Description

Introduction to corrosion coupon

The corrosion coupon is a sheet metal block prefabricated with the same material as the main process pipeline and hangs the metal piece inside the pipeline is to be tested with appropriate coupons so that the corrosion coupon is subjected to the same corrosion conditions as the inner wall of the pipeline. After a certain period of time, the coupon is taken out and weighed again, and the corrosion rate is calculated by the formula. In this way, more accurate corrosion of the inner wall of the pipeline can be obtained. Due to different specific requirements, corrosion coupons can be divided into the following categories:

(1) Strip coupon

The strip coupon is the most commonly used corrosion coupon. It has two holes at one end for fixing the coupon. The most commonly used sizes for strip coupons are 76.2mm ×19.0mm× 3.2mm and 76.2mm × 12.7mm × 1.6mm.

(2) Ordinary disc-shaped coupons

Ordinary disc hanging plate does not have internal chamfering, it is mainly used to measure the internal corrosion of a multi-phase flow pipeline, for example, three ordinary disc hanging plates can be installed along the top, middle, and bottom of the pipeline on a coupon to monitor the corrosion of the oil – gas – water three relative to the inner wall of the pipeline. The common size of the ordinary disc hanging plate is 31.8mm × 3.2mm, and 3.2mm is the thickness.

Corrosion coupon suspension

Corrosion coupon member “Corrosion coupon member is a device used to fix the corrosion coupon member and hang it firmly in the designated position inside the pipeline. Its types can be mainly divided into the following types:

(1) Thread connection suspension piece is fixed on the welded thread branch pipe platform in the form of a thread connection, corrosion coupon is fixed at the bottom of the thread suspension piece.

Because the pipe can not be in the running state when the corrosion coupon plate is disassembled and installed, and the threaded connection is not suitable for high-pressure situations, the threaded connection suspension is suitable for low pressure and the pipe and discontinuous operation.

(2) Flange hanging member is fixed on the welded flange on the pipe in the form of a flange connection, and the corrosion coupon member is fixed on the bottom of the flange hanging member.

Because of the flange connection form, the flange suspension can be applied to high-pressure occasions, but because the pipe can not be in the running state when disassembling the corrosion coupon plate, the flange suspension is suitable for the pipe is not the continuous operation of the occasion.

Because thread hanging parts and flange hanging parts will face the problem of pipe production and pressure relief when disassembling corrosion coupons, so for long-term continuous operation and can not easily stop production of pressure relief pipes, can be used with pressure disassembly type hanging parts.

(3) The press-disassembly type suspension is an integrated body composed of a set of parts, the main parts of which are: a protective cover, solid cock type fastener, carrier, and corrosion coupon suspension.

The removable suspension can be removed or installed during the operation of the pipeline without affecting the normal operation of the pipeline, so for the continuous operation of the pipeline, the removable suspension is generally used to fix the corrosion pendant.

Pressure disassembly and installation of a corrosion hanger require a set of tools, its specific operation is similar to the working principle of pipe with a pressure opener.

In order to ensure that the corrosion coupons reflect real and reliable corrosion conditions, it is often necessary to place the corrosion coupons in the corroded or likely to occur in the pipeline or equipment, so it is considered. Whether to use a corrosion coupon, you can focus on the following parts or situations.

(1) Fluid blind end;

(2) The presence of high-speed fluid or impact fluid;

(3) Downstream of oxygen mixing points, such as large tanks, pumps, and flash vapor recovery systems, as well as water refill lines for natural gas desulfurization systems;

(4) The parts where condensate accumulates in an acidic gas environment, such as compressor inlet filter, separator, dewatering tower drainage pipeline, and low point of wet natural gas;

(5) Ammonia liquid or ethylene glycol pipelines containing acid gas;

(6) Gas space at the top of ethylene glycol regeneration tower containing acid gas;

(7) Gas-liquid interface.

To accurately measure the corrosion rate in a pipe, follow the following procedures and steps

(1) In the field, before the installation of the corrosion coupon, it is necessary to record the serial number of the corrosion coupon, the installation date, the name of the installation system of the corrosion coupon, and the location of the corrosion coupon;

(2) When installing, it is necessary to prevent pollution to the surface of the coupon;

(3) When taking out the corrosion coupon, it is necessary to record the serial number and removal time of the corrosion coupon and record whether there is abrasion or mechanical damage on the surface of the corrosion coupon. At the same time, it is necessary to observe whether there is a spalling phenomenon on the surface of the corrosion coupon or whether there are other impurities after corrosion, and take photos of the corrosion coupon after taking it out;

(4) The corrosion coupon should be prevented from oxidation after removal, so it is necessary to put the corrosion coupon in a moisture-proof envelope immediately, or in an envelope soaked with volatile corrosion inhibitors, and send it to the laboratory for processing and analysis as soon as possible. Do not grease the surface of the corroded coupon on site. Use soft paper to gently wipe the surface of the corroded coupon to remove moisture. Do not remove the corrosive impurities on the surface of the corroded coupon.

corrosion coupon