, is it in an environmentally sensitive area that might be very difficult to work in should there be a leak or failure. Keep in mind saving money by keeping the wall thickness the same may save you money now, but it probably won't in the long run (don't cut corners, look no farther than the current GoM situation where they saved millions only to pay billions). With a thinner wall thickness, you may also end up inspecting (ILI) more frequently, and repairing any corrosion anomalies in the pipe as burst pressure will be lower in thinner wall pipe, in an area that will probably be expensive to dig if it is an HCA. It is also easier for someone to actually puncture the line with thinner wall if ground disturbance in the area. If it is an area where it is very difficult to get to (river crossing etc.), I would use the thickest wall possible that still allows passage of an ILI tool. BigInch has specified various installation/operating procedures that are normally followed in HCA's, if you want more specific opinions, you can describe your scenario in detail.

 

[09091960]

Hi Guys,

Appreciate all for your contributions.

 

[09091960]

Correction,

7.322 Mpa

Sorry guys

 

[stanier]

Surely the HAZOPS and risk assessment to AS 4360 are the forums to determine this matter.