Membrane wall

Abstract

 Membrane wall of an incinerator of which the steam pipes are made of carbon steel provided with a stainless steel coating, e.g. Inconel 625, by means of helical welding. The co-extending steam pipes are mutually welded together by a connection strip of 100% stainless steel fitted there between. The coating or strip of weld connection contains less than 10 wt% Fe (iron). The used weld rod contains less than 3 wt% Fe.

Description

[0001] It is proposed, to extend the servive life of a membrane wall of an incinerator by providing the steam pipes of carbon steel with a stainless steel (RVS) coating by means of helical welding. Subsequently the steam pipes are assembled into a membrane wall by mutually welding the mutually parallel extending steam pipes with a inter fitted connection strip of 100% stainless steel.

[0002] By helical coat-welding of the stainless steel (e.g. Inconel 625) a sufficiently smooth surface is obtained, which is desirable to weld the RVS coated steam pipe to the RVS (also preferably Inconel 625) connection strip. For an optimised smooth result, the coat-welding of the RVS is carried out MIG welding and TIG disposed.

[0003] It will be appreciated that helical coat-welding means, a.o., a weld bead extending continuous in radial circumferential direction in such a helical manner in axial direction, that succeeding windings of the weld bead mutually contact or (slightly) overlap with the adhacent longitudinal edges, such that a continuous coating of substantially constant thickness is provided.

[0004] E.g. the membrane wall is designed for a waste incinerator. The membrane wall serves as sideway limit of the fire space, wherein a temperature in the range of e.g. 700-800°C can prevail. The membrane wall is cooled by the steam running through the vertical upward extending steam pipes. The membrane wall can however also be provided for other incinerators and possibly be cooled by another fluid flowing through the pipes, e.g. water.

[0005] The membrane wall can be provided as separator wall or as bulk head (at one or both sides exposed to the fire).

[0006] Preferably the same RVS-composition is used for both the coat-welding and the connection strip, having a high corrosion and abrasive strength in relation with the environment within the incinerator.

[0007] Preferably use is made of RVS welding material to weld the connection strip to the steam pipe, preferably with a composition substantially equal to that of the RVS applied in the coat-welded clad layer or the connection strip. The coat-welding of the RVS clad layer and/or the attachment of the connection strip to the steam pipe by welding is preferably carried out in a protective environment, e.g. below a powder cover, to avoid environmental attack of the welding material or surrouding steel. This way of protection is known as such and needs therefor no further elaboration.

[0008] The importance of a completely RVS strip is a.o. that therewith one can avoid that during fixing of the steam pipe to the connection strip by welding the carbon contents within the weld seal becomes to high due to diffusion of carbon from the surrouding steel.

[0009] Convenient RVS types contain Fe, C and alloy components and also Ni and Cr.

[0010] A sufficient durability can be obtained if the connection strip has a width of about 30 mm at the most. If the width is to large, the connection strip wil overheat and early collapse.

[0011] It is also learned that for a durable membrane wall the connection strip must suffice a predetermined straightness and the surface of the RVS welded onto the steam pipe must suffice a predetermined smoothness and layer thickness. Said straightness is preferably within the following range:.... Said smoothness is preferably within the following range:... The layer thickness is preferably between 1.8 and 2.5 mm.

[0012] Alternatively to helical coat-welding it is possible to straight coat-weld the RVS (i.e. with weld beads running in steam pipe longitudinal direction).

[0013] Now an in the drawing shown example is described.

[0014] The drawing shows in fig. 1 a part of a membrane wall 1 in perspective. It is made of mutual parallel extending steam pipes 2 of carbon steel, all around coated by clad-welding of RVS. Slod RVS connection strips 3 are welded to the mutually spaced steam pipers 2. The weld connections are refered 4 (four in steam pipe longitudinal direction extending weld connections for each connecting strip 3 between two steam pipes).

[0015] Fig. 2 shows a steam pipe 2 in detail, showing the helical extending weld bead 5 of the clad-welded RVS coating. The pattern which is characteristic for the machine clad-welding of circumeferentially succeeding circle segment shaped lines 6 in the welding bead, coming from the advancing front of liquid welding material, is only partly shown. The clad-welded coating provides a continuous smooth layer.

[0016] Also other embodiments belong to the invention, e.g. wherein the connection strip 3 contains a core of carbon steel.

[0017] Preferably the strip 3 is made of a composition according to Inconel 625 or 629 or others from the 600- or 700-series. This is also true for the coating or weld connection. Preferably the coating of weld connection or strip contains iron (Fe) less than 10 wt%, preferably less than about 7.5 wt%, more preferably less than about 5.5 wt%, such as less than about 7 wt% or about 5 wt%. The weld rod used for welding (coating, connection strip - pipe) contains preferably Fe less than 3 wt%, e.g. less than about 1.5 wt%, such as less than about 1

Claims

1. Membrane wall of an incinerator of which the steam pipes are made of carbon steel provided with a stainless steel coating, e.g. Inconel 625, e.g. by means of helical welding.

2. Wall according to claim 1, wherein the co-extending steam pipes are mutually welded together by a connection strip of 100% stainless steel, preferably 30 mm wide at the most, fitted there between.

3. Wall according to claim 1 or 2, wherein the coat-welding of the RVS is carried out MIG welding and TIG disposed.

4. Wall according to claim 1, 2 or 3, wherein for the coating and the connection strip the same RVS composition is used of preferably high corrosion and abrasive strength in relation with the environment within the incinerator.

5. Wall according to any of claims 1-4, wherein RVS material is used to weld the connection strip to the steam pipe, preferably having a composition substantially equal to that of the RVS used in the clad-welded coating of connection strip.

6. Wall according to any of claims 1-5, wherein the coating or strip of weld connection contains less than 10 wt% Fe (iron).

7. Wall according to any of claims 1-6, wherein the used weld rod contains less than 3 wt% Fe.

Drawing