[MW:10398] Use of spiral welded pipe indoors

Dear Gents,

Is there any specification to prevent use of helical welded pipe for indoor dangerous flows?

Advantage of helical welded pipe (and the reason for its use) is that it is generally less cost, and it can be produced at large diameters, at significantly less cost than longitudinal seamed pipe.

The disadvantages of helical welded pipe are more significant, and have been a focus of considerable research and debate within the Industry for many years. Of most importance and concern is that the quality of the helical weld can vary considerably amongst manufacturers worldwide. The most agreed concern is the existence of stress concentrations in the helical weld, since helical welded pipe is not cold expanded during the manufacturing process.

In addition, the various design codes require that a joint factor be applied when computing the wall thickness based on internal pressure. The joint factor is dependent upon the material specification, and the "welding" procedure/method used to make the continuous helical weld (i.e. ERW, SAW, etc.) during manufacture.

Each Operating Company generally has their own position regarding use of helical welded pipe on their projects. Some oil companies do not allow use helical welded pipe for process and even any pressure service due to the poor past performance and experience with this type of pipe. Some Companies do not allow use of helical welded pipe for "on-plot" piping/portions of pipelines inside facilities areas, but may allow use of it "off plot" outside the facilities plot limit boundaries.

There have always been two positions regarding the use of helical welded pipe. Economics will promote the use of this line pipe (since it can be significantly less expensive), Engineers are very cautious regarding the use of such pipe.

The maximum shear stress for hot service helical welded pipe segments occurs along the helical weld; - orientation is close to 45 degree. If there is significant shut-down and start up events of the line during the operational life, fatigue of the spiral weld can be a consideration.

There is a considerable helical welded pipe in service nowadays but in new plants is limited mainly to return water line service.

Helical welded pipe is generally discouraged in any service involving axial fatigue loading.

Against helical welded pipe stand also difficulties during installation:

1- Trying to avoid the weld lines intersecting branch (pipe to pipe) connections while watching for weld ends at the ends of the main spool not aligning with weld ends of adjoining spools.

2- IT is difficult to weld pipe support assemblies to helical welded pipes while trying to avoid the spiral weld lines on the pipe.

3- Method of manufacturing leads to a larger area of heat affected zone. Again a problem with welding supports and branches.

Case:

Configuration:  2 lines from blowers operated  taps a  manifold 

Materials: Manifold  helical welded pipe Ej=1, welded elbows from same pipe

branches from blowers helical welded pipe, Ej=1, hot bended elbows

Process:

Hot air from 2 blowers is delivered to process, one in spare starts only case process requires.

Temperature: 165 Celsius

Pressure 1.4: Bar

Flow: variable up to 24.000 Nm3/h wet

Location : Indoors, along main stairway, Europe.

I&C: No ESD input for ambiental temperature (designed yet).

My concerns: 

Shear of spiral weld due to fatigue leads to :

1. Up to 31.5 t/h hot air turns the access stairway if not the entire building in a 165 ºCelsius 1.2 MW hot air oven.

(Please support with a time -temperature – distance simulation).

2. Insulation cover blows blocking the single escape way .

Kindly share your experience

Sincerely, 

Dorin

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