Malleable Iron Pipe Fittings – Inspection Guide

by | Apr 8, 2022 | Industry Knowledge, Service


The main use for malleable iron pipe fittings is for pipeline systems, as connectivity pieces. However, the applicability range is much wider.

Malleable iron technology includes a casting process in a pearlitic matrix. We are talking about malleable iron with a metastable carbide structure. The quality of the malleable iron pipe fittings might differ. So, before purchasing such products you need to be sure that the quality of the fittings you order will be just as expected. Thus the inspection process is highly important to ensure a high-quality product.

This guide includes the precise procedure for a successful malleable iron pipe fittings inspection.

PART 1. Preparation Before the Actual Inspection

This is a preamble to the actual inspection. It is the responsibility of both the product manufacturer and the purchaser.

Who will participate?

The manufacturer representative is usually a salesperson.

The purchaser’s representative, a person in charge of the pipe fittings inspection, an inspector.

Time for inspection: the inspection will take place within a time frame of 4 – 3 days before loading.

Location for inspection: this location is provided by the manufacturer who has to ensure a suitable space. This means the space has to be large enough to allow the dismantling of each piece and a thorough inspection.

Tools to be used during inspection: Ring Gauge, Plug Gauge.

Manufacturer departments included in the inspection: the quality inspection department, the production department, warehouse personnel.

Internal self-inspection report from the manufacturer: a first self-inspection will be executed by the manufacturer on a 5% representative sample of one type of product, and a minimum of 20% from the total number of malleable iron pipe fittings. At the end of this inspection, the manufacturer drafts a report which is then forwarded to the purchaser.

Third-party inspection: if such a third party is agreed to perform an inspection, it has to deliver the inspection results to the purchaser on spot.

PART 2. Inspection On-spot

Step 1. Gauge Verification

This step applies when the inspection team on behalf of the purchaser brings its tools to perform the inspection. The respective tools must first be verified against the tools of the manufacturer’s production department. In case of differences, both parties need to agree upon a commonly recognized standard that will serve as the inspection starting point.

Step 2. The actual Inspection

The inspection order.

1st Procedure: Inspection of packaging

The actual packaging; inspect if the general aspect (both internal and external packaging) is clean if the packaging material is intact;

Labels: check if all regulations are covered, and followed through;

Pallet: check if the pallet is firm and neat, take a picture of the full pallet. Also inspect the number of pellets, according to the order.

2nd Procedure: Inspection of malleable iron pipe fittings’ appearance

Appearance: check for any through-holes, trachoma, casting bumps on the surface, leakage plating on the galvanized areas. The zinc layer needs to be uniformly spread, with no large blocks. The pipe fittings need to feel smooth, without any visible bulge or scratches.

Outer diameter: this measurement needs to conform with the standard size provided by the contract. You need to perform measurements on the outer diameter of the sample pieces and register them. They need to correspond to the standard level provided within the contract.

Length: The length is measured according to the method specified for this procedure by the procedure standard.

Wall thickness: The wall thickness is measured at the middle section for each malleable iron pipe fitting. The measurement will be performed three times in three subsequent points, and then the average value shall be registered.

Thread (inspection with the plug gauge and the ring gauge):

The internal thread is measured with the plug gauge. Whereas the external thread is measured with the ring gauge. Ring gauges differ depending on NPT, G, or BSPT threads. The pipe fittings’ threads must always be smooth.

Internal / External: according to the production standard, the thread has to be at the base area of the ring gauge, with a +/- 14 degree.

Appearance: check if there are no broken teeth on the internal thread, nor any bumps on the external thread.

Chamfers: they are a must for pipe fittings. The chamfer deviation has to correspond to the provided reasonable levels.

Sampling Method

Thread axis angle: standard sizes – 180 degrees, 90 degrees, 45 degrees, with a maximum acceptable error level of +/- 0.5 degree;

Airtightness: the inspection will be performed on 4 or 5 samples from each product size. The sample pieces are immersed in water at 0.7 MPa pressure, and no air bubble must appear for the product to qualify as valid.

Zinc layer thickness: The zinc layer is measured at the pipe fitting surface with a side thickness gauge. The inspection is performed on 3 to 5 galvanized products. The measurements are performed on a minimum of 10 points, the average value of all these measurements is registered as the reference value for zinc level thickness. However, this average value must be of minimum 70µm, with the lowest value in any point no less than 63 µm.

Peeling of zinc layer: this inspection is performed with copper sulfate solution, by immersing the malleable iron pipe fittings in it.

Mechanical performance: this requires specific experiments. The sample pipe fitting is placed in the servo-hydraulic press which determines its mechanical performance: elongation rate; 10%; 350 MPa. Upon the purchaser’s request, the flattening test can be performed on the pipe fittings.

PART 3. Summary

After the end of the inspection, all data from each inspection point is registered in a standard table.

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The summary will include the number of defective items, as well as the items that correspond to the provided standard. The proportion between the two will also be registered, and depending on this value, the purchaser can decide whether it accepts or rejects a specific pipe fitting batch.


The purchaser has the option to either return the defective pipe fittings at the manufacturer’s workshops for repairing works or to request the replacement with new items.

If repairing has been performed, a re-inspection procedure will be applied for these items. They will not be shipped until they pass the second inspection.

Sign and Stamp

The inspection report must be signed and stamped by the purchaser’s inspector. Only afterwards the malleable iron pipe fittings are considered accepted and ready to ship.